Wildlife crossings increase bat connectivity: Evidence from Northern Germany

Although roads are important cultural objects in our society, they can have negative impacts on the environment. Bat populations are affected by roads in several ways, including habitat loss, death due to collision with vehicles, and reduced habitat connectivity. In recent years, different mitigation practices have been introduced to help animals safely cross roads, reduce road kills, and minimize habitat fragmentation. This study aims to investigate to what extent two types of existing wildlife crossings (a green bridge and an underpass) on the A21 highway (in Northern Germany) are used by bats. All-night acoustic recordings of bat activity at the wildlife crossings, on the highway, and in the surroundings show that bats use both mitigation structures. Our results indicate that bats use mitigation structures depending on their degree of clutter-adaptation: Species from the genus Myotis, which are highly clutter-adapted, were the most recorded in the underpass, while Pipistrellus spp., which are less clutter adapted, were the most recorded on the Green Bridge. Contrary to expectations, many bat passes were registered on the highway as well. Long-term monitoring studies are needed (including counting of bat fatalities) to clarify if further mitigation measures are needed. In conclusion, the use of wildlife crossings as mitigation structures can be effective, mostly for clutter-adapted species (Myotis spp. and Plecotus auritus).