Comparing the effectiveness of short-focal camera trapping, live trapping, and soil eDNA for surveying small mammals: A case study on Eurasian water shrew (Neomys fodiens)

Small mammals are potential bio-indicators of various ecosystems and their populations are often studied. However, many small mammal species are difficult to detect due to their small size and elusive behaviour. Camera trapping and live trapping are commonly employed survey techniques, but they both have their limitations. Recently developed techniques such as adjusted short-focal camera trapping and environmental DNA (eDNA) are promising new approaches, but their relative performance remains poorly quantified. We compared the effectiveness of three survey protocols for detecting a semi-aquatic and elusive small mammal, the Eurasian water shrew (Neomys fodiens), by (1) short-focal camera trapping, (2) live trapping, and (3) soil eDNA. During September and October 2022, we surveyed 20 transects of each 100 m in length alongside the Kleine Dommel, a lowland brook in the Netherlands. The effectiveness of the three survey protocols was compared based on detection probabilities. Short-focal camera trapping yielded a significantly higher detection probability than the eDNA protocol. Detection probabilities between short-focal camera trapping and live trapping and, between the eDNA protocol and live trapping, were not significantly different. Short-focal camera trapping is an effective technique to survey Eurasian water shrews. Furthermore, this method detected additional species compared to live trapping and is non-invasive and less labour-intensive. Short-focal camera trapping showed a promising method for small mammal surveys in general and we recommend further evaluation of its applicability for other small mammal species.