The smell of familiarity: conspecific faeces influence roost exploration and occupation in wild Bechstein's bats

Sociality is widespread in the animal kingdom, but it typically requires individuals to be able to discriminate group mates from nongroup mates. Bats account for approximately 20% of all mammal species and display a high variety of social structures. Being mostly nocturnal, they often rely on olfaction for orientation and communication. However, little is known about the role of olfaction in their choice of communal roosting sites, where colony members aggregate during the day. Here, we test the response of female Bechstein's bats, Myotis bechsteinii , a forest-dwelling bat species characterized by socially closed maternity colonies, from one maternity colony to novel roosts containing conspecific faeces. In the field, we performed a pairwise choice experiment by providing RFID-tagged bats with box pairs containing either same- or foreign-colony faeces. Using data obtained from automatic RFID loggers, we quantified individual behaviours related to roost exploration and occupation. We found that female Bechstein's bats explored and occupied boxes containing faeces from their own colony more than those with foreign-colony faeces. This difference decreased with faeces age. Our findings shed new light on the use of olfactory cues in bats' roosting decisions and point at odour as a potential mechanism involved in the maintenance of Bechstein's bat social structures. • We let wild Bechstein's bats choose roosts with own- or foreign-colony faeces. • The first individuals finding a box pair visited each treatment equally. • Later, bats explored and occupied more roosts with faeces from their own colony. • This preference was stronger when faeces were fresh. • We suggest that female Bechstein's bats use conspecific odours in roost selection.