Hanging out in tents: social structure, group stability, male behavior, and their implications for the mating system of Ectophylla alba (Chiroptera: Phyllostomidae)

Abstract

Bats show the greatest variety of mating strategies in mammals. Social structure can be influenced by roost characteristics, for example, if the roost is defendable and its availability limited, it becomes an important resource that partially determines the mating system type. In the species that use tents as roosting sites, it has been suggested that males can defend the tent in order to attract and have access to females. Ectophylla alba is an obligate and exclusive tent user, and it has to build tents periodically. Its mating system has been classified as polygyny by its resource defense, and it has a temporary group structure of one male and several females. This study seeks to determine the composition and stability of the groups of this species and to learn whether males defend the tent or the females in it in order to gain copulations. This study was conducted in 2006 in Tirimbina, Biological Reserve in Sarapiqui, Costa Rica, where groups of bats were captured (N = 38). The individuals were marked (N = 98), and their reproductive status was determined. The behavior of the individuals was recorded with video cameras and infrared light (300 h total). Throughout the year, some individuals were more closely associated to other individuals, determining that groups are stable independent of the reproductive season. The proportion of males in the groups does not vary according to reproductive season, and in most groups, there is more than one adult male. The males spend different amounts of time in the tents and do not show antagonistic behavior with other members of the group. Based on the social structure, the classification of the mating system should change to “a stable group of several males and females,” which may be confirmed in the near future by the results of an ongoing paternity study.