CSIRO PUBLISHING
Wildlife Research, 2007, 34, 342–351
www.publish.csiro.au/journals/wr
Diet of a native carnivore, the spotted-tailed quoll (Dasyurus maculatus), before and after an intense wildfire James P. Dawson A,E, Andrew W. Claridge B, Barbara Triggs C and David J. Paull D A
Department of Environment and Climate Change, Biodiversity Conservation Section, Metropolitan Branch, PO Box 1967, Hurstville, NSW 2220, Australia. B Department of Environment and Climate Change, Parks and Wildlife Group, Southern Branch, PO Box 2115, Queanbeyan, NSW 2620, Australia. C ’Dead Finish’, via Genoa, Vic. 3891, Australia. D School of Physical, Environmental and Mathematical Sciences, University College, University of New South Wales, Australian Defence Force Academy, Northcott Drive, Canberra, ACT 2600, Australia. E Corresponding author. Email:
[email protected]
Abstract. The relationship between the diet of the spotted-tailed quoll (Dasyurus maculatus) and the abundance of its prey was investigated in rain-shadow woodland habitat in southern New South Wales for one year before and two years after a high-intensity, broad-scale wildfire. Scats were variously collected from quoll latrines and live-trapped animals during winter for each of the three years and analysed to determine prey items. Estimates of abundance of key grounddwelling and arboreal medium-sized mammals were simultaneously obtained using plot-based survey techniques and spotlighting. Over the duration of the study, quoll diet was dominated by medium-sized mammals, particularly brushtail possums (Trichosurus spp.) and lagomorphs (rabbit and hare), followed by small and large-sized mammals. After the fire there was a shift in utilisation of food resources in response to significant changes in prey availability. Monitoring revealed that brushtail possums, lagomorphs and bandicoots were all significantly less abundant in the winter following the fire, and populations of lagomorphs, but not possums, then increased in the second winter after the fire. Quolls adapted to this by taking significantly more lagomorphs in each of the two years after the fire and by taking advantage of a short-term increase in the availability of carrion. The results of this study reaffirm that the spotted-tailed quoll is adaptable in its utilisation of available food, and that fires are not necessarily detrimental to the species and its prey base.
Introduction The need to understand the effects of fires, including frequency, intensity and spatial patterns, on habitat structure, food resources and den sites of the spotted-tailed quoll (Dasyurus maculatus) and other large dasyurids has been previously recognised (Jones et al. 2003). A primary concern has been that fires, including wildfire and low-intensity management burns, remove vegetative cover, destroy hollow logs and trees that are used by spottedtailed quolls and their prey for cover or refuge, and lower prey abundances to the detriment of resident quoll populations (Jones et al. 2003; Belcher 2004). These views no doubt arise from the fact that high-intensity wildfires directly kill many animals and usually result in dramatic changes to structure of habitat (Newsome et al. 1975; Catling 1991; Coops and Catling 2000). However, longer-term studies (Newsome et al. 1983; Catling et al. 2001) indicate that, contrary to this belief, wildfires may not be as destructive to fauna as previously thought. The spotted-tailed quoll is a solitary, opportunistic predator of predominantly vertebrate prey (Settle 1978; Belcher 1995; Jones 1997). Dietary studies have shown the species to be primarily a predator of medium-sized mammals (500–5000 g) (Belcher 1995, 2000; Jones and Barmuta 1998; Burnett 2001; Glen 2005). Although a reliance on one or two medium-sized © CSIRO 2007
mammal species appears to be consistent across diet studies, different habitats provide different primary prey resources (Belcher 1995; Jones and Barmuta 1998; Belcher 2000; Burnett 2001; Glen 2005). In this study, the winter breeding-season diet of a population of the spotted-tailed quoll was investigated in dry rain-shadow woodland habitat for one year before and two years after a highintensity, broad-scale wildfire. The collection of spotted-tailed quoll scats both before and after the fire provided an opportunity to examine the ecological response of the species and its prey in a greatly altered habitat. Dietary response of the spottedtailed quoll to fire has not previously been examined. Study area and methods Study area The study was undertaken within the catchment of the Jacobs River and its lower tributaries, Ingebirah Creek and Thatchers Mountain Creek, in the Byadbo Wilderness Area of southern Kosciuszko National Park, ~40 km south of the town of Jindabyne, southern New South Wales (Fig. 1). The 4000-ha study area, which has previously been described by Claridge 10.1071/WR05101
1035-3712/07/050342
Quoll diet before and after wildfire
