Anthropogenic foods sustain free-roaming cats on a Mediterranean island, but neutering reduces wild bird consumption

The domestic cat Felis catus is a predator, variously regarded as a pet, pest or pest controller, making its management ecologically and socially complex. On islands, wildlife predation by cats is a major conservation concern. Knowledge of the ecology of free-roaming cats is essential for identifying the variables that influence their predatory behaviour, for regulating their populations and for controlling their negative effects. We assessed the seasonal diet of free-roaming cats, including the importance of anthropogenic foods, using stable isotope analysis, on Linosa. This small Mediterranean island is home to the largest Scopoli's shearwater Calonectris diomedea colony in Europe and an important stop-over site for migratory passerines. We also compared the diet of neutered and unneutered cats, to investigate whether differences in husbandry practices influence consumption of wild prey. Cat diets mainly comprised anthropogenic foods during summer and autumn. Consumption of Scopoli's shearwaters increased during the early chick-rearing period and shifted towards passerines during the autumn migration. Invasive mammals in cat diets were primarily European rabbits Oryctolagus cuniculus. Unneutered cats consumed more shearwaters and passerines than neutered cats. Neutered individuals relied more heavily on pet foods rather than pasta, possibly indicating improved husbandry conditions. Overall, anthropogenic foods likely support the high cat densities observed on Linosa, and wild prey consumption, primarily by unneutered cats, fluctuated according to availability. Free-roaming cats are protected by Italian Law 280/91, and their populations can be managed only with non-lethal methods. Enhanced cat husbandry and compulsory reproductive control via neutering combined with adoptions could significantly reduce consumption of wild prey.