Résumé
Cats (Felis catus) introduced on islands have strong impacts on biodiversity, and the main conservation actions to protect native fauna is cat eradication or control (i.e., regular culling). The situation is more complicated on inhabited islands because unowned cats coexist with owned cats. The social acceptance of cat control implies separating the impacts of unowned and owned cats. We investigated the spatial ecology and impacts of owned and unowned cats at a seabird colony in a periurban area on Reunion Island (Indian Ocean). We used multiple methodologies to investigate this question: GPS-tracking of cats, camera-traps at seabird nests, cat scat analysis and cat control. Owned cats had small home ranges and did not forage at the seabird colony. Unowned cats had larger home ranges and foraged at seabird colony. We identified two kinds of unowned cats, stray cats and semi-feral cats. Stray cats relied on food waste and rarely foraged at seabird colony. Semi-feral cats foraged mostly in natural habitats, including the seabird colony and rarely used food waste. Semi-feral cats were very active at the seabird colony and several preyed upon seabirds. Restaurants are an abundant source of food for cats and help sustain populations of unowned cats. Control of unowned cats during this study resulted in reduced cat activity at the seabird colony. To minimize negative impacts of cats on seabirds, our results suggest that the most effective strategy includes the permanent control of unowned cats, efficient management of food waste and sterilization of owned cats.