POPULATION FLUCTUATIONS OF THE NEW HOLLAND MOUSE
PSEUDOMYS NOVAEHOLLANDIAE AT WILSON’S PROMONTORY
NATIONAL PARK, VICTORIA
B.A. WILSON, N.M. WHITE, A. HANLEY AND D.L. TIDEY
Wilson BA, White NM, Hanley A and Tidey DL, 2005. Population fluctuations of the New
Holland mouse Pseudomys novaehollandiae at Wilson’s Promontory National Park, Victoria.
Australian Mammalogy 27: 49-60.
The New Holland mouse (Pseudomys novaehollandiae) was first recorded at Wilson’s
Promontory in 1972 in heathland vegetation, but has not been located in this habitat
subsequently. The species was not trapped again until 1993 when it was found in calcarenite
dune woodland on the Yanakie Isthmus. The aims of this study were to assess the population
dynamics and habitat use of the species in this dune habitat. Mark-recapture trapping was
conducted at three sites from 1999 to 2002. One site was located on low (0 - 5 m), flat sand
dunes and open swales, another on medium (5 – 10 m) vegetated dunes, and the third on high
(20 m) steep vegetated dunes. The three sites had not been burnt for 30 to 50 years. The
abundance of P. novaehollandiae was related to understorey vegetation density and differences
in population densities on the sites are likely to be related to the primary succession stages on
the sand dunes, rather than fire history. The maximum density (24 ha-1) recorded at one site was
very high compared to other Victorian populations, however this was followed by a substantial
decline in numbers within the year. At another site a small population declined to extinction.
Populations on the isthmus are thus capable of achieving high densities but may decline
quickly. Rainfall patterns may have affected the population fluctuations, but further research is
required to elucidate fully the factors involved in the long-term dynamics of this species.
Key words: Pseudomys novaehollandiae, mammals, Australian rodents, population
fluctuations, succession.
BA Wilson, NM White, A Hanley and DL Tidey, School of Ecology and Environment, Deakin
University, Geelong, Victora 3217, Australia. Email: [email protected]. Manuscript
received 23 March 2004; accepted 17 August 2004.
THE
New
Holland
mouse
(Pseudomys
novaehollandiae) occurs in New South Wales
(NSW), Victoria and Tasmania, predominantly in
coastal locations (Keith and Calaby 1968;
Posamentier and Recher 1974; Hocking 1980;
Wilson 1991, 1996). Recently however, it has also
been found at sites up to 100 km inland in
Queensland and NSW (Read 1988; Townley 1993;
Van Dyck and Lawrie 1997). The species occurs in
dry tall closed heath and open heathland, woodland,
sclerophyll forest with a dense understorey and on
vegetated sand dunes (Braithwaite and Gullan 1978;
Fox and Fox 1978, 1984; Wilson 1991, 1994; Quin
and Williamson 1996). It exhibits a preference for
early successional vegetation (Posamentier and
Recher 1974; Braithwaite and Gullan 1978; Fox and
Fox 1978, 1984; Fox and McKay 1981; Wilson 1991;
Haering and Fox 1997). The species also has a
preference for floristically rich vegetation with a
substantial understorey cover, but with less cover at
lower strata (< 20 cm) (Fox and Fox 1984; Wilson
1991; Haering and Fox 1997; Lock and Wilson
1999).
In Victoria, P. novaehollandiae is considered to
be in a demonstrable state of decline and has been
lost from up to six localities (Cranbourne, Hummock
Island, Langwarrin, Reeves Beach, Tyabb and
Mullundung) in the past 20 years (Quin 1996; Wilson
1996). The species remains extant at only four
localities in Victoria: Providence Ponds, Loch Sport,
Wilson’s Promontory and Anglesea, although
animals from Anglesea are considered now to be
limited to captive colonies (Seebeck et al. 1996;
Wilson 1996; Lock and Wilson 1999). P.
novaehollandiae has been listed under the Flora and
Fauna Guarantee Act 1988, and is considered
‘Endangered’ (Seebeck et al. 1996; Wilson 1996;
DSE 2003).
At Wilson's Promontory the species was first
recorded in heathland vegetation in 1972 and then not
until 1993 when it was located in calcarenite dune
50
AUSTRALIAN MAMMALOGY
woodland on the Yanakie Isthmus (Quin 1994). Since
then it has been recorded at 21 sites on the Isthmus
(Quin 1996; Quin and Williamson 1996; Atkin and
Quin 1999). Surveys conducted at Wilson’s
Promontory between 1991 and 1993 suggest that
populations once found in heath vegetation are no
longer extant (Quin 1996; Wilson 1996). As there is
no information on population ecology or habitat use
of P. novaehollandiae at Wilson’s Promontory the
aims of this study were to investigate the population
dynamics and habitat and burrow use of the species.
