Cat predation on Stewart Island

Three years of census work by the Yellow-eyed Penguin Trust has suggested that penguins may be in decline on Stewart Island. The cause and rate of this decline are not known, but feral cats are suspected to play a role because they are the only land-based predator on Stewart Island large enough to kill a penguin. The decline does not appear to be food related, as surveyed pest-free islands have healthier penguin populations.

Feral cats on Stewart Island were introduced from Europe. Early European settlers brought cats to New Zealand from 1769 onward, as a control agent on rat infested ships. However, it may have taken around fifty years for a feral population to become established on the mainland. Ships have visited Stewart Island since 1804, and in 1909 Cockayne reported cats to be “common”.

There is no evidence that they grow any larger than cats which live in a domestic setting. Male cats on Stewart Island average 3.4 kg and females 2.6 kg. Cats are efficient predators and hunt diurnally and nocturnally. They will live in almost all habitats. Their diet is composed mainly of rats (60%), although birds (19%) and invertebrates (15%) together compose a significant portion.

This research proposal covers a five-year study into whether the control of cats has a positive effect on the breeding success of yellow-eyed penguins on Stewart Island. One area will have as many cats killed as possible and another will be left as a control area. We are hopeful that this will show us that the fledging success in the targeted area is greater.

The Yellow-eyed Penguin Trust is seeking funding for a five-year study into the impact of cats on yellow-eyed penguins. The funding for year one has been guaranteed by the Yellow-eyed Penguin Trust (thanks to our unexpected donation from Contact Energy) and this will take place October 2003-March 2004. The project will again be supervised by our Projects Officer, David Blair.