Behavioural ecology of reintroduced beavers (Castor
fiber) in Klosterheden State Forest, Denmark
Masters thesis
Lena Marie Bau
Department of animal behaviour
University of Copenhagen
February 2001
Supervisor Torben Dabelsteen
___________________________________________________________________________
Contents
1.
2.
3.
4.
Preface (in Danish)
Resume (in Danish
Introduction
Biology of the beaver
4.1.
Taxonomy and social organisation
4.2.
Appearance
4.3.
Vision, hearing and sense of smell
4.4.
Teeth
4.5.
Locomotion
4.6.
Scent marking glands
4.7.
Reproduction and longevity
4.8.
Foraging
4.9.
Construction work
4.10.
Dispersal and territoriums
4.11.
Predators and diseases
5. General materials and methods
5.1.
Study area
5.2.
Recordings of signs of activity
5.3.
Direct observations and video recordings
6. Time allocation and foraging behaviour
6.1.
Introduction
6.2.
Results
6.2.1.
General results and methods
6.2.2.
Direct observations
6.2.3. Infrared video recordings
A. Methods
B. Ethogram
6.2.4.
Non-remote controlled recordings
6.2.5.
Remote controlled recordings
A. First sightings
B. Time budget
C. Variation in time allocation over the observation season
D. Variation in time allocation over the active period
E. Behavioural events
6.2.6. Foraging behaviour
6.3. Discussion
7.
Scent marking behaviour
7.1. Introduction
7.2. Results
7.2.1. Data on scent mounds in the release area
7.2.2. Data on scent markings from video recordings
7.2.3. Estimates of territory sizes
7.3. Discussion
8.
Dam building behaviour
8.1. Introduction
8.2. Methods
8.3. Results
8.3.1. Infrared video recordings
8.3.2. Transition matrices and flow diagrams
8.3.3. Data on beaver constructions found within the study area
8.4. Discussion
9.
Conservation perspectives
10. Sources of error
11. Conclusion
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References
Appendix
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
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1. Forord
I modsætning til den gængse indgangsvinkel
på et biologispeciale, hvor en problemstilling
inden for et ofte velafgrænset emne bliver
undersøgt, så var indgangsvinklen til dette
speciale at undersøge de aspekter af bæverens
adfærd efter reintroduktionen, der var mulig
at undersøge under de givne forhold. På
baggrund af disse undersøgelser skulle det
være muligt at vurdere succesen af
reintroduktionen.
Specialet er skrevet til en målgruppe bestående
af mennesker, der dagligt arbejder med
aspekter
af
bæverens
adfærd
eller
forvaltningen af bævere, og som derfor vil
have en særlig interesse i at få kendskab til
resultaterne.
I Europa er der efterhånden en stor gruppe
mennesker, der arbejder med eller for reintroduktion af bæveren. For at gøre
resultaterne tilgængelige for disse mennesker,
har jeg valgt at skrive specialet på engelsk.
Jeg har fået stor hjælp og støtte i forbindelse
med feltarbejdet og vil i den forbindelse gerne
benytte chancen for at takke skovrider Thomas
Borup Svendsen, som har været en uvurderlig
hjælp under hele projektet. Ligeledes vil jeg
sige tusind tak til Jørn Pagh Berthelsen og
Aksel Bo Madsen, Danmarks
Miljøundersøgelser, som udover at stille
udstyr til rådighed også bidrog med hjælp og
vejledning utallige gange.
Tusind til Keld og Birgit Olesen, der i mere
end to måneder lagde have og hus til, og tak til
Kurt og Åse Kristensen for tilladelse til at
observere på deres jord.
Tak til Kirsten Rud Jensen og Karen Ifversen
for jeres hjælp, tålmodighed og ikke mindst
jeres humor! Og tak til alle I andre ved
Klosterheden statsskovdistrikt. Tak til Sten
Asbirk, Skov- og Naturstyrelsen. Og ikke
mindst tak til Rune Kargo og Liat Romme
Thomsen for samarbejde i felten og for utallige
diskussioner! Tak til min vejleder Torben
Dabelsteen. Ligeledes tak til Safi Darden og
Sandra Schmitz for hjælp og godt studiemiljø.
Jeg vil også gerne takke Frank Rosell,
Høgskolen i Bø, Norge, som lærte mig
”kunsten” at observere bævere. Tak til Anett
Schumacher, Naturschutz Zebster Ackerland,
Tyskland for hjælp og husly i forbindelse med
en feltekskursion.
Økonomisk bistand blev ydet af Skov- og
Naturstyrelsen,
naturforvaltningskontoret,
samt Torben og Alice Frimodts Fond og De
Københavnske Uddannelseslegater.
_________________________________________________________________________ 2
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
2. Resume
Fra bæverne blev udsat i oktober 1999 og frem
til marts 2000 blev der, først på ugentlig basis
og dernæst hver anden uge, foretaget
registreringer af alle tegn på aktivitet på alle
udsætnings-lokaliteter. Dette inkluderede at
registrere: 1) arter af vedplanter, der var
fourageret på, 2) hvor langt fra vand dyrene
havde bevæget sig for at fouragere, og 3)
diameteren på de fældede eller afgnavede
arter. Ydermere bestod registreringen i at
notere data omkring dæmningsbyggeri,
hyttebyggeri og duftmarkeringer.
I perioden marts-juni 2000 blev der ligeledes
foretaget direkte observationer på fire
lokaliteter samt videooptagelser af dyrene i en
familie-gruppe.
Videooptagelserne
blev
foretaget ved hjælp af infrarødt lys tilkoblet et
kamera. Udstyret var udlånt af Danmarks
Miljøundersøgelser, Kalø.
Totalt blev der fourageret på 10 forskellige
træarter, hvoraf pil og birk tilsammen
udgjorde cirka 88%. Derudover blev der
fourageret på mindst fire ikke-forveddede
arter. 95% af planterne, der blev afgnavet eller
fældet, fandtes inden for fem meter fra vand.
Den maksimale afstand fra vand til et træ, der
var fourageret på, var 27 m. Omkring 88% af
alle afgnavninger og fældninger målte tre cm
eller mindre i diameter. Det største træ, der
blev fældet, målte 18 cm i diameter.
Ved at bruge et kamera udstyret med
infrarøde lamper var det muligt at videofilme
bævere i deres aktive periode. Der blev filmet i
alt 310 timer på en enkelt lokalitet, hvoraf der i
187 timer var en iagttager tilstede.
Dyrene var hovedsageligt aktive fra kl. 21.00 til
kl. 05.00. Næsten 68% af tiden var allokeret til
fouragering (heraf blev der ædt græs i 54% af
tiden). Dyrene åd græs i perioder af op til 35
minutters varighed. Da andelen af tid allokeret
til fouragering på græs aftog over
observations-perioden, ansås det for værende
sandsynligt, at efterhånden som løvtræerne
sprang ud, blev disses skud og blade
foretrukket.
Dyrenes fouragering var
korreleret
med
hyppigheden
af
vagtsomhedsadfærd.
Cirka 12% af tiden byggede bæverne på dæmningen, og omkring otte procent blev allokeret
til svømmeadfærd. Otte procent af tiden
brugte dyrene på pelspleje, enten egen pels
eller ved gensidig pelspleje to dyr imellem.
Motivationen for dæmningsbyggeri var især
høj i begyndelsen og slutningen af den aktive
periode. Dæmningsbyggeri i den første del af
den aktive periode faldt sammen med, at
dyrene ofte fou-ragerede, kort efter de første
gang blev set, og at grene, der netop var
fourageret på, blev brugt til at bygge med. Den
høje motivation i slutningen af en aktiv
periode syntes forklaret ved, at motivationen
for at æde formindskedes, efter at dyrene
havde allokeret store dele af natten på
fouragering, og derved blev det muligt for
bæverne at allokere tiden på anden adfærd.
I Klosterheden blev der i de første fem
måneder efter udsætningerne fundet meget få
duftmarkeringer, og det var ikke muligt at
definere territoriegrænserne på baggrund af
disse alene. Således måtte andre tegn på
aktivitet (fourageringspladser og fældninger)
og mulige eksisterende barrierer så som veje
og bebyggelse indgå. På denne baggrund var
det muligt at estimere størrelsen på seks
territorier. Gennemsnitstørrelsen var 4.7 km.
Bære-kapaciteten der blev beregnet på
grundlag af gennemsnitsstørrelsen var i
overensstemmelse med en tidligere beregning.
Et højt energiforbrug ved daglig markering af
territoriegrænser, den meget lave vandstand i
mange af vandløbene, mulig anderledes
adfærd (resultatet af at være udsat i ukendt
område) samt den lave populationstæthed var
forklaringer på den lave forekomst af
duftmarkeringer.
Ved analyse af videooptagelser fra den aktive
periode blev flere aspekter af bæverens adfærd
under dæmningsbyggeri beskrevet. På intet
tidspunkt blev der set mere end et individ
bygge
på
dæmningen.
Dette
er
i
overensstemmelse
med
tidligere
undersøgelser. Hverken rækkefølgen af de
enkelte
adfærdselementer
i
byggesekvenserne, placeringen af materialet på
dæmningen eller materialetyper, som blev
brugt til at bygge med, forekom tilfældigt.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Resultaterne indikerede, at byggeadfærd er
adaptiv, og for-delen ved dette er sandsynligvis
en optimering af energiudnyttelsen. Muligvis
var resultaterne en funktion af de fysiske
parametre på den pågældende lokalitet.
Bæverne byggede dæmninger på to lokaliteter
og
disse
dæmninger
resulterede
i
oversvømmelse af ca. fire hektar. Heraf var
omkring en hektar på privat jord. Det må
forventes, at der i fremtiden kan opstå konflikter
med
lodsejere
på
grund
af
enten
oversvømmelser eller andre skader forårsaget af
bæveren.
Minimum fire unger blev født, ingen døde dyr
blev fundet og bæverne blev enten på udsætningsstederne eller slog sig ned meget tæt på
udsætningsområdet. På baggrund af disse facts
kan det konkluderes, at reintroduktionen i det
første år har været en biologisk succes.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
3. Introduction
Denmark is part of the European beaver’s
historic range. The beaver is thought to have
become extinct in Denmark more than 1000
years ago due to over-hunting and destruction
of habitat suitable for the species (e.g. Nolet,
1997).
The beaver is considered a keystone species in
the sense of its ability to create dynamics in its
surroundings. By cutting down trees clearings
are made which allow for the growth of lightdemanding species and by building dams
beavers flood areas creating new habitats for
many species of insects, amphibians and birds.
When beavers have depleted an area of food
they leave the area. This results in the break
down of dams and eventually the flooded area
will be drained and changed into meadows.
When the National Forest and Nature Agency
commenced
preparations
for
the
reintroduction of the beaver to Denmark the
main purpose of the reintroduction was
because of the species ability to create
dynamics in its habitat. Large areas in
Denmark have been drained due to heavy
agricultural use. Moreover, as a member of the
EU Denmark is obligated to investigate the
possibility of reintroducing former naturally
occurring species according to the Habitat
Directive article 22a (Rådets Direktiv, 1992).
Furthermore the European beaver is listed in
the Bern Convention as a protected species
(Miljøministeriet, 1990).
In 1998 the National Forest and Nature Agency
published a management plan for the beaver
in Denmark. The plan was based on the IUCN
(International Union for the Conservation of
Nature) guidelines for re-introductions (Miljøog Energiministeriet, 1998).
Four areas were designated as possible release
sites and in those particular areas public
hearings took place. Particularly the anglers
opposed very strongly against the reintroduction. They feared that beaver dams
would create ponds and thereby destroy
spawning areas of salmon fishes.
The result was that permission to release
beavers could only be given for one site in
Denmark.
In October 1999 eighteen beavers were
captured in Germany and released in the
Flynder å system, Klosterheden State Forest,
Denmark.
The objective of this masters thesis was to
carry out behavioural studies that will add
information to the knowledge of the behaviour
of reintroduced beavers.
It was decided by the National Forest and
Nature Agency not to mark the beavers for
individual recognition. The decision posed
several disadvantages to the present study: It
was impossible to distinguish between beavers
of different age classes and sexes as well as it
was impossible to make certain of the family
group an individual animal belonged to.
It was decided to concentrate on the following
aspects of beaver behaviour:
1) Time
allocation
and
foraging
behaviour
2) Scent marking behaviour
3) Dam building behaviour
An evaluation of the reintroduction was made
on the basis of the results.
Each of the three aspects are introduced and
discussed in separate sections although a
section on general materials and methods
concerns all three aspects.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
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4. Biology of the beaver
4.1. Taxonomy and social organisation
The beaver belongs to the class Mammalia, the
order Rodentia, the family Castoridae and the
genus Castor. The two extant species are: Castor
fiber – the European beaver and Castor
canadensis – the North American beaver. The
two species are very similar in morphology,
mode of life and behaviour although Castor
canadensis is somewhat bigger and generally
has a larger litter
(e.g. Wilsson, 1971;
Patenaude, 1983; Novak, 1977). For Castor
canadensis and Castor fiber the chromosome
number is 40 and 48 respectively (Zernahle
and Heidecke, 1979) and therefore the two
species cannot mate and produce viable
offspring.
In the following text there will be no
distinction between the two species concerning
morphology, mode of life or behaviour unless
well-documented differences are reported.
Beavers are primarily nocturnal with an active
period that last from dusk to early morning
(e.g. collett, 1897; Curry-Lindahl, 1967; Buech,
1995; Wheatley, 1997), but in places with no
disturbance they can also be active during
daytime (e.g. Curry-Lindahl, 1967).
The beaver is semiaquatic and always lives
near water. Beavers live in small colonies or
family groups with approximately 2-7
members in the European beaver. The
American beaver live in larger family groups,
2-12 members (e.g. Bradt, 1938; Novak, 1977;
Danilov and Kan’shiev, 1983). The family
group consists of an adult reproducing pair,
their one-year old offspring as well as young
of the year (e.g. Bradt, 1938; Hay, 1958;
Aleksiuk, 1968). Beavers are monogamous and
according to Brooks et al. (1980) the presence
of adults with normal hormonal function may
be sufficient to inhibit additional reproduction
in the family group.
Both the male and yearlings contribute to the
rearing of the young (Patenaude, 1983).
The pair bonding can last more than seven
years. Svendsen (1989) reported that all
beavers that lost a mate remained in the
territory until they found a new mate.
4.2. Appearance
The beaver is the largest rodent in Europe with
a combined head and body length of 75-100 cm
and a tail length of 30-40 cm. Average adults
weigh 18-20 kilograms with a maximum
weight of 35 kilograms (e.g. Wilsson, 1971;
Zurowski and Kasperczyk, 1986).
The colour of the skin varies from greyish
brown to black brown. Even though partial
albinism occurs, which leads to different
patterns and markings of the fur, the animals
never have red eyes (Lovallo and Suzuki,
1993).
The fur consists of two layers; the outer layer –
guard hair – 5-6 cm long, and an under-fur
that consists of hairs 2 cm in length. The fur is
very thick. Approximately 23000 under-fur
hairs per square centimetre grow on the
ventral side and 12000 on the dorsal side. From
every hair follicle 15-30 under-fur hairs and
one to several guard hairs grow. The fur
functions as isolation when in water. The outer
layer of hair lies as a cover on top of the inner
layer and thereby prevents water and dirt from
reaching the skin. It also creates a layer of air
near the skin, which enhance the insulation
and help buoyancy. The winter fur is shed
early in spring and in September the animals
begin to grow new winter fur (e.g. Rosell and
Pedersen, 1999).
4.3. Vision, hearing and sense of smell
Visual communication does not seem to be of
great importance as the animals are primarily
nocturnal (e.g. Rosell et al. 1998). The eyes are
small and placed high on the head. The vision
is bad, - the optic nerve being small relative to
the size of the eye. Even though the vision is
evolved for night vision the retina lacks the
light reflecting crystals tapetum lucidum, which
occurs in almost all nocturnal mammals to
enhance vision in the presence of very little
light (Walls, 1967; and Hartman and Rice, 1963
(referred to in Richard, 1983); Rosell and
Pedersen, 1999). Rosell and Pedersen (1999)
argue that this structure is missing in the
beaver because the species has only recently
_________________________________________________________________________ 6
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
become nocturnal and therefore the structure
is not yet fully evolved.
As an adaptation to the semi-aquatic mode of
existence the beaver has “see-through”
membranes that automatically glide over the
eyes when the animal dives. These membranes
function as protection against particles and
prevent eye liquid from being washed away
(Salvesen, 1927).
The ears are small and hairy and the hearing is
well evolved. The ear canal is large and
possibly the beaver can also hear vibrations
when being underneath the water surface
(Rosell and Pedersen, 1999). The opening of
the ear can be closed while diving by folding
the ears and closing the auditory meatus (e.g.
Salvesen, 1927; Rosell and Pedersen, 1999).
The sense of smell is very well evolved. The
nose is relatively large, and the nostrils are
located laterally. In between the nostrils the
nose is bare which allows for more information
to be gathered that had the part been hairy
(Rosell and Pedersen, 1999). Nostril closure
occurs during diving (e.g. Salvesen, 1927;
Reynolds, 1993).Besides being a very
important part of the communication system
the beaver also uses the sense of smell to locate
eatable plants, allowing the beaver to detect
for example an aspen several hundred metres
away (Doucet et al., 1994).
4.4. Teeth
The incisors are important tools for the beavers
as they are used both for eating, cutting,
felling, cleaning of the fur and transportation
of kits and branches (e.g. Wilsson, 1971).
The beaver has four incisors; two in the lower
jaw and two in the upper jaw. The incisors are
large and chisel shaped and on the outside
they are covered with a layer of orange
coloured enamel (Salvesen, 1927). The inside is
covered with a white layer of dentine (Rosell
and Kile, 1998). Furthermore the incisors are
root open, growing continuously (Rosell and
Kile, 1998). Sharpening of the incisors occurs
both by the use of the teeth, but also by rapid
movements of the jaw that allow for the teeth
to sharpen against each other. This behaviour
begins when the animals are about 1,5 months
old (Wilsson 1971).
There are four molars in both sides of the
upper and lower jaw. These are made of hard
enamel and soft tooth bone. The molars are
used for grinding plant material (e.g. van
Nostrand and Stephenson, 1964).
The beaver can chew under water by way of
shifting the position of the epiglottis and
thereby protecting the larynx and trachea from
the entrance of water. Also an elevated part of
the tongue block water entry ( Coles, 1970).
4.5. Locomotion
Both front and hind feet have five toes with
strong nails. The hind feet have webs between
the toes – another adaptation for the semi
aquatic mode of life (e.g. Jenkins and Busher,
1979). The 5.finger of the front feet functions as
a thumb and makes it possible for the beaver
to grasp and twist a branch while eating the
bark (e.g. Wilsson, 1971). Furthermore the
front feet are used for digging, carrying
material while swimming, carry building
material as well as carrying kits. During
swimming the front feet are held under the
chin and close to the body.
The nails on the three outer toes on the hind
feet are flat, thick and blunt while the two
inner toes are bend, sharp and serrated. On the
second inner toe the nail is double – one
growing perpendicular to the other – creating
a claw that the beaver use for grooming (e.g.
Wilsson, 1971).
Usually the beaver walks on all four legs, but it
can also walk on the hind feet alone in an
upright position. When doing so the tail
stabilises the posture (Carlson and Welker,
1976).
