Prey switching by stoats (Mustela erminea): a supplemental food experiment

Abstract

Context Prey switching by invasive carnivorans to changing food supply could severely impact on endemic prey of conservation importance, but experimental evidence for prey switching in carnivorans is rare. Stoats (Mustela erminea) were introduced to New Zealand and now threaten survival of many native birds, reptiles and invertebrates. Aim Our primary objective was to see whether abundant food caused stoats inhabiting an alpine grassland site to alter the rate at which they preyed upon weta (Orthoptera : Hemiandrus sp.), hares (Lepus europeus), birds and mice (Mus musculus). Methods We used dead rabbits as supplemental food in a before-after-control-impact experiment. Stoat scats were collected from a treatment and non-treatment site before and following food supplementation. Percentage frequency occurrence of the different prey types was assessed for the two sites during each experimental phase. Conclusions Stoats ate fewer ground weta and hares, the two most abundant prey types, when supplemental food was added. In contrast, consumption of mice remained relatively stable at both sites throughout the experiment, and the consumption of birds declined at both sites. Implications Our experiment suggests that stoats may continue to eat scarce endemic prey at similar per capita rates even when alternative prey are available. However, endemic prey that are locally or regionally abundant may be indirectly impacted by fluctuations in alternative prey.