SCHMAEMAN, C.N.*; MENDON�A, M.T.: Non random mating in big brown bats?

Very little is known about the mating systems of temperate vespertilionid bats. Available data is usually anecdotal and only represents a snapshot of which males are successfully mating in the population. Furthermore, there has been no study monitoring male mating success over time. We have been investigating reproductive behavior of big brown bats, Eptesicus fuscus, in captivity for several years. From Dec-Mar (the breeding season) 1999-2001, male and female bats were housed in large environmental flight cages and given varying temperature regimens that stimulate mating activity. In each of the seasons, individuals were observed nightly for 8 hour periods and scored for attempted and successful mounts by males and for female rejection and proceptivity. Males varied in both number of attempted (0-39, and 0-42 in each season) and successful (i.e. intromission) mounts (0-23 for each season). The percent of males attempting to mount was similar in the two seasons: 77.5% (N=40) and 72.3% (N=55), respectively. However, most of these males had few successful matings (72.4 and 73.4% had 0 to 5 successes for each year respectively). Only 12.9 and 12.2% had 10 or more successful matings. There was no significant correlation between an individual male’s mating score and females exhibiting rejection or proceptive behavior toward him. Male mating success also did not correlate to forearm length (year 1 p=0.70, R²= .024; year 2, p=.65, R²= .016) or weight (year 1, p=0.17, R²= .095; year 2, p= .68, R²= .018). The males with the highest number of successful mounts were, in fact, intermediate in size. It appears that factors other than size may account for the differential success in mating by males.