Assessing the detectability of the Irish stoat Mustela erminea hibernica using two camera trap-based survey methods

Monitoring small mustelids like weasels Mustela nivalis and stoats M. erminea is challenging as they are rarely seen, leave scant field signs and display avoidance behaviour towards traps and monitoring devices. The Irish stoat M. erminea hibernica is a subspecies endemic to Ireland and the Isle of Man, and despite being widespread in Ireland, no information exists on its population status due to the difficulty of detection. We compared the efficacy of two camera trap methods to detect Irish stoats in counties Mayo and Galway, Republic of Ireland. Firstly, the ‘Mostela’ (a modified camera trapping device comprising a camera trap and a tracking tunnel inside a wooden box) and secondly, an external camera trap deployed outside the box. We used a single-season occupancy model to estimate the probability of detection and occupancy of Irish stoat using these two methods at 12 sites. Both methods detected stoats, at 17% of sites inside the Mostela and 33% of sites on the external camera, although this non-agreement was not statistically significant. Detection probabilities were low, with wide and largely overlapping confidence intervals for both methods. Occupancy probabilities were relatively low, and the occupancy probability for the external camera was very close to the naïve occupancy estimate. We evaluate the potential applicability of both methods for future work to assess the population and conservation status of this little-studied species.