The tail consists of two parts; 1) the base of the
tail which is the narrow part that extends the
body and which is muscular and furred, and
(2) the flat part without hair and muscles
which is covered by small “scales”. The scales
are not real scales, but in fact depressions in
the tough leathery skin. Along the scale edges
there are small bristle hair (Carlson and
Welker, 1976).
The tail base controls the flat part of the tail
and the tail is used for forward driving power,
manoeuvring, steering and diving while
_________________________________________________________________________ 7
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
swimming. The movement of the tail is usually
upwards and downward, but lateral
movements are possible (e.g. Wilsson, 1971). A
very important function of the tail is its ability
to store fat and thereby work as an energy
reserve. The shape of the tail varies through
the year according to an increase or a decrease
in the amount of fat (e.g. Carlson and Welker,
1976; Aleksiuk, 1970). Furthermore the tail
functions as a heat exchanger in regulation of
body temperature (Carlson and Welker, 1976).
The tail also serves as a means for producing
alarm signals, which is another very important
function. When disturbed a beaver will dive
and while doing so it will slap its tail on the
water surface thereby producing an alarm
signal that will warn other members of the
family group (e.g. Collett, 1897; Tevis, 1950;
Wilsson, 1971). Besides tail slapping long
distance acoustic signals are poorly evolved in
the species (Rosell et al., 1998).
The hind legs are the main source of forward
driving power while the animal swims, but
also movements from the tail and the body
contributes to the swimming mode (e.g.
Wilsson, 1971). When the beaver swims in the
surface of the water at slow pace the hind legs
are moved alternately in a paddling motion
(e.g. Reynolds, 1993). When swimming
underneath the water the hind legs move
together and the tail and body makes
undulating movements in the vertical plane
(e.g. Wilsson, 1971; Carlson and Welker, 1976).
When swimming near the bottom the hind legs
are held stretched backwards and the body
and tail movements create the forward driving
power (e.g. Wilsson, 1971). When swimming
fast the hind legs are moved together and the
tail movements are synchronised with the leg
movements so that when the tail makes a
downward movement the legs are brought
forward (e.g. Wilsson, 1971).
A beaver can remain under water for up to 15
minutes, but usually they swim to the surface
to breathe after 4-5 minutes (Irving and Orr,
1935). In a laboratory study on diving in
beaver the decrease in heart rate was found to
be 79%, arterial O2 fell, cardiac output
decreased and blood flow to the heart and
brain increased (McKean, 1982).
Fig.1. The location of castor sacs and anal glands of
beavers (after Svendsen, 1978).
4.6. Scent marking glands
The urethra, the anus and the reproductive
organs open into the same opening, the cloaca,
which is located underneath the base of the tail
(e.g. Jenkins and Busher, 1979).
Beaver of both sexes possess anal glands and
castor sacs and they lie in a subcutaneous
cavity located along the underside of the base
of the tail between the cloaca and the pelvic
girdle (e.g. Svendsen, 1978) (Fig.1).
The secretion of both castor sacs and anal
glands is used in scent marking (e.g. Svendsen,
1978; Butler and Butler, 1979; Walro and
Svendsen, 1982; Rosell and Bergan, 1998).
Castoreum mixes with urine and is excreted
through the urethra whereas secretion from
the anal glands is excreted through openings
located on both sides of the urethra. The
beaver deposits the secretion on mounds made
of either mud or leaves and other plant
material, or both (e.g. Aleksiuk, 1968;
Svendsen, 1980; Müller-schwarze et al., 1983).
The anal glands are well developed in the
animals first year of living, and two important
functions of the secretion are: 1) the
maintaining of the water-repellent quality of
the fur and 2) revealing information on the
individual depositing the secretion (e.g.
Bollinger et al., 1983; Walro and Svendsen,
1982; Sun and Müller-Schwarze, 1997, 1998a,
1998b). The castor sacs are poorly developed
and empty in newly born, but no differences in
_________________________________________________________________________ 8
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
structure are evident between kits of more
than 5 months old or adults (Svendsen, 1978).
4.7. Reproduction and longevity
Sexual maturity is reached at the age of 1.5-2
years (e.g. Larson, 1967).
The testicles are located in the abdominal
cavity, which is unusual in mammals.
Openings in the muscular system in the
abdomen allow for the movement of the
testicles so that they can remain under the
skin. It is reasonable to assume that the reason
for the testicles being located under the skin is
that the beaver spends so much time in cold
water. Cold water will cool down testicles
located on the outside of the body and thereby
reduce the sperm’s ability to swim (e.g.
Bollinger et al., 1983).
Usually mating takes place in the water basin
of the lodge, but it can also take place outside
the lodge or inside the lodge. During mating
the female lies on the back in the water surface
while the male floats on the side holding on to
the female with his front feet or the teeth (e.g.
Hediger, 1970). The cloaca is placed so that
they cover each other and the penis, which is
3.0-3.5 cm long, can then be inserted. The
mating act lasts around 0.5-3 minutes and can
take place several times during the female’s
heat that lasts 12-14 hours (Doboszynska and
Zurowski, 1983). If mating does not result in
fertilisation the heat can be repeated 2-4 times
with intervals of 7-12 days (Doboszynska and
Zurowski, 1983).
Mating usually takes place in January or
February and the gestation period lasts
approximately 107 days (Doboszynska and
Zurowski, 1983). The kits are born in May-June
(e.g. Curry-Lindahl, 1967).
Salvesen (1927) found the litter size to be 2-4
kits in European beaver, which is in
accordance with that found by Danilov and
Kan’shiev (1983). They found the average litter
size in European beaver to be 2.7 whereas it
was 3.2 in American beaver. Litter size is one
of the most significant indices distinguishing
the two species (Danilov and Kan’shiev, 1983).
At birth the eyes are either completely open or
partially open, opening 2-4 hours after birth
(e.g. Hediger, 1970). The fur is thick and
woolly and the kits weigh 500 – 550 grams
(e.g. Lancia and Hodgdon, 1983).
The kits are good swimmers at the age of one
week, but the ability to dive and stay
submerged is not complete until the age of
approximately 2 months. This is due to the fact
that kits are not able to close the nostrils and
fold the ears and closing the auditory meatus
until the age of 2 months (e.g. Lancia and
Hodgdon, 1983). They remain in the lodge
until they are 5-6 weeks old. Approximately 10
days after birth they begin to eat plant
material, but they suckle until the age of 1-2
months (e.g. Lancia and Hodgdon, 1983).
Bradt (1947) suggested longevity periods of 11
years (referred to in Larson, 1967). Novak
(1977) reports of a beaver at 16 years of age
and Larson (1967) found an individual at 20
years of age. Payne (1984) and Heidecke (1984)
reports average age to be 7-8 years.
4.8. Foraging
Beavers are herbivorous animals. Near the top
part of the very large stomach a cardiac gland
is located. This gland is 6-7 cm long, four cm
wide and approximately two cm thick. The
gland has eight openings into the stomach and
the function is to secrete a secretion that
contributes in digestion (Currier et al., 1960).
The fermenting tube is similar to the gut in
ruminants and it is located in the caecum and
in the upper part of the large intestine (Currier
et al. 1960). The very large caecum
(approximately 40 cm’s long) is an adaptation
in non-ruminant herbivores and the caecum
contains microorganisms that break down
cellulose. Currier et al. (1960) found cellulose
break down to be approximately 33%.
Caecotrophy, the periodic ingestion of material
produced in the caecum, further increases the
efficiency of digestion (e.g. Jenkins and Busher,
1979; Buech, 1984).
During winter and late fall bark is the main
food source (e.g. Nolet et al., 1994). In spring
and summer beavers forage on leaves, shoots,
buds, bark and twigs of deciduous trees (e.g.
Curry-Lindahl, 1967) as well as on aquatic and
herbaceous plants, which constitute a great
deal of the food (e.g. Bradt, 1938; Tevis, 1950;
_________________________________________________________________________ 9
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Curry-Lindahl, 1967; Macdonald et al., 1995).
Even though at least 80 tree species and 149
herbaceous species are registered as potential
beaver food (Macdonald et al., 1995) populous
(Populus spp.) especially trembling aspen
(Populus tremula), willow (Salix spp. ) and birch
(Betula spp.) are preferred (e.g. Collet, 1897;
Aldous, 1938; Hall, 1960; Lahti and Helminen,
1974; Curry-Lindahl, 1967).
Since the ability to move around on land is
relatively poor in beavers the species is
dependent on water as the main route for
escaping. Therefore beavers usually forage
within less than 10 metres from water and they
rarely walk more than 100
metres from the water edge (e.g. CurryLindahl, 1967; Simonsen, 1973; Frendin,
1979).Nolet and Rosell (1994) reported that
beavers in the Biesbosch,
Netherlands,
foraged no longer than 6 metres from the
water edge. Some authors report that the
beaver has a very high preference for aspen
and that the animal will walk several hundred
metres to get to an aspen (e.g. Histøl, 1989;
Doucet et al., 1994).
Beavers forage selectively and food selection
has been suggested to be dependent on trunk
diameter, distance from the waters edge as
well as which species co-exists in the foraging
area (e.g. Jenkins, 1978, 1979; Stocker, 1983;
Histøl, 1989).
In an investigation on selective foraging in the
Netherlands, Nolet et al. (1994) concluded that
a mixed diet is necessary for the beaver in
order to avoid large amounts of secondary
metabolites and to enable detoxification of
these secondary metabolites. Furthermore a
mixed diet provides complementary nutrients
(Nolet et al., 1994).
In an investigation in Massachusetts, USA,
Jenkins (1979) found that 6 genus of felled
trees constituted 90% of the total number of
trees felled or cut. The investigation showed
that food preferences might vary from season
to season and from year to year and that
beavers, by removing small pieces of bark,
could assess whether the quality i.e. the
nutritional value is too low (Jenkins, 1979).
Feeding sites are very easy to recognise; they
are found near the waters edge, often close to
the lodge, and branches from which the bark
has been eaten are scattered around (pers.
obs.). Foraging sites are often used
continuously and therefore beaver trails are
created making it easy to recognise these sites.
At latitudes where the ponds and waterways
freeze during winter beavers begin to gather
branches and twigs for a food cache in the
autumn (e.g. Collett, 1897; Salvesen, 1927;
Novakowski, 1967; Aleksiuk, 1970). These
branches and twigs are secured on the bottom
of the pond or stream outside the lodge. The
food cache provides the winter food when ice
prevents the beaver from leaving the pond or
stream to forage elsewhere (Jenkins, 1979).
4.9. Construction work
Beavers live in ground burrows, lodges built of
branches and twigs or in nests (e.g. Zurowski,
1992).
Lodges are usually built in habitats where it is
impossible for the beaver to dig into the bank
of the streams/rivers or lakes. These lodges
often have oblong shapes, as the entrance must
be covered by water in order to keep predators
away (Zurowski, 1992). The building material
comes from trees and bushes that the beavers
fell.
A family group can inhabit more than one
lodge at a time (e.g. Lahti and Helminen, 1974;
Zurowski, 1992). Zurowski (1992) found that
when territories contained more than one
lodge these were often used as extra protection
for the family group during summer nights. In
some cases the parturition took place in this
additional lodge. In winters when the water
level was low near the preferred lodge, the
secondary lodge was used.
Ground burrows are found where the banks
are high and the ground is soft enough to dig
in. Often ground burrows are made
underneath the roots of trees, as the roots will
prevent the roof from collapsing. Sometimes
the ground burrow is overbuilt with branches
(e.g. Curry-Lindahl, 1967).
The beaver digs the tunnels with its front feet
and like the lodges, the burrow contains one or
more chambers. The entrance of a ground
burrow can be placed above the water surface
_________________________________________________________________________ 10
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
or under water, in which case the entrance will
be covered with branches (e.g. Cocks, 1880;
Collett, 1897).
The nests are depressions in the ground. They
are located under bushes, under a felled tree or
by tree roots. Nests are made and used mainly
in spring and summer (e.g. Salvesen, 1927).
Besides building lodges beavers build dams
where necessary. Dams are built to raise the
waterlevel and to ensure a constant water level
of more than 50 cm’s (e.g. Frendin, 1979). As
well as making sure that the entrance of the
lodge is constantly under water, a water level
of at least 50 cm’s is necessary to provide a
quick route for escape (e.g. Macdonald et al.,
1995). Moreover, the increased water level
increases the availability of deciduous trees
near the water edge, and facilitates the
transportation of building material (e.g. Rosell
and Parker, 1996). Building material consist of
branches, grass, and mud (e.g. Salvesen, 1927).
4.10. Dispersal and territories
The juveniles leave the family group at
approximately two years of age to find an
available territory and a mate (e.g. Bradt, 1938;
Townsend,
1953;
Curry-Lindahl,
1967;
Hartman, 1997; Svendsen, 1980).
In Sweden, Hartman (1997) found that five out
of nine radio-tagged beavers left the family
group as 1-year olds, before their second
winter, and at least one of them reproduced at
two years of age. Population density was low
at the time compared to a level reached later
on. Hartman (1997) suggests that deviations
from normal population density affect both the
age of dispersal and the age of reproduction.
Svendsen (1989) found that the 2-year olds
could delay dispersal and remain in the family
group in areas with high habitat saturation.
Hartman (1997) also suggested that delayed
dispersal was a consequence of lack of
available habitat in populations with high
density.
Territories along waterways average 3
kilometres, but vary from 0.5-12.8 kilometres
(e.g. Macdonald et al., 1995). Frendin (1979)
mentions territory sizes of 250-600 metres in
brook habitats. Hartman (1997) found one
family group per 7.6 kilometres of waterway in
an area with low population density. Busher
(1987) found that the average length of stream
occupied by a family group was 0.47 km in
1977 and 0.80 km in 1979. The size of the
territory primarily depends on food quality
and season.
4.11. Predators and diseases
Wolfs, bears, wolverines and lynx are
considered to be the most important predators
on beaver (e.g. Tyurnin, 1984; Rosell et al.,
1996). Especially wolfs are considered to play
an important part in the predation on beaver
where the two species live sympatrically. An
investigation in Canada showed that 44% of
wolf faeces, in summer, contained beaver
remains (referred to in Rosell et al., 1996).
The beaver’s worst enemies in present time are
humans and diseases. In The Netherlands 30%
of the causes of death were related to humans
and 50% was related to diseases (Nolet et al.,
1997).
Destruction of habitat, lodges, dams and food
caches is examples of human factors that affect
beaver populations, but also road kills and
poaching affect population size. Esteve (1988)
found that 37% of beavers died in road kills in
France (Referred to in Rosell et al., 1996) and
Stocker (1985) found that 16% died in road
kills in Switzerland (referred to in Rosell et al.,
1996).
Seven North American beavers - Castor
canadensis – were introduced in Finland in 1937
(Lahti and Helminen, 1974) and this species
poses another threat to European beaver by
way of competition. As mentioned earlier that
the North American beaver reproduces faster
i.e. their average litter size is larger and
therefore the population increase in North
American beaver is usually higher (Lahti and
Helminen, 1974).
The most common diseases found in Castor
fiber are different types of infections in the
intestinal tract, for example the beaver fluke
Paramphistomum castori, parasites and pseudo
tuberculosis. Rosell et al. (1996) report of high
_________________________________________________________________________ 11
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
levels
of
the
parasites
Stichorchis
subtriquetrus and Travassosius rufus – both
helminths
Tularemia is found in North American
beaver, while European beaver seem
resistant to some degree (Rosell et al., 1996).
The disease is caused by a bacterium
Francisella tularensis and it is the only disease
found in beaver that has not yet been found
in Denmark (Andersen, 1997).
Extremely cold winters can cause beavers to
starve to death (e.g. Aleksiuk, 1968; Tyurnin,
1984; Rosell et al., 1996).
In very dense populations fights between
dispersing individuals and resident beavers
can lead to large wounds and cuts and
possible death (Rosell et al., 1996). Stocker
(1985) found that 16% beaver in Sweden
died from intraspecific competition (referred
to in (Rosell
et al., 1996)
_________________________________________________________________________ 12
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
5. General materials and methods
5.1. Study area
Situated in the western part of Denmark,
Klosterheden is only 20 km from the North Sea.
The climate is temperate with the average
temperature for July being 15 degrees Celsius and
average temperature of –2 degrees Celsius for
January. Average annual precipitation is 850 mm.
Klosterheden State Forest is approximately 7000
hectares of 90% coniferous trees and 10% broadleaved species. In the gorges small streams run
and non-coniferous species growing in the gorges
are mainly willow (Salix sp.) and birch (Betula
pubenscens and Betula pendula). At several places
in the forest the streams have been artificially
dammed and small lakes and ponds created
(Blom-Hansen, 1998). The main water system is
Flynder å consisting of two large streams; Flynder
å and Dride å, and several smaller streams
(Appendix 1).
Eighteen beavers were captured in the Elbe area,
Germany and released in Denmark in two
successive releases. Before the beavers were
transported to Denmark blood samples were taken
in order to determine any cases of tularaemia, the
only beaver disease known not to occur in
Denmark (Andersen, 1997). The beavers were all
tattooed on the web of a hind foot.
On the 8th of October 1999 ten individuals were
released at four sites in Klosterheden State Forest.
Not all individuals were sexed (table 1).
On the 22nd of October 1999 eight individuals
were released at four sites. Only one individual
was sexed (table 2).
Site
1
2
3
4
Kit <1 year
Juvenile 1-2 years
Adult 2-5½ years
Adult >5½ years
M, F
F, M
F
M, F
M
2 individuals,
sex unknown
Table 1. Sex and age of the first 10 individuals caught in Germany and released in Denmark early October 1999. F=
females, M= males.
Site
2
3
5
6
Kit <1 year
Juvenile 1-2 years
1 individual, sex
unknown
2 individuals, sex
unknown
Adult 2-5½ years
1 individual, sex
unknown
Adult >5½ years
M + 1 individual of
unknowns sex
2 individuals,
sex unknown
Table 2. Age of the 8 individuals caught in Germany and released in Denmark during the second release in late October
1999
_________________________________________________________________________ 13
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
5.2. Recordings of signs of activity
The reintroduced beavers either belonged to
family groups or pairs except in two cases
where individual beavers were released. The
release sites amounted to six locations, all
lakes. Artificial lodges had been built at each
site, and at four of the sites two lodges were
built (appendix 2).
For the first month after the reintroduction
(October 8th - November 8th 1999) recordings
were done on a weekly basis. Thereafter
recordings took place every other week until
the middle of March 2000.
By traversing the release sites and adjacent
waterways by foot during daytime, all signs of
activity within an approximate zone of 30
metres from the waters edge were recorded.
Signs of activity included cuts and felled trees,
trails, foraging sites and feeding sites, scent
mounds, dams and any type of den. Foraging
sites refers to places where the trees were
felled and cut or grass bitten off, whereas a
feeding site refers to places where food items
have been dragged to the waters edge to be
eaten there.
The distance from the water to plants foraged
on was recorded and the diameter of all cuts
and felled trees was measured. Felled tree
diameter was measured just below the level of
the felling, approximately 15-20 cm above
ground whereas the measurement of cuttings
occurred at various levels.
Every branch or stump was cut with a knife
after it had been measured so that on later
recording they would not be mistaken for new
cuttings.
Data recorded on scent mounds included the
material that they were made of and whether
the smell was strong or weak.
