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Theses, Dissertations, Professional Papers
Graduate School
1986
Play behavior and dominance relationships of
bighorn sheep on the National Bison Range
Christine C. Hass
The University of Montana
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Hass, Christine C., "Play behavior and dominance relationships of bighorn sheep on the National Bison Range" (1986). Theses,
Dissertations, Professional Papers. Paper 7375.
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Pla y Behavior and Dominance Re l a t i o n s h i p s
of Bighorn Sheep on the Nat ional Bison Range.
by
Christine C. Hass
B.A.,
P re s en t ed
Un i v e r s i t y of Montana,
1983.
in Partial Fu lfillment of the Requir e me n ts
for the Degree of Master of Arts
UNIVER S IT Y OF M O N T A N A
1986
Approved by:
Chairman,Board^of
Examiners
D€?an, G ra duate School
Date
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Hass,
C hr i stine C ., M.A.,
Novemb e r 1986
P l a y Behavior and Dominance Relatio n sh i ps
of B i gh o rn Sheep on the National Bison Range.
Director:
Zoology
{96 pp.)
Donald A. Jenni
A 27-month s tu d y of bighorn sheep (Ovis canadens i s )
on the National Bison Range, Montana, focused on two
asp e c t s of social behavior: play behavior and dominance
relations.
Data co l lected from the lambs supported the
Motor T ra ining Hypothesis for the function of play
behavior, but not the Social Co h esion or Social
C o m p e t i t i o n Hypotheses.
Male lambs played more than
female lambs, and lambs chose partners closest to t h em
in size and age.
The most common components of play
were those patterns used in intraspecific conflict and
pr edator evasion.
The number and sex of available play
p a rtners influenced the amount of pl a y more than did
mat e r n a l investment.
Peak p la y periods coincided with
the period of most rapid growth.
These data are
co n s i s t e n t with the hypoth esis that pla y behavior,
under c er t ai n environmental and social constraints,
pr ovides lambs with immediate, as well as delayed,
m otor training benefits.
D ominance rel ationships among bighorn rams and ewes
were e x amined to q u a n t i f y structure, development, and
r ep r o d u c t i v e correlates of rank.
Both rams and ewes
e x h i b i t e d hi g hl y stable hierarchies that were s t ro n gl y
c o r r e l a t e d with age.
Dominance re latio nships were not «
e v i d e n t until after the sheep were one year old
B eh a vi o r a l interactions, p a r t i c u l a r l y among the rams,
we re c l o s e l y tied to dominance rank.
Direct
r ep r od u ct i ve benefits of high rank, in terms of more
b re eding opportunities, were obvious for rams.
No
r ep r od u ct i ve benefits, in terms of lamb weight, lamb
sex, date of estrus or lambing, nor nursing du r at i on or
rate, could be found for ewes.
11
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ACKNOWLEDGEMENTS
I w o ul d like to express m y sincere g r at itude to all the
people and ag encies who s u pp o r t e d the r es e a r c h that went
into
this thesis:
First,
I wo u ld
like to thank m y advisor,
the o p p o r t u n i t y to s t u d y the NBR bighorns,
support,
assistance,
and encouragement.
and
for
for pr oviding
I w ould al so like to
thank the other me m be r s of m y committee,
O 'Gara,
Don Jenni,
Phil Motta and Bart
for their gallant a tt e mp t s at guiding m y e d uc a t i o n
and research.
J.T.
Hogg shared
information on the NBR herd,
as well as m a n y insightful comments.
L. Scott Mills assis t ed
w it h data c o ll e c t i o n du ring Se ptember
1983.
N BR was funded by grants
C r o c k e t t Club,
(to Dr. Jenni)
Camp Fire Conservation,
N o r t h A me r i c a n Wi ld Sheep.
The s t u d y on the
from the Boone and
and the F o u n d a t i o n
for
Additi o na l aid was provided by
the U M Depart m en t of Z oology and the Mon tana Cooper a ti v e
W i l d l i f e R es e ar c h Unit,
Range,
and the U.S.
the staff of the National
Fish and Wildlife Service.
Bison
Critici s ms by
Joe Ball and Beth Flint on e arlier d rafts are g r e a t l y
a ppreci a te d .
T hanks also to Phil Wright and Bart O ' Gara for
n e c r o p s y i n g sheep,
favors,
e x a m i n i n g carcasses,
and nu merous other
large and small.
Sp ecial thanks to the Z oo l og y and W il d li f e grads,
their e n l i g h t e n i n g critici sm,
a d v i c e , and humor.
Ill
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for
T A B L E OF C ON T EN T S
Page
ABSTRACT
.......................................................
ACKNOWLEDGEMENTS
Ü
.............................................
LIST OF TABLES
ill
........................................ v
L I S T OF F I G U R E S ................................................. vi
CHAPTER
I.
INTRODUCTION.
..............
1
II.
M AT E RI A LS AND METHODS
.............................
9
S t u d y A r e a ............................................... 9
S t u d y P o p u l a t i o n ................
10
Data C o l l e c t i o n ........................................ 12
C e n s u s e s .......................
12
O b s e r v a ti o ns
................................... 13
E t h o g r a m .......................................... 15
C a l c u l a t i o n s and St a ti s ti c s ........................ 16
Play P at terns and R a t e s ......................... 16
Maternal I n v e s t m e n t .............................. 17
Dominance A s s e s s m e n t .......................... 17
I nt e ra c ti o n R a t e s .............................. . 2 0
R ep r o du c ti v e Correlates. ..................... 21
III.
S T RU CTURE A N D F U N C T I O N S O F PLAY B E HA V IO R
. . . .
23
Results.
.............................................23
S u r v i v o r s h i p .................................... 23
Structure of P l a y .................................24
M aternal I n v e s t m e n t .............................. 36
D i s c u s s i o n .............................................37
IV.
S TR U CT U RE A N D D E V E L O P M E N T
O F THE D O M I N A N C E H I E R A R C H I E S ....................... 46
R e s u l t s ................................................. 46
R a m s ............................................... 46
Ewes
60
L a m b s ............................................... 76
D i s c u s s i o n .............................................78
S U M M A R Y ........................................................... 89
L I T E R A T U R E C IT E D
.............................................
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91
L IS T O P TABLES
Table
1
2
3
Page
C o m p o s i t i o n of the NBR herd on
1 September 1982-4. .
11
T o ta l p l a y patterns initiated and
received by lambs in 1983 ..........................
31
D i s t r i b u t i o n of Mounts by the
..........................
two male lambs in 1983.
32
4
Win-loss matrix
for
rams, 1 9 8 2 ......................
47
5
W i n- l o s s m a t r i x
for
rams, 1 9 8 3 ......................
48
6
W i n- l o s s m a t r i x
for
rams, 1984 ......................
49
7
M e a n Dominance Values for class II,
III, and IV r a m s ......................................... 53
8
Do m inance Values and ages for rams
. . . .
59
9
Wi n -l o ss m a t r i x for ewes, 1982 ......................
62
10
L o c a t i o n s of d i s p l a c e m e n t s by e w e s .................... 64
11
W i n - l o s s m a t r i x for ewes, 1 9 8 3 .................
65
12
W in - lo s s m a tr i x for ewes, 1 9 8 4 ..................
66
13
D o mi n an c e V al u es and ages for ewes 1982-4
1982-4
V
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. . . .
77
L IS T OP FIGURES
Figure
1
Page
D is t r i b u t i o n of play bouts d u ring
the summer o b s e r v a t i o n periods .....................
25
D ur a t i o n s of p l a y bouts v ersus the
,
number of p l ayers involved ..........................
26
Male and female initiated play
p at t er n s in 1983 ......................................
28
To t al contact and d i s p l a y patterns
to male and female lambs in 1983 ...................
29
5
W e e k l y s u c k l i n g and p l a y rates,
.............
34
6
P l a y rates and g rowth rates
. . . . . .
41
7
R a m Dominance Values v er su s age
for all three y e a r s ...................................... 51
8
R a m Dominance Values versus Dominance
V alues following year for all three y e a r s .............. 52
9
R a m D o mi nance Values versus copulation
rate and number of ewes b r e d ...........................54
2
3
4
10
11
1982-4
for lambs.
I n t e r a c t i o n rates for rams, 1983
and 1984 ...............................................
55
P at t er n s used in r a m d om i nance
interactions, by rank-gr o up s ........................
57
12
Ewe D o mi nance Values v e rs u s age
for all three y e a r s ..................................... 68
13
Ewe Dominance V alues ve r s u s Dominance
Va lu es follow i ng y e a r ................................... 70
14
Ewe Do minance Values v ersus w ei ghts
of male and females l a m b s .............................. 71
15
I n t e r a c t i o n rates for ewes, 1983
and 1984 ..................................................
73
R a t e s of d i s p l a y and c on tact
d i s p l a c e m e n t s for ewes, 1 9 8 4 ..........................
74
16
V I
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CHAPTER I
INTROD U CT I ON
The d e v e l o p m e n t of behavior
in a n y given species
o ften the result of two processes;
maturation
of innate behavior.
and p s y c h ol o g ic a ll y )
B i g h o r n sh e ep
learning and the
Anim als mature
influences on behavior
(Geist 1971,
1982).
(Ovis c an a d e n s i s ) are
for a s t u d y of d evelopment.
p ro n ou n c e d sexual dimor phism;
as ewes and have m u c h
rams weigh up to twice as muc h
larger horns.
m a t u r i t y at 1-3 years of age,
intriguing a n imals
T h e y are social ungulates with
d i f f e r e n t d e v e l o p m e n t a l regimes.
Ewes and rams
whereas rams may reach sexual
but do not ac hieve
until
(Blood et al.
6-8 years of age
J o r g e n s o n and W i s h a r t 1984).
full body size
1970,
Geist 1971,
Gr o wt h rates differ not on ly
but also am on g herds
(Geist 1971,
S h a c k l e t o n 1973)
and a mo n g years on the same herd,
on the a v a i l a b l e
forage
(Horejsi
B ig h or n s of all ages play;
ewes e x h i b i t both social and
Berger
1979).
soci al rank,
1976,
lambs,
Bunnell
1978).
yearlings,
locomotor play
d e p e n di n g
rams and
(Geist 1971,
Lambs are born to females that differ
and
live
in
in g roups of mixed age and sex that
pre s e n t a v a r i e t y of pa r tners
sexes,
fol low
Ewes reach adult size and
m a t u r i t y at 1-2 years,
b et w e e n the sexes,
( p hysically
at d i f f e r e n t rates; d if f e r e n t i a l growth
rates m a y have pr o fo u n d
C l u t t o n - B r o c k et al.
is most
as well as other
(ewes and y e ar lings of both
l a m b s ) to play with.
The amount
of
p l a y i n g by lambs r e p o r t e d l y va r ie s with physical e n v i r on m en t
1
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a nd g r o u p size
Shackleton
(Berger
1979),
1973), and maternal
This study is not the
Geist
(1971),
(1980)
p o pu l at i on q u a l i t y
Sh a ck l e t o n
in vestment
(Geist 1971,
(Horejsi
1976).
first to a dd r es s pl a y in bighorns.
(1973),
Horejsi
(1976)
and Long
used the amount of playing observed as relative
m e a s u r e s of p o pu l a t i o n vigor.
Berger
(1979,
1980)
stu died
the s t ru cture and e c o l o g y of p la y in three d if f er e nt
p op u l a t i o n s of bighorns.
dyadic
None of these s t udies fo cused on
interactions between known
individuals,
however.
c o n j u n c t i o n with other studies of b i gh o rn behavior,
In
access
was o bt a in e d to a r e l a t i v e l y small bigh orn herd
(50-60
animals)
These a nimals
si t ua t ed on the Nat ional Bison Range.
range wi t hi n a fenced enclosure,
indiv id u al s
but are not
in the po p ul a ti o n were known,
c l o s e l y mo n it o r e d on a year-ro u nd basis,
"captive” .
All
and could be
a p r e - r e qu i si t e
for
a d e t a i l e d study of development.
Studies of p la y behavior continue
p ro b l e m s
of d e f i n i t i o n
(Bekoff and Byers 1981, F a g e n 1981).
For the purpo s es of this study,
(1981:300)
definition:
to be plagued by
I use Bekoff and Byers*
"Play is all motor a c t i v i t y performed
p o s t - n a t a l l y that ap p ea r s to be purposeless,
pat t er n s
in which motor
fr om other c on texts m a y often be used
forms a nd a l tered tempor al sequencing".
in m od i fi e d
Among ungulates,
p l a y is often d i v i d e d into l o c o m o t o r - r o t a t i o n a l play,
includes running and
which
jumping components;
includes all patterns which
and social
w h ic h
play,
involve more th an one
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3
indiv id u al
(Byers 1984).
In this study,
I focused on social
play,
p a r t i c u l a r l y contact and d i s p l a y patterns pe r fo r me d
among
lambs.
N um e ro u s h ypotheses have been g e n e r at e d to e x pl a in the
be nefits of play beha vior
summary).
Of these,
situ ations.
(see Fagen 1981 for a r e v i e w and
m a n y were not testable
in field
I chose to test three of the h ypotheses by
o bs e r v i n g a fr e e -r a ng i ng herd,
and by re viewing the
li terature concern i ng the natural h i s t o r y and e c o l o g y of
other b i g h o r n herds :
I.
The Motor Tr a in i ng Hypothesis.
R ep e a t e d ex e rcise has nu m e r o u s beneficial,
p o t e n t i a l l y beneficial,
effects,
and s tr e n g t h e n i n g muscles,
c a p a c i t y and ef ficiency,
a c t i o n s pe r formed
therein).
or
including thickening bones
i ncreasing c a r d i o p u l m o n a r y
and
increasing the e f f i c i e n c y of
(Bekoff and Byers 1981 and references
These phy sical and ne ur ological
pr ocesses have
b ee n lumped together under the t e r m "motor training".
B eh a vi o rs can thus be fine-tuned,
so animals
learn how and
wh en to p e r f o r m t h e m in the co r re c t environ m en t al and social
c on t ex t s
(Fagen 1981,
t ra i n i n g benefits,
Bekoff
1984),
If play provides motor
the follo wi n g might be expected:
b eh a v i o r should occur
(1) pl a y
in both sexes and appear early in life
(during the most rapid gr ow t h phase);
(2) social play
p a t t e r n s should resemble a du l t a gg r es s iv e and sexual
behavi o rs ;
and
(3) male
lambs
(because rams s h o w greater
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k
variance
1984a})
c hoose
in re pr oductive su ccess than ewes
(Geist 1971,
shou ld ex h ib i t more social p l a y than females,
partners that are cl osest
Hogg
and
to t h e m in size or age to
provide r i go r ou s and ch a l l e n g i n g play.
II. The Social C o h e s i o n Hypothesis.
S ocial at t a c h m e n t s m ay be formed,
m a i n t a i n e d or s tr e n g t h e n e d
in play
act as "social g l u e " (Fagen 1981)
(Bekoff
reduce
that p l ay together m a y be more
playmates,
and less
(Bekoff
therefo re,
might be expected:
(Bekoff
1977).
1984),
It is
Individuals
inclined to remain with their
likely to disperse.
play than male
P la y m a y
but the amount of play that m a y
its t e n d e n c y to d i sp e rs e
more social
1977),
by k ee ping groups cohe sive
and r e d u c i n g the t e nd e n c y to d is perse
not w h et h er an a nimal plays,
and social bonds
(1)
lambs,
The
following,
female lambs should e x hibit
because
females tend to
r e m a i n w i t h the ewe group on their natal range,
while males
tend to di s pe r s e with the rams to se parate ranges when 1-4
years old
groups,
(Geist 1971);
(2)
lambs should play in same sex
be cause r am and ewe gr o up s are separate
the year; and
(3) p l a y s hould be a coopera t iv e venture
w hich all players benefit;
if ever,
in
do m in a nc e r e lationships need not
be formed e a r l y and should not be e v ident
D om i n a n c e
for most of
in p la y bouts.
reversals should be c o m m o n and pl ay should rarely,
es calate
into a fight.
III. The Social C o m p e t i t i o n Hypothesis.
"If a juvenile can reduce the b od y gr o wt h of his
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5
•playmates'
by g a in i ng dominance,
p e r m a n e n t di s a d v a n t a g e "
he
(Geist 1978
inflicts upon t h e m a
:3).
c h a r a c t e r i z e d by d o mi n an c e hierarchies,
b e n e f i ci a l
life,
In sp ecies
it might be
4---
to obtain do m in a nc e over one's peers e a r l y in
and to use that dominance,
stre ss upon
of living"
(potential)
(Geist 1978
hypotheses,
in p l a y bouts,
c o m p e t i to r s and
).
to
inflict
increase their
"cost
To be co n si s te n t with this
(1) do m in a nc e r e l a t i o n s h i p s should be formed
e a r l y and d o mi n a n t a nimals should use their rank to control
interactions,
separated
(2) because
for most of the
rams and ewes are g e o g r a p h i c a l l y
year and the most
intense
c o m p e t i t i o n for r es o ur c es p r o b a b l y occurs within r a m and ewe
groups,
lambs should play
same sex,
and
(3) be cause
forage and bedding sites,
p r e f e r e n t i a l l y with lambs of the
rams m a y not only
as ewes do,
compete for
but they also compete
for d o m i n a n c e posit i on s and br e ed i ng o p p o r tu n it i es
(dominance
may be more c l os e ly tied to reprod u ct i ve success),
male
lambs
s ho u ld p l a y more th an female lambs.
