Intracolonial social distance, signaling modality and association choice in the greater sac-winged bat (Saccopteryx bilineata)

Abstract

Understanding patterns and motivations for social spacing greatly illuminates the structure and internal dynamics of given groups or social systems. The highly social, polygynous greater sac-winged bat, Saccopteryx bilineata, represents an excellent model for social spacing analysis, since the choice of individual roost-sites within a day-roost constitutes an enduring, often repeated decision about relative proximity to conspecifics. Day-roost colonies consist of one or multiple harem groups, each with several females and a single male. Additionally, non-harem males without females may be present. A social-distancetime-budget metric revealed that harem males, females, and non-harem males differed significantly in their respective spatial associations while roosting. Harem males and females were most closely associated, with harem males located at the center of harems instead of at the borders. Non-harem males associated significantly closer with one another than with harem females that they were trying to access. The signaling modality mediating social interactions depended on the respective social distances between communicating bats. Our results suggest a concentric social organization based around harem males, which may select roost sites in closest possible proximity to females to enhance courtship signal strength. This constitutes an interesting deviation from the normative form of harem maintenance, patrolling borders, in mammals.

Evidence of social preferences in big brown bats (Eptesicus fuscus)

“…For example, several tropical species form harem organizations, often with stable female group membership across years, and research on these systems tend to emphasize group dynamics and mating success (Voigt et al 2001;Heckel and von Helversen 2002). Fulmer and Knörnschild (2012) examined social interactions between sacwinged bats (Saccopteryx bilineata (Temminck, 1838)) and found preferential roosting in proximity to harem-mates, although only across sexes. Although mating behaviour and social organization is well documented in many bat species, few studies have focused on intrasexual interactions among mainly single-sex colonies, such as maternity colonies.…”