Does the foraging ecology of feral cats change after the eradication of foxes?

Invasive species control has resulted in unintended consequences where the control of one species causes increased impacts of a co-occurring species. Red foxes ( Vulpes vulpes ) and feral cats ( Felis catus ) co-occur throughout Australia—with control and regulation of fox’s commonplace, a greater understanding of how feral cats will respond in the absence of foxes is needed. In this study we use feral cat diet to assess potential prey switching after red fox control. Feral cat stomach contents were sampled between 1983 and 1994 on Phillip Island, Victoria, Australia when both feral cats and red foxes were abundant; and again from 2016 to 2019 when foxes were eradicated. A total of 277 feral cats were sampled between 1983–1994 and 415 from 2016 to 2019. Although we did not track feral cat diet throughout the red fox decline, diet comparisons between the two time periods suggest no substantial shift in feral cat diet with only slight increases in invertebrates and black rats observed. Invasive prey (European rabbits, black rats, and house mice) still formed the majority of feral cat diet. We further reinforce the role of seasonality, surrounding land use and sex as factors influencing cat diet. Our results suggest red fox control in the presence of cats may still achieve conservation benefits with feral cats maintaining a comparable diet, dominated by invasive species, despite fox control—though this may be context dependent. Given the abundance and frequency of invasive prey species within cat diet, we further support the idea that invasive prey control could be a viable indirect method to control the impacts of feral cats.