Roost selection in the pipistrelle bat,Pipistrellus pipistrellus(Chiroptera: Vespertilionidae), in northeast Scotland

Availability of suitable roost sites may limit bat distribution and abundance. We compared nine internal and 26 external features of 21 known roost buildings with those of 17 random buildings in northeast Scotland, U.K. (57°N) to assess whether pipistrelle bats,Pipistrellus pipistrellus(55-kHz phonotype) are selective in their use of roosts. Bats did not select roosts with specific structural attributes. Compared with random buildings, roosts were closer to a tree over 10m tall and had a greater percentage cover (of trees over 10m tall) within a radius of 50m. Trees may provide benefits by providing shelter and thus ameliorating the microclimate of the roost. Cover may also provide protection from predators so that bats are able to emerge earlier, thus increasing foraging time. Bats in the present study emerged 11min earlier from roosts with 29% cover than from roosts with 3% cover, potentially gaining as much as 10% of their daily energy requirements in this extra time. Roosts were also more likely to have linear vegetation elements leading away from them. These features may be important for navigation, foraging or predator avoidance. Compared with random buildings roosts were closer to and surrounded by a greater area of deciduous woodland within a radius of 0.5km, had a greater area of coniferous woodland within a radius of 0.5km, and were more likely to be found within 0.5km of a major river. All these factors are likely to be beneficial for foraging. A logistic regression model indicated that percentage cover within 50m of the building was the best predictor of the presence or absence of bats roosting in a building.