Movements by stoats (Mustela erminea) and ferrets (M. furo) through rank grass of yellow‐eyed penguin (Megadyptes antipodes) breeding areas

Abstract

Predation by introduced stoats (Mustela erminea) and ferrets (M. furo) may be contributing to the decline of yellow‐eyed penguins (Megadyptes antipodes) on the South Island of New Zealand. Areas of rank grass were established in the hope of reducing predation by physically excluding predators from penguin breeding areas. This paper describes a foot‐print tracking study which showed that stoats and ferrets were recorded twice and ten times respectively more often in rank grass than in grazed pasture. Stoats moved evenly throughout the rank grass, but ferrets restricted their movements to tracks through the rank grass. Ferrets approached penguin nests over 12 times more often than randomly selected sites in grazed pasture, particularly in spring when the penguin chicks are vulnerable to predation. Stoats appeared to avoid areas with high ferret abundance. Mice (Mus musculus)s, an important prey of these predators, were recorded 5–17 times more often in the ungrazed areas than in grazed areas. The concentration of stoats, ferrets and mice in the penguin breeding areas surrounded by rank grass increases the number of encounters between penguin chicks and predators, and so may increase rather than decrease the risk of predation of yellow‐eyed penguins and other ground nesting birds.