The above hypotheses are not m u t u a l l y exclu s iv e and care
must be taken
in interp re t in g results.
The predictions made
are by no means the o nl y implications of these hypotheses,
but m e r e l y those I felt to be most tracta b le
for this s t u d y .
Because
the e v o l u t i o n a r y
it is al m os t
impossible
to d et e r m i n e
forces th a t shaped play behavior,
the h y p o t h e s e s may
r e p r e s e n t effects and not n e c e s s a r i l y functions of play
behavior.
However,
the study of the be n ef i c i a l eff ects ma y
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6
be one w a y to s t u d y function
(Fagen 1981).
The Motor T r a i n i n g hy p ot h es i s
supported
hypothe s is
to date,
b e h a v i o r a l sex d i f f e r e n c e s
V in cent a n d Bekoff
Ungulates
1985),
is the most w i d e l y
based on structure and
in juvenile Canids
1977), M u s t e 1 ids
(Byers 1977,
and P i n n e p ld s
1980;
(Poole
Berger 1979,
(Gentry 1974),
Inter ac t io n s of c ol l a r e d peccaries
Byers
squir re l s
P ri m a t e s
1983,
1984).
1978,
1980;
(Byers and Bekoff
1971) and
indicate possible
b etween pl a y and the establ i sh m en t of d om i nance
but no studies to date have shown that animals
use their d o m i n a n c e
subordinates
Juvenile
Studies of young Co l um b i a n ground
(Poirier and Smith 1974)
hier archies,
Pf eiffer
(T a ya s su t a j a c u ) m a y
(S p e r m o p h i lus c o l u m b i a n u s , Steiner
relationships
Biben 1982),
to name a few.
s up port the Social Co h e s i o n hypothesis
1981,
(Bekoff 1974,
status to
inflict stress on their
in play.
Data on three p o p u l a ti o ns of bi g ho r n sheep in British
Columbia,
Oregon and C al i fo r n i a provided evidence
Motor T r a i n i n g h y p o t h es i s
demonstrated pronounced
b ig h o rn behavior,
(Berger
1979,
Berger also
i n te rp o pu l at i on va r i a b i l i t y in
s h o w i n g the nee d for studies
habitats and of d i f f e r e n t subspecies.
ea ch p o p u l a t i o n
1980).
for the
in d i ff e r e n t
Berger worked with
for two to seven m onths and was often able to
i d e n t i f y the sex of the
lambs.
d id not k n o w m a n y individuals,
However,
perhaps because he
he did not test the Social
C o h e s i o n or Social C o m p e t i t i o n hypotheses.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
7
Bec a u s e the a mount of pl a ying by b i ghorn lambs has been
c o r r e l a t e d to the am ount of ma t ernal
1973,
H o rejsi
m at e rn a l
1976),
investment
(Shackleton
I also ex a mi n ed the r e l a t i o n s h i p between
investment and pl a y behavior.
This s t u d y b e g a n as an e x p l o r a t i o n of the structure of
p la y
in big horns and tests of three hypotheses c o n c e r n i n g the
possible
fu nctions
of p l ay behavior.
One of the h ypotheses
con n e c t e d pl a y beh avior to the d e v e l o p m e n t of do m in a nc e
relations.
rel a tions
However,
few stu dies concerned domin a nc e
in b i ghorn sheep,
—
a l t h o u g h the dramatic
h o r n - t o - h o r n clashes of the rams were w e 1 1-docu mented and
rec o gn i z e d as
important
in d e c i d i n g br eeding pr i v i l e d g e s .
The r e l a t i o n s h i p s b et w ee n horn size,
opportunities
1971),
rank and breeding
of free-r a ng i ng rams were well d e s c ri b ed
but studies of ewes were short-term,
conditions
relations
(Eccles 1981,
Ben nett 1986).
in free-r a ng i ng bighorns,
(Geist
under captive
Data on dominance
p a r t i c u l a r l y ewes, were
s o r e l y lacking.
Rams and ewes live on separ at e
year
(Geist
societies.
1971),
Rams
and e s s e n t i a l l y
indivi d ua l s
exist
in two separate
f o r m bachelor herds composed of s ex ually
mature a n i m a l s r an g in g
(Geist 1971,
ranges for most of the
in age
p e r s . o b s .).
from 18 months to over
10 years
Bachelor herds are co m posed of
that v a r y c o n s i d e r a b l y
s t r o n g ties are ap p a r e n t among the
c h a r a c t e r i z e d by strict protoc ol
in body and horn size.
rams,
No
and the s o c i e t y is
based on body and horn size
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
8
(Geist 1971).
Ewe s o c i e t y is focused on the n u r s e r y group,
lambs and
lactating ewes,
c om p o s e d of
yearlings of both sexes,
some
2 -year- o ld s and other ewes who a ss o ci a te d with the g r ou p for
brief periods of time.
Al t h o u g h ewes reach adult size and
m a t u r i t y at 1-3 y ea r s of age
W is h ar t 1984),
variation
in the bachel or herd
J o r g e n s o n and Wishart 1984).
c o n s i d e r e d p ae d o m o r p h i c
in their behavior,
all members of ewe s o c i e t y
like juvenile males
s oc i e t i e s
Jo r ge n s o n and
s e x u a l l y mature ewes s h o w c o n s i d e r a b l y less
in size tha n the a nimals
(Geist 1971,
rams;
(Geist 1971,
(Geist 1971).
Ewes have been
with re spect to
(except lambs)- m a y behave
The two bighorn she ep
t h e o r e t i c a l l y consist of the b eh a v i o r a l l y
n u r s e r y group,
immature
and the ma t ur i n g and mature bachelor herd.
A lt h o u g h the young rams
leave the n u rsery groups when
t h e y are s e x u a l l y ma t ur e and able to dominate the ewe s
1971),
(Geist
when and h o w d om i na n ce relations de v e l o p among rams
and ewe s has not be e n r e p o r t e d .
A free-r a ng i ng herd of
bi ghorns was st u died to de t er m i n e how the d i ff erent
d e v e l o p m e n t a l r egimes and soc ial organiz a ti o ns of rams and
ewes a f f e c t the s tr u ct u re and d e v e l op m en t of dominance
relations,
and to t r y to co r relate rank with such va r ia b le s
as age and r e p r o du c ti v e success.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
C H A P T E R II
M AT E RI A LS AND MET HODS
S t u d y Area
The s t u d y was c o nd u c t e d on the Na tional Bison Range
(NBR),
a 7504 ha. N a tional Wildli f e R efuge a d m i n i s t e r e d by
the U.S.
Fi sh and Wi l dlife
Service.
The NBR
a p p r o x i m a t e l y 70 k m n orth of M is s o u l a
Montana.
The v eg e ta t i o n
(A q r o p y r o n ) Prairie,
is located
in no r t h w e s t e r n
is c h a r a c t e r i z e d
by Palouse
wit h thick patches of Dpuglas - fi r
(P s e u d o s u g a me nz ies i i ) on the north slopes and sc a ttered
P o n d e r o s a pines
E l e v a t i o n s range
(Pinus p o n d e r o s a ) on the south slopes.
from 788 to 1489 m.
the s o u t h e r n half of the Refuge,
few,
the sheep range
inhabit
an area of steep hillsides
d i s s e c t e d by m a ny small drainages.
whole,
Bighorn sheep
As with the Refuge as a
is s m o o t h l y contoured,
with only a
small rock outcrops.
The NBR is su r r ou n d e d by a 2 . 4 - m game fence that
p re v e n t s e m i g r a t i o n or
u ngulates.
wapiti
immigration of wild
Wild u n gu l a t e s m a i n t a i n e d on the Refuge
(Cerv us e l a p h u s ), bison
amer i c a n u s ), mule deer
(O d o c o i l e u s
(O. v l r g i n i a n u s ) and bighorns.
into ei g ht pastures by raised d r if t
m o v e m e n t s of the bison,
i nc l ud i ng bighorns,
include
(Bison b i s o n ), pronghorns
(A n t i l o ca p ra a m e r i c a n a ), m o u n t a i n goats
de er
(and domestic)
(Oreamnos
h e m i o n u s ), white - ta i le d
The Refuge
is di v id e d
fences that restrict
the
but a l l o w smaller ungulates,
to pass underneath.
Care ful manag em e nt
of all u n gu l at e s on the Refuge pre vents ov ergrazing.
9
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
10
study Population
The b ig h or n s on the NBR were d e s c e nd a nt s of 12 a n im a ls
that were b ro ught to the Refuge
in 1922,
(NBR R e f u g e N a r r a t i v e Reports).
study,
to 53
the number of sh e ep
from Banff,
A l berta
During the course of m y
in the p op u la t io n ranged
from 50
(Table 1).
The bi g h o r n s were h ab i tu a t e d to people and could be
a p p r o a c h e d to w i t h i n
less than 10 m.
The sheep were ob served
f ro m June 1979 t h r o u g h M a y 1902 by anot her observer
1984a);
m y s t u d y began
in June
1982 and terminated
(Hogg
in
S ep t ember 1984.
All of the s h e e p were
characters,
tags.
all
in di v id u al l y r e cognizable b y horn
natural m u t i l a t i o n s such as torn ears,
To facilitate rapid
lambs of 1983 and
identification,
Both the paint and the dye
were s q ui r te d onto the an i m a l ' s coat
This re s ul t ed
were v i si b le
from a hypodermic
in va riable patterns,
by c o u n t i n g h or n a n n u l i .
be r e l i a b l y d e t e r m i n e d
in the
initi ally by J. Hogg
field
(Geist 1966),
"older"
ages w e re n eeded for c a l c u l a t i o n purposes,
for me m be r s of the
in
Because ages of ewes ca nn ot
years or older were c l a s s i f i e d as
calculated
some of which
from m o re than one km through a spotting s c o p e .-
Ages of sh e ep were e s ti m a t e d
1980,
some adults and
1984 were s plattered with sheep
bra n d i n g paint or N ya n zo l A dye.
syringe.
or ear
ewes five
(Hogg 1983).
Wh ere
a mean age was
"older" ewe g r ou p by figuring a
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
1I
T ab l e
1,
Age and sex c o m p o si t io n of the NBR herd on
1 September
1982-4.
Age is in years.
L - lamb.
•- i n d i c a t e s ewes that were estimated to be at least
y ea r s old in
1980.
1982
Ram s
1984
Age
#
Age
#
Age
#
10
3
1
11
1
11
1
10
1
10
1
3
1
9
2
9
1
8
1
8
7
7
3
1
5
1
9
8
7
6
5
3
2
6
3
2
3
1
4
1
4
2
2
2
3
2
3
5
1
5
2
2
2
2
1
5
2
1
2
L
2
L
Total
Ewes
1985
22
23
19
7+
9
8+
9
9+
8
6
3
7
3
8
3
5
6
5
3
1
7
4
3
1
6
3
1
3
1
4
1
5
1
2
5
5
4
5
1
5
3
2
5
5
L
4
3
1
4
L
2
T otal
27
31
32
H er d Total
50
55
51
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five
12
y e a r l y m o r t a l i t y rate of 11.7%
of 12 years.
(Geist 1971)
Ages of s h ee p bor n
and a m a x i m u m age
in 1980 and later were known
precisely.
" L a m b ” refers to an animal that was less tha n 12 months
old,
"yearlings" were
12-23 months,
and
"adults" were two
years and older.
Data Co l l e c t i o n
Cen suses
C en s u s e s were c o n d u c t e d b i - w e e k l y th roughout the year,
except
for the r u tt i n g and lambing periods,
c en s us e s were conducted.
D uring a census,
when d a i l y
an attempt was
made to find all of the s he e p in the population,
d u r i n g the
lambing period,
to find o n l y ewes and
w h e n a co ncerted effort was made
lambs.
c o n d u c t e d d uring the rut
a p p r o x i m a t e estrous d at e s
except
Censuses and observations
( N o v e m b e r - D e c e m b e r ) yielded
for most ewes.
length of k nown g e s t a t i o n p e riods
By adding the
(x = 173.6 d a y s , N = 16;
Hogg 1984a), an a p p r o x i m a t e p a r t u r i t i o n date was obtained
a lmost e v e r y ewe.
I made
intensive eff orts to keep track of
eac h ewe ar ound her p a r t u r i t i o n date,
ca pt ure
lambs soon after birth.
and attempted to
Dom estic ewes reportedly
e s t a b l i s h d i s c r i m i n a t i n g be h avior w ithin the
after b i r t h
for
(Pol ndron and L e N e i n d r e 1979),
first 30 mi nutes
so I waited until
lambs were at least one hour old before a t te m pt i ng to ca pture
them.
L a m b s older than 24 hours were s e l d o m catchable.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
13
After capture,
re corded.
lambs.
lambs were ear-tagged,
In 1984,
and weight and sex were
ra d i o - c o l l a r s were also fitted on nine
Individ u al ewes r e mained
2-12 da y s
f o l l o wi n g pa rturition.
observed,
a ewe ob s er v e d
isolated
from other ewes
for
If the birth was not
in isolation with a lamb less than
five da y s old was a s s u m e d to be the lamb's mother.
C e n s u s u e s co n du c t e d throug ho u t the
lambing period
(roughl y 10 M ay-20 J u n e ) re v ea l ed which ewes were pregnant,
and h o w m a n y a b o r t e d or failed to conceive.
o b s e r v a t i o n s of s h e e p social behaviors,
dominance
interactions,
play,
Op p o r t u n i s t i c
particularly
and e w e-lamb interactions,
were
also n oted d u r i n g censuses.
Observations
Focal
o b s e r v at i on s were conducted on the r a m groups
m a i n l y du r in g September t h rough early November,
o c c a s i o n a l l y t h r o u g h o u t the rest of the year.
in 1982 w e re c o n d u c t e d on an ad l ibitum basis
D ur i ng 1983 and 1984,
of d o m i n a n c e
a l l - o c c u r e n c e s samples
but also
O bs e rv a ti o ns
(Altmann 1974).
(Altmann 1974)
interactions were recorded when group
c o m p o s i t i o n was r e l a t i v e l y stable.
Ad libi tum samples were
rec o rd e d wh en g r o u p c o m p o s i t i o n changed rapidly d ur i ng the
o b s e r v a t i o n periods,
and du r i n g censuses.
O b s e r v a t i o n s of the ewe groups were co nducted
o p p o r t un i st i c,
hi e r a r c h i c a l
m a n y lambs as po ssible
fashion.
in view,
while
in an
I a t te m pt e d to k ee p as
I wa n d e r e d with the
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14
group.
A l l - o c c u r e n c e s s a mp l es of su c kl i ng bo uts were
r ec o r d e d
for all
lambs
in view;
in-view and o u t - o f - v i e w times
were r e co r d e d to the n earest minute,
least two lambs were
in view,
for each lamb.
and neither
one suckling,
a l l - o c c u r e n c e s s a m p l e s of p l a y were als o recorded.
m embers of a group,
including adults,
yearlings,
could be c o n s i s t e n t l y kept
in sight
g ra z in g
in an open area),
in a b u nched group
samples of suckles,
recorded.
play,
If at
then
If all
and
lambs
(e.g., whe n bedded,
or
a l l - o c c ur e nc e s
and do m in a nc e behaviors were
Ad l i b i t u m samp les of p l ay and d om i na n ce
behaviors
were re c o r d e d when g roup c o m p o s i t i o n was c h anging too q u i c k l y
to reco rd accurately.
g ro u p as possible,
a c c u r a t e l y all
I a t t e m p t e d to stay as far
from the
while still b eing close enou gh to identify
focal animals,
with the lambs having highest
pr ior i t y .
The du r a t i o n of all
n earest minute.
a bbrevi a te d ,
in t eractions were rec orded to the
All sheep
resulting
.
identities and behav ioral acts were
in a form of shorthand that
f acilit a te d rapid note-t aking.
Group co m po s it i on was noted
at the b e g i n n i n g of e a ch o b s e r v a t i o n period and all animals
e nt e r i n g a n d
leaving the g r o u p
(and times)
were recorded.