METHODS
Study area
The study was undertaken on the Yanakie Isthmus, in
the northern section of Wilson’s Promontory
National Park in south Gippsland, Victoria (Fig. 1).
The Yanakie Isthmus, an area of approximately
6500 ha, connects the mainland to a granitic
promontory and consists of marine and non-marine
sediments and dune deposits (Quin 1996). The
vegetated parallel dunes are separated by swales
(interdunes) and traverse east west across the
Isthmus. The climate in the area is cool and mild with
few extreme temperatures. The rainfall varies
considerably across Wilson’s Promontory with the
southern and mountainous areas being wetter than the
Isthmus where there is a mean annual rainfall of
960 mm (Parks Victoria, pers. comm.). The
vegetation of this sand dune system has been
classified as Calcarenite Dune Woodland that occurs
on alkaline sand dunes and swales, and Shrubinvaded Calcareous Swale Grassland that occurs on
swales of sand dunes, and is considered to have
previously been grasslands (Davies and Oates 1999).
The woodland vegetation predominantly consists of
an overstorey of Allocasuarina vercilliata (drooping
she-oak), Acacia longifolia var. sophorae (coast
wattle) and Leptospermum laevigatum (coast teatree). The understorey is dominated by Dianella
revoluta (black-anther flax-lily), Lomandra longifolia
(spiny-headed mat-rush) and Acrotriche affinis
(ridged ground-berry) (Quin 1996; Quin and
Williamson 1996; Atkin and Quin 1999). Large areas
are covered by dense stands of L. laevigatum. The
area has a long history of cattle grazing from the
1850s up until 1992 when grazing ceased
(Chesterfield et al. 1995). Significant vegetation
changes on the Isthmus have occurred. An
assessment of vegetation using aerial photographs by
Bennett (1994) found that between 1941 and 1987
areas of grassy woodland declined from 2391 to
815 ha due to the expansion of L. laevigatum. The
Big Hummock sand dune changed from 1941 where
it was predominantly sand with a very low vegetation
cover to a dune dominated by L. laevigatum (20%
cover) in 2001.
Trapping procedures
Preliminary trapping (15 - 30 traps for three nights)
was undertaken in April 1999 at five sites where P.
novaehollandiae had been captured previously (Fig.
1, Table 1). Three sites were selected for
establishment of permanent study grids. Two were
set up in May 1999 HD (High Dune) at DC9 and MD
(Medium Dune) at EP, and one in December 1999
LD (Low Dune) at DC25 (Fig. 1). Trapping on grids
LD and MD was undertaken regularly between May
1999 and December 2002 and from May 1999 until
June 2001 for Grid HD (Table 2).
Fig. 1. Map of Victoria showing locations of P. novaehollandiae populations (1 = Anglesea, 2 = Wilson’s Promontory, 3 =
Loch Sport, 4 = Providence Ponds) and map of Wilson’s Promontory National Park (38o 52' 53', 146o 16' 17") showing
locations of survey sites (EP, DC2, DC9, BH, DC25) and trapping grids HD, LD and MD at Yanakie Isthmus.
50
WILSON ET AL.: NEW HOLLAND MOUSE AT WILSON’S PROMONTORY
Location
Trap-nights
EP
DC2
DC9
BH
DC25
45
45
90
90
90
Total captures
P. nov M. dom R. fu
8
13
0
0
8
5
6
29
2
0
9
2
12
6
2
51
Captures / 100tn
P. nov M. dom R. fu
17.8
28.9
0
0
17.8
11.1
6.7
32.2
2.2
0
10
2.2
13.3
6.7
2.2
Table 1. Capture data at preliminary trapping sites (April 6-8th 1999)
Dates
1999
May 4 – 6
July 29 - Aug 1
Sept 28 – 29
Dec 15 - 17
2000
Feb 29 - Mar 2
April 4 - 6
May 9 - 11
June 13 - 15
Aug 8 - 10
Aug 29 - 31
Oct 3 - 5
Dec 19 - 21
2001
March 20 – 23
June 12 – 14
Dec 9 – 11
2002
May 31 - June 6
Sept 2 - 6
Dec 13 - 17
Location & trap-nights
LD
HD
MD
180
180
120
180
180
180
120
39
175
300
300
300
300
300
300
300
177
180
180
300
300
300
180
180
180
300
312
300
60
153
180
180
90
180
180
174
180
Table 2. Summary of grid trapping at Yanakie Isthmus
(1999-2002).
