Feral cat study on Stewart Island

Despite the fact that the first year of our study into the effects of feral cats on hoiho populations on Stewart Island did not show high rates of predation, we still managed to obtain some useful data.

Grant Harper’s research in an inland forested area on Stewart Island in 2002 found that the average weight for male cats was 3.4 kg and for females was 2.6 kg. Sandy King found almost identical results in the coastal yellow-eyed penguin habitat during our study this season: males 3.4 kg and females 2.5 kg.

However, the two studies differed in what food the cats appeared to be eating. Rats made up 60% of the diet of cats in the inland area, with birds making up 19% and invertebrates 15%. On the coast, rats and possums accounted for only about 30% of the diet, with beetles making up another 10%. Interestingly, 27% of the stomachs were empty. Thankfully this season there is no evidence of yellow-eyed penguins in cats’ diet.

This year no cat predation of chicks was seen. Our previous experience in Otago suggests that predation events may be sporadic and sometimes only occur every 2-3 years. The long-term monitoring that we have instigated will, over time, tell us to what level feral cats are affecting yellow-eyed penguin breeding success.