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An in-depth insight into the roosting behaviour of bats

Our recently published study in the Journal of Zoology has provided a novel and detailed insight into the summer roosting behaviour of three bat species native to the UK. We used a long-term comparative dataset of individually tagged bats across multiple bat box monitoring schemes in south-west England, including our own long-term study in Wytham Woods.

Drawing from this extensive dataset, we were able to reveal subtle patterns of segregation and association within nursery roosts, where adult females group together to raise their young in the summer months. While previous descriptions of these roosts focus on the breeding females, we have shone a light on how the males and non-breeding females, which are often also present, fit into this picture.

The nursery roosts of our three study species, the Bechstein’s bat, Natterer’s bat, and brown long-eared bat vary in the degree of exclusivity, with Bechstein’s nursery roosts being almost exclusively female, whilst the brown-long eared bat nursery roosts include a mixture of males and females. However, we found that the degree of segregation within roosts varied across the three species according to several common factors. We found that during the period when the female bats are lactating and nursing their young, the non-breeding females and males tend to avoid these roosts the most. We also found higher levels of avoidance in larger nursery roosts.

In addition to highlighting these factors, our study has revealed a novel insight into the behaviour of brown long eared bats. Previously this species has been described as exhibiting no sexual segregation within nursery roosts. However, our study found that even males and non-breeding females of this species avoid large groups of lactating females to some degree, suggesting that there is a high cost involved in associating with these groups, such as high levels of parasitism.

Katsis, L. K. D., Linton, D. M., & Macdonald, D. W. (2020). The effect of group size, reproductive condition and time period on sexual segregation patterns in three vespertilionid bat species. Journal of Zoology. https://doi.org/10.1111/jzo.12843