Finding your friends at densely populated roosting places: Male Egyptian fruit bats (Rousettus aegyptiacus) distinguish between familiar and unfamiliar conspecifics

Individual recognition via olfactory, auditory, or visual cues is crucial for animals to form and maintain stable social groups, particularly in large colonies such as those of Egyptian fruit bats (Rousettus aegyptiacus). We tested whether Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifics, using two captive groups of male bats. We recorded the behavioural and auditory responses of focal animals in a binary choice experiment in which they could approach either members of their own social group or unfamiliar individuals. In general, bats preferred to stay close to other bats, familiar or unfamiliar, over resting alone and spent more time in close proximity to members of their own group than to unfamiliar conspecifics. The majority of bats interacted more with the unfamiliar individuals, although this result did not reach significance. We conclude that Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifics. Since only one individual emitted social calls and bats never produced echolocation calls during the experiment, we infer that individual recognition was most likely mediated via olfactory and/or visual cues. The ability to identify familiar individuals may indicate that males of Egyptian fruit bats form stable groups within their large colonies.