Mitigating the effects of a road on amphibian migrations: a Scottish case study of road tunnels

The ever-growing pace of road construction worldwide has become a serious concern for wildlife and natural habitats, resulting in habitat fragmentation and increasing wildlife road fatalities. For amphibians, which are undergoing population declines worldwide, mitigation measures such as road under-passages linked to amphibian-proof fencing may be an effective conservation tool, aiming to reconnect natural habitats and reduce wildlife fatalities. This study assessed the efficacy of road tunnels in a recently developed area by Frankfield Loch, Stepps, North Lanarkshire. Three amphibian tunnels, plus fencing, were put in place during 2010 following the construction of a road in 2006 which separated the loch from a substantial area of marshland, including ponds. In 2015 and 2016, we used custom-made time-lapse cameras within the tunnels to automatically monitor amphibian movements and conducted frog spawn surveys. Numbers of common frogs (Rana temporaria), common toads (Bufo bufo) and newts (Lissotriton spp.) using the tunnels were substantial in both years, though the number of toads decreased significantly between years. We found many frog spawn clumps in the marsh ponds, but rather fewer in the loch. A period of road repair in 2015 was linked with both road mortalities and a change in the pattern of tunnel usage. Additionally, amphibians showed a daily cycle of activity, with nocturnal movements most common. These results indicate important connectivity and usage of both the marsh and the loch, and suggest that this can be effectively sustained through the proper maintenance of tunnels and fencing, which also minimises road mortalities. It remains unknown, however, what proportion of the population crosses the road via the tunnels and how that compares with movements prior to road construction.