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 fragmentation caused by road networks. Wildlife road tunnels are considered the most promising road mitigation measure for amphibians yet generally remain inadequately monitored, resulting in mixed success rates in the short-term and uncertain conservation benefits in the long-term. We monitored a complex multi-tunnel and fence system over five years and investigated the impact of the scheme on movement patterns of two newt species, including the largest known UK population of the great crested newt (Triturus cristatus), a European Protected Species. We used a stage descriptive approach based on capture positions to quantify newt movement patterns. Newt species successfully used the mitigation but the system constituted a bottleneck to movements from the fences to the tunnels. Crossing rates varied widely among years and were skewed towards autumn dispersal rather than spring breeding migration. There was a substantial negative bias against adult male great crested newts using the system. This study indicates that road tunnels could partially mitigate wider connectivity loss and fragmentation at the landscape scale for newt species. However, the observed bottleneck effects and seasonal bias could have population-level effects which must be better understood, especially for small populations, so that improvements can be made. Current requirements for monitoring mitigation schemes post-implementation are probably too short to assess their effectiveness in maintaining connectivity and to adequately understand their population-level impacts.

Road mitigation using tunnels and fences promotes site connectivity and population expansion for a protected amphibian

“…Similar to findings from another road mitigation site (Matos et al 2017(Matos et al , 2018, results from our study show that both great crested and smooth newts moved in greater numbers through the tunnels in the autumn compared to the spring. Many pondbreeding amphibians in the UK make migratory movements towards ponds in the early spring and especially the males gain a reproductive advantage by wintering close to breeding ponds and by arriving early at breeding ponds (Latham and Oldham 1996;Reading 1998;Beebee 2007).…”

“…Although the results from sex ratio remain inconclusive, preliminary data shows that female great crested and smooth newts may make longer distance post-breeding migrations than males, which is similar to the findings at another UK site (Matos et al 2017). Sinsch (1992) found similar results in the natterjack toad (Epidalea calamita) where 90% of males exhibited breeding site fidelity, whereas females moved between ponds to maintain gene flow.…”

“…Numerous studies have attempted to monitor the success of such tunnels, usually using drift fences and pitfall traps at the entrances to tunnels (e.g. Jolivet et al 2008;Pagnucco et al 2012;Matos et al 2017). However, tunnel usage by amphibians appears highly variable both within and between species and pitfall trapping can introduce bias in the data by restricting animal movement.…”

“…Whilst the effectiveness of tunnel and fence systems in improving the population conservation status for different species remains insufficiently understood, overall, this is particularly the case for European newt species, where almost no information is available (Schmidt and Zumbach 2008;Matos et al 2017). This includes the great crested newt, a European protected species which has undergone substantial declines in the UK (Langton et al 2001) but remains relatively widespread and locally abundant and is a main target of road mitigation schemes (Matos et al 2017).…”

“…Whilst the effectiveness of tunnel and fence systems in improving the population conservation status for different species remains insufficiently understood, overall, this is particularly the case for European newt species, where almost no information is available (Schmidt and Zumbach 2008;Matos et al 2017). This includes the great crested newt, a European protected species which has undergone substantial declines in the UK (Langton et al 2001) but remains relatively widespread and locally abundant and is a main target of road mitigation schemes (Matos et al 2017). Whilst newts generally appear to be far less frequently encountered on roads or killed by car traffic compared to most other amphibian species (Petrovan and Schmidt 2016;Kyek et al 2017), road networks can severely disrupt dispersal movements, which are essential for maintaining metapopulation dynamic and viability (Halley et al 1996;Griffiths et al 2010).…”