Recordings of data on constructions and scent
mounds were continued until the end of May
2000.
5.3. Direct observations and video recordings
From late March 2000 until late April 2000
direct observations were carried out at four
sites at irregular intervals. From April 10th 2000
until June 8th 2000 direct observation with the
aid of infrared video recording equipment
were carried out at one site.
A total of five family groups or pairs of beaver
were chosen as subjects for direct observations
(table 3). Site A was only used for infrared
video recordings. The family groups were
chosen mainly on the basis of accessibility of
the lake or stream. The sites had all been
inhabited for at least three months and they all
had lodges or ground burrows made by beaver
(Appendix 2)
_________________________________________________________________________ 14
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Site number
Lake / stream
habitat
Description of site
Min.
number of
beaver
3
A
Stream
B
Pond
West of stream: private
willow/birch/conifer plantation
East: grass field bordering private garden.
Upstream is state forest, downstream it
meets main stream
Artificial duck pond, east side is grass
field, west side grass and deciduous trees.
25 metres to main stream, which runs from
north of the pond and past it
4
Lake
3.3 ha, max., depth 1.4 m. The main stream
runs through the lake. Mainly aspen, birch
and mountain ash available.
2
2
Lake
0.6 ha, max. depth 1.7 m. Surrounded by
forest, mainly spruce. Willow and myrtle
growing downstream
2
5
Three adjacent
lakes
1.4 ha, max depth 1.1 m. South of lakes is a
heath, north is coniferous trees, with birch,
pine and oak.
1-2
2
Table 3. Five sites were used for direct observations between late March 2000 and the beginning of June 2000.
During the observations the observer was
situated across from the den, 20-40 metres
away, on ground level. The view from elevated
points was either blocked by vegetation or
they were located too far away from the dens.
No camouflage equipment was used.
Observations began approximately one hour
before sunset and ended either when bad
weather conditions caused visibility to be very
low or when the equipment was insufficient.
One observer carried out all observations.
Binoculars (Mirador 7x42) as well as a Litton
light amplification night vision system (model
M911A) were used. Additionally a Sony
Walkman was used to play a tape where
intervals of one minute were announced by a
beep. This allowed the observer to observe
more intensely not having to check the time
repeatedly (see appendix 3 on observation
methods).
In order to draw up an ethogram 26 hours of
direct observations on a pair of beaver took
place in Norway in May 1999 in the
municipality of Bø, Telemark. The sampling
rule was focal sampling with continuous
recording as the recording rule. Furthermore
videotaping of two beavers living under seminatural conditions in Germany were made in
order to help create a detailed description of
each behaviour pattern. Behaviour patterns not
seen during observations, but described in the
literature were included in the ethogram
(references to be found in the ethogram,
appendix 4).
For the infrared video monitoring at site (A), a
camera and two infrared lamps were secured
on an elevated platform approximately 3,5
metre above ground. The camera was
connected to a time-lapse video recorder and a
monitor placed inside a shed. Remote
controlling was possible by way of a special
remote control devise. The camera could be
turned in an angle of 180 degrees and
maximum distance from the camera to the
object filmed was approximately 100 metres.
The zoom function made it possible to get very
_________________________________________________________________________ 15
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
close to the animal (Mathiasen and Madsen,
2000). The elevated platform was placed 26
metres from the water and the shelter 45
metres away. Timing of the video was possible
so that recording could take place even in the
absence of an observer. In these recordings the
camera was either focused on the dam or a
grass feeding site next to a group of trees, often
used by the animals. When the camera was
timed to record 3 or 6-hour tapes were used.
During the observations the area in view of the
camera was scanned regularly. Recordings
began as an animal came into sight. When
several animals were in sight the first animal
to move away was filmed. This approach was
used in order to make consistent recordings.
The infrared video recording equipment is
very costly and therefore considerations as to
the safety of the equipment had to be part of
the reasons for choosing an appropriate site.
Safety of the equipment was also the reason
why infrared video recordings were only
obtained from one site.
was therefore an obvious choice. Furthermore,
electricity was made available. Pine trees
growing in front of the ground burrow posed a
disadvantage because the ground burrow
could not be seen with the camera. For
practical reasons the problem was inevitable.
Great beaver activity had occurred in the area.
Around 80 trees (mainly birches) had been
felled, a large dam was built and a ground
burrow was inhabited. Beavers had settled at
this site a few months post-release.
At site A it was not possible to observe up
stream from the ground burrow due to a turn
of the watercourse.
In August 2000 infrared video recordings were
carried out with the sole purpose of finding
out whether kits had been born.
The National Environmental Research Institute
of Denmark supplied all equipment used in
infrared video recordings.
This study focuses solely
performed outside the den.
on
behaviour
Site A was situated on private land and it was
out of sight from any public road or track and
_________________________________________________________________________ 16
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
6. Time
behaviour
allocation
and
foraging
6.1. Introduction
The behaviour of beavers has been studied
extensively: Tevis (1950) studied the summer
behaviour of a family group of beavers in New
York State, but did not quantify the behaviour,
Patenaude and Bovet (1984) focused on grooming
behaviour, Hodgdon and Larson (1973) studied
sexual differences and Brady and Svendsen (1981)
focused on social behaviour. However, data on time
budgets for free-ranging beavers are scarce.
Presumably this is due partly to the fact that beavers
are primarily nocturnal and therefore studying them
under field conditions is a difficult task.
Buech (1995) studied the time budget in three
families of beaver in northeastern Minnesota. The
study focused on behavioural differences between
male and female beaver. Nolet and Rosell (1994)
estimated time budgets for reintroduced beavers in
the Netherlands. Unfortunately the behaviour was
classified into rather broad categories such as
“inactive inside den” and “on bank”.
In Klosterheden State Forest beavers were released
in lake habitats. Later some beavers settled in a
stream habitat. The building of dams is required in
stream habitats in order for beavers to ensure a
water level high enough to cover the entrance of the
den. This behaviour is not required in lake habitats
and therefore it is reasonable to assume that time
budgets differ between these two types of habitat.
This section of the study aims at presenting
estimates of time budgets for reintroduced beavers
living in stream and lake habitats. Moreover data is
presented on the foraging behaviour of the animals
in the study group.
It is assumed that a camera supplied with an
infrared light source should both improve fieldwork
conditions and enhance the quality of the data
obtained.
_________________________________________________________________________ 17
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
6.2. Results
6.2.1. General results and methods
Beavers abandoned two of the release sites
within a month of the reintroduction (1 and 6).
One site was abandoned around late
December (3).
When the direct observations commenced only
two of the six release sites were inhabited for
certain (2 and 4), one site showed a minimum
of activity (5) and three new sites outside the
state forest were confirmed inhabited (either
personal observation or confirmed by forest
staff). Two of these sites (A and B) were
situated in the vicinity of Klostherheden and
one site (C) was situated approximately five
kilometres from the forest (five kilometres
along the waterway). Site A and C both had
ground burrows whereas the den at site B
bears resemblance to a lodge.
From the 27th of March until the 24th of April
on 13 observation nights at four different sites
(2, 4, 5 and B) a total of 29 hours of
observations were carried out. A variant of
focal individual sampling (the individual (s) in
sight was observed) was used as sampling
method and continuous recording was used as
the recording rule (appendix 3). Data showed
that beavers were in sight on average 17.7 % of
the observation time. Range = 0% - 61,9%.
Observation length was 79 minutes – 210
minutes. Contrary to the predictions made
prior to the fieldwork continuous recording
was possible because only rarely was there
more than one individual visible at the same
time.
The term “direct observations” refers to
observations carried out at sites 2, 4, 5 and B
whereas observations carried out at site A are
referred to as “infrared video recordings”.
In August 2000 thirty-six hours of infrared
video recordings were carried out at site A
with the sole purpose to determine whether
kits had been born. One kit was seen at site A.
In November 2000 direct observations at all
beaver sites were carried out simultaneously
by forest staff and 3 more kits were seen at
three different territories (pers.comm. Thomas
Borup Svendsen).
6.2.2. Direct observations
Recording of first sightings i.e. the first time an
animal appeared during an observation day,
showed that on average beavers at site 4
appeared approximately 7 minutes after
sundown, beavers at site 2 appeared on
average approx. 22 minutes after sundown,
beavers at site 5, -69 minutes (only one obs.
night) and at site B they appeared 2 minutes
after sundown, on average.
At site 5 only one beaver was observed and on
the first observation night it did not appear
while it was still possible to use the night
vision equipment. On the second observation
night the beaver appeared, but it was highly
evident that it was disturbed by the foreign
scent (of the observer) as the beaver tail
slapped 5 times total whenever it got close to
the observer.
At site 4 beavers swam out of sight quickly
when they appeared from the ground burrow
(max. number of minutes in view before
swimming out of sight was 16). Two beavers
were the maximum number observed at the
same time. Gathering of food items to be
foraged on in the midst of reeds happened
quite often and posed another disadvantage to
the observer.
The two beavers at site 2 were often visible at
the same time, but they were not observed
being physically close together. On the fourth
observation night one beaver was in sight
approximately 50% of the observation time.
Swimming and foraging behaviour was
observed as was three minutes of grooming
behaviour. Beavers always swam upstream
when they swam out of view even though a
trail led from the lake across the road and
down to the stream.
One beaver at site B appeared early on one
observation night making it possible to
determine its behaviour for approximately 40
minutes. Swimming and foraging behaviour
were the only behavioural states observed. On
one occasion two beavers were observed at the
same time. The second beaver did not appear
until it was dark.
Considering the relatively large behavioural
repertoire of the beaver it did not seem
_________________________________________________________________________ 18
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
probable that the only behavioural states
observed during the direct observations
(foraging, swimming and grooming) at four of
the release sites represented an unbiased
reflection of a time budget.
The light amplification night vision principle
was insufficient unless beavers were in the
water. Beavers do hardly move when
consuming food and so they could not easily
be distinguished from objects in the dark.
Furthermore, beavers swam out of sight
shortly after emerging and even though they
would often return several times their
behaviour during the time they were absent
could not be determined.
Swimming, foraging and grooming behaviour
were the only behavioural states shown and
grooming behaviour occurred less than 1% of
the time. A few times diving was seen and on
one occasion (one observation day at site 5) tail
slapping was observed 5 times. Time allocated
to behavioural states is shown below (fig. 2).
active period. 2) Artificial light could be
applied by way of a car-battery connected to a
strong lamp.
As the aim of the direct observations was to
collect data for the use of estimating time
budgets point 1 was disregarded as an option.
Hodgdon and Larson (1973) used artificial
light and according to the findings in the study
light did not seem to affect normal behaviour.
In Norway artificial light is used in many
studies (pers.obs.). However, the State Forest
staff required that the disturbance were kept at
a minimum level and did not allow artificial
light.
It was impossible to estimate time budgets
from the data gathered during direct
observations.
Direct observations were continued at one site
(A) using infrared video recordings.
6.2.3. Infrared video recordings
A. Methods
80
70
60
percent
50
40
30
20
10
0
site 4
site 2
site B
observation sites
foraging
swimming
grooming
Fig. 2. Percentage of time allocated to behavioural
states during 29 hours of direct observations at three
sites. Site 5 is not included due to insufficient number
of data.
Due to the above-mentioned factors it was
decided to terminate this type of observations.
The decision was taken after several
considerations as to alternatives to the night
vision principle: 1) The observations could be
continued, but would be restricted to the
period between sundown and total darkness
and between sunrise and the end of an beaver-
A total of 316 hours of infrared video
recordings were obtained in the period from
10/4 to 8/6-2000 from site A (appendix 5).
Earliest onset of observations was at 1900
hours and they were terminated at the latest at
0600 hours (one morning recording was
terminated at 08.30 hours). One hundred and
eighty seven hours of observations were
carried out in the presence of an observer. The
remaining 129 hours were recorded by timing
the video recorder to start taping at a certain
time and focusing the camera either on the
dam or on a feeding site close to the den. The
area around the feeding site was often used
and was therefore chosen as an obvious place
to focus the camera. Non-remote controlled
recordings often followed a period of
observations with an observer present.
Three animals was the maximum number of
beaver in view at the same time.
The two types of recordings will be referred to
as remote controlled recordings and nonremote controlled recordings.
_________________________________________________________________________ 19
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
The beaver activity recorded on the video
tapes was broken into units of “beaver
minutes” so that one minute of observation
with two beavers in sight counted as two
“beaver minutes”, minutes with three beavers
in sight counted as three “beaver minutes” and
so forth.
Data from remote controlled recordings and
data from non-remote controlled recordings
were analysed separately. Focal individual
sampling on all individuals visible at the same
time was used for both types of recordings and
continuous recording was used as recording
rule. In situations where several individuals
were visible and one animal left the area in
view of the camera, this individual was
followed.
Because of the lack of markings for individual
recognition the possibility of investigate the
effect of gender and age on the time budget
was impossible.
B. Ethogram
The ethogram below includes only the
behaviour patterns of beavers observed in this
study. For a more complete ethogram on
beaver behaviour see appendix 4.
An “s” denotes behaviour recorded as a
behavioural state and an “e” means that the
behaviour was recorded as a behavioural
event.
Aggressive behaviour (s): An individual will
lunge at or bite at another beaver and fighting
may be initialised. If the animals are in the
water they will often swim in circles trying to
reach each others hind. If on land, an attack
will often lead to the animals standing on the
hind feet and try to get a grip at the other
individuals fur coat with the front feet and
push it backwards.
According to Brady and Svendsen (1981) this
behaviour only occurred when kits begged for food
while an adult was feeding. Often a bite at a kit
would be sufficient to make the kit withdraw.
(Aggressive behaviour was recorded even if
only one element of the behaviour was seen).
Building behaviour (s): By transporting
branches or other material the dam is either
maintained or build larger. The behaviour
pattern was divided into seven elements:
1) S = swimming
2) Sm = swimming and carrying nonbranch material (grass and/or mud)
collected upstream from pond or from
grass field
3) Sb = swimming and carrying branch
4) E = exploring dam (swimming slowly
alongside dam or walking on dam
without adding material or re-placing
material already on dam)
5) G = gathering of mud (in pond in front
of dam)
6) P = placing branch, mud or grass on
dam
7) B = biting or pawing off grass (from
adjacent field)
As dam building was observed at site A only,
where
video
recordings
took
place,
“swimming” and “swimming and carrying
branches” could be distinguished because it
was possible to determine the subsequent
behaviour. If transportation of an item
occurred in water, it was only recorded as
building behaviour if the subsequent
behaviour was “placing the item on the dam”.
Otherwise the behaviour was recorded as
“foraging”.
Dancing (s): The animal makes a series of
body movements beginning with the head and
then spreading to the rest of the body as if the
animal is shaking itself. The movement is
exaggerated so that the head is moved in
circles.
This behaviour often initialises mutual grooming
between two un-mated individuals and the
behaviour seems to express dominance over another
member of the family group (Wilsson, 1971).
Diving (e): By raising the back and tail above
the water surface the animal dove with the
head being the first part under water.
Under certain circumstances diving without
slapping the tail against the water surface indicates
intense danger (e.g. Wilsson, 1971).
_________________________________________________________________________ 20
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
(At site A no recordings of diving were made
unless tail slapping occurred as well because
beavers only dove when having to pass a tree
that was lying across the stream).
Foraging (s): The animal is either eating or
handling food. This category includes
chewing, reaching for a branch or a plant with
its front feet, transporting a food object and
when an animal foraging moves a little
distance in order to obtain more food items
(sensory pauses and intrapatch walking
included).
Grooming (self-grooming) (s): Either the front
feet, hind feet or teeth were used to clean the
fur while the animal was sitting down. Often a
sequence of self-grooming included both the
use of feet and teeth.
Mutual grooming (s): Two individual(s)
groom each other simultaneously using the
teeth and/or front feet. They often do so in
places that the animal being groomed cannot
reach itself (top part of the back, neck and
head).
This behaviour seems very important as an
expression of social contact (Wilsson, 1971) or for
maintaining the condition of the fur in places the
animal can not reach itself (Paternaude and Bovet,
1983).
Pawing with front legs did not include pawing
by the dam or den.
Play wrestling (s): Two animals interacted by
shoving and pushing each other using the
front legs while standing upright on the hind
legs.
Scent marking (e): An animal scraped together
dirt and/or plant material into a mound
followed by placing the cloaca above the
mound for a few seconds while depositing
secretion on top of the mound. Subsequently
the stamping of the hind legs on the mound
could follow this behaviour.
Beavers are territorial and scent mark within their
territory hereby signalling to beavers unknown to
the family group that the territory is occupied (e.g.
Wilsson, 1971, Nolet and Rosell, 1994). It is likely
that the depositing of anal gland secretion makes
individual recognition possible. The anal gland
secretion varies among sexes , but also among the
two species (e.g. Rosell and Bergan, 1998).
Swimming (s): The animal is moving in the
water. Only the top part of the head, and the
nose is above water.
This behaviour was recorded when it was not
possible to determine any other behaviour
such as transporting an item.
Nose touching (e): An animal approached
another, either from in front or from behind,
and shoved its nose at the receiver’s nose or
neck.
Tail slapping (e): By raising the tail and
slapping it hard against the water surface the
animal created a loud noise. Diving sometimes
followed tail slapping.
This behaviour may be a social greeting and kits
will perform nose touching when begging for food
(e.g. Brady and Svendsen, 1981).
According to Wilsson (1971) the behaviour is
response to a moving object, but the behaviour can
also occur after the animal has increased vigilance
in response to a smell or a sound and it functions as
a warning for other members of the family group
(e.g. Salvesen, 1927).
On land (s): The animal was either sitting or
walking on land, but it was not possible to
determine the behaviour of the animal. This
was due either to the animal being too far from
the camera or because bad weather conditions
such as fog resulted in low visibility.
Pawing with front legs (e): An animal scraped
in the dirt or a scent mound with the front feet,
but the animal did not deposit secretion (no
placement of the cloaca above the scent
mound).
Vigilance (e): If the animals are out of the
water it will stop the behaviour it is
performing, and lift the head. Sniffing may
occur at the same time. When the animal is in
water and the head is moved up and down in
quick movements vigilance is also recorded.
(Vigilance was only quantified when the
animals were foraging and are therefore
_________________________________________________________________________ 21
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Comments on the ethogram
Aggressive behaviour was observed only once
in the 316 hours of infrared video recordings.
An individual (the initiator) approached
another (the receiver), but the receiver lunged
at and tried to bite the initiator who responded
by swimming away. The sequence lasted 9
seconds.
Vigilance behaviour was recorded as an event
although it could be argued that due to the
relatively long duration (up to 40 seconds) and
because vigilance presumably consisted of
both listening and sniffing at the same time,
the behaviour could also be recorded as a state.
Play wrestling was only observed once and the
sequence lasted 13 seconds.
Dancing was observed three times. Each time
two animals were within five metres from each
other. There did not seem to be a response
from the animals not performing the
behaviour.
Scent marking was recorded as a behavioural
event although a scent marking sequence
consisted of several elements.
6.2.4. Non-remote controlled recordings
From 129 hours of recording data from only
351 “beaver minutes” (4.5%) were derived. For
78 hours the camera was focused on the
feeding site and for 37 hours the camera was
focused on the dam (during the 14 remaining
hours the camera was focused on different
sites and data were not included). The number
of beaver minutes obtained from the damrecordings was 118 (some of which were
foraging behaviour) and 233 for the foragingsite recordings. These data were not included
in the time budget estimates.
