Density and home range of feral cats in north-western Australia

Context. Feral cats (Felis catus) pose a significant threat to biodiversity in Australia, and are implicated in current declines of small mammals in the savannas of northern Australia. Basic information on population density and ranging behaviour is essential to understand and manage threats from feral cats. Aims. In this study, we provide robust estimates of density and home range of feral cats in the central Kimberley region of north-western Australia, and we test whether population density is affected by livestock grazing, small mammal abundance and other environmental factors. Methods. Densities were measured at six transects sampled between 2011 and 2013 using arrays of infrared cameras. Cats were individually identified, and densities estimated using spatially explicit capture-recapture analysis. Home range was measured from GPS tracking of 32 cats. Key results. Densities were similar across all transects and deployments, with a mean of 0.18 cats km(-2) (range = 0.09-0.34 km(-2)). We found no evidence that population density was related to livestock grazing or abundance of small mammals. Home ranges of males were, on average, 855 ha (+/- 156 ha (95% CI), n = 25), and those of females were half the size at 397 ha (+/- 275 ha (95% CI), n = 7). There was little overlap in ranges of cats of the same sex. Conclusions. Compared with elsewhere in Australia outside of semiarid regions, feral cats occur at low density and have large home ranges in the central Kimberley. However, other evidence shows that despite this low density, cats are contributing to declines of small mammal populations across northern Australia. Implications. It will be very difficult to reduce these already-sparse populations by direct control. Instead, land-management practices that reduce the impacts of cats on prey should be investigated.