Canids potentially threaten bilbies at Astrebla Downs National Park
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CSIRO PUBLISHING
Australian Mammalogy, 2021, 43, 300–310
https://doi.org/10.1071/AM20034
Canids potentially threaten bilbies at Astrebla Downs
National Park
John Augusteyn A,E, Maree Rich B, Georgeanna Story C and Barry Nolan D
A
Queensland Parks and Wildlife Service and Partnerships, PO Box 3130, Red Hill, Qld 4701, Australia.
B
Queensland Parks and Wildlife Service and Partnerships, PO Box 202, Longreach, Qld 4730, Australia.
C
Scat About Ecological, PO Box 45, Majors Creek, NSW 2622, Australia.
D
Queensland Parks and Wildlife Service and Partnerships, PO Box 5332, Airlie Beach, Qld 4802, Australia.
E
Corresponding author. Email: john.augusteyn@des.qld.gov.au
Abstract. The ecological role of canids in arid Australia is unresolved. Some argue they play a role regulating populations
of herbivores and introduced mesopredators such as feral cats (Felis catus) and foxes (Vulpes vulpes). However, evidence also
suggests they pose a threat to native species populations. The aims of this study were to determine the extent of canid predation
on the bilby population at Astrebla Downs National Park, Queensland, to improve our understanding of the ecological role
that canids serve in the park and to determine whether seasonal changes in the canid diet can be used to predict if and when
management should intervene. Canid scats (n ¼ 723) were collected over seven years and their content examined. The
percentage of bilby remains in the canid scats varied from 13 to 85% (mean ¼ 43%) and was 20–100% by volume. In total, 23
vertebrate species were identified in canid scats. The percentage of cat remains was 0–44% (mean ¼ 11%), peaking in 2013
during a cat plague and coinciding with canids actively hunting cats. Fox remains were not detected in dog scats. These results
indicate that canids had a varied diet and at times threatened the bilby population at Astrebla.
Additional keywords: bilby, canids, dietary analysis, Macrotis lagotis, predation, scat analysis, threatened species, wild
dogs.
Received 21 April 2020, accepted 14 August 2020, published online 10 September 2020
Introduction 2008) (Kerle et al. 1992). The combined effect of predation and
The role that wild canids (dingoes/wild dogs (Canis familiaris) drought caused what is known as a ‘predator pit’ – and the pop-
and their hybrids) (hereafter dogs) serve is the subject of debate ulation was not able to recover, even when conditions improved.
(Allen et al. 2011; Glen 2012; Fancourt et al. 2019). Some argue The ability of dogs to be both specialist hunters (Robertshaw and
that dogs help conserve native species by preying on or displacing Harden 1986) and generalist predators means they are well suited
more effective predators, i.e. mesopredator control (Johnson et al. to arid environments that oscillate between periods of abundance,
2007; Brook et al. 2012; Newsome et al. 2015), and controlling the boom periods, and periods when resources are scarce, the busts
herbivores (Letnic et al. 2012). Others consider dogs a threat to (Tatler et al. 2019). It can mean that favoured prey species are
native species (Oakwood 2000; Fisher et al. 2001; Banks et al. targeted even when their numbers become scarce, particularly in
2003) and/or believe the evidence relating to mesopredator reg- areas where alternative prey subsidise their food requirements
ulation is inconclusive (Allen et al. 2011; Glen 2012; Fleming (Allen and Leung 2012).
et al. 2013; Fancourt et al. 2019). The species they prey upon most Although dogs have been living with native species long
likely vary both spatially and temporally (Corbett and Newsome enough that some have evolved an innate antipredator response
1987; Corbett 2001; Doherty 2015), which changes in response to (Steindler et al. 2018), introduced predators and increased food
prey availability or activity (e.g. reptiles in summer (Read et al. and breeding opportunities due to modified land management
2012) and when pups are being reared (Allen et al. 2012)). Dogs practices may be affecting the way dogs now interact with their
also have distinct prey preferences that can sometimes be dis- environment. In an Australia-wide study of dog diets, Doherty
proportionate to prey availability (Robertshaw and Harden 1986). et al. (2019) found that rabbits (Oryctolagus cuniculus), reptiles
The impact that dogs have on a species may depend on how other and arthropods were encountered more frequently in the arid
threats interact. For example, a drought-affected common brush- and semiarid zones compared with other areas. They also found
tail possum (Trichosurus vulpecula) population went extinct after that, where rabbits were rare, the percentage of other medium-
being preyed upon by dogs and other predators, even though they sized mammals increased, suggesting that prior to rabbits, dogs
have coexisted for thousands of years (3500–4000 years: Corbett predominantly preyed on medium-sized mammals (Doherty
Journal compilation Ó Australian Mammal Society 2021 Open Access CC BY-NC-ND www.publish.csiro.au/journals/am
Astrebla dog scat analysis Australian Mammalogy 301
et al. 2019; Tatler et al. 2019), many of which are now either scats were from dogs was obtained from an experienced scat
extinct or threatened (McKenzie et al. 2007; Woinarski et al. analyst using the aforementioned characters as well as the
2014). Thirty-nine native terrestrial species that are Threatened presence of grooming hairs and the pattern of prey contents, i.e.
