The diet of foxes in the Grampians (Gariwerd) National Park

Invasive mammalian predators are among the greatest threats to global biodiversity. Studying an invasive predator’s diet can inform evidence-based management by providing an insight into the species which they may threaten, and the persistence and distribution of their prey. In Australia, red foxes (Vulpes vulpes) have contributed to many extinctions and species declines, most of which have occurred in mammals in the critical weight range (i.e., 35g to 5.5kg). We studied the diet of foxes in the Grampians (Gariwerd) National Park, a large conservation reserve with important biodiversity values in south-eastern Australia. We collected scats using three approaches; (i) systematic transects; (ii) opportunistic surveys undertaken by Parks staff, and (iii) surveys using trained scat detection dogs. Scat contents were identified by an expert. We calculated the frequency of occurrence and proportion of volume of each food item in the sample. We used permutational analysis of variance to assess relationships between environmental variables and diet composition and logistic regression to identify relationships between the occurrence of food items and these variables. Systematic transects and opportunistic surveys returned very few scats, but the detection dog searches were highly effective, which demonstrated their great potential in diet studies. Fox diet in the park is dominated by native mammals, particularly swamp wallabies (Wallabia bicolor). Four threatened species were detected in their diet: brush-tailed rock wallaby (Petrogale penicillata), long-nosed potoroo (Potorous tridactylus), southern brown bandicoot (Isoodon odesulus) and heath mouse (Pseudomys shortridgei). The location of scats containing rock wallaby remains may provide evidence of previously unknown populations. We found evidence of relationships between latitude and distance from the park boundary and overall diet composition and the occurrence of some species in their diet.