Grid LD was established at DC25 east of the
Wilson’s Promontory Road (Fig. 1) on relatively flat,
low (0 – 5 m) sand dunes and open swales. L.
laevigatum (3 – 4 m) formed most of the overstorey,
with dense cover in some areas, and open canopy in
other areas where the tea-tree had collapsed. Major
understorey species include Acr. affinis, Hibbertia
sericea (silky guinea-flower), Centaurium erythraea
(common centaury) and Isolepis nodosa (knobby
club-rush). The area was last burnt in 1967. The
trapping grid consisted of 100 trap sites set in a
10 x 10 grid pattern with 10 m spacing, and
encompassed the crest of the dunes, mid-dune and
swale areas.
Grid HD was established at DC9 west of the
Wilson’s Promontory Road (Fig. 1) on high (20 m),
steep vegetated sand dunes sloping into open swales.
On the dunes the overstorey (8 – 10 m) was
dominated by large All. verticillata), L. laevigatum
and Bursaria spinosa (sweet bursaria) that provided a
dense canopy. Major understorey species included D.
revoluta, Acr. affinis and Geranium potentilloides
(native carrot). The flat, open swales have little
vegetation cover and an open canopy. Fire in the area
was last recorded in 1951. A trapping grid consisting
of 60 trap sites was established in a 6 x 10 grid
pattern with 10 m spacing and included dune and
swale habitat.
Grid MD was established at site EP on medium
height (5 – 10 m) sand dunes and included open
grassy swales, and a grazing exclusion plot (for
another study). The swales and exclusion plot lacked
an overstorey. The dunes overstorey (1.5 – 2 m) was
dominated by L. laevigatum and B. spinosa while the
understorey was dominated by Correa alba (white
correa), Acr. affinis and H. sericea. Acr. affinis with
scattered L. laevigatum dominate the swales. Within
the exclusion plot, Themeda triandra (kangaroo
grass) and Poa poiformis (blue tussock grass) were
dominant. The area was last burnt in 1951. The
trapping grid consisted of 60 trap sites in a 6 x 10
grid pattern with 10 m spacing.
Live trapping of small mammals was undertaken
using
collapsible
aluminium
Elliott
traps
(9 x 10 x 34 cm) (Elliott Scientific, Upwey, Victoria)
baited with a mixture of rolled oats, honey and
peanut butter. Shredded paper placed in the back of
each trap provided nesting material. Each trap was
covered with a plastic bag for protection from
environmental conditions. The traps were normally
set for three consecutive nights with some exceptions
due to poor conditions (Table 2) and were checked at
first light each morning. The identification of
animals, site of capture, weight, sex and routine body
measurements (pes, head, head-body, tail) were
recorded.
Capture rates and population estimates
The capture rates of P. novaehollandiae and the other
major mammal species on the grids were estimated as
captures per 100 trap nights for each trapping
session. Indices of population size of P.
novaehollandiae were estimated as KTBA (known to
be alive) (Krebs 1989), and population density
(KTBA ha-1). Animals entering the trappable
population for the first time were designated as gains.
Individuals that were not recaptured subsequent to
capture and marking were classed as losses. The
51
AUSTRALIAN MAMMALOGY
52
gains and losses of P. novaehollandiae at each site
were calculated. The breeding season was assessed
by recording pregnancies and the timing of juvenile
recruitment. Survival rates of individuals were
estimated as the length of time between first and last
capture.
Vegetation analysis
Floristic and structural vegetation data was obtained
from quadrats (5 x 5 m) established on the three grids
in 2000. The percentage area of the major vegetation
types present on each grid was determined by a
visual assessment and the number of quadrats
sampled in each area determined in proportion to the
area (Table 3). The cover of all plant species was
scored using the Braun-Blanquet scale (MuellerDombois and Ellenberg 1974). Species cover data
were analysed using PATN, developed by CSIRO
(Belbin 1994). The similarity between all pairs of
quadrats was determined with the Bray-Curtis index,
a robust measure of similarity (Faith et al. 1987). The
data was neither transformed nor standardised. The
flexible UPGMA (beta = -0.2) procedure was used to
cluster sites that had similar species composition
(Belbin 1991; Belbin and McDonald 1993).
