Feral cats on Rakiura Stewart Island: population attributes and potential eradication tools

As a major threat to New Zealand’s biodiversity, feral cats (Felis catus) are the subject of planned eradications on a number of offshore islands, including Rakiura Stewart Island. We used camera traps to estimate population density of feral cats on the north-east coast of Rakiura, and to investigate their movement behaviour and detection probability. We also used camera footage to compare the consumption of two types of non-toxic sausage baits (chicken and rabbit) with a view to future use of toxic baits. Population density of feral cats was likely between 1 and 2 cats per km². Non-target species (rats and possums) removed more than half the baits, greatly reducing bait availability for feral cats. Deer and birds (including kiwi) encountered baits but did not eat them. Cats had an apparent preference for chicken over rabbit baits, although small sample sizes prevent firm conclusions. Both bait types appeared to decline rapidly in palatability, and no baits were consumed by cats more than 5 days after deployment. Future trials and baiting regimes should consider ways to improve bait availability. Increased bait density, exclusion of rats and possums and/or more frequent replacement of baits will likely increase encounter rates by feral cats.