or Near Threatened have been found in dog diets (Doherty et al. fragment size and hair damage. The dog scats (n ¼ 723) were
2019). mainly collected along roads and creek lines. Search effort was
At Astrebla Downs National Park (hereafter Astrebla), an not standardised, and the number of scats collected for each
area that contains Queensland’s largest bilby population, dogs period varied according to the number of scats that were present
are known to prey on bilbies (8–25% frequency of occurrence and, to a lesser extent, the time spent collecting scats. Each scat
(% FO) is the proportion of scats containing a prey item) and was placed in a separate paper bag and the collection site was
kowaris (Dasyuroides byrnei) (4% FO) (n ¼105) (Palmer 1999). recorded using a GPS. Three categories of scats were analysed –
Paltridge (2002) found 1.3% FO (n ¼ 77) of dogs scats collected old scats were odourless, dry and white all over; medium-aged
contained bilby remains and considered dog predation combined scats contained some odour with mixed colouration; and fresh
with cat and fox predation to be a serious threat to the future of scats had consistent colouration, and were usually darker with a
the species. Tatler et al. (2019) found the % FO for bilbies to be mucus coating and strong smell. Old scats were considered to
less than 10%. To reduce the risk of predation to threatened have been deposited up to two months prior to collection and
species many organisations have started installing predator were added to the previous survey period/season if the collection
proof fencing, but this option is expensive (Hayward and Kerley date was less than two months from the last survey period.
2009; Hayward et al. 2014). Really old scats (white in colour and disintegrating and most
Although resource shortages have been considered the pri- likely more than three months old) were not collected.
mary driving factor controlling the dynamics of arid fauna
communities, there is increasing evidence that predation may Scat analysis
play an overriding role in shaping species abundance and Scats were oven-dried at 1008C for 6 h, then washed in nylon
composition at times (Pavey et al. 2008; Letnic et al. 2011; bags to remove all but the identifiable fragments. Prey compo-
Greenville et al. 2014). Understanding factors that have recently nents were identified to the lowest possible taxonomic level
changed an ecosystem and shifted the balance in favour of through comparison of remains, such as teeth and claws, with
predators is important to be able to conserve threatened species, known reference material or the literature (Watts and Aslin
particularly in unfenced reserves like Astrebla. The challenges 1981; Triggs and Brunner 2002) and hair identified using the
for wildlife managers are: predicting when predation events are technique described by Brunner and Coman (1974). Bilby hair
likely to occur; understanding how dogs and mesopredators has unique characteristics amongst arid-zone species and is
interact; and knowing whether and when to intervene, i.e. readily distinguished from all other species. The use of an
before, during or immediately after a boom period and/or during experienced analyst also ensured correct identification of bilby
the bust (Pavey et al. 2014; Yip et al. 2015). The aims of this hair. For comparison, samples were pooled into yearly summer–
study were to determine the extent of dog predation on the bilby autumn and winter–spring categories. Scats were not collected
population at Astrebla, improve our understanding of the eco- during winter–spring 2015. Prey data were also pooled into
logical role that dogs serve on the park and determine whether broad taxonomic groups for species that were infrequently
seasonal changes in the dog’s diet can be used to predict if and detected or unable to be identified to species level. Many studies
when management should intervene. have used % FO to report on predator diets (Croft and Hone
1978; Catling 1988; Paltridge 2002; Allen and Leung 2012;
Material and methods Doherty et al. 2019) even though this method tends to over-
represent the importance of small prey items (Corbett 1989).
