Reproductive timing, distribution, and sex ratios of tree bats in Lower Michigan

Summer day-roost selection by eastern red bats varies between areas with different land-use histories

The eastern red bat (Lasiurus borealis) is widely considered to be in decline, inspiring interest in identifying important habitats for conservation in the eastern United States. Unfortunately, knowledge of important day-roosting habitats is lacking for much of the species' range. We examined patterns of day-roost selection by male and female eastern red bats at two study sites in southeastern Ohio, U. S. A, to help fill this information gap. We radio-tagged 28 male and 25 female bats during the summers of 2016-2019 and located 53 male and 74 female roosts. Day-roost selection differed between sexes and study areas. In a mostly even-aged forest with significant historical disturbance, we found males and females roosting in trees located at higher elevations, with no clear selection based on tree or stand characteristics. Specifically, males selected trees with larger diameters located at lower, cooler elevations than females, which selected smaller diameter trees found at higher, warmer elevations. However, in a forest with less historical disturbance and more structural diversity, we found sexes differed in how they selected from available habitats. These data show that heterogeneity in environmental conditions can lead to different patterns in selection, even between sites located within a small geographic area. They also show that eastern red bats sexually segregate on the local landscape in the presence of diverse forest conditions but may not do so in the absence of such diversity. We recommend managing forests to maintain structural diversity across an elevational gradient to provide male and female eastern red bats with suitable day-roosting habitat in southeast Ohio.

Bats and Buildings: The Conservation of Synanthropic Bats

Humans have shared buildings with bats for thousands of years, probably as early as first humans built primitive huts. Indeed, many bat species can be defined as synanthropic, i.e., they have a strong ecological association with humans. Bats have been observed using buildings as roosting and foraging sites, temporary shelters, for reproduction and hibernation. A synanthropic lifestyle may result in direct fitness benefits owing to energetic advantages in warmer roosts, which may ultimately lead to more rapid gestation and faster development of juveniles, or by being less exposed to natural predators in urban environments. All these benefits may allow bats to use buildings as stepping stones to exploit habitats otherwise devoid of roosting structures and may even lead to the expansion of geographic ranges. Yet, the coexistence with humans also comes with some risks. Bats may be exposed to chemical pollutants, particularly preservation chemicals used on lumber or during pest control measures. Bats may also be at risk of direct persecution or they may die accidently if trapped within buildings. In general, eviction of bats from buildings should follow the general rule of avoidance–mitigation–compensation. When considering conservation measures for synanthropic bats, it is most important to assess the role of the building for different life stages of bats. Construction work at buildings should be conducted in a manner that minimizes disturbance of bats. Artificial roosts can replace lost roosts, yet bats will often not accept alternative roosts. Demographic changes in human populations may lead to the abandonment of buildings, for example, in rural areas and to increased conflicts in urban areas when old buildings are replaced by new buildings or when previously unoccupied space in buildings is renovated. We advocate maintenance and enhancement of roosts for synanthropic bats, in addition to outreach and education campaigns, to improve the tolerance of humans for synanthropic bats.