Increased predation on pukeko eggs after the application of rabbit control measures

We have been studying the social behaviour and ecology of pukeko (Porphyrio porphyrio) for over five years at a study site in the lower Taieri River, Otago New Zealand. After an application of rabbit poison in 1995 and the illegal release of rabbit haemorrhagic disease (RHD) in 1997, there was strong anecdotal evidence that rabbit (Oryctolagus cuniculus) abundance on and around our study site had been substantially reduced. In a retrospective analysis, we compared predation rates on the nests of pukeko over a four year period (1991-1994) before the application of these measures and one year after the release of RHD (1998). Significantly more nests were predated in 1998 than in previous years. While we recognise a number of possible explanations for this result, we suggest that one of the most plausible reasons for the increase in predation rates is a shift in diet by the rabbit specialist predator, the Australasian harrier (Circus approximans).