Problematic cats in urban reserves: Implications for native biodiversity and urban cat management

Predation by domestic cats ( Felis catus ) contributes to the extinction and decline of native species worldwide. Managing these cats is challenging in urban environments because they are valued as companion animals. We quantified cat behaviour in six urban reserves with high biodiversity values across the three largest New Zealand cities using camera traps, in an effort to understand cat impacts on urban biodiversity. Individual cats were identified and their detection rates and diel activity patterns analysed. To assess cat impacts on ground nesting birds, we also monitored the nests of the endangered northern New Zealand dotterel ( Charadrius obscurus aquilonius ). The minimum number of cats intruding into the reserves was high (ranging from 7 cats in 8 ha to 98 cats in 70 ha), and cats were active both day and night. Behaviour varied greatly among individual cats. Some cats intruded much more frequently than others, and these were the only individuals preying on native birds. One cat visited dotterel nests every night. Hatching or fledging failed at all the nests that were visited by this cat, even though the nests were not depredated. Our study shows that some cats impact native species more than others, and that identifying and targeted management of these problematic cats could be an effective approach if management of the general population is not feasible. The densities of domestic cats that allow native wildlife to thrive in urban environments is a significant knowledge gap that needs to be addressed.