Study area
Percentage volume estimates (% V) (that is, the proportion of the
Astrebla is surrounded by stock fences and is located 100 km volume of prey matter represented by a species/taxonomic
east of Bedourie in the Mitchell Grass Downs and Channel group), were also included to help address this limitation. The %
Country Bioregions and covers an area of approximately V was visually estimated using a grid within a sorting tray. The
176 000 ha. Cattle grazing enterprises surround the park, all of average volume for each prey group was calculated for all scats
which contain artificial water points. The main bore on Astrebla, within each collection period where the prey group was present.
Ingledoon No. 2 bore (No2), was turned off completely in 2013 The average % V for scats within a collection period was also
but several permanent water points remain, either on-park calculated for bilbies. This calculation was to test the assump-
(Mooradonka Waterhole) or immediately off-park. The great- tion that one scat containing bilby remains was equal to one dead
est distance anywhere on park to the nearest permanent water bilby, by recording a high percentage volume of bilby within the
point is approximately 25 km (Fig. 1). scat. It was also assumed that if a bilby was eaten, its remains
would show in the dog scat. Dogs are known to consume
Scat collection approximately 1.4 kg of food per day (Green and Catling 1977 in
The park was divided into 14 areas, 10 of which were searched Newsome et al. 1983). Male and female bilbies weigh, on
for dog scats on up to 17 occasions during 2012–19 (Fig. 2). average, 1–2.5 kg and 0.8–1.1 kg, respectively (Johnson 2013),
Bilbies were known to be present in each of these 10 areas. Five meaning that a dog could consume one bilby per day.
of these areas were checked 11–13 times and the other five were Seasonal differences in the amount of bilby, long-haired rat
checked 7–10 times. Dog scats were distinguished from other (Rattus villosissimus) (hereafter rat), reptile and bird were tested
scats by their shape and size (Triggs 1996). Confirmation that separately using a paired t-test in QED Statistics (Pisces302 Australian Mammalogy J. Augusteyn et al.
140°0⬘0⬙E 140°30⬘0⬙E 141°0⬘0⬙E
Legend
Water points
Bore
Dam
Earth tank
Permanent waterhole
24°0⬘0⬙S
Semi permanent waterhole
25 km buffer around water
Estate boundary
Tracks
Astrebla Downs and Diamantina
National Parks
24°30⬘0⬙S
0 5 10 20 30 Kilometres
140°0⬘0⬙E 140°30⬘0⬙E 141°0⬘0⬙E
Fig. 1. Astrebla Downs National Park and on- and off-park water bodies, with a 25 km buffer drawn around a few of the key water bodies adjacent to the
national park.
Conservation Ltd 2007). We also used a combination of species 2012 and 2015 (13–24%) than after 2015 (44–85%). Bilbies
and broad taxonomic groups (10 taxa listed in Table 1) to were consumed at a higher rate than most other species or broad
perform a simple regression analysis in Excel to test whether taxonomic groups, regardless of the period, and contributed to
the % FO for rats, which was thought to be a measure of resource an average of 84% of the prey volume within scats and 46%
availability, correlated with the diversity of species consumed. volume within a sampling period. No significant seasonal dif-
ferences were found in the portion of scats containing bilby
Rainfall (t ¼ –0.957, d.f. ¼ 5, P . 0.05), rat (t ¼ 0.960566, d.f. ¼ 5,
P . 0.05), reptile (t ¼ –0.16507, d.f. ¼ 5, P . 0.05) and bird
Rainfall and average rainfall data for No2 were obtained from the
(t ¼ –0.27735, d.f. ¼ 5, P . 0.05) remains. Rats were consumed
Scientific Information for Land Owners database (DES 2019) drill
in all periods except winter–spring 2014 and summer–autumn
system (Silo) (http://www.longpaddock.qld.gov.au/silo). Monthly
2015–16 and were the dominant prey (% V) item when con-
rainfall totals were converted to residual rainfall by deducting the
sumed except in winter–spring 2016 when they contributed to
average monthly rainfall from the actual monthly rainfall.
only 1% of prey scat volume. The % FO for rats peaked in
summer–autumn 2016–17 and this coincided with a slight
Results
decrease in the % FO for bilbies (Fig. 3a). A regression analysis
The % FO and % V of prey species and other broad taxonomic comparing the % FO for rats with the diversity of other taxa
groupings are presented in Table 1. Sixteen mammal species and consumed found that dog prey did not vary during resource
several other taxa that could not be identified to species level pulses (y ¼ 0.017x þ 5.5305, R2 ¼ 0.0007), when rats were
were encountered. No foxes were detected but cats were con- relatively more abundant than other groups. Short-tailed mice
sumed, particularly prior to winter 2016. The proportion of dog (Leggadina forresti) were not detected until the summer of 2016,
scats containing bilby peaked in winter–spring 2018, when 233 after which time they were consistently detected, although at a
of the 274 scats (85% FO) collected contained bilby remains. lower frequency and volume than rats. Reptiles were detected in
The average % FO for bilby was consistently lower between every sampling season, occasionally in high frequencies andAstrebla dog scat analysis Australian Mammalogy 303
Legend
Scat collection areas
More than 60% of collection periods
Less than 60% of collection periods
N Not collected from
Park tracks
0 5 10 15 20 Protected area
Kilometres
Fig. 2. Scat collection areas with the frequency that sites were searched.
