Stable Isotope Analysis Reveals Feral Cat Diet on the Chatham Islands

Implications for the World’s Rarest Seabird, Pterodroma Gagentae

Abstract

Feral cats are significant invasive predators in New Zealand and are widely associated with drastic declines in breeding seabird populations. Suppressing or controlling feral cat populations has been a major conservation focus in large island ecosystems, including Rēkohu (The Chatham Islands). The Chatham Island tāiko (Pterodroma magentae) naturally persists in a single breeding colony after experiencing rapid population declines in the 19th & 20th centuries. A deeper understanding of feral cat ecology and diet is required to ensure control methods maximise conservation benefits. We used stable isotope analysis of feral cat fur, claws, and bone collagen to investigate the ecology and diet of feral cats trapped in the Tuku Nature Reserve on Rēkohu (The Chatham Islands). We predicted that cat diet would be highly specialised among individuals but relatively stable over time. To estimate the relative contribution of available prey to feral cat diets we employed Bayesian mixing models. Standard ellipse areas were used to understand diet stability over time. Our results have implications for the ongoing management of the Chatham Island Taiko.

Supervised by: Cilla Wehi