A
h an d - h e l d di g i t a l s t o p w a t c h was used to kee p track of elapsed
time,
as well as d u r a t i o n s
of select e d behaviors.
P l a y bouts were r ec orded d u r i n g
d u r i n g the summers of 1982-1984,
throughout
the y e a r .
In 1982,
focal o bs ervations
and o p p o r t u n i s t i c a l l y
M o unts were recorded,
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
as well
15
as the number and d u r a t i o n o£ play bouts.
the fo l lowing p a tterns c o m p r i s i n g
In 1983 and
1984,
individual bouts were also
recorded.
Ethogram
The
follow ing patter n s were recorded
in social
interactions du r i n g the study:
C on t a ct Pa t te r ns
Head Butt
(HB): F o r e h e a d or ho rns are used to f o r c e f u l l y bump
the head of another.
Butt
(B): Fo r eh e ad or horns are used to forcefu l ly bu mp the
bo dy of another.
Clash
( C L ) : A v e r y forceful HB preceded by an SLR
(see below)
by one or both sheep.
Touch Heads
(T H ): a light f or e he a d - t o - f o r e h e a d c ontact that
is s us t a i n e d
Sho u l d e r - P u s h
(SP):
position,
arou nd
Neck Wrestle
for at least one second.
Sh o u l d e r - t o - s h o u l d e r contact,
in parallel
in which two s h ee p push side-to - si d e or
in circles.
( N W ) : The head and neck are placed over
of another,
the neck
in p ar allel or a n ti - pa r al l el position,
and used to press the opponents head toward the
ground.
Face-rubbing
(FR): Face or horns are s l o w l y rubbed on the
face or horns of another.
F r o n t - l e g kick
(FK): A fo releg
another,
and c o nt a c t s
is raised and extend e d toward
the o p po nents chest,
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
b el l y or
16
legs .
Pawing
(PW): A front hoof
is used to scr ape the back of a
recli ni n g opponent.
D is p l a y s
(non-contact patterns)
S t r a i g h t - l e g g e d rear
with the
carpus,
(SLR):
A rear on e xt e nd e d hind legs,
forelegs s t ra i g h t or s l i g h t l y bent at the
and head
inclined toward ano ther sheep.
Also re f erred to as a "threat jump" by Gei st
Head Ti p
(HT):
The horns
(or forehead
in young lambs) are
inclined toward a no th e r s h e e p while the chin
tucked
in toward the chest.
(LS):
is
The same pattern has
been c alled a "horn threat" by Geist
Low S tretch
(1971)
The head and neck are
(1971).
lowered and exten de d
on an ev en h or i zo n ta l plane with the back.
Twist
(T): A L o w Stretch
in which the
lowered head
is rotated
on its lo n gitudinal a x i s .
Present
(P): The head
is raised,
with the neck a rched and the
r o s t r u m or i ented parallel to the ground.
C a l c u l a t i o n s and Statistics
Pla y Patterns and Rates
G-t e s t s
(Sokal and Rohlf 1981)
s i g n i f i c a n t d i f f er e nc e s
different
to a c c o u n t
were used to test
for
in the p r o p o r t i o n of patterns used by
individuals and g r o u p s .
F r e q u e nc i es were ad justed
for d i f f e r e n c e s in m e m b e r s h i p of di f fe r e n t sex
classes.
W e e k l y play d u r a t i o n rates were obtained by d i v i d i n g the
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
17
total number of mi n ut e s
in w h i c h play was recorded by the
total number of o b s e r v a t i o n m i nu t es on all lambs c o mb i ne d
(l a m b - m l n u t e s ) for each week.
year.
N o n - p a r a m e t r i c AMOVAs
Week 1 began on 23 June each
(Sokal and Rohlf
1981) were used
to a ssess d i f f e r e n c e s a mo n g years.
M at e rn a l
Invest m en t
Suckl in g rates were used to est imate post-natal m a ternal
Investment.
A l l - i n s t a n c e s samples of s uc kling bouts were
o btained du r in g a l m o s t d a i l y observ a ti o ns of the n u r s e r y
bands.
A s uc k li n g bout began when the lamb was
have g ra s pe d a teat,
head,
judged to
and te r mi n at e d when the lamb moved
v o l u n t a r i l y or otherwise,
aw a y from the udder.
its
Weekly
suc kling rates were obtained by di v i d i n g the total d u ra t i o n
of all ob served su c kles
(in seconds)
o b s e r v a t i o n mi n ut e s on all o bs erved
week.
by the total number of
lambs
(combined)
for a
N o n - p a r a m e t r i c ANOVAs were used to test diffe r en c es
among years;
P e a r s o n ' s coeffic ient,
r, was c a lc u la t ed to
exam ine the c o r r e l a t i o n b e tween play rates and suckling
rates.
Do minance A ss e ss m en t
D o mi na n c e r e l a ti o ns were as s e s s e d by a s se m bl i ng a
wi n-loss m at r ix
(Brown 1975)
based on domina n ce
for ea ch sex.
Wi t h i n r a m groups,
d i s p l a ce m en t s,
and c o u r t s h i p behaviors
Kicks,
interactions,
I s co r ed n o n-contact
(Mounts,
Front-leg
and Twists often a c c o m p a n i e d by g ro wling and
t on g ue - fl i ck i ng )
as wins
for the
initiator, and F a c e - r u bb i ng
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
18
as a w i n for the recipient.
year,
s u b o r d i n a t e rams were
Prior to the onset of rut ea ch
observed b u tt i ng and pu shing
d o m i n a n t rams out of bedding sites,
s u b o r d i n a n c e by P a c e - r u b b i n g
this p re - ru t period,
recor de d as wins
before d i s p l a y i n g
(see also Geist 1971).
on ly n o n - c o n t a c t d i s p l a c e m e n t s were
for the
initiator.
For ewes,
n o n - c o n ta c t d i s p l a c e m e n t s
f ro m b ed d in g sites,
locations,
h or n in g posts,
mineral
licks,
locations were s c ored as wins
the rams.
for the
the winner
as w i n n i n g one
interaction.
i nteractions were also used
a vo i d ci rcularity,
or other spatial
patte rn s Gambol,
fight was recorded
in d o m i n a n c e - s u b o r d i n a n c e
in pl ayful contexts by lambs.
and only when not a cc o mp a ni e d by
P l a y signals
Heel Kick,
(see Berger 1979,
included the rotational
and Neck Twist
Byers 1980)
(Berger 1979).
were also recorded as play
Yearlings and ad u l t s al s o used the above patterns
in pla yful contexts;
s ep arate playful
the p re s en c e of pl a y signals was used to
interactions
from d o m i n a nc e
interactions.
The res ults of the w i n - l o s s m at r i c e s were tested to
determine
If they d i f f e r e d s i g n i f i c a n t l y from r a n d o m order
( Ap pleby 1983).
circular
To
wins and losses be t we e n lambs were onl y
for displacements,
a n y p l ay signals.
signals.
foraging
initiator a n d , as with
of a do m in a nc e
M a n y of the b e ha v io r s used
N od s
contact and
P a c e - r u b b i n g was scored as a win for the recipient.
In both sexes,
assigned
During
This c o ns i s t e d of c o u n t i n g the number of
triads and unknown r e l a t i o n s h i p s
in a group.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
For
19
kno w n relati on s hi p s,
the w inner of the m a j o r i t y of the
e n c o u n t e r s w ih t in that dyad was as s i g n e d a value of 1, and
the loser r ec e iv e d a val ue of 0.
A pp l eby's
(1983) m ethod of
a s s e s s i n g ra n do m n e s s was based on the as s u m p t i o n that
individuals who had not been obs erved
pro b a b i l i t i e s of wi n n i n g an
older
Interaction.
However,
a mo n g rams
individuals w o n 97% of the en c ou n te r s with younger
rams.
W he n two rams of d i s p a r a t e ages had not been observed
interacting,
the older ani mal was a s si g ne d a 0.97 p r o b a b i l i t y
of wi n ni n g the
value of 0.03.
i nt e ra c ti o n and the younger was as signed a
For two rams of the same age whose
r e l a t i o n s h i p was unknown,
eac h
int eracting had equal
a 0.50 p r o b a b i li t y was assig ne d to
(see also R u t b e r g 1986).
Older ewes won in 88% of
i nteractions with yo un ger ewes,
r e l a t i o n s h i p was unknown,
probability,
therefore,
v/hen the
older ewes were assigned a 0.88
and younger ewes a 0.12 probability.
e qual age were ea ch a s si g n e d a 0.50.
used to assess
A chi-sq u ar e d value was
the d e gr e e of r andomness
s i g n i f i c a n t result
Ewes of
in the matrix.
A
indicates a n o n - r a n d o m order and a
t e n d e n c y toward t r a n s i t i v i t y
(A > B,
B > c, therefore A > C).
The degree of l i n e a r i t y of the h i e r a r c h y was ca lculated by
Kenda ll ' s c o e f f i c i e n t K
ranges
f r o m 0 (non-linear)
c o e f f i c i e n t K was used
linearity,
p re s e n t
(Kendall
h,
to 1.0
1962,
Ap p le b y 1983)
(co mpletely linear).
in pr e fe r e n c e to Lan dau's
(Landau 1951),
which
The
index of
due to the lack of information
in each of the matrices.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
20
The p r o b a b i l i t y of l i n e a r i t y within a g r o u p of more than
10 a n i m a l s
1975),
is low (Appleby 1983,
see al s o S c h j e l d e r u p - E b b e
so rather t h an a s s i g n i n g ordinal ranks to the sheep,
c a l c u l a t e d Dominance Values
for each sex
I
in ea ch year using
the w i n - l o s s m a t r i c e s based only on the re sults of re c orded
i nteractions
(not
r el a ti onships).
Eccl es
including probabi l it i es
D om i na n ce V alues
for un known
(Beilhartz et al.
1981) were used as relative measures
were c a l c u la t ed as
of dominance,
and
follows :
D.V.
where xi
1966,
= arcsinVîcI;
is the p r o p o r ti o n of opponents dominated.
These
D.V.s were n o r m a l l y d i s t r i b u t e d and permitted the a p p l i c a t i o n
of p a r a m e tr i c statistics.
only for animals
chosen)
Dominance Values were calcula t ed
inte racting with at least 10%
(arbitrarily
of the other herd members.
I nt e r a c t i o n Rates
A l l - o c c u r e n c e s sam ples c o ll ected
used to d e t e r mi n e
if sheep
interacted at d if f er e nt rates
a c c o r d i n g to their D om i na n ce Values.
ewes and rams were di v id e d
the low est scoring
25%
25%
For each year,
both
into four equal groups comprising
(group A),
(group B) et cetera.
in 1983 and 1984 were
the second lowest sc oring
A computer
p r o g r a m was w r it t en to
co mpute e xp e ct e d rates of i n teraction based on the am ou nt of
time the an imals
in each r a n k - g r o u p were observed
and A l t m a n n 1977),
(Altmann
a s su m i n g ea c h animal had an equal
p r o b a b i l i t y of interacting with an y other
In the group.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
21
These ex p ec t e d rates were then com pared to the observ e d
valu es an d a G-test was used to test for sign ificance.
D om i n a n c e
i nt e ra c ti o n rates were c a l c u l a t e d by d i v i d i n g
the ob s e r v e d number
of d o m i n a n c e be h aviors
in a r a n k - gr o up by
the total number of hours of o b s e r v a t i o n on all m e mbers of
each rank-group.
r a n k - g ro u ps and,
These rates were co m pa r ab l e am ong
for each sex,
a m o n g years.
The sampling
periods were biased toward times of the d a y and times of the
year
in which sheep were most likely to be
summer af t er n o o n s
rams),
for the ewes,
interacting
and a utumn mornings
(e.g.,
for the
and do not re p r es e nt ab so l u t e rates of b e h a v i o r .
R e p r o d uc t iv e C or r el a te s
Simple
c al c ul a te d
" r ep roductive perfor ma n ce " variables were
from ob s er v at i on s co n du c te d d uring the ru tting and
lambing periods.
Focal animal sampli n g of estrous ewes and
a s s o c i a t e d rams al lowed a s s i g n m e n t of estrous and birth da tes
for each ewe,
whereas the number of co pu lations and the
number of ewes bred
cal c ul a t e d
for
(during o b s e r v a t i o n periods)
individual rams.
L a m b birth we ights were
investment,
could be
used as estimates of pre-natal
while n u rs i ng d u r a t i o n s and rates were used to
estimate po st-natal m a te r n a l
began w h e n the lamb was
t er m in a t e d when the
investment.
A nursing bout
judged to have grasped a teat,
lamb moved
and
its head a w ay from the udder.
M e a n n u r s i n g d u r a t i o n was the m e an of all record ed suckles
for a ewe during the summer.
D a il y nursing rate was the
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
22
total n u r s i n g d u r a t i o n
for each ewe d iv i de d b y the number of
m in u t es of c o nt i nu o us o b s e r v at i on on that ewe
o b s e r v a t i o n period.
in an
D aily n u rsing rates were a ve r ag e d over
the s u mmer to o btain mean nu r si n g rates
for each lactating
ewe.
T hese
"reproductive pe rf o rm a nc e " va r iables were
r eg r es s ed ag ainst D.V.s and tested
for c o r r e l at i on with rank
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
C H A P T E R III
STR U C T U R E AND F U N C T I O N S OF PLAY B E HAVIOR
R es u l t s
Survivorship
At the b eg i n n i n g of the study,
surviving
mi d - J u n e 1982,
lambs r e p r e s en t ed the entire su r vi v i n g
for that year,
out of 21 born
and 111.4 hours of
(Hogg 1983).
two
lamb c ro p
Bot h were males,
focal ob s e r v a t i o n s were obtained between
22 J u l y and 7 September.
In 1983,
26 lambs were born;
seven were alive at the end
of June but one male d i s a p p e a r e d on 17 or 18 July,
six lambs
(23%) su r vi v ed until
and weighed,
fall.
Nine lambs were caught
but o n ly one of those survived.
included two males and four
females,
so only
and
Surviving lambs
247.2 hours of focal
o b s e r v a t i o n were c o mp l et e d betw een 25 June and 15 September.
In 1984,
23 lambs were born,
the end of June.
Both were
c aught and weighed,
radio-collars
but on ly two surv ived until
females.
and nine of those were fitted with
in an effort to d et e rm i ne the cause of the high
lamb mor tality.
Three r a d i b - c o l l a r s
10-14 days old and six were r e co v er ed
lambs.
Eleven lambs were
fell off the lambs when
from p redator-killed
P r e d a t i o n wa s p r o b a b l y the cause of most of the lamb
mortality
in this herd.
Focal ob s er v at i on hours on the two
lambs to t al e d 138.7 be t we e n 23 June and 4 September.
No
lambs that were handled su r vi v ed until the end of the summer.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
24
S t r u c t u r e of P l a y
In 1982,
recorded.
40 p l a y bouts,
totaling 84 m inutes were
Bouts lasted up to 10 minutes,
minutes.
with a me a n of 2.3
Because p l a y was re c orded to the nearest minute,
the m i n i m u m bout was ca l cu l a t e d as being one minute
a l t h o u g h the number
1 to 21.
of acts recorded
com m on b et w ee n the two male
lambs;
and BS mo u n t e d JN 16 times.
G = 11.25,
In 1983,
recorded.
(Fig.
This difference was s i gn i fi c an t
331 play bouts t ot aling 672 minutes were
As
lasted up to 22 minutes,
in 1982, m os t pla y occurred during July,
70 p la y bouts were recorded,
Bouts ranged up to nine minutes
1.5 minutes.
Play was
dur i ng e a r l y Ju l y
In 1983,
(Fig.
infrequent,
(Fig.
1).
for a total of 107
long and av eraged
and most play occured
1).
the on l y year
lambs were present,
bout)
with a mea n of
involved 2-7 lambs.
In 1984,
minutes.
Mounts were
JN mo u nted BS 41 times,
few bouts bei ng observed after mid-August
P l a y bouts
in which more than one dyad of
the d u r a t i o n
(number of play minutes per
was s i g n i f i c a n t l y c o rr e l a t e d with the number of players
(r = 0.76,
p < 0.01;
Fig.
2).
B ec a us e 1983 was also the only year
and
1).
p < 0.05).
Play bouts
2.2 minutes.
with
in a minute r anged from
Most p l ay oc curred d u r i n g late J u l y with ve r y few
bouts b ei n g observed after m id - Au g u s t
(G-test,
long,
female
lambs were present,
only data
in which both male
from that year can
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
25
•---• 1982
O
01983
-A 1984
< 30
pfl
K
a
?A-V-6\
u*
14
JUNE
24
AUGUST
JULY
3
SEPT.
DATE
F igure 1.
D i s t r i b ut i on of pl a y bouts (and their r a t e s )
d u r i n g the summer o b s e r v a t i o n periods.