volumes. For example, in summer–autumn 2015–16 reptiles thought to be one of the key drivers of this variation in predation.
were in 64% of scats and contributed 90% of the prey volume. In the arid zone, populations are known to fluctuate between
Pogona sp. and Varanus sp. were commonly encountered. The boom and bust periods (Predavec and Dickman 1994; Greenville
remaining prey, including large macropods, were consistently et al. 2013). The booms usually follow periods of above-average
found at lower frequencies and volumes across the entire sam- rainfall and the busts occur during droughts when predation
pling period. Rabbits were detected only in winter–spring 2018, and/or starvation cause both prey and predator populations to
when five scats contained a low volume of rabbit (,20%). decline (Carstairs 1974; Newsome and Corbett 1975; Predavec
Between 2012 and 2020, monthly rainfall was above average and Dickman 1994, Pavey et al. 2008; Pavey and Nano 2013;
on 18 occasions. Rainfall was often well below average outside Greenville et al. 2014). Some studies of these boom–bust events
of these periods (Fig. 3b). The 2016–17 period was one of have suggested that both bottom-up (food limited) and top-down
potentially higher resources. (predation) pressures interact to regulate native mammals
(Greenville et al. 2014). The scale and the spatial extent of
Discussion these boom events depend on the amount, location and timing of
the rainfall (authors’ obs.). Sometimes patchy rainfall can result
Impact to bilbies in isolated resource pulses or ‘mini-booms’. At Astrebla, the rats
Australia once supported a diverse assemblage of medium-sized and the vegetation that the rats feed on are some of the primary
marsupials that would have fed dingoes (Caughley et al. 1980; drivers of ecosystem productivity (Rich et al. 2014). Tatler et al.
Johnson 2006; Tatler et al. 2019) and thylacines (Thylacinus (2019) found that rats were encountered 4.5 times more often in
cynocephalus) (Figueirido and Janis 2011). Several dog dietary dog diets sampled during boom periods than during non-boom
studies (Allen and Leung 2012; Doherty et al. 2019; Tatler et al. periods. The results from this study also suggest that, in addition
2019) found that rabbits have effectively replaced the medium- to rats, bilbies may help increase predator populations. Bilbies
sized marsupials that are part of the group known as the ‘critical were consumed throughout the study period but peaked, albeit at
weight range’ species (35–5500 g) (Johnson and Isaac 2009). slightly lower % FO than rodents, during the resource booms,
However, at Astrebla rabbits are rare and the original medium- which is similar to the results of Tatler et al. (2019), who found
sized marsupial, the bilby, is still extant. that the occurrence of medium-sized mammals remained high
This study revealed that the extent of dog predation on during resource booms and sometimes was disproportionate to
Astrebla’s bilby population varied. At times predation was their abundance.
low but occasionally the term ‘hyperpredation’ (Smith and Quin When this study commenced (2012), the bilby population
1996) adequately described the extent. Resource availability is was high, but this changed rapidly and by 2013, the population304 Australian Mammalogy J. Augusteyn et al.
% FO % V % FO % V
25.7
14.2
Vegetation
had declined considerably (authors’ obs.), most likely due to
33
80
80
30
10
33
0
1
0
5
0
0
0
predation by both feral cats and dogs (Rich et al. 2014). High
3.3
2.2
10
4
0
3
3
6
0
6
0
1
0
0
3
rainfall in 2010–11 led to an irruption of rodents on Astrebla and
Table 1. Species %FO and %V for each year and season for the main species encountered and a grouped total for the minor species encountered with number of samples (n)
cat and dog numbers increased (Rich et al. 2014). As rat numbers
8.3
15.0
0
5
0
0
0
1
4
4
21
73
20
12
21
dwindled in 2013, both feral cats and, to lesser extent, dogs
Insect
rapidly switched to bilbies and other small mammals on the park
5.8
5.7
13
21
13
0
6
0
0
0
3
3
3
7
6
(Rich et al. 2014), a phenomenon that was also described by
Letnic and Dickman (2010) and Letnic et al. (2011). Cat
58.2
37.2
%V
33
90
18
64
42
30
50
32
46
59
44
100
8
stomachs sampled in the first week of May 2013 contained
Reptile
almost all rat. A third of the stomachs sampled a few weeks later
% FO
25.8
26.2
5
5
12
64
15
12
29
63
30
33
15
29
26
contained bilby remains (authors’ obs.). The sheer number of cats
at the time, which was considerably higher than the density of
35.0
41.8
%V
51
38
73
90
10
38
21
40
44
0
100
0
0
dogs, suggests that feral cats posed the biggest threat to bilbies.
