Capturing the cryptic: a comparison of detection methods for stoats (Mustela erminea) in alpine habitats

Abstract

Context The ability to monitor the spatial distribution and abundance of species is essential for detecting population changes, and assessing the progress of conservation management programs. Stoats (Mustela erminea) are a serious conservation pest in New Zealand, but current monitoring methods are not sensitive enough to detect stoats in all situations. Aims We compare the effectiveness of the most commonly employed method for monitoring mustelids in New Zealand, footprint-tracking tunnels, with two alternative detection methods, camera traps and artificial nests. We were interested in determining whether alternative detection methods were more sensitive in detecting stoats than tracking tunnels. Methods We established a network of tracking tunnels, artificial nests and camera traps within alpine habitat. Devices were checked for stoat detections weekly across two seasons, in spring–early summer and autumn. Differences in detection rates and cost effectiveness among methods were analysed among seasons. Key results In spring–early summer, the time to first stoat detection using footprint-tracking tunnels was 61 days, compared with 7 days for camera traps and 8 days for artificial nests. The rate of stoat detection using artificial nests was significantly higher than it was using tracking tunnels (coef = 3.05 ± 1.29, P = 0.02), and moderately higher using camera traps (coef = 1.34 ± 1.09, P = 0.22). In autumn, when overall detectability of stoats was higher, there was no significant difference in detection rates among the three methods, although camera traps again recorded the earliest detection. Artificial nests were the most cost effective detection method in both seasons. Conclusions Artificial nests and camera traps were more efficient at detecting stoats during their spring breeding season (when they are known to be difficult to detect), compared with the more established footprint-tracking tunnel method. Artificial nests have potential to be developed into a monitoring index for small mammals, although further research is required. Both methods provide an important alternative to footprint tracking indices for monitoring stoats. Implications Our study demonstrated the importance of calibration among different monitoring methods, particularly when the target species is difficult to detect. We hypothesise that detection methods that do not rely on conspicuous, artificially constructed devices, may be more effective for monitoring small, cryptic mammals.