Comparing the efficacy of two camera trapping techniques for assessing the occupancy, detection and activity patterns of small Mustelids in Britain

Increasing concern over the unfavourable population trends and data gaps for many mustelids highlight the need to improve existing monitoring methods, to enable more accurate population assessments. Here, we investigated the efficacy of two camera trapping techniques for the detection of small mustelids, specifically least weasels Mustela nivalis, and stoats M. erminea in England. We deployed two concurrent camera trap techniques - a Mostela (a camera trap enclosed within a box) and an external camera trap at 20 sampling sites during summer 2021. We measured the number of daily detections over time and calculated the probability of detection and occupancy for each species. Our results highlighted the efficacy of the Mostela at detecting weasels whilst significantly reducing the amount of video footage to review. Stoats, however, were rarely detected with either technique, although the external camera appeared to be more reliable than the Mostela. European polecats Mustela putorius were regularly detected inside the Mostela and were detected at a similar rate as the external cameras after an initial period of avoidance. The data collected from the Mostela also highlighted the nocturnal activity of polecats and diurnal activity of weasels. Here, the Mostela provided an effective method to detect and estimate the occupancy of weasels and this may be just as efficient for polecats if deployed for long enough.