Bird
But this was compounded by the enlarged dog population and the
% FO
5.0
16.8
6
0
6
0
3
8
0
18
50
10
10
20
11
cats themselves may have contributed a partial food source for
dogs, extending the time that dogs remained in the area. Stokeld
16.7
36.3
%V
100
0
0
0
0
0
0
0
60
20
63
75
64
Wild dog
et al. (2018) found that dingoes are likely to limit the recovery of
Data are pooled according to season (summer–autumn and winter–spring) and year
threatened species populations and management programs that
% FO
0.3
4.2
focus solely on mitigating cat predation may be inadequate in
13
2
0
6
0
0
0
5
0
1
0
0
2
landscapes where other factors such as the provision of water are
48.5
52.7
%V
0
0
0
0
81
78
50
10
90
98
81
100
100
at play and where dingoes can be another predator.
Cat
Despite over 2500 cats and more than 32 dogs being removed
% FO % V % FO
10.7
10.3
from the park between April 2012 and December 2013 (Rich
36
44
18
13
11
9
0
0
0
1
1
0
4
et al. 2014), bilby and kowari numbers dwindled to the point
0.0
1.8
0
0
0
0
0
0
0
0
0
0
0
11
11
where they were undetectable, by the end of 2013 (authors’
Rabbit
obs.). Although the efforts to control predators did not prevent
0.0
0.3
the bilby population crashing, they probably enabled the popu-
0
0
0
0
0
0
0
0
0
0
2
0
0
lation to recover more quickly. Further, the rapid decline in the
29.2
63.2
%V
Macropod
75
79
82
0
0
0
100
0
100
100
0
100
0
bilby population due to predation meant that they probably had
not depleted all the available resources left from the boom and
% FO
1.0
5.3
0
0
0
0
0
3
3
3
6
0
3
13
10
some food (bulbs, seeds, termites) persisted in the soil. Patchy
rainfall midway through 2016 also helped to boost both rodent
Short-tailed mouse Other small mammal
%V
6.3
7.8
and bilby populations and record numbers of bilbies were
33
22
20
25
5
0
0
0
0
0
0
5
0
recorded in 2015–16 (Mitchell 2015; Augusteyn et al. 2020a).
But this boom was short-lived and between 2016 and 2018 bilby
% FO
3.3
4.2
density declined by up to 96% (Augusteyn et al. 2020a, 2020b,
19
16
1
0
0
0
0
0
0
3
6
0
4
unpublished report) (Fig. 3c) and dog predation was implicated
as being the most likely cause. The percentage of dog scats
%V
24.0
17.2
containing bilby increased in winter 2016 (70% FO) and peaked
70
16
39
44
35
43
40
0
0
0
0
0
0
in winter–spring 2018 (85% FO). Cats were actively managed
throughout the entire period by frequent spotlight shoots.
