Social structure of a polygynous tent‐making bat,Cynopterus sphinx(Megachiroptera)

Abstract

The social structure of an Old World tent‐making bat Cynopterus sphinx (Megachiroptera), was investigated in western India. A combination of census and mark–recapture data over 2 years (1996–98) was used to infer the form of the mating system, compositional stability of social groups and mode of new social group formation. The breeding population of C. sphinx was subdivided into diurnal roosting colonies, each of which contained one to five discrete roosting groups and often one or more solitary bats in adjacent roosts. Bats most frequently roosted in stem tents constructed in the flower/fruit clusters of the kitul palm Caryota urens. Temporal variation in social structure was assessed using visual census data for a subset of the study population over 3 years (1995–98) spanning six consecutive reproductive periods. The sex and age composition of diurnal roosting groups indicated a polygynous harem‐forming mode of social organization, as groups invariably contained a single adult male, 1–37 reproductive females and their dependent young (n= 33 harems). Harem size averaged 6.1 adults in the wet season (n= 19, sd= 3.5) and 13.6 adults in the dry season (n= 14, sd= 8.5). The same harem social configuration was maintained year‐round, despite a high degree of synchrony and seasonality in the timing of reproduction. Juveniles of both sexes dispersed after weaning and sexually immature bats were never present in harems at the time of parturition. Adult females often remained associated as roostmates from one parturition period to the next, and group cohesion was unaffected by turnover of harem males. Adult females frequently transferred among roosts within the same colony, and harems underwent periodic fissions and fusions. The founding of new harems most often resulted from the fissioning of previously cohesive harems within the same colony. However, some harems contained disproportionate numbers of yearling females, indicating that new groups are also founded by nulliparous females of the same age cohort. A significant degree of heterogeneity in age composition among harems was revealed in the 1998 dry season, but was unrelated to age‐stratification of tent roosts. Although formation of new harems may be non‐random with respect to age composition of the founders, founding events are not restricted to newly created tents and often involve recolonization of previously occupied roosts.

Mating system of a Neotropical roost-making bat: the white-throated, round-eared bat, Lophostoma silvicolum (Chiroptera: Phyllostomidae)

“…In contrast, male L. silvicolum with harems were heavier than unsuccessful males throughout the year. We cannot exclude the possibility that this difference in physical condition is an age effect as in other species (Kunz et al 1983;Storz et al 2000). Regardless of age, males that did monopolize a nest, but did not manage to attract females, were of intermediate mass.…”

How Does Africa's Most Hunted Bat Vary Across the Continent? Population Traits of the Straw-Coloured Fruit Bat (Eidolon helvum) and Its Interactions with Humans

“…Studies in other fruit bats have identified heterogeneity in age composition among roosts. For example, there are indications that some harems in Cynopterus sphinx are founded by nulliparous females of the same age cohort (Storz et al, 2000).…”

Clinal variation in body size and sexual dimorphism in an Indian fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae)

“…Available evidence suggests that the degree of polygyny may be subject to a considerable degree of geographic variation in C. sphinx . Information on the mode of social organization and mating system is available for Pune (northern locality; Storz et al, 2000b) and Palayamkottai (southern locality; Storz et al, 2000a). In both localities, the clustering of breeding females in confined roosting spaces facilitates a male mating strategy of resource defense polygyny (Storz et al, 2000a,b).…”

“…In addition to fecundity selection on females, sexual selection on males may also be an important driving force in the evolution of sexual dimorphism in bats. If body size influences suc-cess in territory acquisition and/or mating access to receptive females, the opportunity for sexual selection on male size is expected to be greatest in species characterized by highly polygynous mating systems (e.g., McCracken & Bradbury, 1981;Storz et al, 2000b).…”