Figure 3 below shows first sightings derived
from observation days where non-remote
recordings were not preceded by an
observation period in the presence of an
observer. The first sightings are distributed
into arbitrary half-hour periods. All recordings
of first sightings were gathered from
recordings where the camera was focused on
the feeding site.
total number of first sightings
Vocalisation (e): A high-pitched whistling
sound was recorded twice.
From the 37 hours of recording data from 84
minutes of dam building behaviour were
derived (3.8% of total time focused on the
dam). Fifty-six minutes of the total of 84
minutes were not included in the dam
building analysis due to very low visibility on
the video recordings. Further results on dam
building and scent-marking behaviour are
presented in sections 8 and 7 respectively.
5
4
3
2
1
0
20
,3
21 0-2
,0 0,5
21 0-2 9
,3 1,2
22 0-2 9
,0 1,5
22 0-2 9
,3 2,2
23 0-2 9
,0 2,5
23 0-2 9
,3 3,2
00 0-2 9
,0 3,5
00 0-0 9
,3 0,2
01 0-0 9
,0 0,5
0- 9
01
,2
9
discussed in the same section as foraging
behaviour).
half-hour periods
Fig. 3. Time for first sightings as derived from non-remote
controlled recordings on 12 observation days.
On two occasions beavers were seen for the
first time between 21-21.30, and most of the
time they appeared between 22-23.30.
Beavers are mainly nocturnal and usually
emerge after sundown. The exact number of
minutes after sundown that a beaver was seen
for the first time on an observation night was
calculated (fig. 4). No obvious pattern
emerged. Beavers emerged on average 90.5
minutes after sundown.
The data derived from non-remote controlled
recordings and used in analysis were data on
scent marking behaviour and first sightings as
well as data on dam building behaviour from
six observation periods.
_________________________________________________________________________ 22
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
6.2.5. Remote controlled recordings
From 33 observation days (data from 5 other
observation days were not useable due to low
visibility on the recordings) data from a total
of 2531 beaver minutes were obtained from the
remote controlled recordings at site A. This is
equal to 22.6% of total observation time.
minutes after sundown
180
160
140
120
100
80
60
40
20
(1
3/
5)
9
(2
2/
5)
11
(3
1/
5)
7
(6
/5
)
5
1
(1
4/
4)
3
(2
1/
4)
0
observation day
Fig.4. The number of minutes after sundown that first
sightings occurred on twelve nights of non-remote
controlled video recording was calculated. On
observation day 11 beavers emerged 11 minutes prior
to sundown (a zero scored in the graph).
An active period (a least one individual in
sight) lasted approximately from 2100 to 0600
h. However, observations were not equally
distributed to all hours of an active period.
More observations took place between 2200
and 0400 than between 2100-2200 and 04000600 h.
The observation period was divided into four
arbitrary periods each lasting approximately
two weeks. Period one was 11/4-23/4, period
2 was 24/4-7/5, period 3 was 8/5-21/5 and
period 4 was 22/5-8/6. The time spent
observing did not differ between the four
periods (Kc = 1.551, n.s., p>0.05).
A. First sightings
10
9
8
7
6
5
4
3
2
1
0
20
,3
21 0-2
,0 0,5
21 0-2 9
,3 1,2
22 0-2 9
,0 1,5
22 0-2 9
,3 2,2
23 0-2 9
,0 2,5
23 0-2 9
,3 3,2
00 0-2 9
,0 3,5
00 0-0 9
,3 0,2
01 0-0 9
,0 0,5
0- 9
01
,2
9
total number of first sightings
First sightings were distributed into arbitrary
half-hour periods as shown in fig. 5. As the
ground burrow was out of view of the camera,
beavers might have emerged earlier and
travelled upstream which is why the term first
sightings is used rather than emergence time.
This seems to have occurred at least twice (first
sightings between 00.30 and 01.29) since most
other first sightings occurred between 9 pm
and 11 pm.
half-hour periods
Fig. 5. Occurrence of first sightings
per half-hour basis. N= 33 observation days
of remote controlled recordings
_________________________________________________________________________ 23
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
3
2
2
1
0
half-hour periods
1
Fig. 6C. The distribution of first
sightings in period 3 (8/5-21/5).
Fig. 6A. The distribution of first
sightings in period 1 (11/4-23/4).
4
4
3
2
1
0
20
,3
0
21 -20
,0 ,5
9
0
21 -21
,3 ,29
0
22 -21
,0 ,5
0- 9
22 22
,3 ,29
0
23 -22
,0 ,5
0- 9
23 23
,3 ,29
0
00 -23
,0 ,5
0- 9
00 00
,3 ,29
0
01 -00
,0 ,5
0- 9
01
,2
9
3
total number of first sightings
0
half-hour periods
2
half-hour periods
1
Fig. 6D. The distribution of first
sightings in period 4 (22/5-8/6).
0
20
,3
0
21 -20
,0 ,5
0- 9
21 21
,3 ,29
0
22 -21
,0 ,5
0- 9
22 22
,3 ,29
0
23 -22
,0 ,5
0- 9
23 23
,3 ,29
0
00 -23
,0 ,5
9
0
00 -00
,3 ,29
001 00
,0 ,5
0- 9
01
,2
9
total number of first sightings
3
20
,3
0
21 -20
,0 ,5
9
0
21 -21
,3 ,2
9
0
22 -21
,0 ,5
0- 9
22 22
,3 ,2
9
0
23 -22
,0 ,5
0- 9
23 23
,3 ,2
9
0
00 -23
,0 ,5
9
0
00 -00
,3 ,2
0- 9
01 00
,0 ,5
0- 9
01
,2
9
4
20
,3
0
21 -20
,0 ,5
9
0
21 -21
,3 ,2
0- 9
22 21
,0 ,5
9
0
22 -22
,3 ,2
9
0
23 -22
,0 ,5
0- 9
23 23
,3 ,2
9
0
00 -23
,0 ,5
9
0
00 -00
,3 ,2
0- 9
01 00
,0 ,5
0- 9
01
,2
9
total number of first sightings
The distribution of first sightings per half-hour
basis in the four given periods is shown in
figures 6A-6D.
total number of first sightings
___________________________________________________________________________
half-hour periods
Fig. 6B. The distribution of first
sightings in period 2 (24/4-7/5).
The data in figures 6A-6D did not meet the
requirements for a chi-square test. This was
due to the fact that a large number of zeros
occurred and more than 20% of expected
values less than 5. As seen in the figures no
tendency for a change over the observation
period seemed to emerge.
Calculations of the number of minutes after
sundown that beavers first appeared on the
different observation days showed no obvious
pattern (fig. 7). The average time for first
sighting was 78 minutes after sundown.
Dividing the observation period into the above
mentioned four arbitrary periods and testing
for difference in number of minutes after
sundown that firs sightings occurred revealed
_________________________________________________________________________ 24
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
no difference between the periods (Kc = 3.31,
n.s., p>0.05). Beavers there fore, seemed to
appear from the den at an approximate time
after sundown
number of minutes after sundown
275
250
225
200
175
150
125
100
75
50
25
0
0
2
4
6
8 10 12 14 16 18 20 22 24 26 28 30 32 34
observation day
Fig. 7. Number of minutes after sundown that
first sighting occurred on the different
observation days of the observation period.
The first behaviour to be performed after first
sightings is shown below (table 4).
Behaviour
Foraging
Building
Grooming
Swimming
Number of
occurrences
20
8
3
2
Table 4. The table shows the first behaviour to occur
after first sighting on the different observation days
(not including the animals swimming into view of the
camera).
_________________________________________________________________________ 25
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
B. Time budget
The estimate of the time budget was based on
data derived from the 2531 beaver minutes
from the remote controlled video recordings
(figure 8).
It must be kept in mind that due to the lack of
markings for individual recognition, the time budget
is based on the behaviour of three individuals of
unknown sex and age and therefore without
care being taken as to the possible individual
differences.
3.4%
2.3%
swimming
1.1%
5.4%
foraging
building
groom
mutual gr.
12.2%
7.7%
duck pond
on land
67.9%
Fig. 8. Time budget for the family group of beavers at site A
based on a two-months observation period.
As seen in figure 8 the animals spent more
than two thirds of the beaver minutes
foraging. Grasses were eaten in 54.1% of the
time, wooded plants was eaten in 44.5% of the
time and in 1.4% of the time it was not possible
to determine whether grass or wooded plants
were foraged on. The total amount of beaver
minutes allocated to swimming constituted
7.7%.
The beavers spent 12.2% of the time on dam
building. All dam building work were carried
out at the same dam. As the ground burrow
could not be seen on the recordings it was not
possible to determine how much time was
allocated to maintenance/building of the den.
Grooming took place in 5.4% of the time. The
duration of grooming bouts was 12 seconds – 8
minutes and 25 seconds. Mutual reciprocal
grooming occurred in 2.3% of the time (26
times total). Mutual grooming lasted from 17
seconds to 8 minutes and 29 Seconds. On 17
occasions mutual grooming was initiated by
nose touching behaviour and 8 times mutual
grooming was seen without recognisable nose
touching occurring prior to mutual grooming.
On one occasion a walking animal passed
another individual who grabbed a hold of the
passing animal with its teeth and front legs.
This led to mutual grooming
Beavers were observed in the duck pond for
3.4% of the time. Due to the limitation of the
zoom function in the camera and quite often
due to poor weather conditions most of the
time it was impossible to determine the
behaviour of the individuals seen in the duck
pond. Beaver behaviour patterns observed for
certain in the duck pond included swimming
and foraging.
“On land”-behaviour were recorded when the
animal was partly hidden behind vegetation
(and behaviour could not be determined) or
when the animal was seen on land, but the
distance was too far so that the behaviour
performed could not be determined.
_________________________________________________________________________ 26
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
C. Variation in time allocation over the
observation season (April 11th – June 8th
2000).
Time allocated to different behaviour patterns
on the different observation days is shown in
figure 9. On land behaviour is not included.
(Appendix 6 show time allocated to the
different behavioural states as separate
graphs).
275
250
beaver minutes
225
200
175
150
125
100
75
50
25
33 (8/6)
31 (31/5)
29 (26/5)
27 (24/5)
25 (17/5)
23 (14/5)
21 (11/5)
19 (9/5)
17 (4/5)
15 (2/5)
13 (28/4)
11 (26/4)
9 (24/4)
7 (22/4)
5 (19/4)
3 (15/4)
1 (11/4)
0
observation day
swimming
building
foraging
grooming
mutual gr.
in duck pond
on land
Fig. 9. Time allocated to behavioural states per observation day over the observation season. Beaver minutes: one
minute of video recording with two individuals in sight counted as two beaver minutes.
The occurrence of events during the
observation period is shown below (fig. 10)
_________________________________________________________________________ 27
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
40
total number of events
35
30
25
20
15
10
5
1
(1
1/
3 4)
(1
5/
5 4)
(1
9/
7 4)
(2
2/
9 4)
(2
4
11 /4)
(2
6
13 /4)
(2
8/
15 4)
(2
/
17 5)
(4
/
19 5)
(9
21 /5)
(1
1
23 /5)
(1
4
25 /5)
(1
7
27 /5)
(2
4
29 /5)
(2
6
31 /5)
(3
1/
33 5)
(8
/6
)
0
observation day
alert-grass
alert-branch
tailslap
nosetouch
scent mark
Fig. 10. The graph shows the occurrence of behavioural events per observation day over the observation
season (April-June 2000).
The use of the sites within the territory
changed over the season as evident from the
decline in time spent in view of the camera
(fig. 9).
There was a strong decline in time allocated to
foraging over the observation period and
building behaviour mainly occurred from late
April until the middle of May (fig.9).
Scent marking behaviour occurred throughout
the observation period, tail slapping was only
seen a few times and vigilance when foraging
on grass was the predominant behavioural
event shown (fig. 10).
Total number of beaver minutes allocated to
foraging behaviour (fig.9) was split into time
allocated to foraging on grass and branches.
the number of beaver minutes allocated to
foraging on grass was plotted against the
occurrence of vigilance behaviour, a distinctive
pattern emerged (fig.11). The pattern was not
so distinctive when time allocated to foraging
on branches was plotted against vigilance
behaviour (fig.12). In figures 11a and 12a the
number of beaver minutes allocated to
foraging and the occurrence of vigilance
behaviour are plotted as the x- and y-variables
respectively.
_________________________________________________________________________ 28
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
0
occurrence of vigilance behaviour
0
33
5
31
20
29
10
27
40
25
15
23
60
21
20
19
80
17
25
15
100
13
30
11
120
9
35
7
140
5
40
3
160
1
beaver minutes
___________________________________________________________________________
observation day
foraging
vigilance
Fig. 11. During the analysis of the video recordings it was recorded whether the
animals foraged on grass or wooded plants. This graph shows the number of beaver minutes allocated
to foraging on grass. When the occurrence of vigilance behaviour performed while the animal (s) were
foraging on grass were plotted in the same graph a distinctive pattern emerged. Beaver minutes: one
minute of video recording with two individuals in sight counted as two beaver minutes.
y-variable (occurrence of
vigilance behaviour)
40
35
30
25
20
15
10
5
0
0
25
50
75
100
125
150
175
x-variable (beaver minutes allocated to foraging on grass)
Fig. 11a. Occurrence of vigilance behaviour plotted against the numer
of beaver minutes allocated to foraging A line of tendency is shown.
_________________________________________________________________________ 29
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
10
140
beaver minutes
8
100
7
6
80
5
60
4
3
40
2
20
occurrence of vigilance
behaviour
9
120
1
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
0
1
0
observation day
foraging
vigilance
Fig. 12. Beaver minutes allocated to foraging on wooded plants and the occurrence of
vigilance behaviour while foraging on wooded plants during the observation period Beaver minutes:
one minute of video recording with two individuals in sight counted as two beaver minutes.
y-variable (occurrence of vigilance
behaviour)
10
9
8
7
6
5
4
3
2
1
0
0
25
50
75
100
125
x-variable (beaver minutes allocated to foraging on branches)
Fig.12a. Occurrence of events plotted against the number of beaver
minutes allocated to foraging on branches. A line of tendency is shown.
Spearman rank correlation coefficient showed
a strong correlation between beaver minutes
allocated to foraging on grass and the
occurrence of vigilance behaviour ((rs)c = 0.933,
n=33, p<0.001)..
Correlation was also found between beaver
minutes allocated to foraging on branches and
the occurrence of vigilance behaviour,
although the correlation was not as strong ((rs)c
= 0.396, n= 33, p<0.05).
_________________________________________________________________________ 30
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
D. Variation in time allocation over the active
period
As mentioned earlier an active period lasted
from approximately 21.00 to 06.00 hours. The
time allocated to different behavioural states
(derived from 2531 beaver minutes) during
arbitrary one-hour periods was calculated
(fig.13). The same numbers are shown in
percent (fig.14).
800
700
beaver minutes
600
500
400
300
200
100
0
21.00- 22.00- 23.00- 00.00- 01.00- 02.00- 03.00- 04.00- 05.0021.59 22.59 23.59 00.59 01.59 02.59 03.59 04.59 05.59
one-hour periods
swimming
foraging
building
groom
mutual gro.
duck pond
on land
Fig. 13. The active period was divided into arbitrary one-hour periods and time
allocated to behavioural states was calculated. The calculations were made on the
basis of data from the entire observation period (N=2531 beaver minutes), which
explains the high number of beaver minutes in the time periods. Beaver minutes: one
minute of video recording with two individuals in sight counted as two beaver minutes.
_________________________________________________________________________ 31
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
100%
90%
80%
70%
percent
60%
50%
40%
30%
20%
10%
0%
21.00- 22.00- 23.00- 00.00- 01.00- 02.00- 03.00- 04.00- 05.0021.59 22.59 23.59 00.59 01.59 02.59 03.59 04.59 05.59
One-hour periods
swimming
foraging
building
mutual grooming
duck pond
on land
groom
Fig. 14. The active period was divided into arbitrary one-hour periods and
the amount of time allocated to different behavioural states in the different
one-hour periods were calculated and shown in percent.
Beavers were most active (in front of the
camera) during the first half of the active
period (fig. 13). As seen in figures that 13 and
14 foraging behaviour was the predominant
behaviour in all one-hour periods except
between 5 and 6 a.m. The number of minutes
spent foraging decreased over the night and
foraging constituted between 37.0 and 80.4% of
a one-hour period. Building behaviour were
performed all time periods, but occurred most
often early in the active period and the
behaviour was predominant late in the active
period (5-6 a.m.) where it constituted 49.9% of
total number of beaver minutes. Building
behaviour was the second mostpredominant
behaviour in five out of nine one-hour periods.
Most grooming behaviour was performed
before 2 a.m.. Mutual grooming occurred
between 22.00 and 04.00 hours though the
behaviour was shown most often between
22.00 and 00.00 hours.
_________________________________________________________________________ 32
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Time allocated to swimming decreased over the
active period, however, swimming constituted an
approximately equal percentage of total number of
beaver minutes in all one-hour periods.
Beavers were seen in the duck pond at all hours
during the night except from 5-6 a.m.
_________________________________________________________________________ 33
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
E. Behavioural events
Vigilance behaviour occurred 240 times and
the duration of the vigilance bouts was 2-40
seconds. Vigilance was only quantified when
the animals were foraging and are therefore
discussed in the same paragraph as foraging
behaviour.
Foraging behaviour was divided into two
categories; foraging on grass and foraging on
wooded plants, and the frequency of vigilance
were calculated for both categories (table 5).
Number of
minutes
spend
foraging
Occurrence
of vigilance
behaviour
Frequency of
vigilance
behaviour
Grass
Wooded
plants
929
789
206
1 time per 4.5
minutes or
0.222 time per
minute
Grass
Wooded
plants
Occurrence
of vigilance
behaviour
-GrassOccurrence
of vigilance
behaviour
-Wooded
plantsFrequency
of vigilance
behaviour
-Grass-
34
1 time per
23.2
minutes or
0.043 per
minute
Table 5. The number of beaver minutes allocated to
foraging on grass and wooded plants were
calculated, as was the number of times vigilance
behaviour occurred.
As seen in table 5 beavers were vigilant more
often while foraging on grass than when
foraging on branches. When beavers foraged
on grass they had to move away form the
water whereas when foraging on branches the
animals were sitting in the waters edge.
Beavers were often seen foraging close
together and in order to find out whether there
was an effect in time spent vigilant when
foraging in groups, the two foraging categories
were divided into time spend on foraging
solitarily and on group feeding (table 6).
Group feeding was defined as two or more
individuals foraging within 10 metres or less
from each other. Group feeding on branches
included one or more individuals foraging on
branches and one or more feeding on grass.
Frequency
of vigilance
behaviour
-Wooded
plants-
Solitary
foraging
765 minutes
Group
feeding
164 minutes
767 minutes
22 minutes
169
37
27
7
1 time per 4.5
minutes or
0.221 time per
minute
1 time per
4.4 minutes
or 0.223 time
per minute
1 time per 28.4
minutes or
0.035 time per
minute
1 time per
3.1 minutes
or 0.318
times per
minute
Table 6. Foraging was divided into two categories;
solitary foraging and group foraging. The number of
time vigilance behaviour occurred was used to
calculate vigilance frequency.