Vegetation structure was assessed with the vegetation
contact method. Within each vegetation quadrat
sampled, a structure pole with 10 cm graduations
between 0 – 180 cm was randomly placed in ten
positions. The number of times the vegetation made
contact within each 10 cm graduation was recorded,
with a maximum of five touches. The density of the
vegetation for each height interval was calculated by
averaging the number of contacts in each height class
in each quadrat.
Lower dune
Mid dune
Crest of dune
Dense tea-tree
Fallen tea-tree
Exclusion plot
Total
LD
5 (20)
5 (20)
5 (20)
5 (20)
5 (20)
25
HD
4 (35)
4 (35)
4 (30)
0
0
12
MD
6 (30)
6 (30)
5 (20)
2 (5)
4 (15)
23
Table 3. Number of quadrats for vegetation communities
located on grids. ( ) = estimated % area on grid.
Habitat utilisation
Habitat use was assessed for the 1999-2000 trapping
data. Trap sites within each grid were allocated to
each PATN vegetation group and the number of
captures summed for each group. The mean number
of captures per 100 trap nights of P. novaehollandiae
for each PATN vegetation group was estimated and
tested for significant differences (Kruskal-Wallis
ANOVA). The relationship between vegetation
structural parameters and the captures of P.
novaehollandiae was assessed by stepwise logistic
regression. The parameters investigated were:
vegetation density at ten height classes from 0 10 cm up to 170 - 180 cm and the mean
cover/abundance for total vegetation in the quadrats.
A predictive equation for the likelihood of capturing
P. novaehollandiae was generated. Selected
individuals were coated with a fluorescent powder
prior to being released. After dark, the powder trail
left by the animal was followed using an ultraviolet
light to illuminate the powder. When a burrow was
located, it was marked with flagging tape and the
location recorded.
RESULTS
Capture rates of small mammals
Five small mammal species were captured during the
study: P. novaehollandiae, Rattus fuscipes (bush rat),
Mus musculus (house mouse), Sminthopsis leucopus
(white-footed dunnart) and Antechinus agilis (agile
antechinus). The latter two species were captured
only infrequently. Capture rates at the five
preliminary survey sites are shown in Table 1. There
were no captures of P. novaehollandiae at two of the
sites (DC2, BH). Capture rates at EP, DC9 and DC25
lead to the establishment of grids MD, HD and LD
respectively at these three sites. The capture rates of
the three major species on the three grids are shown
in Fig. 2. Capture rates of P. novaehollandiae on LD
exceeded that of other species from December 1999
until late August 2000 (Fig. 2a) and then decreased.
R. fuscipes were captured consistently with peaks in
April-May 2000, and very few M. musculus were
present. Capture rates of P. novaehollandiae and M.
musculus on grid MD were similar (Fig. 2b). The
highest capture rates of P. novaehollandiae on this
grid were in May 1999 and April 2000, and captures
of R. fuscipes were very low until February 2000 and
then increased to a peak in May 2002 (Fig. 2b).
Capture rates of P. novaehollandiae on grid HD were
low and the species was not captured after February
2000 (Fig. 2c). Captures of M. musculus were high
on this grid, with only occasional captures of R.
fuscipes.
Population dynamics of P. novaehollandiae
A total of 95 (40 male: 47 female and 8 unknown
sex) individual P. novaehollandiae were captured
237 times. Of these 73 were captured at LD, 16 were
captured at MD and 6 at HD. Individuals were
captured between 1 and 14 times. Animals known to
be alive (KTBA) peaked in April 2000 at LD (n =
30), May 1999 at MD (n = 9) and in April 1999 at
HD (n = 4) (Fig. 3). At all sites, numbers were lowest
over the summer months, increasing again as
juveniles entered the populations during late summer
and early autumn. At LD the population decreased
52
WILSON ET AL.: NEW HOLLAND MOUSE AT WILSON’S PROMONTORY
53
Ca pture /100 tn
14
12
10
8
6
Cap tu re /100 tn
20
18
16
20
18
16
14
12
10
8
6
4
2
0
P . nov
M . dom
R. fu
S ept-02
Dec-01
M ar-01
Oc t-00
A ug-00
M ay -00
Feb-00
A pr-99
4
2
0
Da te
P. nov
M. dom
20
Dec-02
Sept-02
Dec-01
May-02
Jun-01
Mar-01
Aug-00
Apr-00
F eb-00
Dec-99
Sep-99
Jul-99
May-99
Apr-99
R. fu
D a te
18
Ca pture /100 tn
16
14
12
P . nov
10
M . dom
8
R. fu
6
4
2
Dec -02
S ept-02
M ay -02
Dec -01
Jun-01
Oc t-00
Jun-00
M ay -00
Feb-00
Dec -99
S ept-99
Jul-99
M ay -99
A pr-99
0
Da te
Fig. 2. Capture rates of the major small mammal species on the three grids a) LD, b) MD and c) HD.
