The role of introduced mammals and inverse density-dependent predation in the conservation of Huttonʹs shearwater Original Research Article

This study investigated the impact of stoat Mustela erminea predation on the endangered Huttonʹs shearwater Puffinus huttoni. Breeding success of Huttonʹ shearwaters was significantly lower in two seasons of stoat control than in eight seasons with no control: suggesting that natural environmental variation has a greater influence on breeding success than stoat predation. Monitoring Huttonʹs shearwaters and mainland colonies of sooty shearwaters Puffinus griseus indicated that small colonies suffered higher predation and lower breeding success than large colonies, demonstrating that predation in these two species is inversely density dependent and explaining the low predation rates observed in the very large Huttonʹs shearwater colonies. The presence of another introduced predator, feral pigs Sus scrofa, within six extinct colonies of Huttonʹs shearwaters and at the boundaries of the two extant colonies, strongly suggests that this species was responsible for the historic contraction in breeding range. Controlling stoats within the two remaining colonies is unlikely to assist in the conservation of Huttonʹs shearwater. Conservation efforts would be better spent protecting the two remaining colonies from pigs and in trying to establish new breeding sites.