Note the decr ease
in pl a y duri ng August.
P l a y rate = play
m in u te s / l a m b - m i n u t e s of observation.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
26
221
r= 0 7 6
P<001
V-
<U
CL
en
<D
3
C
_o
CL
2
5
3
Number
of
6
Players
Fi g u r e 2.
The d u r a t i o n of p la y bouts were s i g n i f i c a n t l y
c o r r e l a t e d with the number of players involved in 1983.
Line d r a w n fr om r eg r es s io n equation.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
27
be used to analyze d i f f e r en c es
b et w e e n male and
In the amount and type of play
female lambs.
Overall,
males were
involved
in more p l a y patterns than females and e x h i b it e d a larger
repertoire.
115.2,
Males
p < 0.001),
initiated more p at terns than females
but either sex was about e q u a l l y likely to
re ceive p la y invitatio ns
For all patterns,
(G = 0.36,
(per lamb)
s i g n i f i ca n t di f fe r en c es were
p < 0.001).
Females
patterns to either sex
c ontact pat terns
the same sex
both
(G = 4.7,
(Fig.
females,
found
( F i g . 3);
for Clashes and SLRs
Fema le
CL,
p < 0.05;
lambs were never observed
with males
Lambs
initiated most
BH, and B) with lambs of
F i g . 4).
(SLR,
displ ay s to males than females
Males and females
HT, T, and P combined)
(G = 12.9,
p < 0.001;
F i g . 4).
initiated a lmost three times more contact patterns
lamb)
than d is plays
(G = 159.3,
(43%) were same- se x dyads,
s a m e - s e x dyads.
with
lambs could participate
wher eas
(initiated and received)
Overall,
lambs
(per
p < 0.001).
Of the 21 possible dyads that
pl ay acts recorded
to
initiating s i g n i f i c a n t l y more
Lambs
in, nine
(G =
3); no s ignificant d i fferences
SP, NW,
initiated more displays
m ales than
initiated more
than females
Twists or Presents.
(TH,
males
initiated a bout the same number of
were found for a n y pattern.
p er f or m in g Mounts,
p > 0.10).
except Mounts,
patterns to other males
10.9,
(G =
44% of the 1441
occurred
in
in 1983 were not playing more
lambs of the same sex than would be expected by chance
(G = 1.26,
p > 0.05).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
28
to ;
30
■
d 'cf
□ ss
_ 20
_o
£
jo
b 10
Q.
cr
w
CD
5
=)
z
IX
MT
TH
SP
NW
MALE
CL
BH
B
SLR
JLl
HT
INITIATED P A T T E R N S
10
£ \
TH
SP
NW
x Q
CL
BH
B
S LR
HT
F E M A L E INITIATED PA T TE R NS
Figure 3.
Number of male initiated patterns (top) and
female initiated patterns (bottom) to male and female
lambs, 1983.
See Methods for a description of patterns.
* = significant at p < 0.001.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
29
contact
display
«r
_o
£
o
<D
tO :
□
?
CL
cr
*
ÜJ
OÛ
IX
(f
Ini t i a t o r
Figure 4.
S um m a r y of total c ontact pa tterns (MT, TH, SP,
NW, CL, BH, and B) and d i s p l a y pat terns (SLR, HT, T, and
P) to male and fema le lambs. Lambs used s i g n i f i c a n t l y more
co nt act than d i s p l a y patterns in p la y bouts.
* =
s i g n i f i c a n t at p < 0.01.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
30
A su c c e s s f u l p la y initiation was followed by more play
p at t er n s b etween
initiator and recipient.
Males su c ce e de d
in
initiating s i g n i f i c a n t l y more pl ay bouts with males than
females
(G = 6.6,
o ften w i t h males
males
p < 0.01),
(G = 7.9,
and
females als o succeeded more
p < 0.01).
initiated more bouts,
Overall,
a l th o u g h
females were succes sful
i nitiating bouts a higher p r o p o r t i o n of the time,
for male success
(G = 10.6,
Males selected among
EL r e c e i v i n g the mo s t
females
initiations.
d i s c r i m i n a t e b e tw e e n the two male
but only one female
lambs
0.001;
JO: G = 18.3,
(G = 79.3,
lambs
(Table
p < 0.01),
with
Females did not
lambs
(G = 1.3, p > 0,05),
(EL: G = 10.1,
p < 0.01;
p < 0.001:
J L : G = 47.9,
D Y : G = 4.5,
p <
p > 0.05).
initiated bouts with males or females closest to t h em
in age.
The two females that made the most pronounced
cho i ce s
2)
23%
(DY) did not di scriminate among the
female
Males
34% vs.
p < 0.01).
L am b s did not p l a y e q u a l l y wi th all other
2).
in
for each other as p l a y partners
(JL and JO, see Table
were known to have a c oe f f i c i e n t of relatedness
(their m o thers were at least half-sisters,
c o m m . ).
The r e l a t e d n e s s of the other
mothers,
is not known.
M al e s m o un t ed
two oldest
(Table
3).
C A mo u n t e d
> 0.125
J. Hogg,
lambs,
pers.
or their
females more often than males,
with the
females r ec e i v i n g 78% of the observed Mounts
Of the two male
SI 10 times,
lambs that survived the summer,
and SI m o un t ed C A four times,
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
this
31
Table 2. Total play patterns (MT, TH, SP, N W , CL, Bfl, SI R ,
HT, T, AND P) initiated and received for each lamb dyad in
1983.
Lambs appear across the top of the table in birth
order, * indicates the animal closest in age to the initiator.
Recioient
EL
CA
SI
Initiator
JS'^
JL
DY
JO
EL ?
CA(f
-----
37*
H i5*^
82
—
75*
1
Sid"
35
177
JS d"
2
7
6 ■
8*
3
12
2
17
33
18
0
27
23
8
22
29
-.54 ..
282
202
Total
294.. . 23
'T JS disappeared in mid-July.
—
JL ?
DY ?
JO?
9
65
48
22
27
40
4
—
—
—
73
38
6
21*
44
7
68
32
31*
64.. 39*
222
_199._ .217
—
—
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
To tal
132
507
293
29
153
1,31
196
1441__
32
Table 3.
Distribution of Mounts by the two male lambs in 1983Lambs appear across the top in birth order.
CA
Ini tiator
CA
Cl
"• —
U
SI
10
—
Hecinient
EL
JL
DY
1 14
24
4
22
7
JO
8
4
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
To tal
149
60
35
d i f f e r e n c e was not s ig n if i ca n t
In 1984,
on l y female
(G = 2,6,
lambs were present,
d i f f e r e n c e s could not be analyzed.
f e m a l e - I n i t i a t e d patterns
those of 1983,
however.
initiated more patterns
0.05),
0.05)
1984
in cluding
and
SLRs
p > 0.05).
The number of
(to females)
In 1983,
so sex
could be co m p a r e d
co m pared to 1984,
(Wilcoxon rank s um T = 5.5,
females
p <
s i g n i f i c a n t l y more Clashes (G - 9.5,
(G = 12.5,
p < 0.001).
The
two
p
<
females of
initiated s i g n i f i c a n t l y more contact than d i s p l a y
pat t er n s
(G = 75.4,
p < 0.001).
W e e k l y pl a y rates d if f er e d among the three years.
1982 o bs e r v a t i o n s began on 22 July,
c om p a r e d
for weeks
were a v a i l a b l e
for week 9, 1984).
= 10,
for the last seven weeks
1984
(T =
0.05).
12,
P l a y was
vig o r o u s
1963.
p > 0.05)
infrequent
pl ay bout
Fig.
5).
involving at least eight rams,
M a n y SLRs and Clashes,
K i c k s were observed.
(T
in 1983 than
in she ep other than lambs.
four years,
No
or 1982 to 1984
W e e k l y p la y rates were higher
p < 0.05;
m on t hs to almost
p > 0.10).
found when c o mp aring 1982 to
(Wilcoxon rank s u m T = 13,
p >
(no data
Differences among the
(Fri edman's r andomized blocks x* = 4.07,
s i g n i f i c a n t d i f f e r en c es were
In
so w eekly pla y rates were
6-8 and 10-13 for the three years
three y ea r s were not signi f ic a nt
1983
to
was observed
A
aged
23
in early April of
as well as Ga mbols and Heel
Because the young rams were not ma r ke d
at that time and their rapid m o ve m en t s made
id e nt i fi c at i on by
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
3k
ÜJ
I—
<
▲ — A 1982
0 6
o
o 1983
•
• 1984
cc
0 4
CD
o
z>
CO
A
0 2
I
JUNE
JULY
é
I... I..
AUG UST
SEPT.
ÜJ
h-
< 0 02
cr
V
<
_j
0_
001
0 — —V
JUNE
JULY
AUGUST
SEPT.
DATE
Figu re 5. Bottom: w e e k l y play rates (play
m i n u t e s / l a m b - m i n u t e s of observation) were highest in 1983,
whereas, top, w e e k l y suckling rates (minutes
s u c k l i n g / l a m b - m i n u t e s of observation) were highest in
1984.
O n l y in 1983 was a correl a ti o n found between
s u c k l i n g rate and play r a t e .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
35
ho rn c h a r a c t e r s al m o s t
recorded.
involved
impossible,
In A ugust of 1983,
no q ua n ti t at i ve data were
a nine minute
18 me m be r s of the n ur s er y band,
more than eight years.
The
lambs,
locomotor
aged three months to
year lings of both sexes,
and a d u l t ewes raced up and down a steep road-cut,
m an y Heel Kicks,
Head Tips.
Gambols,
Neck Twists,
D uring late December,
executing
leaps and e x a g g e r a t e d
1983, a 2-year - ol d r a m and
a 3 - ye a r- o ld r a m were observed engaging
T h e y w o u l d Clash,
bout
in a " m o c k - b a t t l e " .
stand back and Present,
and/or Gambol before Clashing again.
then Neck Twist
X observed
four Clashes
in this ma n ne r before a 7-yea r-old r am approa c he d and Clas hed
on the
3-year-old.
The younger
rams then ceased
interacting
and left the area.
I nt e ra c ti o ns am o ng y e ar lings were
infrequent,
u s u a l l y r ef l ec t ed do m in a nc e relationships,
using d o m i n a n c e patterns,
patterns.
and
with one animal
and the other s u bordinance
Pl ay in yearlings ceased about the time when
d e f i n i t i v e do m in a n c e relat i on s could be ascertained.
In 1982,
the male
lambs were observed on two occasi ons
p laying w i t h ewe yearlings,
a small
2-year- o ld ewe.
and on two occasions pla ying with
No lamb-yearling pla y was observ ed
in 1983 or 1984.
Dominance
and
intera c ti o ns a m on g the lambs were n e g l i g a b l e ,
in no year was
it pos sible to a s si g n a ny ranks to them.
The s h e e p did not appear to be se ttling ranks until after one
year of age.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
36
Maternal
investment
Of the
study,
data,
20 lambs that were we i ghed
o n l y one survi ve d
in the course of the
long enough to provide a n y pl ay
so no c o m p a r i s o n s b e t w e e n weight and p l ay could be
made.
However,
the years
(Fig.
w e e k l y suckl in g rates could be co mpared among
5).
S i g n if i ca n t d i f f e r e n c e s were noted
w e e k l y s uc k l i n g rates
for the three years
F r e i d m a n ' s r a n d o m i z e d blocks,
weeks
6-13,
lambs
in 1983
lower than
lambs
x» = 10.3,
(weeks 6-13,
p < 0.01).
in 1982 had higher suckling rates than
in 1984
(T = 1, p < 0.05).
higher su c k l i n g rates than those
Lambs
in 1983
(T = 0, p < 0.005).
in suckling rates can be d i r e c t l y attrib u te d
of lactating ewes each summer
The two lambs
in 1982 were nursed by four ewes
the six lambs
(1.3 ewes/lamb),
ewes
but
in 1984 had
to the number
ewes/l a mb ) ,
For
(Wilcoxon signed ranks T = 5, p < 0.05),
The d i f f e r e n c e s
in
(see Hass 1984).
(two
in 1984 were nursed by eight ewes
and the two lambs
in 1984 were nursed by six
(three ewes/lamb).
For 1982 and 1984,
the c o r r e la t io n s b etween we e k l y
suc k l i n g rates and we e k l y pl a y rates were not signifi c an t
(1982:
r = 0.06,
p > 0.05;
1984,
r = 0.07,
1983 a s trong positive c o r r e l a t i o n was
0.01).
rates
Overall,
p > 0.05),
found
(r = 0.78,
Fig.
p <
the c o r r e l a t i o n of suckli n g rates to play
for the three summers was not s ig n if i ca n t
> 0.05,
but in
(r = 0.11,
5).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
p
Discussion
Of the three h y p o t h e s e s tested
57
in this study,
Motor T r a i n i n g H yp o th e s i s was supported.
used pa t te r ns
o n ly the
The most c o m m o n l y
in soc ial play bouts of lambs were patt erns
used b y ad ults
in c o u r t s h i p and
intr aspecific conflict.
Male s played s i g n i f i c a n t l y more than females,
and exhibited
s i g n i f i c a n t l y more of the two most common components of the
male d o m i n a n c e
pers.
also
o b s .).
fight;
the C l a s h and the SLR
Less r it u al i z e d
a m on g c o ur s i n g rams
tending and cours in g rams,
Heads,
Butts,
while T o u c h Heads,
Tips,
Twists,
included Shoulder Pushes,
Included SLRs,
IV).
obs.).
Butt
Fights
and Presents,
Butt Heads,
and P re sents were all used
Butts,
Head
in dominance
During play,
pa tterns more often than displays,
(Chapter
(pers.
Clashes,
Shoulder Pushes,
dis p la y s and d i sp lacements.
interactions,
In teractions around
(Hogg 1984a,b) and bet ween
C l as h es and T o u c h Heads
between ewes u s u a l l y
1971,
fights or brawls among rams
included Shoulder Pushes and Butts.
estrous ewes,
(Geist
lambs used contact
whereas
in dominance
di s p l a y s were used more often than co ntacts
Al t ho u gh Geist
(1971)
refers to a sheep that
rests his chin on the neck or back of another as p er f or m in g a
v es tigal neck
fight,
the N e c k - W r e s t 1 ing observed
bouts was not o b se r v e d
Shackleton
1973,
Eccles
in a d ul t sheep
1981).
(also noted by
The oldest s heep I s aw
p e r f o r m i n g this p a t t e r n were y e ar l in g rams.
horns of the older
pattern,
but
in lamb play
The large curled
rams ma y prevent the e xe c ut i on of the
it also ap pears absent
in the ewes,
who are less
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
J;8
r e s t r i c t e d morhologically.
M a l e s e x hibit a greater va riance
than
females
(as e s ti mated by the number of copulations
(Geist 1971,
Hogg 1984b));
if pl ay has a ny influence on the
s u b s e q u e n t d e v e l o p m e n t of skills
success,
influential
in repr oductive
males mi g ht be e xp e ct ed to pla y more than females,
especially
in the perfo r ma n ce of patterns relating to rank
acquisition.
The da ta presented here support this
do data p r es ented by Berger
p o p u l a ti o ns of bighorns,
(Capra
in reproductive success
ibex),
Byers
and Pfeiffer
(Oryx d a m m a h ).
(1979,
1980)
(1977,
(1985)
idea, as
for other
1980)
for Si berian
ibex
for s c im i ta r -h o rn e d oryx
A c o r r e l a t i o n between sexual d i m o r p h i s m in
adul ts and sexual d i m o r p h i s m in play appears to be w idespread
(Bekoff 1974,
Biben 1982,
Sachs and Harris,
to name a few),
a ls o e v i d e n t
monomorphic
G e n t r y 1974,
1978,
but s ex ua l ly di m or p h i c play was
in s c i m i t a r - h o r n e d oryx,
(Pfeiffer
Symons
1985),
which are s e xu a l l y
sugges t in g that vari ance
in
r e p r o d u c t i v e success ma y influence play more than d i ff e re n ce s
in a d ul t size or g rowth rates.
Lambs ap p ea r ed to cho ose partners that would pr ovide the
mos t c h a l l e n g i n g play,
u s u a l l y those cl osest
in age.
The
lambs d i d not s h o w a s i g n i f i ca n t preference to play with
lambs of the same sex.
less t h a n the two male
s ig n if i ca n tl y ,
lambs were
The two
lambs
and my overall
female
lambs
in 1984 played
in 1982, a l t h o u g h not
impress ion was that
less m o ti v at e d to play than were males
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
female
(see M e a n e y
39
et al.
1985).
This
w h y p l a y rates
maternal
lower level of m ot i va t io n might explain
in 1984 were so low,
investment
(as estimated by suckling rates).
were less succes sf u l
with males,
in spite of greater
in initiating pla y with females than
which might have encouraged t he m to play with
other males,
as Byers
sizes are small,
(1980)
these data,
suggests.