after a peak in April-May 2000, with KTBA being
much lower in 2001 and 2002, than at similar times
in 2000 (Fig. 3a). KTBA at MD also declined after
the April 2000 peak with KTBA never exceeding
four (Fig. 3b). At HD the population was low until
February 2000, after which there were no further
captures (Fig. 3c). The maximum density of P.
novaehollandiae at LD was 24.3 animals per hectare
(April 2000), at MD 20 ha-1 (May 1999), while the
peak density at HD was much lower (4.4 ha-1),
recorded in April 1999.
Pregnant females were recorded from October
until March and juveniles (classified as animals of
17 g and under) were captured from December until
May. The maximum number of juveniles (n = 20)
was captured between December 1999 and May
53
0
Apr-99
Jul-99
Aug-00
Aug-00
Jun-00
May-00
Apr-00
Feb-00
Dec-99
Sep-99
Dec-02
Dec-02
May-02
Sept-02
May-02
Sept-02
Jun-01
2
Dec-01
4
Jun-01
6
Dec-01
8
Mar-01
10
Dec-00
12
Mar-01
14
Dec-00
Month
Oct-00
16
Oct-00
Aug-00
Aug-00
Jun-00
May-00
Apr-00
Feb-00
Dec-99
18
Jul-99
Dec-02
May-02
Jun
Dec-00
Aug-00
Jun-00
Apr-00
Dec-99
Jul-99
Apr-99
0
Sep-99
Apr-99
0
May-99
Number of individuals KTBA
18
May-99
Number of individuals KTBA
Number of individuals KTBA
54
AUSTRALIAN MAMMALOGY
18
16
14
12
10
8
6
4
2
16
Month
14
12
10
8
6
4
2
Month
Fig. 3. Population estimates (KTBA) of P. novaehollandiae on the three grids a) LD b) MD and c) HD. * months when
trapping was not undertaken.
54
WILSON ET AL.: NEW HOLLAND MOUSE AT WILSON’S PROMONTORY
2000, while only three were captured in 2000-2001
and one in 2001-2002 breeding seasons. Survival
rates for adult males and females were similar (means
= 4 ± 1.7 and 4.3 ± 2.8 months respectively). The
highest monthly gain of 21 individuals was recorded
in April 2000 at LD (Table 4) and was minimal at
HD. Losses were highest in May and June 2000 at
LD (12 and 17 respectively) (Table 4). There was
little difference observed in the gains or losses of
males and females.
Month
April 1999
May 1999
July 1999
Sept 1999
Dec 1999
Mar 2000
Apr 2000
May 2000
June 2000
Aug 2000
Aug 2000
Oct 2000
Dec 2000
Mar 2001
June 2001
Dec 2001
May 2002
Sep 2002
Dec 2002
MD
HD
LD
Gain Loss Gain Loss Gain Loss
7
4
8
3
1
1
2
1
2
0
0
0
1
0
0
1
1
1
1
6
5
1
2
0
1
3
2
4
0
21
0
0
6
0
2
8
12
0
0
0
0
3
17
2
3
1
2
3
3
1
6
0
4
3
0
3
1
0
2
4
1
2
0
0
0
1
0
3
0
1
0
6
0
0
0
3
0
Table 4. Summary of gains and losses on each grid. - = not
trapped.
Vegetation analysis
A total of 52 vascular plant species were located at
the three sites. At LD 34 plant species were recorded
along with a high amount of bryophyte cover and
fungi. At MD there were 41 plant species, with little
litter or bryophyte cover while at HD there were 24
plant species and a high litter layer. The frequency of
fungi recorded at the sites varied from n = 40 at LD
to n = 9 and n = 0 at MD and HD respectively. PATN
analysis revealed two vegetation groups. Group 1 (23
quadrats) was dominated by Acr. affinis, L.
laevigatum, B. spinosa, D. revoluta, Dichondra
repens (kidney weed), G. potentilloides and H.
sericea. Group 2 (37 quadrats) was dominated by A.
serrulata, L. laevigatum, C. erythraea, G.
potentilloides, and I. nodosa. Group 1 quadrats were
predominantly located on lower to mid dunes, and
group 2 mainly on mid dunes to dune crests. The
upperstorey at the three sites varied. At LD the
upperstorey was dominated by L. laevigatum (3 –
4 m), with dense cover in some areas, while in other
areas the tea-tree had collapsed opening up the
55
canopy. At MD the canopy (1.5 – 2 m) was
dominated by All. verticillata, L. laevigatum and B.
spinosa providing high canopy cover. At HD the
upperstorey of tall trees (All. verticillata) was 8 –
10 m in height. The vegetation density at Grid LD
was higher than the other two sites in all height
classes from 0 – 180 cm except for 160 – 170 cm
where Grid MD was greater (p < 0.05).