et al. (2004, 2005), has an elevation range from ~300 m along the Snowy River up to 900 m in the north-east. The Byadbo Wilderness Area is in a rain-shadow created by its proximity to the Great Dividing Range that rises directly to the west. Mean annual rainfall is less than 600 mm. The major vegetation alliance in the study area is a dry community of white box (Eucalyptus albens) and tall white cypress pine (Callitris glaucophylla) woodland below 650 m, with a strong altitudinal gradient that comprises yellow box (E. melliodora) woodland above 650 m, grading through long-leaved box (E. nortonii) woodland to mountain gum (E. dalrympleana) open forest above 950 m. Fire The fires of January and February 2003 variously affected over 1.5 million hectares of land in New South Wales, Victoria, and the Australian Capital Territory (DEC 2004). While the area affected by fire was extensive, its intensity was patchy (Mansergh et al. 2003). Fire severity in Kosciuszko National Park was mapped by the Department of Environment and Conservation (NSW) in 2003 on the basis of measuring the impact of fire on different vegetation types. Impact mapping utilised Landsat imagery by measuring the change of a derived normalised burn ratio (NBR) between images taken before and after fire (T. Barrett, DEC NSW, pers. comm., 2003). Changes in the normalised burn ratio are influenced by a decrease in aboveground green biomass and vegetation cover, increased char and consumption of fuels, an increase in exposure of mineral soil and ash, a change to lighter-coloured soil and ash, and decreasing moisture content (T. Barrett, DEC NSW, pers. comm., 2003). The fire in the Jacobs River study area resulted in a very high impact, indicating that it was a fire of very high intensity
Wildlife Research
343
(Fig. 2). In the northern two-thirds of the study area, the fire completely removed ground layer, mid-storey and canopy vegetation, incinerating all logs and resulting in the loss of large numbers of hollow-bearing trees. Evidence of the death of large numbers of mammals was apparent soon after the fire, with carcasses of small mammals, possums, rabbits, wallabies, kangaroos, wombats and horses found within the study area (J. Dawson, pers. obs.). Some smaller vegetation patches in the southern section of the study area were impacted less severely, to a moderate level (partial canopy scorch, with the upper canopy remaining green), while some very small patches could be categorised as low impact (canopy intact but the understorey burnt). Scat identification and collection Scats were collected from 90 individual latrine sites located during the study as well as from live-trapped animals (Dawson 2005). Latrines were identified during searches of the study area that targeted rock outcrops and rocky riparian corridors (Claridge et al. 2004; Dawson 2005). Scats of the spottedtailed quoll were identified in the field based on a combination of size, shape, smell, composition and locality (Triggs 1996). The period of collection was between late April and early September for three consecutive years (2002–04), coinciding with the winter breeding season (Edgar and Belcher 1995; Jones et al. 2001), a time of year at which deposition of scats at latrines is thought to peak (Belcher 1995). Each scat collected from a latrine was treated as one sample, as was all scat material found in a trap at the time of a live-capture. A limitation of this method is that the number of scats produced per meal by quolls is unknown (Jones and Barmuta 1998) and the captive feeding trials required to determine this figure
Fig. 1. Location of the Jacobs River study area (boxed) and sites of additional spotlight surveys at Paupong and Devils Hole Creeks, in the Byadbo Wilderness Area, Kosciuszko National Park, New South Wales, Australia.
344
Wildlife Research
(e.g. Floyd et al. 1978; for wolves) have not been carried out. Scats were individually placed in labelled, brown paper soilsample envelopes. Identification of prey from scats Identification of mammalian prey was undertaken by microscopic identification of undigested hair and bone matter by established techniques (Brunner and Coman 1974). Identification was provided to species level where possible and genus level where distinguishing species was difficult, although probable identifications were used in some cases. This most often occurred with brushtail possums (Trichosurus spp., most likely the common brushtail possum T. vulpecula) and rats (Rattus spp., most likely R. rattus or R. fuscipes), groups for which distinction to species level has been shown to be unreliable for even highly experienced practitioners (Lobert et al. 2001). Rabbit (Oryctolagus cuniculus) and European brown hare (Lepus capensis) were lumped into a single prey group (lagomorphs) for the purposes of dietary analysis. Non-mammalian prey was grouped, respectively, as bird (feathers), reptile (scales), insect or plant (seeds). Multiple prey items in individual scats were listed where detected (up to two), as was the presence of groomed quoll hairs.
Fig. 2. fires.