As seen in table 6 the occurrence of vigilance
behaviour did not differ between solitary and
group feeding behaviour while foraging on
grass. When beavers foraged on wooded
plants they were vigilant much more often
when group feeding than when feeding
solitarily.
Other behavioural events
“Tail slapping” was only observed 5 times
during the 316 hours of observation. Tail
slapping was followed by diving two times.
On the last three occasions tail slapping was
followed by swimming and on all three
occasions the animal swam around in the same
area where it had just tail slapped.
“Nose touching” was observed a total of 21
times. On 17 occasions nose touching initiated
mutual grooming, one time it initiated
_________________________________________________________________________ 34
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
aggressive behaviour, 2 times one animal
swam away after nose touching and on one
occasion an animal followed another after nose
touching.
“Scent marking” was observed 46 times (both
remote controlled and non-remote controlled
data included). Scent markings seen during an
observation night were checked the next day
and often no actual scent mound was
recognisable.
“Pawing with front feet” occurred four times.
No placing of the cloaca above the pile was
seen subsequently.
6.2.6. Foraging behaviour
The plant species foraged on in Klosterheden
State Forest are listed below (table 7). Of the
beaver’s preferred species willow was the only
one that was available in large quantities at all
release sites. Since none of the listed species
appeared to have been avoided at any site the
table presents a total of species foraged on, all
sites included.
Wooded species
Non-wooded species
Alder (Alnus sp.), el
Cattail (Typha sp.),
dunhammer
Beech (Fagus
Common reed
sylvatica), bøg
(Phragmites australis),
tagrør
Birch (Betula sp.),
Meadowsweet
birk
(Filipendula ulmaria),
alm. mjødurt
Black cherry
(Prunus serotina),
glansbladet hæg
Mountain ash
(Sorbus aucuparia),
alm. Røn
Oak (Quercus sp.),
eg
Pine (Pinus sp.), fyr
Spruce (Picea sp.),
gran
Trembling aspen
(Populus tremula),
bævreasp
Willow (Salix sp.),
pil
Danish terms are included.
Bog myrtle (Myrica gale, mosepors) was also
cut but there was no evidence of the species
being utilised as food source, rather it was
used as building material. Additionally, at site
A several grasses and herbs were eaten, but
the plants were not characterised to species
level.
The percentage of each wooden species
foraged on is shown below (table 8). The
calculations were based on cuttings and felled
trees from all release
sites and presented as a total. This is due to the
fact that no estimates of the species
composition were made prior to the
reintroduction.
Species
Willow
Birch
Oak
Beech
Aspen
Pine
Alder
Mountain ash
Black cherry
Spruce
Percentage of total number of
cuts and felled trees (percent)
71.5
17.1
6.3
1.0
1.0
0.8
0.7
0.7
0.5
0.4
Table 8. The percentage of cuts and felled trees of each
species. The numbers are totals of all cuts and felled
trees at the release sites.
94.8% of plants foraged on was found less
than five metres from the waters edge. The
maximum distance travelled from water to a
foraging site was 27 metres.
88.6% of cuts and felled trees measured three
centimetres or less in diameter (more than 2900
cuts and felled trees measured).
Maximum diameter of a tree felled was 18 cm
at the cutting height, approximately 20-cm
above ground level.
Tabel 7. Plant species foraged on in Klosterheden State
Forest between October 1999 and March 2000.
_________________________________________________________________________ 35
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
6.3. Discussion
6.3.1. Direct observations - perspectives
Although it was impossible to estimate time
budgets based on the data gathered from
direct observations in the present study some
interesting aspects can be considered. If
observations had revealed a difference in time
allocation between stream and lake habitats
several questions could be asked: 1) did
beavers in stream habitats allocate less time to
foraging? 2) If less time was allocated to
foraging, could this in some way be
compensated for, e.g. perhaps by a different
foraging strategy? 3) Do beavers in stream
habitats compensate for the time allocated to
building behaviour by increasing the length of
the active period?
6.3.2. First sightings
No difference in time for first sightings was
found to occur over the observation period
and beavers emerged at approximately the
same number of minutes after sundown
during the entire observation period. It is
highly likely that a prolonged observation
period lasting several seasons would have
revealed other results. If the amount of light
entering the den determines the onset of an
active period there would be a large difference
between the active periods of summer and
winter. If the active period is expected to be
approximately the same length independent of
season, it must be expected that an internal
mechanism onset the active period.
6.3.3.Time budget
The time budget in the present study was
based on observations from one family group
only. This means that generalisations on
beaver behaviour cannot be made on the basis
of the findings in the present study, or at least
generalisations must be made with caution.
In this study most time was found to be
allocated to foraging, building and swimming
behaviour, which is in accordance to the
findings of Busher and Jenkins (1985, referred
to in Buech, 1995). Busher and Jenkins found
feeding and swimming behaviour to be the
two most predominant behaviours in stream
habitat, and Buech (1995) found that most
time was allocated to feeding, swimming and
being-in-lodge behaviour.
Buech (1995) found that females and males
spent 31.1% and 33.2% respectively, on travel
within the territory. In the present study
beavers spent 7.7% of the total number of
beaver minutes (active time) on swimming.
Nolet and Rosell (1994) found that beavers
spent considerable time swimming (max. of 6.3
hours per day) during the first two years after
re-introduction to the Netherlands.
There are several explanations as to why
swimming behaviour constituted so little time
in the present study. First of all, the amount of
time spent on swimming must be an
underestimate due to limitations of the
observation method. Beavers were often seen
travelling downstream from the dam and
upstream and out of sight. Secondly, streams
of low water level are difficult for a beaver to
swim in and therefore beavers might not
allocate much time to travel in these habitats.
Thirdly, reintroduced animals might behave
differently because they have not yet adapted
to the habitat and therefore spend much time
near the den rather than for example exploring
the surroundings.
The ground burrow at site A in this study was
situated in stream habitat whereas in Buechs
(1995) study beavers lived in lake habitat. The
study of Nolet and Rosell (1994) concerned
beavers in river habitats and the difference in
types of habitats may be the cause of the
differences in time allocated to swimming.
Mutual grooming occurred in 2.3% of the time.
Mutual grooming was directed at the head,
neck, flank and back areas, areas that cannot
be reached during self-grooming. This finding
is an agreement with the findings of Patenaude
and Bovet (1984) who reported that 80% of
mutual grooming elements was directed at
these body parts and that less than 10% of selfgrooming acts were directed at the same spots.
The authors suggest that the function of
mutual grooming is essentially to maintain the
conditions of the fur and that maintenance of
social bonds or appeasement has little or no
_________________________________________________________________________ 36
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
part in it. Patenaude and Bovet (1984) based
their conclusions on the following findings: 1)
grooming acts were limited to areas of the
body which could not be reached by selfgrooming, 2) the rate of mutual grooming
fluctuated from month to month similarly to
the rate of self-grooming, and 3) there was no
indication that between weaned animals, some
individuals were consistently groomers or
groomees.
Wilsson (1971) on the other hand suggests that
mutual grooming seems to be a very important
expression for social contact all through life,
and suggest that mutual grooming has a
function of decreasing aggressive behaviour
between family members. Wilsson (1971)
studied mostly animals in captivity whereas
Patenaude and Bovet (1984) studied freeranging animals, which could be a possible
explanation of the differences. Brady and
Svendsen (1981) studied social behaviour in a
family of beaver (Castor canadensis) , but do not
mention mutual grooming as a social
interaction
In the present study mutual grooming was
either initiated by nose-touching (17 times), or
by an animal grabbing hold of another
individual as it passed by (once) and 8 times it
was not possible to determine the preceding
behaviour. According to Eisenberg (1967)
nose-touching is a common rodent posture
used to reduce social distance.
Besides initiating mutual grooming 17 times,
nose-touching led to one incident of aggressive
behaviour, and twice nose-touching resulted in
one beaver following each other swimming in
the present study.
Motivation for mutual grooming in this study
seemed largest between 2200-2400 h which is
also the time where most first sightings
occurred Beavers usually emerge one at a time
(Townsend, 1953) and if appeasement is a
function of mutual grooming it seems likely
that beavers would engage in mutual
grooming at the beginning of the active period
upon the first encounters outside the den. It
seems reasonable to assume that some social
interactions must exist and be expressed in a
species like the beaver where family groups
live closely together for long periods of.
It seems reasonable to assume that in this
study nose-touching functioned as a social
greeting behaviour that usually initiated an
appeasement or social contact behaviour as
mutual grooming. Aggressive behaviour was
only observed twice and the group seemed
very homogenous, foraging side by side for
long periods of time.
12.2% of active periods were allocated to dam
building behaviour in this study. Buech (1995)
found that female beavers on average spent
6.4% on building behaviour (lodge work and
food-cache work) and males spent 11.1% on
building behaviour (also lodge and food-cache
work). However, females have been reported
to spend more time on dam and lodge
construction than males (Hodgdon and
Larson, 1973), but Busher and Jenkins (1985,
referred to in Buech, 1995) reported the
opposite. At no time in the present study did
more than one beaver perform dam building
behaviour, but whether it was the same animal
or whether both sexes participated in building
the dam remain uncertain It does not seem
reasonable to make generalisations on time
allocated to dam building behaviour because
the extent to which dam building is required
depends on the physical parameters within a
habitat.
Motivation for building behaviour seemed
particularly high between 2300-2400, 0400-0500
and 0500-0600 h. 22.1%, 19.2% and 49.9%
respectively was spent on building in these
three time periods. These findings agree with
the findings of Buech (1995) who found
construction peaks (lodge and food-cache
work) to be between 2200-2400 and 0300-0400
h.
Motivation for building between 2200 and 2400
hours coincide with peaks in foraging
behaviour. Foraging on branches at the
beginning of an active period would result in
easy-to-obtain building material. Often beavers
were observed to add branches just foraged on
to the dam. Having spent much time on
foraging in a large part of the active period
would presumably decrease the motivation for
feeding behaviour thereby leaving more time
to engage in other behaviours. This could
explain the peak late in the active period.
_________________________________________________________________________ 37
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
6.3.4. Variation in time allocation between
April 11th and June 8th 2000
There was a change in the behaviour of the
beavers concerning the use of sites within the
territory over the observation season, i.e. the
time beavers spent in vicinity of the camera
declined over the season.
Time allocated to foraging behaviour declined
over the observation season suggesting that in
early spring where deciduous trees did not yet
have leaves grass constituted a large
proportion of the amount of food consumed.
Later on in the season buds and leaves as well
as herbs and aquatic plants were available and
therefore grass consumption decreased. The
result was that beavers foraged elsewhere, out
of view of the camera.
Time allocated to dam building behaviour was
relatively large from late April to the middle of
May, but decreased hereafter. An obvious
interpretation of the cause of the termination
of building behaviour is that the dam at this
point in time had the required effect, i.e. the
water level was appropriate. However,
observations in august showed that the dam
had been built much longer. Rather, the
decrease in time allocated to dam building
behaviour seemed to coincide with the
building of another dam upstream the den.
6.3.5. Variation in time allocation over the
active period
In this study beavers were most active (i.e. in
view of the camera) during the first half of the
active period. It seems likely that motivation
for foraging must be high after a long period of
rest in the den and since the grass field in view
of the camera constituted a major food source
this would explain the amount of time spent
there during the first half of the night. After
foraging for a while motivation for foraging
presumably decreased leaving more time to
engage in other behaviours.
6.3.6. Foraging and vigilance behaviour
Beavers in the present study allocated
approximately
68%
time
to
foraging
behaviour. In comparison Buech (1995) found
that females and males allocated 44.1% and
34.6% time respectively to foraging. The large
difference between the findings of the two
studies may be due to the methodological
approaches applied. Buech (1995) used radio
telemetry and was therefore able to follow the
subjects around whereas data in this study
were derived from video recordings where
only a small fraction of the territory could be
seen. It is likely that the grass field in view of
the camera was the preferred foraging site and
so time was allocated to other behaviour
patterns when the animals were out of view.
This would result in an overestimate of total
time spent foraging.
Buech (1995) found that adult females
allocated most of the time to feeding in both
late spring and summer whereas males spent
more time exploring the territory. Though
males participate in the care of young, females
keep close to the den when kits are confined
inside the den (Paternaude and Bovet, 1984). A
beaver kit was observed in August 2000. It is
possible that the foraging behaviour of the
female parent may account for the large
amount of time allocated to foraging in the
present study. At this time of year she would
be lactating and therefore energy requirements
would be increased.
Beavers in Klosterheden foraged on grass in
54% of the time allocated to foraging. Grazing
periods lasted up to 35 minutes. The decrease
in time allocated to foraging on grass
coincided with the trees coming into leaf. That
beavers graze in the manner shown on the
video recordings have not been recorded
earlier, and grazing may have been foraged on
due to the lack of other available species.
According to Brown (1999) a forager can
respond to its cost of predation by choosing
the amount of time spend in the food patch
and/or by adopting a particular level of
vigilance. By transporting branches to the
waters edge for consumption and by foraging
close to the water (94.8% of all cuts and felled
trees in the present study were found less than
five metres from the water) beavers do seem to
adopt a certain level of vigilance, at least when
foraging solitarily, where the frequency of
vigilance were six times less than while
foraging on grass. When the animals foraged
on grass they had to move away from the
_________________________________________________________________________ 38
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
water – the route of escape – and this seemed
to increase the level of cautiousness.
Occasionally foraging took place for more than
10 minutes without the animal being vigilant.
However, the number of beaver minutes
allocated to foraging on grass and the
occurrence of vigilance was strongly
correlated. Beaver minutes allocated to
foraging on branches and the occurrence of
vigilance was also correlated, but not as
strongly. The long foraging bouts without the
animal being vigilant seem to be explained by
individual differences.
The level of vigilance while the animals
foraged on branches increased when they were
feeding in groups. Beavers foraging on
branches may have been preoccupied with and
aware of the behaviour of beavers feeding
close by. It may be that branches are a more
valuable food source and thus worth
defending. Brady and Svendsen (1981)
however, found that beavers did not generally
defend branches that were dragged to the
water.
Brady and Svendsen (1981) measured the
tendency for beavers to initiate or avoid group
feeding by recording whether animals initiated
foraging within a five-metre zone from another
individual. The authors found that beavers
actually avoided group feeding. In the present
study beavers often foraged in groups (less
than 10 metres from each other) and
sometimes beavers foraged side by side in
physical contact. An advantage of group
feeding is that time spent on being vigilant is
reduced per individual and therefore more
time can be allocated to foraging. This is
reported of many birds and herbivores
(Brown, 1999). However, in the present study
there was no difference in the frequency of
vigilance behaviour whether beavers were
group- feeding or feeding solitarily on grass.
Beavers usually forage solitarily (e.g. Tevis,
1950;Hodgdon and Larson, 1973; Brady and
Svendsen, 1981) and the fact that beavers often
foraged in groups in the present study may be
due to the fact that grass was the only
abundant food sources at the particular time of
year. If grazing was a local phenomenon there
is no reason to assume that the level of
vigilance should change .
Generalist herbivores must have a mixed diet
in order to avoid large quantities of secondary
metabolites (Nolet et al., 1994). Beaver
positively selected non-willow species that
were very uncommon in the Biesbosch,
Netherlands, and the authors suggest that
beavers selected them for their complementary
minerals or in order to avoid dietary
deficiencies (Nolet et al., 1994). At site A in the
present study beavers were often seen to
forage on pine trees. Both needles and bark
were eaten. Jenkins (1979) reports that pine has
a greater concentration of one or more
important nutrients than the bark of some
deciduous trees in spring. Beavers at site A
might have been lacking of certain minerals or
nutrients.
Approximately seventy percent of all cut and
felled trees were willow. Willow is described
as on of the preferred species (Collet, 1897;
Aldous, 1938; Hall, 1960; Lahti and Helminen,
1974; Curry-Lindahl, 1967; Aleksiuk, 1970), but
the large quantities of willow foraged on in
Klosterheden seems merely to reflect that this
was the only abundant deciduous species
available, i.e. beavers did not seem to
positively select the willow. However, Nolet et
al. (1994) suggest that in the Biesbosch beavers
satisfied their caloric need with Salix, but used
non-willow species as complentary mineral
sources. Birch was the second most cut and
felled species, and at some sites within
Klosterheden beavers cut nearly all birches
available.
Apart from willow and few small birches, oak
was the only abundant deciduous species at
site 5, which explain the relatively large
percentage of oaks cut or felled. Oak is not a
preferred species, and the fact that oak was cut
to this extend reflect the low quality of this site
as beaver habitat. Beaver abandoned site 5
approximately by the middle of March 2000. If
beavers positively select non-willow species,
and they are in fact dependent on a mixed diet,
it is the impression that only a few sites in
Klosterheden forest will be able to sustain a
family group of beavers in the long run
because winter food (bark) will be the limiting
factor.
_________________________________________________________________________ 39
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Nearly ninety percent of cuts and felled trees
measured 3 cm or less in diameter and 94.8%
of plants foraged on was found less than 5
metres from water. Willow bushes (usually
with most branches less than 5 cm) grow along
all streams in Klosterheden so these two
factors coincide. However, beavers prefer
branches less than 5 cm in diameter (Aldous,
1938; Hall, 1960; Novakowski, 1967).
The maximum distance travelled from water to
a foraging site was 27 metres. This distance was
measured at site 5 where the oaks were found
between approximately 10-30 metres from the
water. These findings are in agreement with
those of Curry-Lindahl (1967), Simonsen (1973)
and Frendin (1979) who found that beavers
usually forage within 10 metres from the water
and rarely travel more than 100 metres from
water to a foraging site.
_________________________________________________________________________ 40
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
7. Scent marking behaviour
7.1. Introduction
Beavers scent mark by depositing castoreum
and/or anal gland secretion on scent mounds,
which are piles of mud, debris, plant material
and branches scraped together by the beavers
(e.g. Müller-Schwarze and Heckman, 1980;
Svendsen, 1980; Tang et al., 1993). The main
function of scent marking appears to be
maintaining of territorial rights (e.g.Hay, 1958;
Aleksiuk, 1968; Rosell and Nolet, 1997) and
recognition/discrimination of relatives through
phenotype matching (Sun and MüllerSchwarze, 1998a, 1998b). According to Sun
and Müller-Schwarze (1997) new territory
owners frequently mark their territories
independently of season whereas residents of a
longer time span mainly scent mark during
spring and early summer where dispersal takes
place.
Nolet and Rosell (1994) drew territory
boundaries partly on the basis of scent
mounds. Their study group were beavers
reintroduced to the Netherlands in 1988-1991
in sequential releases. The first beavers to
settle claimed very large territories, measuring
up to 36.5 km (both bank sides included), but
three years later the average territory size had
decreased to 6.4 km (Nolet and Rosell, 1994).
Prior to the reintroduction of beavers to
Denmark it was estimated that Klosterheden
has a carrying capacity of 11 family groups or
44-77 individuals (Blom-Hansen, 1998). If
reintroduced beavers in Denmark claimed
territories of the same size as in the
Netherlands, the estimated carrying capacity
will be hugely overestimated.
By locating scent mounds in Klosterheden it
was be possible to determine territory
boundaries and thus to estimate territory sizes.
On the basis of these findings, carrying
capacity of the release area was calculated
_________________________________________________________________________ 41
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
7.2. Results
7.2.1. Data on scent mounds in the release area
Data gathered on scent mounds found at the
release sites during the first seven months after
the reintroduction are shown below (table 9).