% FO
5.5
9.2
15
22
31
0
0
0
0
0
0
5
9
6
7
Unlike cats, dogs were not controlled between 2014
and 2018. The large bilby population and the presence of rats
% FO % V
61.5
45.5
in 2016–17 are thought to have led to an increase in the dog
85
72
99
10
75
70
46
47
64
74
74
0
0
Rat
population. We speculate that the cause of the 2018 winter and
40.0
23.3
spring hyperpredation event was due to there being more dogs
0
0
5
57
32
47
10
89
77
24
23
16
32
and bilbies and a higher encounter rate between the two species,
77.0
76.3
%V
particularly after the rat numbers dwindled towards the end of
100
68
81
20
90
96
52
84
75
90
77
87
84
Bilby
2017. The % FO for rats peaked in summer–autumn 2016–17
% FO
40.0
46.2
and then declined, suggesting that the rodent population had
13
15
18
14
27
70
50
44
61
85
71
49
43
dropped and/or the dogs shifted their prey preference to other
Sum–Aut avg
Win–Spr avg
species. The lack of rats and other prey meant that bilbies
Sum–Aut
Sum–Aut
Sum–Aut
Sum–Aut
Sum–Aut
Sum–Aut
Win–Spr
Win–Spr
Win–Spr
Win–Spr
Win–Spr
Win–Spr
Seasonal
became the main target and because there was no other readily
Average
period
available food source for dogs to shift to, bilbies were selectively
hunted disproportionately to their population size and bilbies
156
8
274
313
410
723
34
17
11
10
19
39
79
31
45
became scarce. A limitation of our study is that we do not have
n
information on either predator numbers or prey availability,
All years
All years
All years
2012–13
2013–14
2015–16
2016–17
2017–18
2018–19
other than bilby density and general observations made during
2013
2014
2016
2017
2018
2019
Year
line-transect surveys. Therefore, we cannot be confident thatAstrebla dog scat analysis Australian Mammalogy 305
(a) 100 300
90
No of samples Bilby %FO
250
80
Long-haired rat %FO Bilby average
Number of samples
70
200
60
% FO
50 150
40
100
30
20
50
10
0 0
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
(b) 150
100
Residual rainfall (mm)
Residual rainfall
50
0
–50
–100
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
(c) 6
5
Bilby density
Bilbies per km2
4
3
2
1
0
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
Sep
Jan
May
2011 2012 2013 2014 2015 2016 2017 2018 2019 2020
Date
Fig. 3. (a) The % FO for bilby and rat in dog scats collected from Astrebla between 2012 and 2020 and grouped into
season (summer–autumn and winter–spring) and year. Sample size and the average % FO for bilby (43%) for the period are
included. (b) Monthly rainfall deviation from the mean (annual average ¼ 232 mm) (residual rainfall) for the Ingledoon
No2 bore on Astrebla using SILO Data Drill (DES 2019). (c) Astrebla bilby population density, 2014–19 (Augusteyn et al.
2020a, 2020b).306 Australian Mammalogy J. Augusteyn et al.
prey groups were selected relative to their population size. The dog predation even on the open, treeless plains by living in bilby
events described above follow a similar pattern to that observed burrows and in the tree-lined creeks (Rich et al. 2014).
in the early to mid-1990s (McRae 2004). Palmer (1999) and Dogs on Astrebla were not controlled between 1997 and 2012
McRae (2004) both considered dogs to have an impact on bilbies and between 2014 and 2018 and were most likely in stable pack
during the ‘bust’ and during ‘mini-boom’ periods and the results structures. Pettigrew (1993) attributed the invasion of cats in the
from this study agree with these findings. early 1990s to a reduction in dog numbers, even though McRae
Newsome et al. (1983) and Paltridge (2002) described four (2004) disputed this argument, stating that only four dogs were
major prey categories for vertebrate predators including staple, removed and not 50 as suggested. The lack of any dog control in
supplementary, opportunistic and seasonal staples. We suggest the lead up to the more recent 2013 cat/dog plague, suggests that
that bilbies at Astrebla fall into the staple (a food source that cat populations can reach plague proportions in response to an
predators rely upon through time) category because they were abundance of rodents and not because their populations are
encountered in every season sampled. They may also occasion- released from dog predation.
ally represent an opportunistic (during boom periods) food The arid-zone fauna, prior to the introduction of cats and
source when high numbers of bilbies provide an extra resource foxes, would have naturally existed in a constant fluctuation
that enables predator populations to increase. between population booms followed by population crashes. The
change from having one major predator (dingo or thylacine) to
two or three with the introduction of cats and foxes may have
Ecological role been enough to disrupt this cycle to the point where some local
Our results are consistent with several studies (Smith and Quin extirpations have occurred or may occur in the future. Even
1996; Doherty et al. 2019; Tatler et al. 2019) that found that dogs though predation has been considered a major cause of species
have a flexible diet and perform a mixed ecological role. How- decline in general (Finlayson 1961; Woinarski et al. 2014), dogs
ever, unlike other studies (Pavey et al. 2008; Tatler et al. 2019), and, to a lesser extent, cats (1824–86: Abbott 2002), have
the diversity of dog prey did not seem to vary significantly coexisted with native species (Gibson et al. 1994; Fisher et al.