Habitat utilisation
There was no significant difference in the captures of
P. novaehollandiae in the two floristic groups
determined by PATN, and there was no significant
difference in the presence of P. novaehollandiae with
relationship to the percentage frequency of individual
plant species. The presence of P. novaehollandiae
was significantly different (p < 0.05) between the
understorey height categories except at the 70 –
90 cm level. Logistic regression analysis using
backward stepwise entry of variables resulted in three
structural variables as being significantly related to
the presence of P. novaehollandiae. These were
vegetation density at 20 – 30 cm and 60 – 70 cm, and
the total cover of vegetation. The equation formed in
this model was z = 0.619 + 1.69 (X1) + 1.16 (X2) +
1.25 (X3), where X1 = density at 60-70 cm, X2 =
density at 20-30 cm and X3 = total vegetation cover.
A total of 16 individual P. novaehollandiae were
successfully traced to burrows and the entrances of
13 separate burrows were located. Distances from the
site of capture to the burrow entrance varied from
less than one metre to over 400 m. Animals would
rarely follow a direct route to their burrow. One
burrow was found to be used by five individuals over
three trapping sessions. Burrow entrances were
usually 30 – 60 mm in diameter. Some burrows were
located in open areas while others were well hidden
under fallen material, or partially hidden under leaf
litter. On two occasions, multiple entrances were
found for what was presumed to be one burrow
system. Three separate entrances were found at LD
all within 60 cm of each other, while two separate
entrances were found at HD, 20 cm apart. All
entrances were obvious due to the presence of
fluorescent dye on the walls.
DISCUSSION
The small mammal communities at the three sites on
the Yanakie Isthmus consisted of three dominant
species P. novaehollandiae, R. fuscipes and M.
musculus, with occasional captures of A. agilis and S.
leucopus. These are similar in composition to those
recorded at other sites where P. novaehollandiae has
been trapped in Victoria: Anglesea (P.
novaehollandiae, A. agilis, S. leucopus, R. lutreolus
(swamp rat), R. fuscipes, M. musculus, R. norvegicus
55
AUSTRALIAN MAMMALOGY
56
(brown rat)) (Wilson 1991; Lock and Wilson 1999),
Loch Sport, Providence Ponds (P. novaehollandiae,
R. lutreolus, M. musculus) (Hollis, 1999; Wilson
1996; Vance 2001). In NSW the small mammal
communities where P. novaehollandiae occurs are
similar in species composition however two
pseudomyine rodent species are often present (Fox
and McKay 1981; Fox and Fox 1984; Kemper 1990).
The relative abundance of the three major small
mammal species differed between the study grids. At
LD P. novaehollandiae was present in a higher
abundance, than the other two species. At MD P.
novaehollandiae and M. musculus were present in
similar abundance, and at HD M. musculus was in
higher abundance than P. novaehollandiae, which
occurred in small numbers.
Population dynamics of P. novaehollandiae
Pseudomys novaehollandiae was most abundant at
Grid LD where the highest density (24.3 ha-1) were
recorded. Grid MD had a lower population density
and the population at Grid HD was very low. The
large differences in population densities at the three
sites indicate that conditions at the sites differed.
These may be related to factors such as food
availability and habitat conditions (e.g., vegetation
structure, floristics, soils).