Scent mounds measured approximately 25 cm in
diameter and 10 cm in height.
Week
Site
Material
41
41
41
41
42
42
43
44
46
46
2
2
6
8
10
15
15
3
3
4
2
3
2
2
2, down stream
5
5
3
2, down stream
7
7
7
3
3
Ground mat.
Moss, grass
Ground mat., cones
Moss, grass
Moss
Ground mat.
Ground mat.
Ground mat., plant mat.
Ground mat., plant mat.
Grass, moss, needles
Grass
Ground mat., plant mat.
Ground mat., twigs, grass
Ground mat., twigs, grass
Ground mat., twigs, grass
Moss, plant mat.
Moss, grass, twigs
Strong/weak
smell
S
W
S
W
S
S
S
S
S
W
S
W
W
W
S
W
W
Table 9. Scent mounds found at the release sites and adjacent waterways in the period October 1999- March 2000.
Site 7 is a small lake in Klosterheden State Forest that was not used as a release site. Site 7 was made part of a
territory for at least a five-week period. Week number 41 to 52 was in 1999 and week number 2 to 15 was in 2000.
Twice at site 4 (week 43 and 44) there was a
strong smell of beaver at a foraging site, but
there was no evidence of an actual scent
mound. This also occurred at artificial lodge
number two (the one not inhabited) at site 3
twice in week 41 and once in week 44. There
was a very strong smell of beaver at the
secondary artificial lodge at site 5, in week 2.
7.2.2. Data on scent markings from video
recordings
When analysing the infrared video recordings
from site A data on 46 scent markings were
obtained (table 10). The data included site for
scent marking, duration of scent marking
behaviour, time and date.
_________________________________________________________________________ 42
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Date
Site
Duration (in seconds)
Time
11/4
17/4
17/4
17/4
19/4
19/4
19/4
20/4
20/4
20/4
20/4
20/4
21/4
22/4
22/4
22/4
23/4
24/4
24/4
24/4
24/4
24/4
25/4
25/4
25/4
25/4
25/4
26/4
27/4
27/4
28/4
28/4
1/5
3/5
3/5
4/5
4/5
4/5
10/5
11/5
11/5
18/5
18/5
24/5
30/5
31/5
Feeding site
Foraging site
Foraging site
Foraging site
Feeding site
Foraging site
Foraging site
Feeding site
Feeding site
Foraging site
Foraging site
Foraging site
Foraging site
Foraging site
Feeding site
Feeding site
Foraging site
Feeding site
Feeding site
Dam
Foraging site
Feeding site
Feeding site
Feeding site
Feeding site
Feeding site
Feeding site
Dam
Feeding site
Feeding site
Feeding site
Feeding site
Foraging site
Stream bank
Dam
Stream bank
Stream bank
Dam
Foraging site
Feeding site
Feeding site
Dam
Dam
Dam
Dam
Stream bank
6
9
12
12
12
8
12
13
12
10
15
14
7
13
7
9
6
18
17
12
11
13
12
18
6
7
8
16
10
17
14
15
15
6
6
9
10
17
8
10
8
8
11
7
8
11
23.39
22.47
23.52
01.51
22.33
22.38
22.39
22.33
22.40
23.00
23.05
23.10
23.36
22.30
22.58
01.28
22.46
23.42
00.20
00.39
00.50
00.54
22.10
22.29
22.30
22.32
23.06
00.06
22.37
22.52
22.49
23.29
22.24
23.59
01.49
22.33
22.38
00.50
23.34
00.30
00.36
22.58
03.35
22.28
02.07
22.56
Table 10. Data on scent markings observed on infrared video recordings. Feeding site, foraging site, dam and stream
bank are all places within site A (appendix 5).
_________________________________________________________________________ 43
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Scent marking behaviour lasted between 6 and
18 seconds. The behaviour included pawing
with the front feet, placing the cloacae above
the pile scraped together, and depositing scent.
Stamping the hind legs on the pile for a couple
of times occasionally followed these scent
marking sequences.
beavers scent mark shortly after emerging
from the den to begin an active period.
The maximum number of scent markings in
one observation day was 5.
Foraging behaviour preceded scent-marking
behaviour in 24 of 46 cases. Swimming
occurred 11 times prior to scent marking,
building preceded scent marking behaviour
five times, mutual grooming preceded scent
marking behaviour twice and four times
grooming occurred prior to scent marking.
The animals scent marked on four different
spots. Tventy of the scent markings occurred
by the feeding site, close to the ground
burrow, 10 scent markings occurred at the
edge of the grass field bordering the stream, on
a foraging spot, and eight times the animals
scent marked by the dam. Four scent markings
were observed at another foraging site.
25
20
15
10
5
0
21
.0
021
.5
22
9
.0
022
.5
23
9
.0
023
.5
00
9
.0
000
.5
01
9
.0
001
.5
02
9
.0
002
.5
03
9
.0
003
.5
9
total number of scent markings
The distribution of the scent markings to
different time periods of the active period
(arbitrary time periods) was calculated (fig.
15).
time period
Fig. 15. The active period was divided into arbitrary
one-hour periods and the occurrence of scent markings
in all given time periods were counted.
Most scent markings occurred between 22.00
and 23.00 (69.6% occurred between 22.00 and
24.00) which is also the time where most first
sightings occurred. This finding suggests that
On seven occasions a scent mark made by one
individual was over-marked by another
individual within less than eight minutes later
(one time the interval was 15 minutes).
Scent marking after foraging always occurred
where an animal left the foraging area to enter
the water.
Scent marking behaviour by the dam was
performed following a building sequence on
all five occasions.
7.2.3. Estimates of territory sizes
Due to the low occurrence of scent mounds,
territory boundaries were defined on the basis
of signs of activity along the waterways and
possible natural occurring boundaries such as
roads and houses (appendix 7). In the
estimates, the territories were measured as
kilometres of waterway, both bank sides are
included (table 11). Measurements were made
using a geographical information system, the
MapInfo computer program. Average size was
4.7 km.
Site
Territory size (km)
C
7.4
4
4.6
A
4.2
B
4.0
D
4.0
2
3.8
Table 11. Territory sizes were calculated using the
MapInfo computer programme. Both bank sides were
included in calculations.
_________________________________________________________________________ 44
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Blom-Hansen (1998) calculated the total
stream length within Klosterheden State
Forest (23.6 km) and estimated carrying
capacity for Klosterheden based on territory
sizes found in the literature. The carrying
capacity was found to be 11 family groups or
44-77 individuals.
Using the territory sizes in the present study
the carrying capacity of Klosterheden is 10
family groups or approximately 40
individuals.
However, beavers abandoned four out of six
release site suggesting that not all sites
within the study site were optimal beaver
habitat.
_________________________________________________________________________ 45
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
7.3. Discussion
Peaks in scent marking have been reported to
occur in spring where 2-year-olds leave their
natal site and kits are born (Townsend, 1953;
Svendsen, 1980; Rosell and Nolet, 1997). The
methodological approach, where regular
recordings of scent mounds took place in
October-March, may be the cause that so few
scent mounds were found in the present study.
However, Sun and Müller-Schwarze (1997)
reports that new territory owners frequently
mark their territories independent of seasons.
During the recordings of data on scent
mounds at the release sites in the present
study all mounds of any kind of material
located at or very near the waters edge were
checked for beaver scent. However, as evident
of the video recordings in this study beavers
do not always scrape together large piles of
mud or debris and quite possibly scent
mounds with weak beaver scent could have
been missed during the recordings.
Beaver cannot urinate without mixing urine
with castoreum (Walro and Svendsen, 1982)
and so it is possible that when an individual
spends a relatively long time at a site it has to
urinate thereby leaving scent behind
unintentionally. This would explain why scent
on several occasions was detected at foraging
sites though there was no visible scent mound.
There are several explanations for the low
occurrence of scent mounds in this study:
1) Energy costs of patrolling the territory in
every activity period may be too high, and
beavers would stay in the core area most
of the time.
2) Reintroduced
beavers
may
behave
differently; perhaps they allocate more
time to being vigilant and refrain from
moving too far from the core area, and
making use of the whole territory only on
occasions.
3) The very low water level in the majority of
the watercourses in Klosterheden makes it
difficult for the beavers to regularly travel
the total distance of the territory.
4) Stimuli in terms of scent from other
beavers may not have been present in the
study area where population density was
very low.
The first three mentioned explanations would
all result in a low encounter rate, and hence a
decreased stimulation for scent marking.
Müller-Scwarze and Heckman (1980) found
that the shorter the distance to the nearest
active lodge of its neighboring colony, the
more scent mounds were found at a particular
lodge. Rosell and Nolet (1997) found that the
number of scent markings increased
significantly with the number of neighbouring
territories, and it seems likely that the low
density and thus the low encounter rate in the
present study resulted in the low occurrence of
scent mounds.
Schulte (1998) found that beavers visited castor
fluid (on experimental scent mounds) from
non-neighbour adult males nearly twice as
often as scent from family and neighbouring
adult males. The beavers released in Denmark
were all caught within the same area
(Fläming/Dübener Heide) of Germany and it
can not be ruled out that some individuals
may have experienced encounters with each
other and may even be siblings. According to
Schultes (1998) findings this would result in
decreased responsiveness to scent markings
between familiar animals.
From the video recordings obtained at site A in
the present study data on 46 scent markings
over a two-month period were derived. All
scent markings occurred on five different
places in the vicinity of the den and thus in an
area much used. This is in agreement with
both Rosell and Nolet (1997) who found that
most scent mounds were placed at often used
sites, and Nietsche (1985) who found that the
central part of the territory was more intensely
marked than the peripheries (referred to in
Rosell et al., 1998). Also, Müller-Schwarze and
Heckman (1980) found that of 159 scent
mounds 85% were located on or near trails,
lodges and dams. Butler and Butler (1979)
found that 84% of the scent mounds
constructed were in areas of high activity
rather than at the territory boundaries.
_________________________________________________________________________ 46
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
According to Butler and Butler (1979) scent
marking in beavers serve to bond the family
group. Schulte (1998) suggest that scent marks
reduce the likelihood of agonistic encounters.
Members of different family groups have little
interaction except for spring when dispersal
starts (Sun and Müller-Schwarze, 1997). And
considering the relatively high number of scent
markings within an area close to the den at site
A in the present study, it seems reasonable to
assume that scent marking does serve as a
source of social communication between
family group members, as well as maintaining
territorial rights.
Beavers can discriminate relatives by
phenotype matching on the basis of anal gland
secretion (AGS). AGS is individually specific,
but related individuals have a more similar
profile of the chemical compounds than nonrelated individuals
(Welsh and MüllerSchwarze, 1989; Sun and Müller-Schwarze,
1997).
Beavers also seem to be able to
memorize information in castoreum to
recognize family members, neighbours and
non-neighbours (Schulte, 1998). However,
castoreum is derived from food and since diet
composition
changes
between
seasons,
castoreum may not be a reliable label for kin
recognition without regular contact (Sun and
Müller-Schwarze, 1997).
Beavers deposit AGS when scent marking
(Rosell and Bergan, 1998), but it may not be
used in all scent markings. Since the AGS
profile is stable and because male and female
AGS profiles differ (Sun and Müller-Schwarze,
1998b) it seems reasonable to assume that AGS
codes for information on age and gender, and
perhaps reproductive and physiological status.
Since castoreum and anal gland secretion
seems to have different functions it may be
that anal gland secretion is mainly deposited
in areas of high family group activity and that
castoreum is mainly deposited at territorial
boundaries.
It may, however, be that the many scent
markings in the core area merely reflect that
the core area is particularly worth defending.
Blom-Hansen (1998) found a carrying capacity
of Klosterheden State Forest to be 11 families,
44-77 animals, using the total length of stream
in Klosterheden of 23.6 km. Average territory
size found in this study was 4.7 both bank
sides included. Using the total length of stream
in Klosterheden in the present study, carrying
capacity of Klosterheden is 10 families or
approximately 40 animals and therefore in
accordance with the finding of Blom-Hansen
(1998). However, Kargo (2000) estimated the
amount of vegetation suitable for beaver
consumption in the entire Flynder å system.
Vegetation up to 250 metres from water was
used on the basis of the assumption that
damming activity in time would make access
to the vegetation much easier by shortening
the distance from water to foraging sites. The
carrying capacity of the Flynder å system was
calculated on the basis of a general assumption
that one beaver family uses approximately 10
ha of habitat. Kargo (2000) found the carrying
capacity to be approximately 45 animals as a
total number for the entire Flynder å system as
opposed to the findings in this study where an
estimated 40 animals (10 family groups) could
live in the State Forest alone.
The estimates of carrying capacity of both the
present study and the study of Blom-Hansen
(1998) seems too high considering the
following: Beavers abandoned four out of six
release sites, and it seems unlikely that all sites
in Klosterheden are equally suitable for
beavers. The quality of the sites differ in way
of suitable food, and watercourses may be too
shallow requiring much time allocated to
building behaviour. The animals that settled
in stream habitats settled in larger streams
than the ones in the forest. Presumably small
streams are secondary i.e. of less quality than
other habitat types.
In Biesbosch, Netherlands, 34 beavers (>1 year
of age) were released sequentially between
1988 and 1991. The territories claimed were
initially very large (average 36.5 km of bank,
both sides included), but they decreased over
the years, and in the fourth year after the reintroduction, average territory size was 6.4 km
(Nolet and Rosell, 1994).
Though comparisons must be made with
caution as the territory sizes found in the
Netherlands were estimated several years after
the reintroduction, the territories in the
_________________________________________________________________________ 47
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Flynder å system measured on average 4.7 km
(both bank sides included) and was thus smaller
than the ones found by Nolet and Rosell (1994).
The territory sizes in the present study however,
are relatively large compared to the findings of
Rosell et al. (1998). They found the average size to
be 2.6 km (both banks included) in the southern
part of Norway. Moreover, Welsh and MüllerSchwarze (1989) found a median density of 1
colony per two stream kilometres. MacDonald et
al. (1995) refers to territory sizes between 0.5 and
12 kilometres with an average of approximately
3.0 km.
The relatively large territories in this study may
reflect the poor quality of the habitat.
_________________________________________________________________________ 48
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
8. Dam building behaviour
8.1. Introduction
Beavers build dams to raise the water level
so that the entrance of the den is constantly
covered with water, and to make sure that a
stream provides a quick route for escape
(Frendin, 1979; MacDonald et al., 1995).
Moreover, an increased water level
increases the availability of deciduous trees
near the water edge and facilitates the
transportation of building material (Rosell
and Parker, 1996).
Beavers are stimulated to build dams by the
sound of running water (Richard, 1983) and
dams are usually initiated at the noisiest
place in the stream, i.e. where water flow
over obstacles (Wilsson, 1971; Hodgdon and
Lancia, 1983).
Construction and maintenance of beaver
dens are often connected with reproduction
(Wilsson, 1971; Richard, 1983; Zurowski,
1992).
By using infrared video recording equipment
the following aspects of dam building
behaviour was investigated:
1) Does more than one beaver at a time
contribute
to
dam
building
behaviour?
2) When beavers perform building
behaviour are the elements shown in
a specific order?
3) Is there consistency in the order by
which material is added to specific
places on the dam?
4) Does the sequence of the types of
material added to the dam occur in a
specific order?
Moreover, it is the aim of this section to
present data on all signs of building activity
in the study area.
_________________________________________________________________________ 49
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
8.2. Methods
110 building sequences and a total of 337
minutes of dam building behaviour were
obtained from the infrared video recordings at
site A. There was only one dam in view of the
camera and therefore all data concern the same
dam.
Data on building behaviour were derived from
both remote controlled recordings (310
minutes)
and
non-remote
controlled
recordings (27 minutes).
In this study building sequences included the
following 7 different behavioural elements:
1) S = swimming
2) Sm = swimming and carrying nonbranch material (grass and/or mud)
collected upstream from pond or from
grass field
3) Sb = swimming and carrying branch
4) E = exploring dam (swimming slowly
alongside dam or walking on dam
without adding material or re-placing
material already on dam)
5) G = gathering of mud (from the
bottom of the pond)
6) P = placing branch, mud or grass on
dam
7) B = biting or pawing off grass (from
adjacent field)
Gathering “G” included short swimming bouts
whereas swimming bouts “S” was recorded
when an animal apparently did not carry any
material.
If an animal did not add material to the dam as
the immediate behaviour following a
swimming bout, an “s” would be recorded
rather than “G”.
1)
2)
3)
4)
L = left side of dam
X = middle of dam
R = right side of dam
N = neighbouring side of dam
(material added onto bank rather than
on the right side of dam)
5) P = under water part of dam
While a beaver was gathering material it
would often swim out of sight. However, as
long as it was evident that the beaver was
“working” at collecting material (as could
easily be seen by the waves in the water), time
was calculated as being
part of the element “gathering”. As soon as
waves ceased the building sequence was
analysed as terminated.
Since individual beavers could not be
distinguished from each other it was not
possible to determine whether several
individuals participated in dam building or
whether one beaver did the entire dam
building work.
8.3. Results
8.3.1. Infrared video recordings
At the beginning of the observation period the
dam was approximately 2 metres long. By 8/62000 when the observations were terminated
the dam measured approx. 5 metres in length.
At the beginning of August the dam measured
15 metres.
The hourly distribution of the occurrence of
building sequences is shown below (fig. 16).
Every recording of a building sequence was
analysed with respect to the sequence of
behavioural elements and duration of both the
elements and the total duration of a sequence.
Moreover, the sequence with which the
different material types were added was
recorded, as was the site for placement of the
material on the dam. Different sites on the
dam(appendix 5) was recorded as either:
_________________________________________________________________________ 50
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
35
30
25
20
15
10
5
0
21
-2
1
22 ,59
-2
2
23 ,59
-2
3
00 ,59
-0
0
01 ,59
-0
1
02 ,59
-0
2
03 ,59
-0
3
04 ,59
-0
4
05 ,59
-0
5,
59
total number of building sequences
___________________________________________________________________________
time periods
Fig. 16. Hourly distribution of 110
building sequences recorded on infrared
video recordings.
51.8% of the building sequences occurred
between 2200 and 2400 h.
Building sequences lasted from 24 seconds to
15 minutes and 40 seconds. The range of
duration of the different behavioural elements
recorded is shown below (table 12).
The short durations of both “Sm” and “Sb” are
presumably due to the fact that the first part of
the elements was missed because the area were
being scanned with the camera at the time of
onset of the behaviour.
Behavioural
element
S
Sm
Sb
E
G
P
B
Duration (in
seconds)
8-24
9-77
13-116
10-26
14-169
5-89
14-126
Table 12. Range in duration of
behavioural elements shown in building
sequences.
At no time did more than one beaver work at
the dam.
on the dam and then either continue dam
building work by gathering mud from the
stemmed pond or terminate dam work. 2) A
beaver would swim towards the dam and
upon getting close to the dam the animal
would swim to the edge of the grass field and
bite/scrape off grass and secure it on the dam.
This sequence would either be followed by
gathering mud from the stemmed pond or by
swimming back to the grass field to obtain
more grass. 3) A beaver would swim from
upstream direction towards the dam while
carrying material (mud and/or grass). It
would place the material on the dam and
either continue dam work by collecting mud
from the stemmed pond or terminate building
behaviour. The sequence with which the
different types of material were added did not
seem to occur in a specific order and the exact
place on the dam where the material was
secured seemed to be random
In a total of 51 building sequences the first
type of material to be added to the dam was a
branch. This is equal to 46.4% of all building
sequences.
