The role of temperature on clustering behavior and mating opportunity in Bonin flying foxes

Abstract

Social thermoregulation is an important adaptation for animals living in cold environments, especially for those with high surface area-to-volume ratios. Huddling behavior can influence animal dispersion patterns. However, little attention has been paid to the relationship between huddling behavior and social organization, including mating systems. We studied aggregations of Bonin flying foxes Pteropus pselaphon on Chichijima Island in Japan, which is located at one of the northern limits of their geographical range. Bonin flying foxes aggregate in arboreal roosts, where they form temporary clusters within the colony during winter months. Specifically, we hypothesized that the occurrence and intensity of clustering behavior are affected by ambient temperature; therefore, we examined the relationship between cluster size and ambient temperature. We also investigated the age and sex compositions of clusters and mating behavior to gain insight into the mating system of this species. Field observations showed that P. pselaphon clusters were roughly separated into three groups: males, females, and subadults. Statistical analyses showed that ambient temperature had significant negative effects on the proportion of individuals that formed clusters for all groups. Cluster size decreased significantly with increasing ambient temperature in female and subadult groups. Some female clusters were composed of a single male and multiple females. Marked males were observed excluding other males from the periphery of female clusters, and they monopolized copulations with clustering females. Our findings suggest that clustering plays an important warming role in the species, and that this behavior is exploited by males resulting in a social system that is best described as a form of female-defense polygyny.