The maximum population densities recorded at
LD (24.3 ha-1) and at MD (20 ha-1) are very high
compared to other Victorian populations (Table 5)
including those at Cranbourne, Anglesea and
Langwarrin, which have all become extinct (Seebeck
et al. 1996; Wilson 1996). Populations in NSW (e.g.,
Hawks Nest, Nelson Bay, Port Stephens) have also
been recorded at high densities, however these
populations also subsequently declined to very low
levels (Table 5). The results at Wilson’s Promontory
indicate that populations are capable of achieving
Location
Victoria
*Anglesea
*Anglesea
*Anglesea
*Anglesea
*Cranbourne
*Langwarrin
Loch Sport
Wilson’s Promontory
New South Wales
Hawks Nest
Nelson Bay
Nelson Bay
Port Stephens
Tasmania
St. Helens
high densities and may decline quickly to very low
abundance. Also low-density populations may
decline to extinction, as exemplified by the
population at DC9. Similar results have been found
for populations at Anglesea where small populations
after wildfire in 1983 peaked four to eight years post
fire (3.1 – 5.5 ha-1) and then declined to extinction
(Wilson 1991). Further, the last known population at
Anglesea increased to a high density in autumn 1995
(16 ha-1) before a sharp decline to < 4.5 ha-1 from
June onwards and to extinction in 1998 (Lock and
Wilson 2004). The species thus appears to exhibit a
life-history pattern characteristic of r-selected species
where population irruptions and declines are
common.
The breeding season at Wilson’s Promontory was
from December to May. This is longer than the
season recorded at Anglesea and in Tasmania where
juveniles were captured from January to March
(Norton 1987; Wilson 1991). At Loch Sport, Vance
(2001) first recorded juveniles in the population in
October, indicating earlier breeding than at Anglesea,
Wilson’s Promontory or in Tasmania. In NSW
breeding lasts typically for five months (September
to January) but has been recorded to last up to 10
months from September to July (Fox et al. 1993).
The longer breeding season means that in NSW
females are capable of having up to six litters per
season, while in Victoria and Tasmania populations
may have only 1 – 2 litters. The longer breeding
season also means that first year females can breed,
but this is not the case at Anglesea or in Tasmania
(Norton 1987; Wilson 1991). Due to the length of the
breeding season at Wilson’s Promontory females are
capable of having 2 – 3 litters per season, however no
evidence of this was obtained for individual females
in the current study.
Density
Reference
(number per hectare)
0.5 - 1
0.5 - 3.1
0.9 - 5.5
0 - 16
0.2 - 1.5
0.6 - 1.3
0 - 12
0 - 24
Kentish 1982
Wilson 1991
Mills 1992
Lock 2004
Braithwaite and Gullan 1978
Opie, unpubl. data
Vance 2001
current study
2 - 19
1.5 - 17
9.4
4 - 18
Fox and Fox 1978
Kemper 1980
Thomson 1980
Kemper 1990
1.1 - 11.3
Norton 1987
Table 5. Density of P. novaehollandiae populations. * currently considered extinct.
56
WILSON ET AL.: NEW HOLLAND MOUSE AT WILSON’S PROMONTORY
Population size was lowest in summer and
increased in late summer to autumn as juveniles were
recruited after breeding. Recruitment was highest in
April-May 2000, followed by very low recruitment in
2001 and 2002. All three populations declined in
2001 and the population at HD became extinct. A
significant feature of the populations was the high
loss of animals in May and June 2000. It is unclear if
this was a result of dispersal or mortality. Declines in
juvenile heath mice (Pseudomys shortridgei)
associated with vegetation of older post-fire age were
reported by Cockburn et al. (1981) who concluded
that this was due to enforced dispersal as the habitat
and resources deteriorated. Wilson (1991) proposed
that a similar mechanism might occur for P.
novaehollandiae, with juveniles dispersing in order
to locate patches of habitat of suitable successional
age and available resources. More recently, results
from Anglesea found no evidence that high losses of
juveniles were a result of dispersal, but more likely as
a result of mortality (Lock and Wilson 2004). Such
results indicate that resources may be limiting, but
whether this is related to successional changes in
vegetation structure or declining food resources has
not been determined.
In NSW there is evidence that extension of the
breeding season of P. novaehollandiae is a response
to above average rainfall during the breeding season
(Fox et al. 1993). This would allow maximal
breeding and population increases to occur. The
population abundance of P. novaehollandiae at
Anglesea has recently been found to have a strong
positive relationship to cumulative monthly residual
rainfall (CMRR) exhibiting a 0 - 9 month lag time
(Lock and Wilson 2004). Maximum population
densities were recorded following four years of
above average rainfall and declines during below
average rainfall and drought conditions. The
population fluctuations at Wilson’s Promontory may
also have been influenced by rainfall patterns. The
cumulative annual rainfall experienced in 1999
(778 mm) was well below the long-term average
(960 mm). Although it was above average (995 mm)
for 2000, the monthly rainfall for June, when losses
were high, was extremely low (54 mm) as compared
to the 20-year average of 123 mm. Although
populations of rodents in arid Australia have been
shown to be strongly influenced by rainfall
(Newsome and Corbett 1975; Masters 1993;
Southgate and Masters 1996; Dickman et al. 1999;
Letnic 2003) there is little evidence of rainfall affects
on rodent populations in southern Australia. This
needs to be explored further, but requires long-term
data.
