Many animal taxa exhibit intersexual differences in sociality and resource selection that can result in variation in energy allocation budgets. Asymmetry of reproductive energetics between sexes can lead to intersexual variation in behavior to maximize lifetime reproductive success. Temperate bats show marked intersexual differences during summer when sexual segregation occurs. Although some intersexual differences have been shown in activities during the autumn mating period, they have not been examined in the context of fitness consequences for each sex. We studied autumn swarming activity of little brown and northern myotis bats (Myotis lucifugus and M. septentrionalis) in Nova Scotia, Canada, to test predictions of the hypothesis that intersexual variation in swarming behaviors occurs to maximize fitness. We conducted capture—mark—recapture surveys at swarming sites to characterize the nature and extent of intersexual variation in swarming activities. Relative to females, males occurred in disproportionally large numbers; had longer swarming seasons overlapping the female swarming season; and accounted for a disproportionately large number of recaptures at swarming sites suggesting that they had returned more frequently. No movements among swarming sites, which ranged in pairwise distance from 27.9 to 98.9 km, were detected for either species. Activity at swarming sites was highest early in the season for both species. As predicted, males engaged more frequently in swarming activities than females which likely reflect males maximizing opportunities for mating. Although their activities overlap during this period, differences suggest sex-specific activity budgets and it is likely that for each sex, individuals reconcile energetic constraints differently to maximize fitness.
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Vol. 96 • No. 6