New Zealand Journal of Ecology (1999) 23(1): 95- 100

Trappability and densities of stoats (Mustela erminea) and ship rats (Rattus rattus) in a South Island Nothofagus forest, New Zealand

Research Article
Nic Alterio 1
Henrik Moller 1,2
Kerry Brown 3
  1. Ecosystem Consultants, P.O. Box 6161, Dunedin, New Zealand
  2. Zoology Department, University of Otago, P.O. Box 56, Dunedin, New Zealand
  3. Department of Conservation, Private Bag, Twizel, New Zealand

Stoat (Mustela erminea) density was estimated by live-trapping in a South Island Nothofagus forest, New Zealand, at 8-9 (Jan/Feb 1996) and 15-16 (Aug/Sep 1996) month intervals after significant beech seedfall in autumn 1995. Absolute densities were 4.2 stoats per km² (2.9-7.7 stoats per km², 95% confidence intervals) in Jan;Feb 1996 and 2.5 stoats per km² (2.1-3.5 stoats per km²) in Aug/Sep 1996. Trappability of stoats increased in the latter sampling period, probably because mice (Mus musculus) had become extremely scarce. accordingly, trapping rates of stoats may vary temporally and spatially with food supply rather than only with absolute abundance. Ship rats (Rattus rattus) capture rates doubled between Jan/Feb 1996 and Aug/Sep 1996, but rapidly declined shortly afterwards. Trappability of ship rats also increased in the latter sampling period. These factors must be considered when planning methods of indexing relative densities of stoats and rats.