Facilitating permeability of landscapes impacted by roads for protected amphibians: Patterns of movement for the great crested newt

Abstract

Amphibian populations are highly vulnerable to road mortality and habitat fragmentationcaused by road networks. Wildlife road tunnels are considered the most promisingroad mitigation measure for amphibians yet generally remain inadequately monitored,resulting in mixed success rates in the short-term and uncertain conservation benefitsin the long-term. We monitored a complex multi-tunnel and fence system over fiveyears and investigated the impact of the scheme on movement patterns of two newtspecies, including the largest known UK population of the great crested newt (Trituruscristatus), a European Protected Species. We used a stage descriptive approach based oncapture positions to quantify newt movement patterns. Newt species successfully usedthe mitigation but the system constituted a bottleneck to movements from the fences tothe tunnels. Crossing rates varied widely among years and were skewed towards autumndispersal rather than spring breeding migration. There was a substantial negative biasagainst adult male great crested newts using the system. This study indicates thatroad tunnels could partially mitigate wider connectivity loss and fragmentation at thelandscape scale for newt species. However, the observed bottleneck effects and seasonalbias could have population-level effects which must be better understood, especiallyfor small populations, so that improvements can be made. Current requirements formonitoring mitigation schemes post-implementation are probably too short to assesstheir effectiveness in maintaining connectivity and to adequately understand theirpopulation-level impacts.