Home range and spatial organisation of stoats (Mustela erminea), ferrets (Mustela furo) and feral house cats (Felis catus) on coastal grasslands, Otago Peninsula, New Zealand: Implications for yellow‐eyed penguin (Megadyptes antipodes) conservation

Abstract

This radio‐tracking study reports the home range and spatial organisation of 12 stoats (Mustela erminea), 21 feral ferrets (Mustela furo) and 11 feral house cats (Felis catus) in coastal grasslands surrounding yellow‐eyed penguin (Megadyptes antipodes) breeding colonies, Otago Peninsula, South Island, New Zealand. Fully revealed ranges averaged 133 (±52 SD) ha for 6 male stoats; 83 (±73 SD) ha for 2 female stoats; 163 (± 50 SD) ha for 6 male ferrets; 135 (±44 SD) ha for 10 female ferrets; 207 (±99 SD) for 7 male cats; and 148 (± 63 SD) ha for 3 female cats. Males had larger ranges than females, and the larger predators ranged over greater areas than the smaller predators. Mustelids did not have intrasexual territorial spacing systems. Similarly, mustelid and cat ranges overlapped extensively, though stoats may avoid ferrets and/or cats by using different micro‐habitats. An example on how the logic of this argument applies to protect yellow‐eyed penguins threatened by stoats or ferrets and cats follows: based on minimum home range size, control stations should be placed less than 638 and 964 m apart respectively to ensure all individual predators are at risk of being killed. Investigation of the number of control stations per home range to ensure all trappable predators are killed would allow improved cost‐effectiveness of control programmes. As an interim protocol we recommend control stations spaced 286 and 432 m apart on trapping grids to control stoats and ferrets/cats repectively.