Courtship behaviour and display-site sharing appears conditional on body size in a lekking bat

Leks are aggregations of sexually displaying males visited by receptive females and characterized by intense male-male competition to attract mates. Success in lekking species is often contingent upon male display output and/or lek attendance, with energetically costly displays functioning as an honest indicator of male quality. Furthermore, display spaces are vigorously defended by territorial males, and territory characteristics are often linked to male phenotype. Here we describe the courtship and territorial behaviour of lekking lesser short-tailed bats, Mystacina tuberculata, and both behaviours appear to be conditional on body size. During the breeding season, lekking males occupy and defend small tree hollows and sing for long periods of the night to attract females. Although some males sing alone, others form 'timeshare' singing roosts, where multiple males visit sequentially to sing each night. In our study, solitary males were significantly smaller than timeshare males and individually had both higher song outputs and higher roost occupancy rates, although timeshare roosts had higher overall occupancy rates. There appeared to be no fitness difference between the two male groups, and while one timeshare roost contained relatively closely related individuals (which roost settlement simulations indicate was not a chance event), four did not. We discuss factors that may promote timeshare formation, including competition for access to desired roosts and potential by-product mutualisms. Courtship and sexual selection in bats is largely undescribed, and thus our study provides a useful description of behaviour in a little-studied taxon.