Stability of roosting patterns in a laboratory colony of Carollia perspicillata: neighbors matter!

Social systems of animals are crucially shaped by the distribution of individuals in space and time which reflects their mating system, and sets the framework for individualized interactions. To test for sociality, rather than mere aggregation, in a laboratory colony of C. perspicillata, we explored roosting patterns focusing on group composition and its temporal stability, and related them to body condition, sex and age of the individuals involved. A social network analysis was performed on roosting data of the 23 to 25 bats of the colony monitored over eight months in the animal facility, using SOCPROG 2.8 to determine dyadic half weight association indices, to test for preferred or avoided associations, and to fit models based on standardized lagged association rate. The bats perched in stable, nonrandomly associated groups of an adult male with several reproductive females (harems), of associated bachelors, of a group of two adult males with two females, and a group consisting mostly of juveniles of both sexes. Stability of groups varied considerably; a “constant companions and casual acquaintances” model explained data best. Bats older than one year showed more stable associations than younger animals, had higher association rates, and were associated with more strongly associated individuals. This correlated with a higher “forearm-mass-index” as proxy for body condition. In contrast, the fact that females showed more stable associations than males was not correlated to differences in body condition. In sum, the bats displayed a complex and dynamic social structure in captivity.