according to resource pulses. This may be because the current 2001; Fisher et al. 2014; Abbott 2002; Fancourt et al. 2015) long
study did not start until the end of the 2011–13 rat plague and dogs before some of the more serious declines were observed in the
had already shifted to other prey groups as rat numbers dwindled. mid-1900s (Burbidge and McKenzie 1989). The reason this
McRae (2004) argued that dogs could be beneficial to bilbies balance has suddenly changed, particularly in areas where foxes
due to their interaction with other feral predators (principally are absent, is largely unknown but Aboriginal peoples may have
foxes). Foxes have not been detected on Astrebla and the lack of persecuted non-commensal dogs (Short et al. 2002). The provi-
rabbits, which are often linked to their spread (Saunders and sion of free water, which has improved the extent and reliability
McLeod 2007), may limit their extent. However, Moseby et al. of palatable grasses (Newsome 1975) and favoured large macro-
(2012) showed that dingoes can kill foxes but do not always eat pods, introduced stock and rabbits (James et al. 1999; Corbett
them and therefore the analysis of scats is not a reliable indicator 2001; Fensham and Fairfax 2008; Davies et al. 2010; Allen 2011)
of fox and dog interactions. Southgate et al. (2007) found that and provided breeding opportunities for dogs and other species
foxes prefer habitats that contain rock features and calcareous (Thomson 1992; Short et al. 2002) may have shifted the balance
substrates, which are largely absent from Astrebla. Foxes are in favour of dogs. Large macropods and rabbits are, however,
able to survive without free water, but their daily movement is normally rare at Astrebla and movement data from a study
restricted to only a few kilometres per day (Coman et al. 1991; conducted in the Strzelecki Desert found that dogs regularly
Southgate et al. 2007) which might be problematic at Astrebla. It went 3–5 days without water and were capable of walking
may mean that the park is unsuitable for foxes except possibly approximately 150 km without visiting any water for 22 days
after flood events. Brawata and Neeman (2011) found that at (Allen 2012). This suggests that most parts of Astrebla would be
sites where dogs were uncontrolled, foxes were less likely to be well within reach of the natural waterholes that existed prior to
found within 5 km of water, suggesting that dogs limit fox European settlement and that neither prey increases nor water for
populations. However, this hypothesis does not account for the drinking are likely to be important on the park. However,
few periods when flooding rain creates multiple semipermanent Thomson (1992) found that nearly half of dog dens were located
waterpoints across the landscape and when foxes are still not within 500 m of water and only 19% were more than 2.5 km from
detected on the park. We suggest that more work needs to be a known water source, suggesting that increasing the number of
conducted to determine whether dogs and/or the lack of suitable artificial water sources on neighbouring properties may have
habitat/water are the reasons that foxes are absent from the park. increased the amount of dog breeding and predation on Astrebla.
Dogs were observed hunting cats and scavenging from piles Changes to the livestock industry, with properties grazing
of cat carcasses (authors’ obs.) and this may have contributed to cattle instead of sheep, going organic and/or being used to fatten
the high % FO for cats found in dog scats collected in 2013. cattle instead of breeding (Phelps 2007), are changing the way
Palmer (1999) found 1% FO of dog scats contained cat remains. dogs are being managed (van Eeden et al. 2019). The introduction
Tatler et al. (2019) found that dogs preyed on feral cats and of organic farming, particularly since the mid-1990s (Wynen
suggested that they form an important part of their prey. While it 2006; Phelps 2014), may limit the capacity of landholders to
is possible that dogs may regulate cat numbers or interfere with manage dogs using sodium monofluoroacetate (1080). The
their habitat use, the evidence from the 2013 boom suggests that increased weight and size of the herd potentially reduces the
dogs have very little influence on cat numbers or behaviour impact that dogs can have and consequently the need for graziers
when resources are plentiful. Cats were able to avoid or escape to manage dogs. This shift potentially means that dog numbers areAstrebla dog scat analysis Australian Mammalogy 307
increasing over large areas of land surrounding Astrebla. The lack shot and an additional 16 dogs were baited with 1080 (Rich
of grazing on both Astrebla and the nearby Diamantina National 2018). Cats were also controlled during spotlight shoots. In
Park also means that there are more resources on the parks for 2019, rainfall combined with the predator control possibly
native mammals (Palmer 1999) and food for dogs. Wallach et al. enabled the bilby population to recover by 78% compared with
(2009) found that dog control led to their populations being 2018 (Augusteyn et al. 2020b). These results suggest that con-
socially fractured and fluctuating between below and above trolling predators before their numbers build up is an effective
carrying capacity. Without control, dogs existed at carrying strategy in years following average to slightly above average
capacity and were socially stable. The change of management rainfall. The timing of predator control depends on the size of the
from dog control to no control on neighbouring lands at Astrebla boom and the extent of the bust. During boom years Pavey et al.
