REEDER, D.M.*; KUNZ, T.H.; WIDMAIER, E.P.; Boston Univ., MA; Boston Univ., MA; Boston Univ., MA: Behavioral and physiological responses to group formation in the Malayan Flying Fox (Pteropus vampyrus) vary by sex and group type.

We examined the response to formation of same sex groups (SSGs) and breeding groups (BGs) in captive Malayan Flying Foxes (Pteropus vampyrus). On the day of group formation, injurious fighting occurred between SSG males but not females, with intermediate levels of male-male and male-female aggression in BGs. Despite the ability to space themselves apart by up to 2.5m, SSG females were nearly always grouped together and in proximity (< 0.75m) to each other, whereas identically housed males were more dispersed throughout the enclosure. Within BGs, at least 1 male was solitary; other bats were in small clusters of 1-2 males and several females. Baseline glucocorticoid (GC=cortisol+corticosterone) levels increased significantly in all bats one day after group formation. Except for BG females (where GCs remained elevated for 35 days), GC levels returned to baseline by day 4 after group formation. Males had significantly higher GC levels than females on days 0, 1, and 4. By 35 days, GC levels in SSG males were lower than their original baseline levels and were not distinguishable from females. In contrast, GC levels in BG males remained at baseline levels from day 4 to day 35, thus being significantly higher at day 35 than females and SSG males. Testosterone was variable over the first 4 days, but by day 15 was significantly higher in BG than in SSG males, which may be related to initiation of mating activity. At 35 days, T levels in BG males were significantly less than on day 15, and even significantly less than SSG males, which may be related to the higher GCs in BG vs. SSG males at this time. These results suggest that formation of a new breeding group has more lasting effects on GCs and T than formation of same-sex groups, and that these GC effects vary by sex.