How does a carnivore guild utilise a substantial but unpredictable anthropogenic food source? Scavenging on hunter-shot ungulate carcasses by wild dogs/dingoes, red foxes and feral cats in south-eastern Australia revealed by camera traps

Abstract

There is much interest in understanding how anthropogenic food resources subsidise carnivore populations. Carcasses of hunter-shot ungulates are a potentially substantial food source for mammalian carnivores. The sambar deer (Rusa unicolor) is a large (≥ 150 kg) exotic ungulate that can be hunted throughout the year in south-eastern Australia, and hunters are not required to remove or bury carcasses. We investigated how wild dogs/dingoes and their hybrids (Canis lupus familiaris/dingo), red foxes (Vulpes vulpes) and feral cats (Felis catus) utilised sambar deer carcasses during the peak hunting seasons (i.e. winter and spring). We placed carcasses at 1-km intervals along each of six transects that extended 4-km into forest from farm boundaries. Visits to carcasses were monitored using camera traps, and the rate of change in edible biomass estimated at ∼ 14-day intervals. Wild dogs and foxes fed on 70% and 60% of 30 carcasses, respectively, but feral cats seldom (10%) fed on carcasses. Spatial and temporal patterns of visits to carcasses were consistent with the hypothesis that foxes avoid wild dogs. Wild dog activity peaked at carcasses 2 and 3 km from farms, a likely legacy of wild dog control, whereas fox activity peaked at carcasses 0 and 4 km from farms. Wild dog activity peaked at dawn and dusk, whereas nearly all fox activity occurred after dusk and before dawn. Neither wild dogs nor foxes remained at carcasses for long periods and the amount of feeding activity by either species was a less important predictor of the loss of edible biomass than season. Reasons for the low impacts of wild dogs and foxes on sambar deer carcass biomass include the spatially and temporally unpredictable distribution of carcasses in the landscape, the rapid rate of edible biomass decomposition in warm periods, low wild dog densities and the availability of alternative food resources.

Figure 1. Mean (± SE) estimated bi-monthly harvests of sambar deer in Victoria, south-eastern Australia, 2009−2013.

Data are summarised from references 54−58.

Figure 2. Location of the study in the North East region of Victoria, south-eastern Australia.

Red squares indicate the location of sambar deer carcasses along the six transects. The ‘×’ in the inset indicates the location of the Upper Yarra Ranges National Park, where carcasses were obtained.

Figure 3. Carnivores feeding on sambar deer carcasses.

(a) Wild dog; (b) fox; (c) feral cat. Note the second camera trap on the tree in the background of (a).

Figure 4. Visits and behaviours of wild dogs, foxes and feral cats at sambar deer carcasses

. Behaviours are defined in Materials and Methods.

Figure 5. Daily activity patterns of wild dogs and foxes at sambar deer carcasses.

(a) Mean total daily activity by wild dogs and foxes, with the inner and outer circles indicating 5 and 10 minutes, respectively. (b) Feeding, investigating and moving through behaviours of wild dogs, with the inner and outer circles indicating 5% and 10% of time, respectively. (c) Feeding, investigating and moving through behaviours of foxes, with the inner and outer circles indicating 5% and 10% of time, respectively.

Figure 6. Seasonal relationship between days to first carcass visit by wild dogs and distance to farm.

Medians and 95% highest posterior density interval bounds are shown for the winter and spring seasons.

Figure 7. Expected daily probability of a wild dog visiting a sambar deer carcass.

Probabilities are medians from the posterior distribution with average edible biomass.

Figure 8. Expected daily probability of a wild dog visiting a carcass as a function of edible biomass.

Expected probabilities are medians from the posterior distribution at a carcass 2/or fox.

Figure 9. Expected daily probability of a fox visiting a carcass as a function of distance to farm.

Expected probabilities are medians from the posterior distribution with average edible biomass and are shown for all combinations of season and the previous presence of wild dog and/or fox.

Figure 10. Expected daily probability of a fox visiting a carcass as a function of edible biomass.

Expected probabilities are medians from the posterior distribution at a carcass 2/or fox.

Figure 11. Temporal changes in the edible biomass of carcasses as a function of season and carnivory.

The effects of feeding by wild dogs and foxes are illustrated by including 180(136 minutes) and foxes (154 minutes) spent feeding at a carcass and enabled the effects of foxes to be visible.