Habitat characteristics
The presence of P. novaehollandiae was not related
to the two floristic groups identified but was related
57
to vegetation structure, in particular vegetation
density at 20 – 30 cm and 60 – 70 cm, and the total
cover of vegetation. The importance of understorey
vegetation density and cover for P. novaehollandiae
has been found in other studies (Posamentier and
Recher 1974: Fox and Fox 1978, 1984; Wilson 1991;
Lock and Wilson 1999). At LD there was an open
canopy with dense vegetation cover < 150 cm in
height, together with substantial cover of fallen and
dead vegetation. These features may provide shelter
from predators and sites for burrows. At HD the
larger dunes were dominated by tall, mature Al.
verticillata with low cover in the understorey, and at
MD the habitat was open, flat dunes with an open
canopy and a dense understorey.
Differences in habitat features including
understorey structure of the three grids are likely to
be related to the succession ages of the vegetation.
Previous studies have found that the species exhibits
a preference for early (2 - 10 years) post-fire
succession vegetation (Posamentier and Recher 1974;
Braithwaite and Gullan 1978; Fox and Fox 1978,
1984; Fox and McKay 1981; Haering and Fox 1997)
which is floristically rich, has a substantial cover of
understorey vegetation but less cover at ground level
(Fox and Fox 1984; Wilson 1991; Haering and Fox
1997; Lock and Wilson 1999). At Wilson’s
Promontory however the succession changes are not
likely to be due to fire, as all three sites have the
same post-fire age of 30 - 50 years. Habitat
differences here are more likely to be related to
primary successional processes on the sand dunes
(Walker et al. 1981). The sites at LD and MD are
located on recently established-shifting sanddunes
(Bennett 1994). A series of aerial photos show that
the once bare dunes have been stabilised in the last
60 years (Bennett 1994), initially by L. laevigatum
then followed by colonisation of other plant species.
These sites are in a progressive stage with
establishment of shrubs, mobilisation of nutrients,
and increase in biomass (Walker et al. 1981). The
site at HD occurs on high older sand dunes in an
aging regressive stage with declines in understorey
cover and possibly nutrient decline.
The discovery of populations of P.
novaehollandiae on the Yanakie Isthmus at Wilson’s
Promontory in 1993 was both unexpected and
significant (Quin 1994, 1996). In 1972 the species
was originally recorded in heathlands to the south of
the Isthmus. Subsequently surveys undertaken in the
extensive diverse dry and wet heathlands close to this
record failed to find the species (Wilson 1991; Quin
1994, 1996). Typically P. novaehollandiae occurs in
heathlands (Fox 1982; Hollis 1999), heathy forests
and woodlands (Fox and McKay 1981; Wilson 1991;
Lock and Wilson 1999). The results of the current
57
58
AUSTRALIAN MAMMALOGY
study support evidence that, in Victoria, P.
novaehollandiae is not restricted to heathlands, but
has a wider habitat niche. A study of the vegetation at
Victorian localities where P. novaehollandiae has
been recorded (Wilson and Laidlaw 2003) found that
the species occurred in five structural vegetation
groups:
open-forest,
woodlands,
heathlands,
shrublands and grasslands. Grassland and shrublands
were restricted to coastal sand dunes in south
Gippsland at Reeves Beach, Hummock Island and at
Wilson’s Promontory.
The results of this study indicate that further
knowledge of the long-term fluctuations and
dynamics of P. novaehollandiae, and the effects of
resource availability and rainfall patterns are
required. The role of ecological burning for habitat
and population management at Wilson’s Promontory
is unclear and also needs further attention. Burning of
habitat when below average rainfall or drought
conditions are present is not recommended due to the
likelihood of low populations of P. novaehollandiae
and the possibility of local or population extinctions.
ACKNOWLEDGEMENTS
We extend many thanks to Kylie Slattery, Sarah
Gainey, Jill White for their assistance in the field. We
appreciate greatly the support of Jim Whelan and
Elaine Thomas (Parks Victoria). The research was
carried out under scientific permits issued by the
Department of Conservation and Natural Resources,
Victoria and ethics approval from Deakin University
AEEC. It has been supported with grants from Parks
Victoria.
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