Evaluating survey design and long-term population trends in slow-worms (Anguis fragilis)

Habitat loss and fragmentation from increased development and land use change, are major threats responsible for national declines in slow-worm numbers. The legal protection and priority status afforded to this species has increased the need for species-specific surveys and monitoring to be undertaken. Current reptile survey guidance is outdated and unstandardized, which has the potential for survey results to vary significantly, especially relating to the levels of survey effort needed to obtain meaningful results. Consequently, such survey results are used to inform important ecological decisions, particularly surrounding slow-worm mitigation and conservation. This study was undertaken to determine if and how the number and distribution of artificial refugia impact on slow-worm detectability and additionally, compare slow-worm populations over time between two sites within King's Wood, Challock, UK. Tin size and layout, as well as tin density were identified as key factors that impact slow-worm detectability. Consequently, more slow-worms were recorded using tins 0.25 m2 in size at a density of 40 per hectare compared to using tins 0.5 m2 in size at a density of 20 per hectare. Doubling the number of tins at the site resulted in a doubling of the number of slow-worms, but no change in the number of slow-worms captured per tin. There was no difference in captures between tins laid down for a year and tins laid for a few weeks. Long-term population monitoring suggested that vegetation change is a major factor contributing to declines in slow-worm numbers within a local population. The findings documented in this study, emphasise the need for existing reptile survey guidance to be updated to account for the significant impact refugia density and refugia size has on slow-worm detectability. In addition, slow-worm conservation should be determined on a site-specific level, to ensure the best outcome for slow-worm populations.