Fire impact map for the Jacobs River study area from the 2003
J. P. Dawson et al.
Abundance indices for primary medium-sized prey Estimates of abundance of medium-sized terrestrial mammal prey species were derived for the study area over each of the three years from plot-based activity counts. Animal signs were located by searching the ground over circular plots of 10 m radius from a randomly selected point. The occurrence of bandicoots was determined by the presence of their distinctly conical forage-diggings, considered to be the most efficient way to survey for these animals (Claridge and Barry 2000). This technique was also adapted for use in assessing the presence of lagomorphs, determined from the presence of distinctive scrapes, pellets and burrows. Prior to the fire in 2002, 90 randomly selected plots were surveyed, while 90 and 86 plots were surveyed, respectively, in the two post-fire years of 2003 and 2004. Estimates of abundance of arboreal mammals were obtained using spotlight counts. As spotlight surveys were not carried out in the Jacobs River study area before the fire, an estimate of abundance of possums in the rain-shadow woodland habitat was obtained through surveys conducted in nearby unburnt areas. These included the catchments of Paupong Creek and Devils Hole Creek, ~15 km and ~20 km to the east of the Jacobs River study area respectively (Fig. 1). These sites are linked to the Jacobs River study area across an unfragmented landscape with rain-shadow woodland habitat and contained the nearest area of that habitat that had not been burnt. While it is likely that the abundance of possums in this large area of contiguous habitat would be similar, the use of these alternative sites to provide a pre-fire estimate of possum abundance in the Jacobs River study area is a significant limitation in the interpretation of the results. Spotlight surveys at Jacobs River were undertaken over three nights in September 2003 and then again in May and June 2004. Surveys in unburnt habitat were conducted over three nights between April and June 2004. All surveys commenced at least 30 min after darkness and were conducted by a single observer (J. Dawson). Transects were 500 m long and conducted either on foot or from the back of a vehicle travelling 5.0 kg; medium-sized mammals 0.5–5.0 kg; and small mammals 99%). Medium-sized mammals were the most common prey category at 74% occurrence and 87% biomass. Small mammals were the second most common prey group (16% occurrence), followed by large mammals (8% occurrence). Other prey items (birds, reptiles, insect and plants) made up the balance (7% occurrence). There was a significant difference in the composition of the diet by major prey category (small mammal, medium-sized mammal, large mammal, other) across the years of the study (χ2 >30, d.f. = 6, P < 0.001), indicating a shift in utilisation of food resources by quolls (Table 2). To examine where and when these shifts occurred, each of the major prey categories and, where sample sizes allowed, individual prey species and groups, were further assessed. Medium-sized mammals Over the three winter breeding seasons medium-sized mammals were the most common prey category by both occurrence and biomass. However, the contribution of medium-sized mammals to quoll diet varied significantly across the three years of the study (χ2 = 14.47, d.f. = 2, P < 0.001), with percentage occurrence increasing throughout (Table 2). The composition of the medium-sized mammal component of the diet also differed sig-
346
Wildlife Research
J. P. Dawson et al.
nificantly across the three years of the study (χ2 >30, d.f. = 4, P < 0.001). Brushtail possum was the most important prey item in all three years of the study on both a frequency-of-occurrence and percentage-biomass basis (Table 2). The frequency of occurrence of brushtail possum in the diet of quolls was significantly different across the three winter breeding seasons (χ2 = 27.01, d.f. = 1, P < 0.001), declining each year from 2002 through to 2004. The decline was not uniform, as quolls ate significantly more brushtail possums before the fire in 2002 than afterwards in 2003 (χ2 = 10.48, d.f. = 1, P = 0.001). There was no significant difference in the amount of brushtail possums in quoll scats between the two post-fire breeding seasons of 2003 and 2004 (χ2 = 0.54, d.f. = 1, P = 0.464). Lagomorphs were the second most important prey resource for quolls in this study. The frequency of occurrence of lagomorphs in scats was highly significantly different across the three years (χ2 >30, d.f. = 2, P < 0.001) (Table 2). In 2002 lagomorphs were only the third most frequently occurring prey item, Table 1.
Items identified in scats of the spotted-tailed quoll collected from the Jacobs River study area 2002–04
N Small mammals Rattus rattus R. fuscipes Antechinus agilis Mus musculus Petaurus breviceps Rattus sp. A. swainsonii Cercatetus nanus Acrobates pygmaeus Total Medium-sized mammals Trichosurus sp. Oryctolagus cuniculus/ Lepus capensis Perameles nasuta Pseudocheirus peregrinus Dasyurus maculatus Petauroides volans Ornithorhynchus anatinus Felis catus Hydromys chrysogaster Total Large mammals Wallabia bicolor Macropus giganteus Vombatus ursinus M. rufogriseus Total Other Bird Insect Plant Reptile Total D. maculatus (grooming)
All years (1466 scats) % occurrence % biomass
133 28 23 18 13 6 5 4 1 231
9 2 2 1 1
