Mustela erminea

Conservation programmes in New Zealand often suppress populations of a single invasive predator for the benefit of threatened avifauna. However, the establishment of whole guilds of invasive species has created complex competitor and predator-prey relationships, including some well-described trophic cascades. Trap networks designed to target stoats (Mustela erminea) are poorly optimised to supress a population of weasels (M. nivalis), and may contribute to periodic spikes in weasel numbers due to decreased interspecific competition and aggression.

Stoats and feral cats are key predators of some of New Zealand’s most threatened fauna and landscape-scale control tools are urgently needed. A ready-made meat bait is being developed for use in both aerial and ground-based control operations. As part of the development, two trials with non-toxic versions of the bait were undertaken: one targeting stoats in Fiordland in spring 2020 and the other targeting feral cats in the Mackenzie Basin in winter 2021. The trials aimed to assess the palatability of baits to both target and non-target species.

In New Zealand, ship rats (Rattus rattus) have been implicated in many extinctions, declines, and range contractions of native birds, so ship rats are an important target of predator control. The outcomes of ship rat control operations are difficult to predict due to other factors which affect rat populations including altitude, Nothofagus seedfall, and control of other mammalian pests, particularly brushtail possums (Trichosurus vulpecula) and stoats (Mustela erminea).