1979,
1980).
that m a l e s mo unted
concur with
(Byers 1977,
Unlike the other researchers,
females more than males;
Mou nts were pe r formed on one female
c lo s es t
Although m y sample
for the most part,
other s t u d i e s of c l o s e l y rel ated bovids
Berger
Males
lamb
1980;
I found
the m a j o r i t y of
(EL), who was
in age and size to the two male lambs
in 1983
(Table
3) .
The y e a r - to - ye a r v ar ia t i o n
in the amount of play
o bs e rv e d was p r o b a b l y more a function of the number,
of a v a i l a b l e pl a y partners,
investment.
This
than
and sex,
in the amo unt of maternal
is c o n t r a r y to the findings of Shackleton
(1973) who found a di re ct r e l a t i o n s h i p between maternal
invest ment
(total s uc kling time)
observed.
There m a y be a ma t ernal
below which
d ec r ea s e
1982).
lambs are
each lamb,
investment
i nadequately nourished,
in the a m o u n t of p la y in g
The NBR lambs,
and the amou nt of play
"threshold",
resulting
in a
(M u l l e r - Sc h wa r ze et al.
with more than one ewe nu rsing
were p r o b a b l y well above this threshold.
for
The
importance of the number of play partners was recogn iz e d by
Be rg er
(1979)
who found that desert
lambs,
which occur
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
in
40
s maller
n u r s e r y groups,
in spite
also
played much
of greater maternal
less than m o u n t a i n lambs,
investment.
A lt h ou g h Berger
found a s i g n i f i c a n t c or r el a ti o n between group size and
the number
lambs,
of acts performed
in play sequences of m o u n t a i n
he a t t r i b u t e d much of the restri ct i on of playing by
d e s e r t lambs to a h a za r do u s en vironment.
"p rogram"
1971),
lambs a b o u t the vagaries of the enviro n me n t
(Geist
then lambs s h ou l d use play as a means of learnin g how
to deal w i th ha z ar d o u s environments
(i.e.,
If play serves to
w h e n es c ap i ng
for times of e m e r g e n c y
from predators).
a d e q u a t e l y e xplain the relative
Small groups sizes may
infrequency of play behavior
in de s er t b i g h o r n l a m b s .
The
importance of exercise early in the life of a mammal
has been recogn iz e d
for re views).
(see Bekoff and Byers 1981,
Fagen 1981,
A l t h o u g h I was unable to weigh lambs older
than two days of age,
growth data are available
herds of R o c k y M o u n t a i n bighorns.
from other
The peak p l ay periods of
NBR lambs coinc id e d with the peak gro wth period of lambs
R a m Mountain,
A l be r ta
(Jorgenson and Wishart 1984,
w hich s u gg e st s that p l a y m a y be occur ing at a time
optimal ph y sical d e v e l o p m e n t
Fig.
from
6),
for
in lambs.
Most of the benefits of play are speculated to accrue at
later d e v e l o p m e n t a l
stages
lambs m a y al so have
Immediate benefits
1985).
engaging
(Fagen 1981).
However,
p l ay in
(see Martin and Caro
Young lambs spent a co nsiderable amount of time
in locomotor
play:
stotting ra pidly through rocky
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
41
1902
30
.A —
-A "
MALE LAMBS
(Alberta)
1*-I984
5
’
20
08
I—
X
ÜJ
h<
q:
>-
o
<
ÜJ
_J
CL
5:
04
© --
O
JUNE
JULY
AUGUST
O
SEPT.
F igure 6.
Peak p l a y pe r iods occured du r i n g peak growth
peri ods for lambs.
G r o w t h curve from J or genson and
Wish art (1984).
P l a y rat es r e ca l cu la t ed on a biwee k ly
bas i s .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
42
o ut crops and up and do w n s teep roadcuts.
Stotting was the
fo rm of locomotion used by older sheep when alarmed.
Stott ing p r o b a b l y served to a u d i b l y and v i su a ll y signal
c o n s p e c i f les, and p o s s i b l y d i s t r a c t or confuse predators
also Caro 1986).
(see
La m bs m a y be d ev e lo p i n g skills n ec e s s a r y
for predator evasion,
d u ri n g a period when they are highly
vulnerable.
L ambs are s t r o n g l y a tt r ac t ed to other lambs
Geist
1971).
This m a y promote social play;
play m a y be an a t t r a c t i n g
likewise,
force am ong lambs.
g ro u p in g s of lambs and their mothers may,
force a mo n g lambs,
benefits,
social
Social
therefore,
p r e d a t i o n b y f a c i l i t a t i n g d e t e c t i o n of predators,
p o s s i b l y co nfuse predators.
(see also
reduce
and
If social play is an attrac t in g
then besides
immediate a n t i - p r ed a ti o n
play m a y i nd i re c tl y promote social d ev e lo p me n t by
s i m p l y br i ng i ng
lambs together to interact
(Me a ne y et al.
1985).
A l t h o u g h play a p pe a rs to be a cooperative venture,
s ug g ested by Bekoff
(1977,
ap pears to have little role
bonds a m o n g adult bighorns.
than g ro u ps of rams.
There
1978,
yet the male
it
Groups of ewes are more cohesive
is ample evidence that ewes
(Geist 1971,
Thorne et al.
lambs e xh i bi t ed more play behavior,
lambs did not s h ow a s i g n i fi c an t preference
same sex.
(1981),
in the d e velopment of social
r a r e l y leave their natal groups
1979),
1984) and Fagen
as
and
for lambs of the
Rams u s u a l l y leave the ewe groups to join ram
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
43
groups,
often
far
from their maternal ranges,
suc c ee d
in d o m i n a t i n g the ewes
(Geist 1971,
pers.
the N B R herd, rams over two years of age were
wit h the ewe s
enough,
mat e r n a l groups,
lambs
o b s .).
In
s e l d o m seen
outside of the br eeding season. In t er e s t i n g l y
in two re ported
p o p u l a ti o ns
when they
instances of ewes
both came
(Geist
leaving their
f r om e x pa n di n g
1971, Ke a t i n g 1982).
(high quality)
It also appears that
f ro m high q u a l i t y populat i on s play more
Sh a c k l e t o n 1973).
(Geist 1971,
Pl a y may promote behavioral
flexibility,
p o s s i b l y p r e p a r i n g a n animal to be a success ful disperser
(Geist 1971),
but the r el a t i o n s h i p between pla y and dispersal
shou ld not be looked at too s i m p l i s t i c a l l y
R egardless,
(Fagen 1981).
pl ay does not appear responsible
for the
e s t a b l i s h m e n t of a n y strong ties within groups of Ro c ky
M o u n t a i n bighorns.
D o m i n a n c e r e l a t i o n s h i p s were not evid ent
of l a m b s , and were often hard to d i st i ng u is h
(Eccles 1981).
dominance
m on t hs
in two bison calves stu died d uring their
(Lumia 1972).
BS was older,
summer,
In 1982,
first six
JN mounted BS si g ni f ic a nt l y
and JN e v e n t u a l l y became dom inant to
and larger than JN throughout their
first
but by fall BS appea re d s m a l l e r , with a poorer
q u a l i t y coat,
indica ti n g he ma y have been under some
p h y s i o l o g i c a l stress.
reverse,
in yearlings
A r e l a t i o n s h i p was found between Mounts and
more than the reverse,
BS.
in the behavior
In 1983,
CA mounted SI mote than the
but SI e v e n t u a l l y became dominant.
Again,
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
a lt h o u g h
44
SI was younger,
he e v e n t u a l l y became
A m o n g adult rams.
dominance;
the
Mounts were an
larger
individual.
indication of
when a s u b o r d i na t e a t t e mp t ed to mount a dominant,
he w o u l d suffer
and Clashes.
swift r e t a l i a t i o n
If d o m i n a n c e
in the the form of Butts
relations had
formed
were used to impose stress on subordinates,
in play, and
I would
not
expe ct to see the d o m i n a n c e - r e v e r s a I s observed between the
male
lambs
in pl a y
(see also Bekoff
pl ay bouts among adult rams
obs erved class
II rams
retaliation
Chapter
dom i n a n t
IV),
III
(3/4 curl)
(also repor te d by Geist 1971).
II rams,
I
rams with no
Because horn size
indicator of rank
the a s s u m p t i o n was made
to class
(Montana),
after Geist 1971) and class
m o u n t i n g class
is u s u a l l y a good relat i ve
During spring
in Upper Rock Creek
I (1/4 horn curl;
(1/2 curl)
1978).
(Geist 1971,
that class III rams were
et cetera.
I re j ected the h yp o th e si s that p l ay ma y be a means of
c o m p e t i n g with one's peers based on my observations that 1)
d o m i n a n c e h i e r a r c h i e s were not evident among the lambs, and
2) a m on g ranked adults,
no r e l a t i o n s h i p was apparent between
rank and ex h ib i te d p l ay behaviors.
Hogg
(1984a Tables 2-6)
pro vides ad d it i o n a l e vi dence that a young ram's rank
n e c e s s a r i l y the rank
a d v a n c i n g age,
is not
he ma i nt a in s w it h in his cohort with
e ve n among a group as stable as the NBR herd
(without e m i g r a t i o n or
immigration).
a d v a n t a g e s of o bt a i n i n g do m in a n c e
life m a y be s h o r t - l i v e d
In other words,
the
over one's peers early in
(Smith 1982).
Among yearlings.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
d o m i n a n c e - r e v e r 3aIs were obs erved
r e l a t i o n s ap p ea r ed
to be es tablished;
the y ea r l i n g s d u r i n g
ye arlings)
after
suggests
animals,
1984
10 July.
s et t l i n g d o m i n a n c e
(1971)
P l a y m a y have some role
for ground squirrels,
1981).
b re e d i n g o p p o r t u n i t i e s
in
as Steiner
but among older
re l ations were not re flected
in Fagen
in
(my largest sample size of
P l a y m a y p ro m ot e behavio ra l
any,
no play was observed
relations among yearlings,
dominance
(reviewed
in play until dominance
in play.
f l e x i b i li t y and cr e a t i v i t y
A lt h ou g h bi ghorn rams ma y create
(Hogg 1984b),
the role of play,
if
in the d e v e l o p m e n t and use of creative mati ng strategies
has yet to be explored.
In play,
bi g h o r n s lambs can experiment with their
e n v i r o n m e n t and c o n s p e c i f i c s .
refined,
so the
Behaviors are tested and
lambs may learn when and h o w to p e r f o r m t h em
in co r re c t social and e nv i ro nm e nt a l contexts
F a g e n 1981,
developing
1978),
Smith 1982,
Bekoff
fighting skills
or perhaps
1984).
(Geist 1971,
The lambs m a y be
to be used later
in life
le a rning h o w to get along better
(Poirier an d Smith 1974).
in groups
At the same time they are
rec e i v i n g the b e n e f i t s of repeated exercise.
fre q ue n cy of b ro k en
(Symons
The high
legs among a low-qua l it y popula ti o n of
bigho rn s m a y be the result of a weaker sk e leton re s ul t i n g
fr om infreq u en t p la y
(Geist 1971),
hard to se p arate here.
play,
Detailed,
p o p u l a t i o n quality,
but c a u s e - a n d - e f f e e t are
l on g -t e rm studies r e l a t i n g
dispersal,
and r ep roductive
are n eeded .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
success
C H A P T E R IV
STRUCTURE AND DEVELOPMENT
OF T H E D O M I N A N C E HIERARCHIES
R esults
Rams
D u r i n g the c ourse of the 27- month study,
I nteractions b e t w e e n rams were recorded,
699
including 367
intera c ti o ns o b ta i n e d d uring al m os t 40 hours of
all-occurences
sampling.
I nt e r a c t i o n s be t we e n all possible dyads were never
o bs e rv e d d u r i n g a n y year.
O n l y rams
least 10% of the b ac helor herd were
m at r ic e s
(Tables
4-6).
pairs)
in 1983.
l i n e a r i t y was found
46.96,
109.62,
degree
p < 0.001;
included in the win-loss
The m a x i m u m percent of pos sible dyads
that was a c t u a l l y observed
po ssible
interacting with at
in a n y year was 53%
A s ig n if i ca n t trend toward
in the m at r ic e s each year
1983:
x* = 107.93,
The K valu es also
of l i ne a ri t y
in the hierar c hi e s
1984;
K = 0.94),
(1982:
p < 0.001;
p < 0.001).
K = 0.93;
(72 of 136
x* =
1984 : x* =
indicated a high
(1982;
K = 0.94;
1983 :
indicating that the r a m
h ie r a r c h i e s were h i g h l y transitive.
D u r i n g each y e a r , ye a rl i n g rams re mained with the
n u r s e r y g r o u p and were not
O n l y D o m i n a n c e V al u es
w i t h at
included
(D.V.s)
in the ram hierarchies.
from individuals
interacting
least 25% of the herd were used to correl ate with
other variables.
For rams aged two and older,
s i g n i f i c a n t l y c o r r e l a t e d with age
(1982:
D.V.s were
r = 0.76,
46
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
p < 0.05;
47
Table 4.
V/in-loss ma t r i x
interact ion s,
for rams in
1982, based on dyadic
xi - pro por t i o n of opponents dominated.
M = 253.
L O S E R
TP
SE
BD
BY
ST
21
51
7
4
3
12
6
4
SE
23
9
4
BD
mm mm
8
19
16
CC
CC
TP
GE
BY
ST
38
3B
ML
MG
xi
3
10
1 .00
1
0.80
24
0.67
1
7
0.57
6
2
0.50
2
0.50
2
0.50
4
GE
3B
ML
MG
—
1
—
—
—
0.17
0
0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
48
Table 5 ,
W i n - l o s s m a t r i x for raras in
of o p p o n e n t s dominated.
1983.
Xi =p r o p o r t i o n
N = 290*
L o s e
r
CC SE TP MC ST BD BY 3 B GE M L M O PY HK SR RH SK
CC
SE
TP
MC
ST
BD
k BY
<D
3B
C
c GE
•H M L
MG
—
1
—
3
6
11
9
—
1
12
—
1
1
1
9
1
3
2
1.00
4
5
3
1
1
4
—
37
—
2
2
2
2
5
5
1
1
4
13
SR
RH
0.80
1
1
1
2
2
2
1
3
0 .5 6
0.56
2
4
4
1
2
1
4 —
0 .7 1
0 .7 0
1
1
14
—
6
PY
HK
1
0.80
3
2
1
3 —
0.91
1
4
6
21
2
1
4
2
—
Xi
0 .4 5
0 .4 4
4
3
0.38
3
1
0 .3 3
8
2
—
0.20
0
—
SK
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0
——
0
49
T a b l e 6.
W i n - l o s s m a t r i x for rams in
of o p p o n e n t s dominated,
xi = proportion
1984.
N = 162.
L 0 S E R
SE T P BD MG BY GE ST HK SK PY SR RH JN BS
SE
TP
——
6
—
1
BY
GE
ST
5
8
3
11
——
——
1
5
2
2
5
—
2
2
1
1
1
4
1
2
2
1
4
2
3
1
7
4
1
3
——
2
—
SR
1
RH
1
BS
1
2
PY
JN
1
1
3
1 .00
3
1
6
HK
SK
1
1
1
2
BD
MG
1
——
——
xi
1
1 .00,
1
0.80
0.67
2
0.66
0. 64
1
0.38
0.50
1
0.33
2
0.29
1
0.14
0.1 4
1
——
5
——
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0.08
0
50
1983:
r = 0,83,
p < 0.01;
and a n y ram* s D.V.
his D.V.
1984:
r = 0.86,
p < 0.001;
Flg.
one year was s i g n i f i c a n t l y co rrelated with
the next year
(r = 0.86,
S i g n i f i c a n t d i f f e r e n c e s were
p < 0.01; F i g . 8).
found between mea n D.V.s of rams
wi t h in d i f f e r e n t h or n size cl a ss e s
(after Geist 1971);
II rams had lower D.V.s
III rams who had lower
D.V.s t h a n class
than class
IV rams
(t = 3.67,
The number of c o p u l at i on s per
not c o r r e l a t e d wi t h a ram's D.V.
9),
D.V.
was,
7),
however,
class
p < 0.01, Table 7).
100 observ at i on hours was
(r = 0.15,
p > 0.05;
Fig.
s i g n i f i c a n t l y correl a te d with the
number of d i f f e r e n t ewes each r a m was observ ed copula ti n g
with
(r = 0.48,
p < 0.05;
F i g . 9).
Ra ms with higher D.V.s
dominance
D.V.s
Fig.
(displacements,
(1983:
10),
G = 47.87,
while the
initiated more displays of
courtship)
p < 0.001;
than did rams with lower
1984:
ind ividuals with the
G = 7.16,
p > 0.05;
lower D.V.s received
more d o m i n a n c e d i s p l a y s than e x pected based on g roup
composition
(1983:
0.05;
Fig.
