Temporal, species-specific variation in activity patterns of bats (Chiroptera) along a boreal river basin in Västerbotten, Sweden

Drivers of bat activity (calorific burden, roosting requirements, prey availability, and perceived predation risk) affect all bats. However, bats of boreal forests must manage the increased pressures of low temperatures, ephemeral food sources, lack of darkness, and a short active season. Moreover, nursing female bats in high latitudes must also manage greater roosting requirements, decreased foraging ranges and the calorific burden of lactation. In an acoustic survey of a boreal river in Västerbotten, Sweden, we placed 12 full-spectrum bat detectors along the watercourse for three deployments throughout the active bat season to examine activity patterns. Our results show novel, species-specific, temporal patterns in bat activity. In Myotis bats, activity was restricted to inland sites during the deployment corresponding to the bat lactation period, moving towards the coastal flads in subsequent deployments (when young would be volant). Bats during the lactation period also showed more feeding call sequences and earlier nightly emergence than later in the season. These novel results indicate that forest-roosting bats in intensively managed boreal landscapes may be particularly vulnerable compared to more synanthropic bats, particularly during the key post-parturition period when they are reliant on tree roosts.