In species where conspecifics form discrete social groups, the production of signals advertising group membership may promote cohesion among group members. Female little brown bats (Myotis lucifugus) show high fidelity to maternity roost sites where they aggregate in large numbers every spring to rear young. While the presence of group-specific signatures has been demonstrated in the echolocation calls of this species, differential clutter at recording sites may account for the observed differences. Bats optimize their ability to maneuver and detect prey within a given environment by tailoring their echolocation calls to physical attributes of that environment. Therefore, if clutter is responsible for the apparent group specificity in the calls of little brown bats, groups of bats experiencing similar levels of clutter at roost entrances should emit similar calls. We examined the effect of differential clutter on the emergence calls of M. lucifugus by comparing recorded echolocation calls of bats emerging from three maternity roosts in Georgian Bay, Ontario. The roosts varied in distance from each other and in their proximity to surrounding clutter. The more distant group emerged in an environment with clutter deemed intermediate to the two more proximate roost entrances and yet was the most acoustically distinct. The finding that similarity among emergence calls correlated better with spatial proximity than with the level of clutter around roost entrances is consistent with the development of true group-specific signatures in the emergence calls of M. lucifugus.
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