Roost Composition and Sexual Segregation in a Lowland Population of Daubenton's Bats (Myotis daubentonii)

Using data from 1100 day roosts containing a minimum of 9424 Myotis daubentonii bats, we compare the distribution of adult males, adult females, and juveniles, within SchweglerTM box roosts distributed across 394 ha of woodland adjacent to a river corridor in lowland England. Five social groups, containing both males and females (each comprising 55–230 adult bats per annum, using 37–127 known roosts per colony), occupy discrete roosting areas to which individuals show high inter-annual fidelity. Natal philopatry is also high, compared to between colony movements, for both sexes in our study population. Despite considerable spatial overlap and variability in roost composition over the summer (April to October), related to temporal changes in reproductive status, there is sexual segregation within day roosts. Bachelor (adult male dominated) roosts are situated significantly further from water than maternity (adult female or juvenile dominated) roosts on average. This spatial partitioning between maternity and bachelor roosts operates within rather than between colony home roost ranges, however, with adult males from some social groups found roosting closer to water than are adult females from adjacent colonies. The co-occurrence of maternity and bachelor groups roosting in close proximity, including extensive spatial overlap in roosts occupied, and temporal overlap during roost sharing between the sexes, provides novel insights into social organisation and potential drivers of sexual segregation and mating strategies for this widespread and common species within lowland habitats.