10).
D.V.s
in 1983,
G = 51.53,
To see
1984;
G = 7.00,
A l t h o u g h rates varied s i g n i f i c a n t l y with
but not
were not s i g n i f i c a n t
0.05).
p < 0.001;
in 1984, d i f f e r e n c e s between years
(Wilcoxon signed ranks T = 15,
if individuals wi th higher
p >
D.V.s were
in t e r a c t i n g at hi gh er rates be c au s e t h ey had more
subordinates available
e x p e c t e d v a lu e s to take
to interact with,
I adjusted the
into ac c ou n t the number of
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
p >
5
1982
1983
982
984
1984
983
CD
3
O
>
CD
60
O
C
O
C
£
o
o
30
6
3
9
Age
F igure 7. R a m D om i na n ce V alues were s i g n i f i c a n t l y
c o r r e l a t e d with age d ur i n g all three years (1902: r =
0.76; 1983: r = 0.83; 1984: r = 0.86).
Lines dr a w n from
r e g r e s s i o n equations.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
52
en
60
y = 0-67x+ 2 7 72
CD
O
r=0 8 6
30 -
p<0 01
Û
30
60
90
Dominance Value
Figure 8.
Ram's Dominance Values in one year were
s i g n i f i c a n t l y correlated with their Dominance V al u es the
following y e a r . Line drawn from r e g r e s s i o n equation.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
55
Table 7 .
class II,
C o m p a r i s o n of mean Dominance Values for ranked
III,
and IV raras (after Geist
1971).
rajns r e m a i n e d w i t h the ewes and were not ranked.
Class I
All
three y e a r s combined.
Horn Class
II
III
IV
M e a n Age
2.0
5.8
7.4
Total N
9
15
16
M e a n D.V.
Student's t
p - value
15.72^
^ 57.57
65.15
5.50
4.99
<0.01
<0.001
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
54
-10
I
<
O
*0
<ü
o
w
c
o
20
V.
CD
(/)
-
CD
5:
_o
=J
Q.
O
O
LU
d
z
40-
30
Dominance
60
90
Velue
F igure 9. Domina n ce Values of rams were not correla t ed
with the number of c op u l a t i o n s per 100 o bs e rv a ti o n hours
(triangles, b ro k e n line; r = 0.15, p > 0.05}, but were
s i g n i f i c a n t l y co r re l a t e d wi th the number of d i ff erent ewes
individual rams were observed breeding (circles,
c o n t i n u o u s line; r = 0.48, p < 0.05),
Lines drawn from
r e g r e s s i o n equations.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
55
Dominance
Subordinance
12
g 1983
Q
1984
I
081
<
0 4
04
o
ui
>
LU
O
LU
08
12
A
B
C
D
A
B
C
D
RANK-GROUPS
F ig u r e 10.
Rates o£ d o m i n a n c e and s ubordinance dis plays
for rams in 1983 and 1984.
Rank-groups: A = lowest 25% of
ranks, B = second lowest 25%, C = second highest 25%, D =
h ig h es t 25% of ranks.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
s u b o r d i n a t e s each gr o up had a va i l a b l e to
it.
These
’’r a n k - s p e c i f i c ” values were tested a g ainst the observed
values,
and again,
high ra n king rams
and l o w ra n ki n g rams
< 0.001;
1984;
fewer t h an ex pected
G = 10.62,
wi th h igher D.V.s were
rate than were
p < 0.05),
indeed
0.001;
than did higher
1984:
G = 19.76,
1984 : G = 47.94;
d i f f e r e nc e s were
(potential
114.08,
G = 29.47,
p
indicating that animals
initating patterns at a higher
initiated more subordinance
rank ing rams
p < 0.001).
r eceived more su b o r d i n a n c e d is p l a y s
0.001;
(1983:
lower ra nk ing animals.
Rams with lower D.V.s
d is p l a y s
initiated more patterns,
p < 0.001;
(1983: G = 38.60,
p <
Higher ranking animals
(1983;
Fig.
G = 46.02,
10).
p <
These
inde pendent of the number of domi nants
interactants)
p < 0.001;
1984:
a v ai l ab l e to each group
G = 19.10,
The d i f f e r e n c e s a pp a re n t
(1983: G =
p < 0.001).
in the rates of dominance and
s ub o r d i n a n c e d i splays were al so r e ad i ly visible when broken
d ow n by pattern.
As might be expected,
rams with higher
D.V.s performed a higher p ercentage of d is placements and
c o u r t s h i p behaviors,
while
m o s t l y Fa ce-Rubbing;
the reverse was true
r eceived
The b e havior of rams toward other rams
( F i g . 11).
lower ranking rams
was c l e a r l y linked to their rela tive rank
Five d o m in a n c e
in rank,
for patterns
in the group.
fights were observed betw een rams during
the co u rs e of the study.
c ha n ge s
initiated
T hree of these resulted
w h er e as two of the
in absolute
fights were between
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
57
100
X3
<D
.tz
c
I
I I Face-R ubb ing
Q
Displacem ents
50
Courtship
<^0
T?
0>
>
0)
50-
o
0)
cr
100
I
i
7
B
D
Rank-Groups
Figu re 11. P a tt e r n s used in d o mi n an c e interactions of rams
were r e f l e c t i v e of d om i na n ce r a n k . Rank-groups: A =
lowest 25% of ranks, B = second lowest 25%, C = second
h ig h es t 25%, D = hi ghest 25% of ranks.
First column in
eac h g r o u p f ro m 1983, second c olumn from 1904.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
58
y e a r l i n g s whose rank was p r e v i o u s l y undetermined,
rank c h a n g e s were a l so detected,
were not s e e n .
In some cases,
al t ho u g h fights or turnovers
(e.g.,
MG,
BY, and GE, Table
8), a s u b o r d i n a t e r a m o b tained a higher D.V.
pre vious dominant,
six other
than his
but the dyads were not observed
i n t e r a ct i ng to d e t e r m i n e
if an actual turnover had taken
place.
I n t e r a ct i on s a m o n g y ea rl i ng s and among 2-year olds were
infrequent.
In 1982,
the five yearlings could not be ranked
w it h in the cohort w it h certainty,
2-year-olds,
as
r el a t i o n s h i p s am o ng three of them still could
not be a s c e r t a i n e d
e a r l y 1983,
and a year later,
(note SR, RH, and SK in Table 8).
During
interactions b e tw e en the two yearlings began to
a ppear one-sided,
w i th JN e x h i b i t i n g c ou r tship behavior to,
and m o u n t i n g BS, wi t h no d om i n a n c e reversals apparent.
dominance
fight was ever ob served b et w ee n the two,
No
and JN
c on t i n u e d a cting as the do mi n a n t until the end oE the study
when t h e y were 28 m o n t h s old
P l a y bouts
(Table 8).
involving the two male yearlings
summer of 1984 were also one-sided,
d o m i n a n c e displays,
(Neck Twists,
with SI ex hibiting
and C A s ub o rd i na n ce displays.
d om i n a n c e r e v e r s a l s were apparent,
Gambols,
etc.)
w ha t a p p e a r e d to be a long
in the
No
even though play signals
were often present.
(3+ hours)
On 21 July,
dominance fight between
C A and SI was al so a c c o m p a n i e d by occasi onal play signals.
No c h a n g e
in r e l a t i o n s h i p was e v ident after this lengthy
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
59
Table
6.
Dominance
Va l u e s and ages for those raras in
1982-4 that i n t e r a c t e d w i t h at least
herd.
D . V . s p ri o r to rut each year,
who w e re d i s c a r d e d
10^ of the ba chelor
^indica t es those
from calcul at i on s due to the small
n um b er of o b s e r v e d in t e r a c t i o n s .
Arrows indicate
i n s t a n c e s w h e n one r a m d om i n a t e d ano ther with a higher
D om i na n ce Value.
1982
Ram
D.V.
Age
Ram
1983
D.V.
Age
1984
Ram
D.V.
Age
CC
90.0
8
CC
90.0
9
SE
9 0.0
8
TP
63« 4
7
SE
72.5
TP
9 0.0
SE
54.7
6
TP
6 3.4
7
8
BD
63.4
9
8
BD
6
MC
6 3.4
9
MG
54.7
4
BY
49.1
45.0
6
yST
57.7
4
BY
54.3
8
ST
45.0
/ BD
56.8
7
GE
52.9
4
*GE
45.0
3
2
I BY
48.2
7
ST
49.8
5
3B
24.1
5
3B
48.2
6
HK
45.0
3
ML
0
5
/GE
4 2.4
3
*SK
35.3
3
MG
0
2
Vb
4 1.8
6
PY
3 2 .3
3
MG
38.3
3
SR
22.2
3
/PY
35.1
2
RH
22.2
vhk
26 •6
2
JN
16.8
3
2
BS
SR
0
2
RH
0
2
*SK
0
2
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
0
2
SO" 6 l
interaction.
Rams a p pe a re d to ad vance
default,
as younger rams
in the h ie r a r c h y either by
joined the b o t t o m of the hierarchy,
or b y a c t i v e l y figh ting their w a y up the ranks.
instance,
the r am SE, was ranked
3rd in the
For
fall of 1982.
had a c h i e v e d that p os i ti o n not only by default,
He
along with
his cohort,
but al s o a dv a nc i ng over the members of his cohort
by fig hting
(Hogg 1984a).
4th and
5th.
During
The other 6-year-olds were ranked
late December
1982,
de f e a t e d TP for the second place spot.
onset of rut
alpha ram,
in November
1983,
at the age of seven
SE battled with and
Sh ortly after the
he battled CC and became the
(Table 8).
Ewes
D ur i ng the s t u d y period,
I recorded 1425 displace ments
and s u b o r di n an c e di s pl a ys b etween ewes,
including 466
i nt eractions r e co r de d d ur i ng almost 100 hours of
a l l - o c c u r e n c e sampling.
All
compile w i n- l o s s m at rices
As w it h the rams,
were
incomplete.
never ob s er v ed
exclu de d
(Table 9).
for each year.
the wi n -loss ma trices
for the ewes
Five of the 27 ewes present in 1982 were
inter a ct i ng with a n y other ewes and were
from analyses.
interacting,
interactions were used to
O n l y 100 pairs were observed
or 28% of the
351 p o t e n t i a l l y interacting dyads
B et w ee n 22 Ju l y and 7 September
i nt eractions were recorded be tween ewes
1982,
174
in the nursery band.
The m ea n g r o u p size of the n u r s e r y band was 19.3 ± 4.8, which
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
62
•H
X
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1>NO
CNNÛ
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NO
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CO
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63
Included two
sexes,
some
(male)
lambs,
la ctating ewes,
2-year-old ewes,
yearlings of both
and a s sorted no n-lactating ewes
that a s s o c i a t e d with the g r ou p for variable
Of the
were
166 d i s p l a c e m e n t s rec orded
f r o m b e dding sites,
min e ra l
licks
two
(one each),
from s p atial positi o ns
(1%) were
In 1983,
Table
(e.g.,
were observed
from
or from the path al ong which
22.2
+ 5.7
as well as the female
interacting too
few times to include
in
D i s p l a c e m e n t s of lambs by ewes were not
were r e c o r d e d be t w e e n
(Table
11).
sites,
36% were
50%
included
(175)
64% were
f r om spatial positions,
licks,
In 69%
(244)
23 ewes.
Interactions
of the 351 possible dyads
Of 569 displa ce m en t s,
fr o m mine ral
sites,
(31%) were
one ewe di s placed another
Four ewes,
the w i n- l o s s matrix
(Table 10).
from horning posts and
The n u r s e r y group av eraged
the hierarchy.
were
(68%)
10).
(including 6-7 lambs).
recorded;
113
596 d i s p l a c e m e n t s and subordinance dis plays
were recorded.
lambs,
in 1982,
and the remaining 51
the spot where she was standing,
she was walking;
periods of time.
from bedding
and the rema ining 2%
hor ning posts and foraging positions
of the displ ac e me n ts
the d i s p l a c i n g ewe did not recline
from bedding
in the newly
v ac a te d b e d .
In 1984,
were recorded.
18.4
± 3.8,
female
655 d i s p l a c e m e n t s and subordinance displays
During the summer,
incl uding two lambs.
lambs were not
included
the n u r s e r y group averaged
Four ewes and the two
in the m a trix
(Table 12).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
64
Table
10,
L o c a t i o n s of displac eme nts by ewes during the
s u m m e r s of
1982-4.
Percent of total in parentheses.
Locations
Bedding
Spatial
Mineral
Horning
Sites
Po sit ion s
Licks
Posts
Forage
Total
1982
115
(68)
31
(31)
1 (<1)
1 « D
0
166
1983
3^5
(64) 201
(36)
3 (<l)
8 (1)
2 «1)
369
1984
308
(39)
198
(38)
4 (<l)
3 (<1)
526
13 (2)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
65
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Table 12 V.'in-loss matrix for ewes in 1984. Xi = proportion of opponents dominated. N = 655.
■CDD
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OH HT
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3
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—
-
7
1
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— —
HT
DE
5
1
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—-
2
3
12
2
2
2
1
1
1
1
UI
4
2
3
5
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10
3
—
5
1
1
1
1
1
4
12
3
1
2
1
2
1
5
4
1
7
1
1
2
1
2
3
2
3
4
1
2
2
4
1
1
1
2
2
6
1
1
2
2
3
1
8
6
4
9
5
3
2
2
1
7
3
1
3
2
2
1
1
1
2
5
2
2
1
4
0 .9 4
4
3
0 .8 9
3
2
0 .8 2
3
1
0 .8 2
1
4
0 .7 6
4
1
1
0 .7 2
1
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5
2
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8
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— —
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5
4
1
3
2
3
1
3
3
4
3
2
1
2
1
1
1
1
1
— —
3
1
5
3
2
1
1
2
3
3
0 .6 0
1
1
0 .5 8
2
2
1
0.55
2
1
2
0.53
2
3
4
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2
1
1
1
0 .4 0
3
2
4
6
0 .4 0
3
4
11
0.33
3
8
8
2
2
0 .3 1
1
5
1
3
0.50
2
0.14
2
5
1
4
1
2
1
5
RG
1
Di
1
JL
0.64
1
EL
JO
5
7
—
0 .6 7
1
3
1
0 .6 7
2
2
0 .6 8
1
1
1
10
2
2
3
1
EY
im
2
— —
2
4
SH
1
7
2
TT
LL
7
3
BR
CD
2
3
—
BE
55
2
1 .0 0
1
—
0 .1 0
- -
0.05
5
— —
10
— —
0.05
0
m
m
o7
O n l y 230 of the 435 potential
i nteracting.
Fi f ty - n i n e
d i s p l a c e m e n t s were
p ositions,
dyads
percent of the 526 recorded
from b e dding sites,
and the r em a ining
4% were
h o r n i n g posts and foraging po sitions
displacements
(53%) were observed
from be d di n g sites,
38% were from spatial
from mineral
licks,
(Table 10).
Of the 308
24% resulted
in the
d i s p l a c i n g ewe o c c u p y i n g the just vacated site.
D u r i n g all three years,
significantly non-random
X» - 171.7,
p < 0.001;
the hierarchies were
(1982:
x* = 147.4,
1984 : x* = 192.7,
p < 0.001;
p < 0.001).
1983:
The ewe
h i e r a r c h i e s did not de m on s tr a te the linearity of the ra m
hierarchies
(1982:
K = 0.73;
Unlike the r a m hierarchies,
matrix,
the greater
hierarchy
number
(for example,
1983: K = 0.79;
K = 0.71).
the more complete the win-loss
of triangles present
see Table 12).
s y s t e m w o u l d p r o b a b l y underes t im a te
r e l a t i o n s h i p s a m o n g the ewes;
be mo re r e p r e s e n t a t i v e
1984:
in the ewe
An ordinal ranking
the comple xi t y of the
Dominance Values were felt to
of the e w e ’s ranks relative to the
other e w e s .
D o m i n a n c e V a l u e s were s i g n i f i c a n t l y correlated with age
(1982:
r = 0.93,
= 0.78,
p < 0.01;
p < 0.01).
1983:
r = 0.73,
p < 0.01;
Among ewes less than 4 years of age,
was s i g n i f i c a n t l y more c l o s e l y related to age
tha n a m o n g ewes 4 years and older
0.05;
all
1984:
three yea rs combined.
(r = 0.50;
F i g . 12).
D.V.
(r = 0.81),
t = 2.27,
A ewe's D.V.
one year was s i g n i f i c a n t l y co r re l at e d with her D.V.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
the
r
p <
in
68
90-
y=l2 95x4- 0 9 7
r = 0 81
p<0-0l
(D
O
c
o
c
E
o
y =4 0 9 x 4 - 2 9 2 2
Û
r=0 5 0
2
4
6
8
p < 0 01
10
Age (in years)
Figure 12.