may mean that dogs are transitioning from a socially fractured to a (2014) and Yip et al. (2015) suggested waiting until the bust
recovered state. However, the rapid fluctuation in the carrying before attempting control. However, the evidence from the
capacity of the land, as conditions oscillate between boom and 2011–13 boom suggests that the transition from boom to bust
bust, may mimic the impact of control and hinder the recovery and the subsequent shift in prey can occur rapidly, leaving
process, thereby causing the dog population to remain above little time to effectively reduce predator numbers. Letnic and
carrying capacity and socially fractured. The combination of Dickman (2006) also found that predators had their strongest
higher dog populations, other feral predators and changes to dog impacts on native mammals in the 1–2 years following very high
management practices are potentially what is causing the decline rainfall and considered this time to be the most critical for
and/or extinction of some threatened species populations (Allen wildlife managers. Palmer (1999) considered dogs to have the
and Fleming 2012). greatest impact on bilbies during droughts and data from this
study suggest that controlling dogs during the bust period has
Seasonality merit. We therefore recommend that for major booms control
commences before predator numbers build and continues until
Being able to predict when predators are likely to target a threat-
predator populations are reduced to the point where they are not
ened species enables managers to be more strategic and more
impacting threatened species. For ‘mini-booms’ predator con-
efficient, and potentially reduce the extent of some of the large
trol could occur when predators increase their preferences for
fluctuations that have occurred in the bilby population at Astrebla
bilbies. Predator control is also recommended during droughts
in the past. The type and amount of prey consumed is generally
and periods of low resource availability, particularly if they
thought to be dependent on the abundance of the prey relative to
immediately follow a resource pulse.
other prey items (Paltridge 2002; Pavey et al. 2008). However, for
Regardless of whether dogs do or do not regulate mesopreda-
favoured prey this may continue to the point where it is no longer
tors at Astrebla, the extremely high % FO for bilby observed
in proportion with prey abundance (Robertshaw and Harden
during this study suggests that dogs are major predators of bilbies
1986). Understanding different predator–prey cycles and how
such that the impact of predation outweighs any potential benefit
abiotic factors drive these cycles is critical to enable targeted
afforded through mesopredator regulation. We therefore consider
intervention without the need for large-scale, onsite population
that it is appropriate at times to reduce both cat and dog popula-
studies each time. In the arid zone, rainfall is considered to be the
tions, such as during seasonal boom–bust resource cycles, when
main driver of ecosystem productivity (Dickman et al. 1999;
dog populations are high, or they are likely to be targeting bilbies.
Morton et al. 2011; Read et al. 2012; Greenville et al. 2016) but
The capacity of the Astrebla population to recover from a major
evaporation rates and temperature may also be important. The lack
predation event also highlights the resilience of the population
of a significant seasonal difference in the % FO for bilby, rat,
and that it is possible to maintain a healthy population without
reptile and bird was surprising. Predation was expected to be
having to resort to expensive predator-proof fences.
greater for mammals in winter than for reptiles, which are usually
less active when conditions are cool (Greer 1989; Paltridge 2002).
The lack of seasonal difference could be due to the broad seasonal Conflicts of interest
categories used in the analysis (summer–autumn and winter– The authors declare no conflicts of interest.
spring), both of which include warm periods. These categories
were chosen to increase the number of the samples and to pick up Acknowledgements
the influence of rain, which usually falls during summer. How- Thanks to all the Queensland Parks and Wildlife Service staff and volun-
ever, the study was punctuated by above-average rainfall in winter teers, including the Conservation and Wildlife Management personnel from
2016. Grass seed production and germination (temperatures must Sporting Shooters Association of Australia for helping to collect scats.
exceed 158C: Orr 1975) and the rats may not have been able to Thanks go to Rhonda Melzer, Marnie Augusteyn, Ross Goldingay and the
respond to the rain until the following summer, which caused a lag two anonymous reviewers for their comments on earlier drafts and to
in the results. We suggest that more work is required to model seed Anthony Pople, Alistair Melzer and Graeme Armstrong for their assistance
production of Mitchell grass and the mechanism by which rats with the data analysis. This research did not receive any specific funding.
reach both plague and subplague proportions to better predict
when predator control is likely to be required. References
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