In 29.1% of the building sequences the first
type of material to be added was material
gathered from upstream the pond. This means
that approximately 75% of the building
sequences commenced with material being
collected upstream from the dam, i.e. without
the beaver (s) having been close to the dam
prior to collecting the material.
Two thirds of the building sequences where a
branch was the first type of material to be
added to the dam occurred at the beginning of
the active period (2100-0000 hours).
8.3.2.Transition matrices and flow diagrams
A transition matrix was constructed (table 13)
and Haldane-Dawson statistics were used to
test whether the transitions between the
behavioural elements of building behaviour
were performed at random. The test showed
that behavioural elements were not performed
in random order (µ= 133.4, P< 0.00084)
(Appendix 8).
Dam building behaviour was performed in
mainly three ways. 1) A beaver would swim
from upstream direction towards the dam
carrying a branch; it would secure the branch
_________________________________________________________________________ 51
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
1
S
Sm
Sb
B
G
P
E
2
S
Sm
Sb
B
G
P
E
32
28
2
7
196
31
1
58
53
9
6
S
214
6
1
6
31
Table 13. Transition matrix showing elements of
building behaviour. Data were derived from infrared
video recordings.
A second transition matrix was constructed
where only the site for placement of the
material on the dam was included (table 14).
It was tested whether the material was placed
on the dam at random sites. Using chi-square
statistics showed that the placing of material
did not occur at random sites (χ2=115.03,
p<0.01).
1
P
L
X
R
N
P
L
X
R
N
10
3
24
11
10
2
6
14
33
13
3
2
4
17
35
9
2
4
4
6
9
2
7
3
1
E
6
Table 14. Transition matrix showing transitions
between different places on the dam.
A flow diagram based on the transition matrix
in table 13 was constructed (fig.17). Transitions
that occurred more often than expected by
chance are shown. Thick arrows indicate ratios
(between observed and expected values) of
11.9-14.6 whereas thin arrows indicate ratios of
1.9-3.2.
32
Sm
B
28
G
196
58
Sb
214
53
P
2
Fig. 17 Flow diagram showing transitions between
the elements of building behaviour. G: gathering of
mud, S: swimming, Sm: swimming and carrying
non-branch material, Sb: swimming and carrying
branch, E: exploring dam, P: placing material on
dam, B: biting and pawing off grass.
The flow diagram shows that three transitions
occurred much more often than expected by
chance. The flow diagram also shows that dam
building mainly consisted of gathering mud
from the bottom of the pond and placing the
mud on the dam.
A flow diagram based on the transition matrix
in table 14 was constructed (fig.18) Only
transitions occurring more often than expected
by chance are shown.
P
X
7
10
L
14
33
R
35
24
N
9
9
Fig. 18 Flow diagram showing transitions between the
places where material was added onto the dam. P:
under-water part of dam, X: middle of dam, L: left side
of dam, R: right side of dam, N: neighbouring-ground
side of dam.
_________________________________________________________________________ 52
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
As seen in the flow diagram most transitions
occurred between the same places on the dam,
i.e. if an animal began adding the material to
the middle of the dam for example most often
the next material to be added was also placed
on the middle of the dam. The flow diagram
also shows that adding material to the right
side of the dam most often occurred in
separate building sequences.
A transition matrix showing only transitions
between the types of building material added
onto the dam (table 15) was constructed. Data
was derived from the transition matrix in table
13. A chi-square test was not a valid test in this
situation because more than twenty percent of
expected numbers were less than five and a
Fisher exact test was used instead to test
whether the sequences with which the
different types of material were added to the
dam deviated from homogeneity. Results
showed that the transitions between the
different types of material added to the dam
deviated from homogeneity (p=0.000391) and
thus occurred in a specific order.
b
m
B
G
b
1
m
B
G
1
1
23
2
25
11
14
18
138
Table 15. Transition matrix showing transitions
between types of material being added to the dam. B:
branches, m: mud and /or grass, B: grass, G: mud
gathered from the bottom of pond in front of dam
A flow diagram made on the basis of data in
table 15 is shown below (fig. 19).
b
23
G
138
25
m
B
11
Fig. 19. Flow diagram showing transitions
between the type of building material added to
the dam.
The flow diagram shows that most often mud
was used in dam building sequences. And
even though branches or material gathered
upstream was used initially beavers would not
swim back to collect more branches or
material, but instead continue dam building by
using mud from the bottom of the pond.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
8.3.3. Data on beaver constructions found
within the study area.
Data on beaver constructions found in
Klosterheden State Forest between October
1999 and June 2000 are shown below (table
16). Details on the different constructions can
be seen in appendix 9.
Site
Type of construction
2
Dam
2
2
Dam
Dam
2
Dam
2
Dam
2
Channel
2
3
Ground burrow
Food cache
3
Food cache
4
Ground burrow
5
Repairing of artificial
lodge
Ground burrow
dam
A
A
A
Dam
A
Dam
B
Ground burrow
C
Ground burrow
D
Ground burrow
Measures
(length L, height H,
width W, depth D)
L=0.75 m, H=0.30 m,
W=0.30 m
L=1 m, H=0.50 m,
W=0.30 m
L=0.75 m, H=0.30 m,
W=0.30 m
L=1 m, H=0.50 m,
W=o.30 m
L=1 m, H=0.50 m,
W=0.50 m
L=3-4 m, H=0.50 m,
W=0.50 m
L=0.50 m, H=0.30 m,
W=30 cm
L=0.50 m, H=0.30 m,
W=0.30 m
L=10 m, W=0.40 m,
D=0.50 cm
L=1 m, H=1 m,
W=1 m
L=1 m, H=1 m,
W=1 m
L= 2m, H=75 cm,
W=0.50 m
L=15 m, H=0.75 m,
W= 0.50 m
L=3-4 m, H=0.65 m,
W= 50 cm
L= 2 m, H=0.50 m,
W=0.30-0.40 m
Diagonals = 2 m
Building material
Time of year as week
number
(year in brackets)
Willow, bog myrtle
twigs
46 (1999)
50 (1999)
Willow, bog myrtle
twigs
48 (1999)
50 (1999)
Willow, bog myrtle,
spruce branches,
mud
6 (2000)
10 (2000)
Willow, bog myrtle
twigs
Willow, bog myrtle
twigs
Mud was removed
6 (2000)
6 (2000)
52 (1999)
Unknown
Willow branches
44 (1999)
Willow branches
Covered with
branches
44 (1999)
Mud, branches
6, 8, 10 (2000)
48 (1999)
6 (2000)
Birch and pine
branches, mud, grass
48 (1999)
31 (2000)
Willow branches,
mud
Between 18-21 (2000)
Willow branches,
mud
Between 18-21 (2000)
Branches of unknown
species, mud
Unknown
Branches of unknown
species
Unknown
Branches of unknown
species
Unknown
Table 16. Building activity from October 1999 – June 2000. An arrow indicates that data concern the same dam
as mentioned above.
_________________________________________________________________________ 54
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Ground burrows were built at all occupied
sites, but only at two sites did beavers build
dams. At site 2 the dams resulted in
insignificant flooding during the study
period. By November 2000 however, twelve
new dams were built at the site resulting in
the flooding of approximately one-hectare of
forest area (pers.comm. Thomas Borup
Svendsen, 2000).
At site A the dam reached the length of 15
metres and resulted in the flooding of
approximately one hectare of private grass
field.
Two food caches were built at site 3.
However, the food caches were small and
beavers abandoned the site without using the
caches.
55
___________________________________________________________________________
8.4. Discussion
At no time did more than one beaver perform
dam building behaviour in the present study
and usually only one beaver was visible at the
dam. On one occasion a beaver was adding
material to the dam as another animal
approached the dam carrying a branch. The
first beaver ceased its building behaviour and
swam out of sight while the animal arriving
continued to build. Sieber (1993) hand-reared
two beaver kits (Castor fiber) and reported that
building behaviour commenced in the fourth
month of life. These findings suggest that
building behaviour is a highly innate
behaviour probably triggered by both the
sound of running water and reproduction
(Wilsson, 1971; Richard, 1983; Zurowski, 1992).
At the onset of dam building, at least in small
streams, solitary building behaviour may be
explained by spatial limitations, i.e. physical
space is limited to one animal carrying a
branch. The advantage of solitary building
behaviour could be that due to a reduced level
of vigilance behaviour in the animal
performing building behaviour, the risk of
predation would only be increased for this
particular individual. For solitary building to
be an advantage however would also mean
that the individual performing building
behaviour would be dependent on responses
to predators by the other individuals in the
family group. It was often observed that an
animal would be foraging upstream from the
dam while another individual was performing
dam building behaviour. But at no time did an
animal forage near the dam while another
beaver was working on the dam.
Neither the transitions between behavioural
elements of building sequences nor the
transitions between places on the dam onto
which material were added occurred in a
random order. Moreover, the way in which the
different types of material were added to the
dam did not occur in a random order. These
findings suggest that building behaviour is
adaptive i.e. the behaviour is performed in a
way that offers an advantage for the animal, in
this case presumably optimising the energy
spent on the particular behaviour. It may also
reduce the time that an animal is at high risk
for predation.
Further studies including data on the building
of several dams, i.e. a larger sample size, are
needed in order to determine whether the
building strategies in the present study merely
reflect the physical parameters present at this
particular site.
Certain transitions between behavioural
elements occurred approximately 13-fold more
often than expected by chance. Grass was
easily accessible and occurred in large
quantities. If beavers do not distinguish
between types of material to be used in dam
building, i.e. any material is useable, then the
animals
would
optimise
the
energy
expenditure and risk avoidence by collecting
material close by the dam. This would account
for the high rate of transitions that included
the swimming- and grass elements.
The element of exploring also followed the
element of swimming much more than
expected by chance. A plausible explanation
would be to assume that this behaviour is
adaptive, and that the cost of exploring the
dam is counterbalanced by the gain in terms of
the information gathered, i.e. where to place
material on the dam for example. Another
plausible explanation could be that the animals
were still being stimulated to explore the dam
as water was still running through the dam
and over obstacles because the dam had not
been completed.
Approximately 75% of the building sequences
seemed to commence even when the animal
was far away from the dam. It is possible that
the sound of water running through the dam
or over obstacles stimulated beavers to build
even at a distance far away from the dam. It is
however, also possible that the branches that
had just been foraged on stimulated building
behaviour. Or upon emerging from the den debarked branches stimulated the beavers to
build. Sixty-six percent of building sequences
where branches were used occurred between
2100 and 2400 h, i.e. only a short while after
the animals emerged from the den and since
the first behaviour to occur after first sightings
________________________________________________________________________ 56
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
most often was foraging (section 6) this seems like
a reasonable explanation.
Zurowski (1992) found that the birth of kits
stimulated lodge building and lodge maintenance
work. There also seems to be a correlation between
den building and reproduction in the present
study; kits wereborn in at least four out of six
occupied sites (pers.comm. Thomas Borup
Svendsen 2000).
________________________________________________________________________ 57
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
9. Conservation perspectives
An immediate evaluation of the success of the
reintroduction can be made on the basis of a
few obvious criteria; 1) reproduction, 2)
mortality, and 3) the extend to which beavers
remained in the release area. At least four kits
in four different territories were born. This is
equal to a 22% population increase. Of
eighteen beavers one individual was hit by a
car, but the animal recovered and was released
again within a week. No animals were found
dead. Considering that six territories were
occupied and activity at one other site
indicated the presence of at least one beaver,
makes mortality seem quite unlikely at least
during the first year after the release. In the
present study individual markings, e.g..
coloured ear tags would have enabled a more
precise count of individuals at each territory
and thereby making the estimate of mortality
more exact. In comparison Nolet et al. (1997)
found mortality to be 36% (Biesbosch National
Park) and 73% (Gelderse Poort) in the first
year after reintroduction of beavers to the
Netherlands. Infectious diseases, especially
yersiniosis and leptospirosis, constituted 50%
of the mortalities. In the Biesbosch beavers
were released sequentially over four years and
this is believed to have resulted in a high
number of territorial conflicts. Territorial
conflicts added to the stress of being released
in an unfamiliar habitat. This is assumed to
have resulted in more cases of infectious
diseases (Nolet et al., 1997). In the Gelderse
Poort beavers were released at the same time.
However, the release was done in September
(compared to late October and November for
the Biesbosch releases) and leptospires
survived in the warm surface water and
caused several deaths (Nolet et al., 1997).
Although beavers abandoned four of the six
release sites in the present study, they either
settled within the forest area or in the vicinity
of the forest. Of the six existing territories the
one furthest away from the forest was
approximately 5 km. This fact indicates that
the approach towards pointing out potential
release sites were appropriate.
One essential aspect of the evaluation of the
success of the project, however, could not be
determined due to the lack of individual
markings. It was impossible to assess whether
pairs or family groups were split up after the
release. If this was the case the separation from
the family group is likely to have added to the
stress of being released in an unfamiliar
habitat and it would be worth considering
releasing individual 2-year-olds in spring
where dispersal usually occurs rather than
releasing family groups or pairs as in the
present reintroduction.
Approximately four hectares of terrain were
flooded and small ponds were created. Since
the main reason for reintroducing beavers to
Denmark (Miljø- og Energiministeriet, 1998)
was to have this species create dynamics and
increase
the wet areas of the country it must be
concluded, that at least on the small scale the
goal has been reached. Only time will show
whether this will also effect biodiversity
However, there is no doubt that in the future,
conflicts with private landowners due to
flooding of terrain must be expected. It is
stated in the management plan for beavers in
Denmark that no compensation will be given
for beaver damages because in general no
compensation is given for wild life damages.
Sieber (pers.comm.. 2000) reports of a fairly
inexpensive way of attempting to prevent
conflicts with landowners due to beaver
damages. When beavers are believed to be
dispersing to a new area private landowners
are contacted and told which precautions that
can be taken e.g. fencing of valuable trees. This
strategy often results in people awaiting the
beavers with a certain interest (pers comm.
Sieber 2000).
Though scepticism towards the reintroduction
was widespread among people, the beavers
have been a tremendous public success
increasing the visitors to the forest by
approximately 50% (pers.comm. Thomas
Borup Svendsen).
Based on these three criteria the reintroduction
can be considered a success so far.
________________________________________________________________________ 58
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Eighteen beavers were released which is in
the lower limit of that recommended by
IUCN, species survival commission (The
International Union for the Conservation of
Nature) for reintroductions in order to
ensure a viable population that can resist
disadvantages resulting from inbreeding.
The Swedish beaver population that at
present time numbers approximately 100000
originates from 80 beavers reintroduced in
1930´s to 1940´s. Studies have shown that
the genetic variation is very low and
presumably this has not caused problems
(Hartman et al., 1993). Moreover, a second
release is scheduled for autumn 2001 in the
county of Århus. Assuming that both
populations
survive
the
long-term
perspectives will be a large viable
population of beavers in the western part of
Denmark. Kargo (2000) estimated the
carrying capacity for this part of Denmark to
be approximately 4500 animals.
________________________________________________________________________ 59
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
10. Sources of error
The fact that the beavers were not marked for
individual
recognition
posed
several
disadvantages in the present study.First, the
estimated time budget was based on the
behaviour of three individuals in one single
family group only and no distinctions between
sexes could be made. Hodgdon and Larson
(1973) and Buech (1995) found that time
allocation differed among sexes. Second, only
approximate numbers of the individuals at
each site could be obtainable. Third, though
data obtained from the video recordings
concerning dam building behaviour were very
detailed it was impossible to determine
whether one or several individuals actually
participated in dam building. Fourth, no
distinctions could be made concerning the
frequency with which the different sexes and
age classes scent mark. Fifth, and perhaps most
importantly markings would have resulted in
the possibility of assessing whether family
groups and pairs (as caught in Germany) were
split up post-release. All the disadvantages i.e.
very few data from very few individuals,
made generalisations impossible except on a
very low level and it also meant that valuable
information was unobtainable.
The observation method used in the video
recordings also constituted a source of error.
Only a very limited area of the territory could
be seen with the camera. The result was that
beavers were visible only for approximately
25% of the observation time. Moreover, the
den was out of view of the camera. Buech
(1995) found that beavers spent around 17% of
an active period inside the den.
Prolonging the observation period quite
possibly would have revealed differences in
time allocation between seasons as beavers
spend more time performing building
behaviour in autumn where branches are
stored in caches and dens are repaired by
adding mud and new branches.
Whether beavers did in fact actively select the
species foraged on or whether the foraging
data merely reflect that beavers foraged on
whatever was available remains uncertain
because no investigations as to the species
composition and quantity of food sources was
carried out prior to the re-introduction.
The estimates of territory sizes were based on
few scent mounds as well as signs of activity
and what appeared to function as natural
barriers (e.g. roads). Using these territory sizes
in calculations of carrying capacity may have
resulted in biased estimates. However, the
result was in agreement with that found using
theoretical territory sizes.
Having to traverse all areas by foot limited
both the frequency with which the areas were
checked and the size of the area covered. This
means that signs of activity in remote areas
might have been missed.
Though the two species of beavers are
reported to be very similar in morphology,
mode of life and behaviour (e.g. Wilsson, 1971;
Patenaude, 1983; Novak, 1977) there may be
differences and not considering this facts in all
comparisons may be a source of error.
________________________________________________________________________ 60
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
11. Conclusion
An estimate of a time budget was made on the
basis of infrared video recordings. All
recordings were obtained from one site only
and therefore caution had to be taken when
data was compared with results from other
studies.
Grass constituted a great proportion of the
food source before buds and leaves were
available in large quantities. The number of
beaver minutes allocated to foraging was
correlated with the frequency of vigilance
behaviour. However, there was no difference
in the frequency of vigilance behaviour
between solitary- and group feeding when
foraging on grass. Individuals did not seem to
benefit in terms of a reduced level of vigilance
when foraging in groups. The frequency of
vigilance behaviour was higher when beavers
foraged on branches in groups than when
foraging solitarily on branches. An explanation
was that beavers foraging on branches paid
more attention to other foraging individuals
rather than being alert at certain intervals.
Average size of six estimated territories was
4.7 km, which is smaller than territories
claimed in the Netherlands following
reintroduction, but larger than averages given
for other study areas. Beavers did not disperse
to sites far from the release area and it was
regarded as evidence of the suitability of the
approach used to point out possible release
sites.
The estimated carrying capacity of the forest
area was in agreement with an earlier estimate
for the area, but seemed too high due to the
low quality of some sites within the forest.
Data derived from infrared video recordings
concerning dam building behaviour showed
that neither the elements of building
sequences, the placement of the material on the
dam or the different types of material added
occurred at random.
The building of dams resulted in the flooding
of approximately 4 hectares of terrain and thus
the main goal of the management plan was
reached, at least to a lesser extent.
At least four kits were born resulting in a
population increase of 22%. No beavers were
found dead, but some could have died without
being found. It is assumed that in the present
study marking of the beavers for individual
recognition, e.g. using coloured ear tags would
have enhanced the possibility of more exact
estimates of both the number of individuals
belonging to each territory and the number of
deaths.