Ewe D o mi n an c e V alues were signifi c an t ly
co r r e l a t e d with age. All three years combined.
C o r r e l a t i o n c o e f f i c i e n t s s i g n i f i c a n t l y different between
ewes less than four years old, and those four years and
older (t = 2.27, p < 0.05).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
69
fol l ow i ng year
g re a t er
(r = 0.75,
p < 0.01).
The correla t io n was
for ew es less than 4 years of age
a m o n g older ewes
(r = 0.53;
Fig.
13),
(r = 0.71)
than
but the d ifference
in
c o r r e l a t i o n c o e f f i c i e n t s was not significant.
A ewe's D.V.
whet her m e a s u r e d
was not related to her estrous date,
f r o m the onset of rut
or from the m e di a n date
(r = -0.19,
(r = -0.23,
p > 0.05).
p > 0.05)
Consequently,
D.V.s and birth d a te s of lambs the following summers were not
correlated,
s eason
0.09,
whether measu re d
(r = 0.02,
p > 0.05).
p > 0.05)
from the first birth of the
or from the medi an date
( r =
D.V.s of ewes the previous summer,
which
might have a f fe c t e d the ewe's c on d it i on at conception,
r e l a t i o n s h i p to the sex of lambs
0.05).
A ewe's D.V.
(T-test,
t = 0.08,
p < 0.01),
(r = 0.21,
p >
the pr e vious summer was significantly,
n e g a t i v e l y c o r r e l a t e d with the weight of her male
-0.78,
had no
lamb
(r =
but not w it h the weight of her female lamb
p > 0.05;
F i g . 14).
I also examined the
influence
of a e w e 's age the pre vious year on the weight of her lamb.
The w ei g ht s of male
age
(r = -0.87,
0.03,
lambs were n e ga t iv el y cor related with ewe
p < 0.01)
p > 0.05).
but female weights were not
D o mi nance Values of lactating ewes were not
related to mean n u r s i n g d u r a t i o n s
rates
(r =
(r = 0.06)
or mean nursing
(r = 0.06).
D u r i n g an ea rlier s t u d y of m ot h e r - y o u n g re lationships of
the B is o n Range bighor n s
(Hass 1984),
c la s se s of l a ct ating ewes:
I identified three
those that nursed only their own
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
70
90
<4 years
V .
r = 0 71
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r =0 5 0
p<005
30
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1
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30
Dominance
60
90
Value
Figure 13.
Ewe's D o mi nance V a lues one year were
s i g n i f i c a n t l y c or r el a t e d with their Dominance Values the
following year.
C o r r e l a t i o n c o e f f i c i e n t s between age
grou ps not significant. Lines d r a w n from regression
equations.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
71
O Maie
en
O Female
Female lambs=
y = 0 0 l x + 3-85
r = 0 21 p> 0 0 5
•
50
*
!
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y= - 0 * 0 3 x + 5 41
r= —0 * 7 9
p<C0'0l
-
20
Dominance
40
Value
60
Previous
80
Summer
F igure 14.
E w e ’s D o mi nance V alues were not related to the
w eight of their female lambs, but were negatively
c o r r e l a t e d with the w eight of their male lambs. All three
years combined.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
72
lambs
(00 ewes),
(0+ ewes),
those that nursed their own and other
and ewes that had lost their
lambs to predation,
but c o n t i n u e d to nurse the su r vi v in g lambs
H elpers had the h i gh e st D.V.s
lowest m e a n valu es
= 49.0).
= 5.08,
(Y = 42.4),
(Helpers).
00 ewes had the
and 0+ ewes were
in between
(Y
(One-way ANOVA,
F
p < 0.03).
lower r a nk i ng ewes
(1983:
85.54,
while
p < 0.001),
d i s p l a c e d more
composition
Fig,
the number
39.58,
= 69.3),
The d i f f e r e n c e s were s ignificant
Ewes with high D.V.s
0.05;
(X
lambs
initiated more d is p la c em e nt s than
G = 185.72,
p < 0.001;
15).
G = 54.66,
In 1983,
p < 0.001;
based on group
1984 : G = 14.87,
this diffe rence was
but
in 1984,
p <
independent of
of su b o r d i n a t e s av a ilable to each group
p < 0.001),
G =
individuals with lower D.V.s were
f re q ue n t l y than expected,
(1983:
1984:
no di ff erences were
(G =
found
bet w e e n o bs e r v e d d i s p l a c e m e n t rates and those expected based
on the number of s u b o r d i n a t e s available to each group
0.57,
(G =
p > 0.05).
In 1984,
I r ec o rd e d the patterns used to displace other
ewes.
These were
Heads)
and
lumped
" displays"
into "contacts"
(Low Stretch,
i nteraction rates we re calcul at e d
(Fig.
16).
25.85,
Head Tip,
for the
SLR), and
four rank groups
Di splays were re corded more than twice as often
as contacts.
patterns.
(Butt, Paw, Touch
All r a n k- g ro up s used more displays than contact
Higher r an k in g ewes
p < 0.001)
and d i sp l ay s
initiated more contac ts
(G = 84.30,
p < 0.001)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
(G =
than
73
□
08
1984
Q
ÜJ
h-
<
</)
t
0 4
a>
o
ÛC
c
g
o
o
(D
C
û
LU
>
0 4
LU
O
LU
cr
08
-
-
A
B
C
D
Figure 15. Rates of d i s p l a c e m e n t s for ewes, 1983 and 1984
R a n k - g r o u p s ; A = lowest 25% of ranks, B = second lowest
25%, C = second hi g h e s t 25%, D = hi ghest 25% of ranks.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
74
CONTACT
(/>
0>
o
q:
□
DISPLAY
02
c
q)
E
<u
o
o
0 2
CL
CO
'o
cc 0*6
A
B
C
R a n k -G ro u p s
D
YM
YF
3
4
5+
Age
Figu re 16. Rates of d i s p l a y and co nt act displace ments for
ewes, 1984.
Rates were d e p e n d e n t on both rank and age.
R a n k - g r o u p : A = lowest 25% of ranks, B = second lowest
25%, C = second h ig h e s t 25%, D = highest 25% of ranks.
YM
= y e a r l i n g males, YF = y ea r li n g females.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
75
e x p e c t e d based on gr o up composition.
However,
observed
v al u e s did not differ s i g n i f i c a n t l y from those expected based
on the number
p > 0.50,
of s u b o r d i n a t e s a v ai lable
displays:
G = 5.13,
(contacts:
p > 0.10).
were e q u a l l y l i k e l y to receive displays,
composition
(G = 2.58,
more contacts,
p > 0.50),
G = 1.68,
All rank-groups
based on group
but lower ranks received
and higher ranks fewer than expected based on
g ro u p c o m p o s i t i o n
(G = 9.94,
p < 0.05;
Fig.
16).
Be cause the r a nk - g r o u p i n g s might be ma sking some
a g e - r e l a t e d differences,
sheep,
rates of d i s p l a y and contact di s placements were
r ec a l c u l a t e d
older
p a r t i c u l a r l y among the younger
for y ea r li n g ewes,
and ewes aged 3, 4, and 5 and
(there were no 2-year-old ewes in 1984).
c al c ul a te d rates
for the y ea rling rams
(Fig.
I also
16).
Again, all
gro ups pe r fo r me d more d is plays than c o n t a c t s , and there was a
significant
< 0.001)
rams
increase with age
and d i s p l a y rates
for both contacts
(G = 92.07,
(G = 29.31,
p < 0.001).
initiated more of both contacts and displays
y ea r li n g females.
Yearling
than
Ye a rl i ng s of both sexes received more than
1/3 of the contact d i sp l ac e me n ts ,
19% of the ewe group;
al t hough they made up only
the d i f f e r e n c e s between observed and
expec te d values were not s i g n i f i ca n t
(G = 5.02,
Y ea r li n gs
receive a higher
(both sexes)
did,
however,
p r o p o r t i o n than e x pe c t e d of di splays;
29.87,
p < 0.001;
Daily
p
Fig.
p > 0.10).
72 of 147 displays
(G =
16).
interaction rates were s i g n i f i c a n t l y correlated
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
76
w it h the m a x i m u m d a i l y t e m p e ra t ur e s
(r = 0.48,
p < 0.05),
not w it h m i n u m u m d a i l y t e mperatures
(r = 0.23,
p > 0.05;
t e m p e r a t u r e s r e c o r d e d at NB R headquarters,
sheep range,
Although
and o b ta i n e d
about 10 km from
from NBR Narrative Reports).
locations of interactions were not recorded,
c on s i s t e d
of ewes d i s p l a c i n g each other
the shade,
wh i ch mi g h t a c co u nt
m a x i m u m t e m p e ra t ur e and
D u r i n g the study,
of which
five r es u lt e d
but
most
from bedding sites
in
for the re lationship between
interaction rates.
nine d o mi nance
in c h anges
fights were observed,
in rank.
An ad ditional 21
rank c ha n g e s were d e t e c t e d by the results of dominance
interactions.
Most of the rank changes were the results of
3- and 4 -y e ar - ol d s a d v a n c i n g
in the hierarchy.
The lowest
ra nking ewes were g e n e r a l l y the yearlings and 2-year-olds
(Table 13).
Yearlings
s e l d o m interacted among themselves,
a nd d o m i n a n c e r e l a t i o n s h i p s among th em were sometimes
d i f f i c u l t to determine.
dominance
of age,
maki ng
r el a t i o n s h i p s were evident.
clear-cut
By three to four years
ewes a c t i v e l y fought their w a y up the hierarchy,
it possible
for a 4-yea r-old to be quite high ranked.
A lt h o u g h v a r i a b i l i t y
older ewes,
age
By two years of age,
(Table
in the Do m inance Values
th ey did not appear
increased in the
to lose rank with
Increasing
13).
Lambs
D is p la c em e nt s ,
eith er
from bedding sites,
p o s i t i o n s or forage were e x t r e m e l y rare
spatial
in lambs.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
During
77
Table
13.
D o m i n an c e Va l ue s and ages
1984 that i n t e r a c t e d wi t h at least
* indicates
those d is c ar d ed
for those ewes in 1982-
10% of the nursery group.
from further calculations due to
the small n u m b e r of o bs e rv e d interactions.
Arrows indicate
i n s t a n c e s wh e n one ewe d o m i n a te d a n ot h er with a higher D.V,
1982
Ewe
D.V.
Age
90.0
7+
90.0
7+
69.3
Ewe
198 4
D.V.
D.V.
Age
8+
8+
8
7+
76.7
76.0
70.3
6
9+
67.8
5
67.2
4
61 .0
6
65.9
8+
54.7
6
8+
54.7
4
61.0
61.0
8+
9+
54.7
6
59.1
7
4
52.9
3
56.3
7
4
52.2
5
6
7
45.0
7+
30.8
48.2
3
58.3
35.3
35.3
32.3
51 . 5
2
41.4
5
4
5
37.8
6
3
2
2
2
3
4
3
6
3
8
20.7
1
36.7
36.7
35.3
33.2
20.7
1
31.5
16.8
1
28.7
2
2
3
16.1
1
24.1
2
3
O
2
14.9
7
3
0
1
14.0
2
2
1
S3
13.6
3
Ewe
Age
9+
kOH,
9+
7
)Ej
^HE
SH'
8
5
7
3
4
1
1
1
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
78
1983,
five d i s p l a c e m e n t s were recorded
l am b - h o u r s
(rate = 0.0041 displaceme nt s /h o ur ) ,
o n l y one d i s p l a c e m e n t was re c orded
c o n s i d e r a b l y lower than those
16).
Before
in 1984
These rates were
found for yearlings
in 1984
lambs were a year old, males were
c o n s i d e r a b l y larger than females,
dominance displays
and
in almost 280 lamb-hours
(rate = 0.0036 d i s p l a c e m e n t s / h o u r ) .
(Fig.
in more than 1200
and e v id ently dominant,
fr om male to female were recorded,
as
as well
as f em a le - t o - m a l e s u b o r d in a nc e displays with no dominance
rever sa l s o bs erved b e tween the sexes.
Yearling rams usually
bec ame d o m i n a n t to the adult ewes when 13-18 months old,
after w h i c h they d i s s o c i a t e d with the nu rsery groups and
joined the ba chelor herd.
D i s c u s si o n
Well-de fined,
s ta b le h i er a rc h ie s existed for both sexes
of bighor n s on the NBR.
linear,
R a m hierarc h ie s were strongly
but ewe h i e r a r c h i e s were not. The hierarchies
for
both sex es were a b s o l u t e
(Wilson 1975), and rank did not
change with s i t u a t i o n or
location.
Other st udies have a s s u m e d bighorn ram hierarchies to be
linear
(Geist 1971,
Hogg 1984a),
support that a s s u m p ti o n.
but provide little data to
The p r o b a b i l i t y of a linear
hie r a r c h y oc c uring by ch a nc e
in a group of more than 10
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
79
animals
is remote
relations
Indeed,
(p « 0.001,
A p p l e b y 1983),
p r o b a b l y do not d e v e l o p by chance
but do minance
(Chase 1982).
the s t r e n g t h of the li nearity of the ram h i er a rc h y
s u g g e s t s that rams are behaving
deviation
in such a way as to minimize
f r o m linearity.
Rams,
and to a lesser extent ewes, are polymorphic.
Ran)î is c o r r e l a t e d wi th age,
size a nd h o r n s i z e - t w o
(Geist 1971,
Hogg 1983,
which in rams
is related to body
important aspects of fighting ab ility
Table 7).
Strange rams are probably
c ap able of e s t i m a t i n g relative rank by horn size
1971),
so it is possible that few reversals would s h ow up
until more tha n 10 animals were present
class
(Geist
(see Sc h j e l d e r u p - E b b e
1983 for d i s c u s s i o n s
size classes,
Chase 1982, and Appleby
of the magic number 10).
Among horn
" r e c o g n i t i o n ” of gross morphological characters
is p r o b a b l y all that
is necessary,
d e t a i l s w i t h i n horn classes,
recognition
1975,
in each horn size
while recognition of finer
perhaps approaching individual
(Barnard and Burk 1979), m a y promote the
a p p e a r a n c e of d o m i n a n c e r e v e r s a l s , or triangles,
more t h a n 10.
size c l a s s
in groups of
A m on g the b i gh o rn rams of the NBR, no horn
(of a n i m a l s w h ic h were observed
n u m b e r e d more t h a n 10.
interacting)
ever
Groups this small may indeed be
transitive.
The be h av i or
rank
here.
in the group,
of rams was shown to be linked to their
a l t h o u g h age effects are hard to separate
No t only do rams ga i n in rank,
and priority of access.
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80
w i t h age,
but as a result o£ this advanc em e nt
hierarc h y,
subordinate
in the
the rams s witch f ro m acting a g gr e ss i ve l y
to a c t i n g a g g r e s s i v e l y dominant;
interacting at
r ates g re a t e r than e x pe c t e d based on group composition or the
number of a v a i l a b l e
interactants.
As the close r e l a t i o n s h i p be tw een age and rank
indicates,
rams m a y a dv a nc e
in the hi e rarchy simp ly by
g et t i n g larger and g r ow i ng more horn, while smaller rams join
the h i e r a r c h y at the bottom.
relationships
Definitive dominance
first a pp e ar e d
two years of a g e .
(were observed)
between one and
During this time the young rams were also
s et t l i n g d o m i n a n c e r e l a t i o n s h i p s with the ewes;
y ea r l i n g ewes,
ewes.
first the
then m oving up the ranks to the bigger,
T h e y a pp e ar e d to test each ewe
older
in the group,
p e r f o r m i n g the typical r a m dom in a nc e p at terns-courtship and
n o n - c o n t a c t d is p l acements.
Some ewes appeared to concede
ri ght away,
while oth ers r e buked the young rams until the
rams b ecame
large and s tr o ng en ough to physically overpower
them.
B y the time rut began,
d o m i n a n t to all the ewes.
the yearling rams appeared
At this time,
they began to
interact w i t h the big rams as th e y joined the ewes on the
r ut t in g area.
F o l l o w i n g the rut,
the yearling rams usually
left w i t h the b ac helor herd, al t h o u g h they might be observed
w i t h the ewes
for brief p eriods of time duri ng the next year.
O nc e the young rams
joined the bachelor herd,
they still
a p p e a r e d to be s e tt l i n g d o m i n a n c e re lations among themselves.
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81
W i t h i n a cohort,
NBR,
even among a group as stable as that on the
fights and upsets c o nt in u ed to occur until at least six
y ears of age.
Upsets also occured between cohorts.
nine or 10 years of age,
On occasion,
younger
rams d e clined r ap i dl y in condition.
rams
(5-6 years)
a nd b e a t i n g these old rams
suc c es s fu l ).
Usually,
and were not o bs e r v e d
After
were observed
fighting
(although th ey were not always
however,
the old rams became solitary
interacting with the other rams;
D o m i n a n c e Values cou ld not be calculated
for them.
The
s w i t c h f r o m the n u r s e r y group to the bachelor herd was
a c c o m p a n i e d by a change
pa tterns.
in the ratio of c o n t a c t -t o -d i sp l ay
Interactions among lambs were c h aracterized by
more c o n t a c t than d i s p l a y patterns
once d o m i n a n c e relat i on s developed,
c o m m o n than con tacts
(Chapter
III),
whereas
di s plays became much more
(see also Geist 1971,
p.
170).
The rams on the NBR are preven ted from emigrating,
likewise,
study.
no stra nge rams were added to the group duri ng this
The d e ve l o p m e n t a l ch an ges of dominance relations of
the y o u n g rams have been reported elsewhere
Geist 1971),
(Blood 1963,
but the d e v e l o p m e n t of rank relations,
s wi t ch f r o m the ewe g ro u p to the ram group,
appears to
c o r r e s p o n d more w i t h sexual d e v e l op m en t tha n age,
Among a herd of Dali's sheep
not yet d o m i n a n t to ewes
in Alaska,
and the
per se.
2-year-old rams were
(S. B r a i n e r d , pers.
comm.), and
a m o n g b ig h o r n s of the Pecos W i ld e rn e ss of N ew Mexico,
2 - y e a r - o l d rams still a s s o c i a t e d with the ewes and were
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82
o b s e r v e d going through the same behavioral changes observed
in y e a r l i n g rams on the NBR
(pers.
b ig h or n s of upper Rock Creek,
o b s .).
Montana,
Among high quality
large male
lambs
(10-11 m o n t h s old) were seen s wi t ch i ng back and forth from
ewe g r ou p s to ra m groups, a l t h o u g h
in teractions between the
male lambs and ewes were not observed
(pers.
obs.).
rate,
b i g h o r n herds exhibit profound differences
rates
(Buechner 1960,
Geist 1971, and others),
At any
in growth
and these
d i f f e r e n c e s may have d r a m a t i c effects on the development of
d o m i n a n c e re lations.
Likewise,
it is not unusual for rams to
join and leave d if f e r e n t bachelor
(Geist 1971).
herds
in their
What effects these changes
lifetime
in group
c o m p o s i t i o n have on the d e v e l o p m e n t and s t ab i li t y of
d om i na n ce ranks w i t h i n groups are unknown.
One of the h y po t h e s i z e d benefit s of high rank
increase
in the number
of breedi n g opportunities,
s up p o r t e d b y this st u d y and others
1984a,b).
(Geist 1971,
is an
which is
Hogg
C op u la t i o n rate varies sl i g h t l y with the mating
s t r a t e g y utilize d
(tending,
c o ur s in g or blocking)
of w h i c h m a y be d e p e n d a n t on rank
(Hogg 1984a,b).
the choice
Whether or
not a c o p u l a t i o n was successful was not possible to determine
in the field.
d a y estrus,
Ewes are bred r e p e a t e d l y throughout their 1-2
often by m a ny d i f f e r e n t rams of disparate ranks.
A l t h o u g h a high r an k i n g r a m m a y have more breeding
opport u ni t ie s ,
mu ch more needs to be known about s pe r m
c o m p e t i t i o n before the r e l a t i o n s h i p be tween rank and
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83
r e p r o d u c t i v e success
in b ig h or n rams
is understood
(Hogg
1984a,b).
Ewes are less p o l y m o r p h i c than rams,
their b o d y and horn size by ages
J o r g e n s o n and Wi s ha r t 1984).
2-3
reaching most of
(Blood et al.
Rank was s ig n if i ca n tl y
c o r r e l a t e d with age, as has been found with other
u ngulates:
red deer
1975);
(B. t a u r u s ; Hall 1986), Pere David *s deer
d a v i d i a n u s ; P. Schoknecht,
pers.
comm.);
(Townsend and B a i l e y 1981);
po ni es
Clutton-Brock
reindeer
bison
et al.
1976);
roe deer
(Rutberg 1983,
b i g h o r n ewes
1986);
white-tailed deer
(R a n g i fer t a r a n d u s ;
and a small captive group of
During each year, at least 12
and the more ewes
the more trian gl e s a p parent
Other st u di e s of ungul a te s have
animals
(Elaphurus
(Equus c a b a l l u s ;
r an k ed ewes were three years and older,
n um e r o u s trian g le s
C h il l in g ha m cows
(C ap re o l u s c a p r e o l u s ; Espmark 1974);
(Bennett 1986).
this catagory,
female
(Cervus e l a p h u s ; Hall 1983); d a i r y cows
(Bos taurus ; Re i nh a rd t and R e in hardt
E sp m a r k 1964),
1970,
in
in the ranks.
found similar
results:
in isomor phic gro ups of more than 10
(Beilharz and M ylrea 1963,
C l u t t o n - B r o c k et al.
Espmark
1976, Co l l i s 1976,
1964,
Hall 1986, Rutberg
1986).
W hi l e high d o m i na n ce rank m a y pro vide rams with more
b r e e d i n g opportunities,
less clear.
Presumably,
the be n efits of high rank to ewes are
h ig h rank w o u l d a l l o w a ewe access
to limited resources and p o s s i b l y reduce stress
(Cherkovich
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84
and T a t o y a n 1973),
condit i on ,
allowing a ewe to m ai ntain a better bo dy
the benefits of which could be passed on to her
of fspring.
A mo n g red d e er hinds
dominant
(Clutton-Brock et al.
hinds co n c eived earlier,
1984,
1986),
bore a higher percentage of
m a l e s t h an females and af fected the breeding success of their
sons more than their daughters.
i mp o rtant
factor
The body size of males
in br eeding success) was related to growth
and n u t r i t i o n du r i n g the
( Cl u tton-Brock et al.
first 18 months of life
1984,
1986), a factor greatly
influenced by the amount of maternal
( Cl u tton-Brock et al.
ewes
1982).
investment
The body condition of Dali's
(jO. dalli ) m a y affect horn growth of their ra m Iambs for
up to five years
ewe
(an
fo llowing birth,
lambs to a lesser extent
but appears to affect their
(Bunnell 1978).
Horn size
is an
im portant c o m p o n e n t of fighting a bi l it y and rank among both
b i g h o r n and thinhorn rams
(Geist 1971, but not the only
component,
comm.),
J- Hogg,
pers.
leading to the p o ssibility
that the bo dy c o nd i t i o n of a ewe during gestation and
l a c t a t i o n ma y influence her s o n ’s reproductive success,
pe rhaps more tha n that of her daughters
T ri v e r s and Wi llard
(as hy pothesized by
1973).
In a s t u d y of do m in a n c e relations
C a l i f o r n i a b ig h or n ewes,
a g e - r e l a t e d hierarchy.
Eccles
However,
(1981)
in a captive group of
found a stable,
horn lengths and body
w eights were not s t r o n g l y c or r el a te d with Dominance Values,
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85
an d d o m i n a n t s did not have higher q ua l i t y diets or different
a c t i v i t y budgets than su bordinates.
for b i g h o r n ewes
(Gel<6t 1971).
The prime breeding age
is r ep o rt e d to be from five to seven years
In the NBR ewes,
the mean Dominance Value for
this age g r o u p was 54.08 ± 9.57,
s li g h t l y above the median.
W e i g h t s of ewes were not mea sured during this study,
a m o n g ewe six years old and older,
but
b od y condition
d e t e r i o r a t e d o b v i o u s l y with age, al though rank did n o t .
Youn ger ewes
invested more,
while older,
and/or higher ranking ewes appe ared to invest
more
in their
female
pre-natally,
lambs.
is gr e at e r am o ng males and
Variance
invested more
in female
t h e y are
Bunnell 1978).
ewes
both pre- and post-natally,
than
in prep.), and male
lambs
for a ewe to produce than female l a m b s .
ewes might be pr o ducing heavier
(male)
lambs when
in better c o nd i t i o n and can afford the added cost.
As a ewe's
might
Overall,
(Hogg and Hass,
a p p a r e n t l y cost more
Therefore,
investment than among females
1982,
in male lambs,
lambs
in reproductive success
is p ro bably more c l osely related
to e a r l y g r o w t h and p a rental
(see C l u t t o n - B r o c k et al.
in their male lambs,
r eproductive potential declines with age,
invest more
in her female offspring and
" r e p r o du c ti v e value"
(Clutton-Brock et al.
she
increase her
1982).
B e c a u s e b o d y c o n d i t i o n de clined with age, al though rank
di d not,
little r e l a t i o n s h i p was seen between rank and
maternal
investment.
However,
the sheep on the NBR are
g e n e r a l l y in e x c e l l e n t condition,
and are not limited by
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86
forage.
In other habitats,
the a c c e s s
(to forage,
where seasons are more severe,
water,
bedding sites)
obtaina ble by
h i g h rank m a y Indeed make the difference between good and
poor b o d y condition,
s urvival,
which.
If not only affecting ewe
m a y af f e c t the r e productive success of offspring
born to ewes of d i f f e r e n t i a l rank.
Ewes on the NBR s eldom
u se d their rank to obtain access to some limited resource,
but more often a p pe a r e d to be either mainta i ni n g a m i n i m u m
p er s o n a l d i s t a n c e or reinfor c in g rank relations.
The rates
of d i s p l a c e m e n t s ap p e a r e d to be more a function of the number
of s u b o r d i n a t e s a v a i la b le to eac h ewe,
than an increase
in
a g g r e s s i v e n e s s w it h rank, as was found among the different
r anks of the rams.
E cc l es
(1981),
These findings diff ered from those of
who found a signi ficant c orrelation between
a g g r e s s i v e n e s s and Do m inance Value of bighorn ewes.
However,
he m e a s u r e d a g g r e s s i v e n e s s by counting the number of
a g g r e s s i v e en c ou n t e r s
adjust
Inltated by each ewe, and did not
for gr o up c o m p o s i t i o n or the number of possible
Interactants.
The advantages,
to ewes,
m a i n t a i n i n g high d om i na n ce ranks
of obtaining and
(on the NBR)
remain unclear.
D i s p l a y s are p h y s i o l o g i c a l l y less c o s t l y to bighorns
than c o n t a c t pa t t e r n s
then,
(MacAurthur et al.
1981).
As expected
ewes used d i s p l a y s over twice as often as contact
p at t e r n s to d is p la c e other ewes.
f r o m t hose
of E c cl e s
Again,
these results differ
(1981) who found contacts more
f r e q u e n t l y used than displays.
In a small captive group.
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87
h i g h r a n k i n g b i gh o rn ewes u t i l i z e d d is plays more often than
did
lo w -r a nk i ng ewes
(Bennett 1986).
The displays used by
ewes are more subt le than those of rams
1981,
pers.
(Geist 1971, Eccles
obs.), and ratios of d I s p l a y- t o- c on t ac t patterns
us ed m a y be biased b y co n d i t i o n s and observer ability.
For the first few years,
ewes advanced
in the hierarchy
by de f au l t as y o unger ewes joine d the bo t t o m of the
hierarc hy,
after w h i c h th e y fought their way up the ranks.
V a r i a b i l i t y in Do m inance V a l u e s
increased with age,
factors
Ewes us ua lly associated with
involved are unknown.
the n u r s e r y band for their
first few years.
years old or older tended to a s so ciate
2-5 animals.
but the
Barren ewes four
in unstable groups of
These ewes o c c a s i o n a l l y joined the nursery
g r o u p for short periods of time.
Barren ewes older than
seven yea rs s e l d o m joined the nu r s e r y groups;
of their time alone.
h i e r a r c h y fell
they spent much
All of the ewes not included
in the
into this "older" catagory.
I found little evidence that ewes, as a group,
b e h a v i n g like juvenile males.
r a n k / a g e - s p e c i f i c behaviors,
Ewes,
like rams,
exhibited
and ewes did not appear
b e h a v i o r a l l y ma t u r e until a ro u n d
5 years of age.
Sex ually
mature ew es did not behave a g g r e s s i v e l y subordinate,
young rams.
indeed,
g en e ra l o cc u re d at a mu ch more subtle
(Hass,
as did
The d r a m a t i c ho rn d i splays of the rams appeared
as g r a d e d signals a m o n g the ewes;
rams
were
unpub.
data).
This
communication
in
level than among the
is not suprising,
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as ewes do
88
not have
large^
curled horns to hide facial expression.
U nl i k e p re v i o u s stu dies of ca ptive ewes
1986),
the ewes on the NBR interac ted
o b s e r v e d n um e ro u s d om i n a n c e
fights.
(Eccles 1981,
frequently,
Bennett
and I
Ewes rare ly disperse
f ro m t h ei r natal ra n ge s and f o r m a m atrilineal so ciety
c o m p o s e d of mothers,
1984).
Rams,
their natal
on the other hand,
ranges,
b ac h el o r h erds
daughters,
aunts,
sisters,
e t c . (Hass
often disperse far from
and m a y belong to several different
in their lifetime
(Geist 1971).
B i g h o r n rams and ewes form two separate societies that
are not o n l y g e o g r a p h i c a l l y s e pa rated for most of the year,
but are d i s t i n c t
g roup members,
in their group structure,
commun ication,
relatedness of
and st ructure and development
of their d o m i n a n c e hierarchies.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
S UMMARY
The o n t o g e n y of behavior,
whether
it involves
or the m a t u r a t i o n of innate b e ha vi o ra l processes,
s a d l y n e gl e ct e d ar ea of big horn research.
t r e m e n d o u s v a r i a b i l i t y in organizational,
r e p r o d u c t i v e s t r a t e g i e s used by bighorns
habitats,
learning
has been a
Considering the
developmental,
and
in different
the o n t o g e n y of these strategies should be a
frui tful area of research.
B e c a u s e of this v a r i a b i l i t y evident in different herds,
to make stateme n ts about the function or benefits of play
behavior or d o m i n a n c e relations/
species,
NBR,
could be m i s l ea d in g
in bighorn sheep as a
if not paten tl y false.
On the
the p l ay of b i gh o r n lambs appeared to provide motor
t r a i n i n g benefits,
but did not appear to affect subsequent
so ci al st r uc t u r e or d o m i n an c e relations of the herd.
However,
groups,
lambs p r o b a b l y learn,
in play,
how to get along in
h o w to fight, and h o w to deal with the environment.
Lambs m a y be d e v e l o p i n g physical, as well as social,
skills
n e c e s s a r y for predator e vasion duri ng a period when the y are
h i g h l y vuln erable.
te st ed
But e x a c t l y what
in this study.
d at a on inter- and
is learned could not be
Due to the current lack of comparative
intra-sexual pla y behavior, and
d e v e l o p m e n t of d o m i n a n c e relat ions under different growth
regimes,
the ef f ec t s of the r el a ti v e l y lush habitat and high
lam b m o r t a l i t y are unknown.
D o m i n a n c e r e l a t io n sh i ps did not d ev e lo p until after the
s h e e p were one year old.
response,
This
is p ro bably a maturation
d e p e n d e n t on the gr o wt h /p h ys i ca l development of the
89
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
90
y o u n g sheep.
R oc k Creek
in e x t r e m e l y high q u a l i t y herds,
like the Upper
herd, d o m i n a n c e r el a ti on s m a y be developing in the
lambs b e fo r e th e y are a year old.
Maternal
Influence and
s u b s e q u e n t r e p r o d u c t i v e success of herds with different
g r o w t h rates c ou l d v a r y d r a m a t i c a l l y from that observed on
the NBR.
B o t h rams and ewes e xh i bi t ed ve ry stable hierarchies
that were s t r o n g l y co r re l at ed with age.
Social behavior,
p a r t i c u l a r l y a m o n g rams, a pp e a r e d dependent on r a n k ,
m a n i f e s t e d p r i m a r i l y through dominance and subordinance
displays.
Ra t es of ra n k- r el a te d be haviors were reflective of
the s ep a r a t e r a m an d ewe societies.
be nefits,
o bv i ou s
Direct reproductive
in terms of more breeding opportunities,
for h i g h - r a n k i n g rams.
rank for ewes,
in this study,
were
Reproductive benefits of high
remain obscure.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
L I T E R A T U R E C ITE D
Al tmann, J. 1974. Observa t io n al study o£ behaviour;
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Behaviour, 49,227-267.
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Altmann, S.A. and Altmann, J. 1977. On the analysis of rates
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Appl eby, M.C. 1983. The p r o b a b i li t y of linearity in
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B eilhartz, R.G. and Mylrea, P.J. 1963. Social position and
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Bekoff, M. 1974. Social play and play soliciting b y infant
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