Based on the facts that reproduction occurred,
no beavers were found dead and the beavers
remained in or close to the release area it is
concluded that so far the reintroduction has
been a success.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
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Jenkins, S.H. 1979. Seasonal and year-to-year differences in food selection by beavers. Oecologia, 44: 112-116.
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Zurowski, W. 1992. Building activities of beavers. Acta Theriologica, 37(4): 403-411.
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Acta Theriologica,31(24): 311-325.
________________________________________________________________________ 67
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 1
The map shows Denmark and the study area, Klosterheden State Forest, in red.
(After Kargo 2000).
________________________________________________________________________ 68
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 2
4
4
(2)
3
4
(2)
D
2
2
(2)
1
2
(0)
(1)
◊
5
4
(1)
B
A
(3)
◊
(2)
◊
6
2
(0)
C
(2)
◊
⊕
The map shows the study area, Klosterheden State Forest, and part of the Flynder å system. Release
sites (1-6) and new occupied sites (A-D) are shown in bold. ■: Artificial lodges, ◊: beaver-built
dens, ⊕: Signs of activity, but no den found. Numbers below site number/letter show the number
of individuals released and numbers in brackets are maximum number of individuals seen at the
site.
1 km
1:59000
N
↑
________________________________________________________________________ 69
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 3
Considerations on observation methods
As a preliminary observation exercise 26 hours
of observation on free ranging beaver (Castor
fiber) were conducted in Norway, May 1999.
According to Altmann (1974) a variant of focal
sampling is the best choice under field
conditions where it is impossible to recognise
individuals. Altmann (1974) suggest that the
focal individual be chosen at random and that
this particular individual is observed for as
long as it is visible. A slightly different method
was used in Norway. All individuals visible at
the same time were focal individuals for as
long as they were visible. Continuous
recording was used as the recording rule
(Martin and Bateson, 1993). The aim of the
exercise was to obtain as many data as possible
on different behaviour patterns in order to be
able to draw an ethogram partly on the basis of
these observations. The time budget shown
below (fig.1) is the sum for all individuals
studied (N=7 from three different sites).
Time allocated to
behavioural states
4.4%
35.2%
2.3%
58.1%
swim
forage
groom
on land
Fig. 1. Time budget based on data gathered
from 26 hours of observation on beaver (Castor
fiber) in Norway, 1999.
However, continuous recording turned out to
be an inappropriate method when more than
two individuals were visible at the same time.
It was decided to use instantaneous sampling
rather than continuous recording for the
observations in Denmark.
Buech (1995) studied North American beavers
(Castor Canadensis) living in lake habitats in
northeastern Minnesota. Although radio
transmitters had been implanted in several
individuals this devise was mainly used to
locate the individuals. Once an animal was
located observations were done when the
animal was visible to the observer. The focal
individuals were predetermined and
instantaneous sampling with 1-minute
intervals was used as the recording rule.
Buech (1995) used his recordings to estimate
time budgets so 1-minute intervals also
seemed suitable for the observations in
Denmark.
When using instantaneous sampling data on
behavioural states are scored (Altmann, 1974).
In order to be able to record data on
behavioural events one-zero sampling was
applied as well. After every one-minute
interval it was recorded whether an event had
occurred. If two individuals were visible, but
only one individual had performed a specific
behavioural event e.g. tail slapping, a 1(2) was
scored. If two out of two visible animals tail
slapped during a given interval a 2(2) would
be scored.
Observations in Klosterheden State Forest
turned out to be more difficult than expected.
Several sites were abandoned shortly after the
release, at one site the present individual (s)
were extremely shy and at the remaining sites
only rarely was more than one individual
visible at the same time. This made it possible
to use continuous recording as well as record
all events without one-zero sampling.
________________________________________________________________________ 70
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 4
Ethogram
The ethogram showed below was based on a
total of 26 hours of observations on a pair of
free ranging beavers in southern Norway.
Furthermore the ethogram was based on video
recordings of beavers living under seminatural conditions in Germany. Behaviour
patterns not seen during the preliminary
observations, but found in the literature are
included.
All
behaviour
patterns
except
from
“coecotrophy” and “dancing” were observed
during the study period.
The types of behaviour listed below are
behaviour patterns performed by the animals
during their active period.
Where the function of certain behaviour has
been described in the literature this is written
in italics.
Aggressive behaviour (s): An individual will
lunge at or bite at another beaver and fighting
may be initialised. If the animals are in the
water they will often swim in circles trying to
reach each others hind. If on land, an attack
will often lead to the animals standing on the
hind feet and try to get a grip at the other
individuals fur coat with the front feet and
push it backwards.
According to Brady and Svendsen (1981) this
behaviour only occurred when kits begged for food
while an adult was feeding. Often a bite at a kit
would be sufficient to make the kit withdraw.
(Aggressive behaviour was recorded even if
only one element of the behaviour was seen).
Coecotrophy (s): The animal is sitting down
and the tail is projected forward between the
legs. The head is bent forward towards the
cloacae and with the front feet the animal
presses against the rectum and eats the faeces
produced in the caecum.
Many rodents and lagomorphs eat a special type of
faeces; a green thick substance, that is produced a
while after the animal stops eating (Wilsson, 1971,
Buech, 1984).
Building behaviour (s): By transporting
branches or other material the dam is either
maintained or build larger. The behaviour
pattern was divided into seven elements:
8) S = swimming
9) Sm = swimming and carrying nonbranch material (grass and/or mud)
collected upstream from pond or from
grass field
10) Sb = swimming and carrying branch
11) E = exploring dam (swimming slowly
alongside dam or walking on dam
without adding material or re-placing
material already on dam)
12) G = gathering of mud
13) P = placing branch, mud or grass on
dam
14) B = biting or pawing off grass (from
adjacent field)
As dam building was observed at site A only,
where
video
recordings
took
place,
“swimming” and “swimming and carrying
branches” could be distinguished because it
was possible to determine the subsequent
behaviour. If transportation of an item
occurred in water, it was only recorded as
building behaviour if the subsequent
behaviour was “placing the item on the dam”.
Otherwise the behaviour was recorded as
“foraging”.
Dancing (e): the animal makes a series of body
movements beginning with the head and then
spreading to the rest of the body as if the
animal is shaking itself. The movement is
exaggerated so that the head is moved in
circles.
This behaviour often initialises mutual grooming
between two un-mated individuals and the
behaviour seems to express dominance over another
member of the family group (Wilsson, 1971).
Diving (e): By raising the back and tail above
the water surface the animal dives with the
head being the first part under water.
Under certain circumstances diving without
slapping the tail against the water surface indicates
intense danger (Wilsson, 1971).
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Foraging (s): The animal is either eating or
handling food. This category includes
chewing, reaching for a branch or a plant with
its front feet, transporting a food object and
when an animal foraging moves a little
distance in order to obtain more food items
(sensory pauses and intrapatch walking
included).
Grooming (self-grooming) (s): Either the front
feet, hind feet or teeth were used to clean the
fur while the animal is sitting down. Often a
sequence of self-grooming included both the
use of feet and teeth.
Mutual grooming (s): Two individual(s)
groom each other simultaneously using the
teeth and/or front feet. They often do so in
places that the animal being groomed cannot
reach itself (top part of the back, neck and
head).
This behaviour seems very important as an
expression of social contact (Wilsson, 1971) or for
maintaining the condition of the fur in places the
animal can not reach itself (Paternaude and Bovet,
1983).
Nose touching (e): An animal approaching
another, both from in front or from behind,
will shove its nose at the other one’s nose.
This behaviour is a social greeting and kits will do
nose touching when begging for food (Brady and
Svendsen, 1981).
On land (s): The animal is either sitting or
walking on land. This category will be used
when it is not possible to determine what the
animal is doing.
Pawing with front legs (e): The animal scrapes
the dirt or a scent mound with the front feet,
but the animal does not deposit secretion (no
placement of the cloaca above the scent
mound).
Play wrestling (s): Two animals interact by
shoving/pushing each other using the front
legs while standing upright on the hind legs
(Wilson, 1971).
Scent marking (e): With the front legs the
animal scrapes the ground thereby gathering
dirt and/or plant material into a mound.
Sniffing may occur at the same time. Following
the scraping the animal places the cloaca just
above the mound for a few seconds while
depositing secretions. Hereafter the animal
may scrape or stamp the mound with the hind
legs.
Beavers are territorial and scent mark within their
territory hereby signalling/warning beavers
unknown to the family group that the territory is
occupied (Wilsson, 1971, Nolet and Rosell, 1994).
It is likely that the depositing of anal gland
secretion makes individual recognition possible. The
anal gland secretion varies among sexes but also
among species (Rosell and Bergan, 1998).
Swimming (s): The animal is moving in the
water. Only the top part of the head, and the
nose is above water.
This behaviour was recorded when it was not
possible to determine any other behaviour
such as transporting an item.
Tail slapping (e): By raising the tail and
slapping it hard against the water surface the
animal creates a loud noise. This behaviour
can also take place on land where the animal
will slap the tail hard against the ground.
Prior to tail slapping increased alertness can occur
and both the alertness and the actual tail slapping
constitute alarm (Buech, 1995).
According to Wilsson (1971) the behaviour is
response to a moving object but the behaviour can
also occur after the animal has increased alertness
in response to a smell or a sound.
Tail slapping (e): By raising the tail and
slapping it hard against the water surface the
animal created a loud noise. Diving sometimes
follows tail slapping.
According to Wilsson (1971) the behaviour is
response to a moving object, but the behaviour can
also occur after the animal has increased vigilance
in response to a smell or a sound and it functions as
a warning for other members of the family group
(e.g. Salvesen, 1927).
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Vigilance (e): If the animals is on land it will
stop the behaviour it was performing, and
either stands on its legs, with the hind legs
bend and the front legs stretched and the head
lifted, or it may remain in the same body
position, but the head is lifted. Sniffing may
occur at the same time. When the animal is in
water and the head is moved up and down in
quick movements vigilance is also recorded.
social contact; 1) when an animal tries to get in
contact with a member of the family group it
will produce a high whistling sound. 2) When
several individuals are in close contact with
each other a long series of high and low
pitched notes will occur. 3) Young beavers
often make complaining sounds. 4) Kits less
than one month old make rattling noises when
caught (Wilsson, 1971).
Vocalisation (e): All types of vocalisation will
be recorded in this category.
A high-pitched whistling sound was recorded
twice. The vocalisation occurred while the
animals were in the den.
Wilsson (1971) distinguishes between four
different types of vocalisation, all as part of
________________________________________________________________________ 73
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
________________________________________________________________________ 74
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 6
Time allocated to different behavioural states
on the different days of the observation period
(“on-land” behaviour not included). In the
analysis of the video recordings a minute with
two beavers in sight counted as 2 beaver
minutes, two minutes with three beavers in
sight counted as six beaver minutes and so
forth.
building
40
18
35
16
30
beaver minutes
beaver minutes
swimming
14
12
10
8
6
4
25
20
15
10
5
2
0
0
0
5
10
15
20
25
30
0
35
10
20
30
40
observation day
observation day
mutual gr.
grooming
18
16
40
14
beaver minutes
beaver minutes
35
30
25
20
15
12
10
8
6
10
4
5
2
0
0
0
10
20
30
observation day
40
0
10
20
30
40
Observation day
________________________________________________________________________ 75
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
in duck pond
280
260
240
220
200
180
160
140
120
100
80
60
40
20
0
30
25
beaver minutes
beaver minutes
foraging
20
15
10
5
0
0
10
20
30
obserrvation day
40
0
10
20
30
40
observation day
________________________________________________________________________ 76
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 7
4
D
2
B
A
C
The map shows the study area, Klosterheden State Forest. Estimated territory sizes are shown in
red.
1 km
N
1:52000
________________________________________________________________________ 77
Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
___________________________________________________________________________
Appendix 8
It was tested whether the transitions between behavioural elements in the building sequences were
performed in random order. A Haldane-Dawson test was chosen because more than 20 percent of
expected values were less than 5 and because the large number of zeros occurring in the transition
matrix makes the data unfit for use in a chi-square test.
Ε (χ2) = N (k-1)(m-1) / N-1
Var (χ2) = ((2N / N-3) x (v1-w1) (v2-w2)) + N2 / ((N-1) x (w1w2))
where
v1 = (k-1) (N-k) / (N-1)
v2 = ((m-1) (N-m)) / (N-1)
w1 = (Σ N/Ni – k2) / (N-2)
w2 = (Σ N/Nj – m2) / (N-2)
µ = (χ2 - Ε (χ2)) / square root of Var (χ2)
Ε (χ2) = 644 x (7-1) (7-1) /643 = 36.06
v1 = (7-1) (644-7) / (644-1) = 5.94
v2 = 5.94
w1 = Σ (644/32) + (644/28) + ……(644/2) – 72 / 642 = 0.67
w2 = 0.19
Var (χ2) = 142.998
µ = 133.4, p<0.00084
S
M
(1.89)
(2.80)
(1.65)
(2.52)
(19.71)
58
(30.08)
χ=25.92
(3.42)
S
P
32
(11.83)
χ=34.39
(10.35)
M
P
B
G
I
31
(2.24)
χ=369.26
1
(11.98)
χ=10.06
6
(0.41)
χ=76.21
(0.12)
(18.28)
(0.63)
(0.18)
K
(123.34)
7
(14.04)
χ=3.53
196
(75.02)
χ=
1
(2.59)
χ=0.98
2
(0.74)
χ=2.15
B
G
I
K
(1.84)
(10.63)
(0.30)
(2.63)
28
(1.61)
χ=432.60
9
(19.19)
(9.30)
(0.26)
(2.30)
(3.11)
(2.18)
214
(110.99)
χ=95.60
(12.63)
53
(27.49)
χ=23.67
(3.13)
(11.66)
(67.46)
(0.40)
(0.12)
(0.35)
(16.71)
(2.33)
6
(1.89)
χ=8.94
(0.07)
(2.33)
(0.02)
(0.17)
(0.58)
(Expected values in brackets).
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Behavioural ecology of reintroduced beavers (Castor fiber) in Klosterheden State Forest, Denmark
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Appendix 9
Details on the building activities in the release
area
Site 4: In week 6 (2000) it was discovered that
beavers had built a new ground burrow
approximately 2 metres from the artificial
lodge that they had been using from the
release until then. The entrance of the ground
burrow was under water between two willow
bushes. Branches from the artificial lodge had
been used to cover the ground burrow. Access
to the ground burrow was impossible because
it was situated on a small island in the lake.
Measurements therefore were not obtained.
Site 2: Between week 44 and 46 (1999) the first
beaver dam was built. Situated approximately
10 metres down stream from the lake, the dam
measured 75 cm in length, 30 cm in width and
it was 30 cm in height. It was made of thin
willow and bog myrtle branches. The stream
was approx. 50 cm wide before the dam was
built and the dam made the stream 1.0-1.5 m
wide for a 5 m distance.
Two weeks after (week 48, 1999) another dam
was discovered. It was built 50 m downstream
the first one and had the same measurements.
Neither of the dams seemed to stem water
deep enough for the beavers to swim in. Two
weeks later both dams had been built larger
and now they measured approx. 1 m in length
and 50 cm in height.
By the time of the termination of the fieldwork
beavers did not maintain the conditions of
these two dams
During week 52 (1999) it was discovered that
beavers had dug a canal approx. 40 cm wide
and 50 cm deep leading from the upstream
part of the lake and further upstream around
10 metres to a large area of willow. Before
beavers dug the canal there was water there
but it would have been too shallow for the
beavers to swim in.
In February (week 6, 2000) three small dams
were discovered in the stream valley between
site 2 and a lake upstream from site 2. One was
situated approx. 25 m upstream from the lake.
It was the largest one measuring 1 m in length,
50 cm in height and 50 cm in width. It was
made of willow, bog myrtle and spruce
branches. Mud was added as well. The two
other dams were situated upstream from the
first one and measured 50 cm in length, 30
in width and 30 cm in height. They were made
of bog myrtle and willow branches. Four
weeks later the largest dam had been built
larger and measured 3-4 meters in length, 50
cm in height and 40 cm in width. Where the
stream ran through the dam larger branches of
spruce and willow had been applied but the
dam was mainly made of mud and twigs. The
dam stemmed a large foraging area of willow
(approximately 100 square meters) and it was
deep enough for beavers to swim in.
In spring (May 2000) an entrance to a ground
burrow was discovered in the lake right across
from the artificial lodge. The entrance had
been dug out in the lake bottom and continued
into the bank. It was very well disguised, as
there were no other recognisable signs of a
ground burrow.
Site 3: What seemed to be two food caches
were found in week 44 (1999). Each food cache
measured approximately 1 x 1 x 1 m and
consisted mainly of willow branches. They
were situated across from the artificial lodge
on the other side of the lake. In one of the
caches branches were laid on top of each other
in a neatly arranged order parallel to each
other. In the other cache branches were laid on
top of each other in no particular order.
Site 5: Beavers began to repair the artificial
lodge in week 6. Mud and new branches were
added to the lodge and this work continued all
through week 10 as seen of the trails leading
from the water edge and up to the back of the
lodge on both sides.
At several sites beavers tried to stop the water
from flowing through the pipes where the
water is led under the roads and into streams
Appendix 9
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on the other side of the road by placing
branches and grass in the pipes.
Building activity at new sites
Site A: Around week 48 (1999) beaver activities
was discovered on private land bordering on
State Forest property. A ground burrow with
two entrances above water level was found.
Later on (exact date unknown) beavers made a
new ground burrow situated under the roots
of a large spruce tree. The entrance was under
water and covered with branches, as was the
top of the ground burrow.
A dam was built measuring 2 m in length, 75
cm in height and 50 cm in width. The building
material was mainly branches, but also mud
and grass were added. Beavers had built the
dam where half a tree trunk had fallen across
the stream. During the course of this study the
dam was enlarged and by the beginning of
August the dam measured 15 m in length. As
water kept running out on the side of the dam
beavers kept building it larger. The height
measured less than half a metre on this part of
the dam and it was mainly made of mud and
grass.The area flooded by this dam was
approximately 2 hectares whereof one hectare
was private grass field.
During the month of May 2000, 2 other dams
were built. These were located upstream from
the ground burrow (approx. 50 m) and were
located within 15 m of each other. The largest
one measured 3-4 m in length, 65 cm in height
and 50 cm in width. It was made mainly of
willow branches and mud. The dimensions of
the other dam were smaller: 2 m in length, 50
cm height and 30-40 cm in width.
Stemming the water at these three parts of the
stream resulted in approx. 100 meters of water
deep enough for the beavers to swim in.
Site B: At the end of 1999 a new ground
burrow/lodge was built on private land in an
artificial duck pond. Beavers had to walk 25 m
on land in order to get to the main stream of
the water system. The ground burrow was
located underneath birches and pine trees. The
entrance was under water and covered with
branches. Above ground the burrow was
covered with branches (species unknown). The
ground burrow measured 2 m diagonally.
At two other sites (C and D) ground burrows
were made. At both sites the ground burrows
were situated underneath bushes and both
were covered with branches. Entrances were
under water.
At site D a dam measuring 1 m in height and
2-3 m in length was discovered around in the
summer of 2000. The dam was located in a
stream in the middle of a stream valley. It did
not seem to be prime beaver habitat as apart
from willow bushes the main tree species
growing in the vicinity are spruce.The dam
was mainly made of thin willow branches.
Appendix 9
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