Dispersion and site fidelity in a tent-roosting population of the short-nosed fruit bat (Cynopterus sphinx) in southern India

Abstract

Patterns of dispersion and site fidelity were investigated in a tent-roosting population of the short-nosed fruit bat, Cynopterus sphinx (Megachiroptera), in southern India. A local population of C. sphinx occupied diurnal roosts in a variable subset of 45 stem tents constructed within the dense foliage of mast trees (Polyalthia longifolia). Individually marked tent-roosting bats were visually censused over the course of a 38-d interval spanning the postpartum oestrus period. On any given day, 33.3–85.7% (mean = 60.8%, SD = 14.2) of adult males roosted singly, with the remainder holding harems of 1–10 breeding females (mean = 3.01, SD = 0.79). Average harem sex ratio was 2.8-fold higher than the adult sex ratio of the total tent-roosting population within the study area, indicating the potential for a high variance in male mating success within a single breeding season. Bats of both sexes typically occupied one primary tent, interspersed with shorter periods of residency in alternate tents. Males exhibited a significantly higher degree of roost fidelity than females. Some females roosted sequentially with different males and with different combinations of females, whereas others remained continuously associated with a single male and/or particular female roostmates over the duration of the census period. There were no statistically significant relationships between physical characteristics of tents and rates of occupancy by males or females. Intermittent transfers by females between groups suggest that the defence of diurnal roosts by males represents a more profitable mating strategy than the direct defence of compositionally labile female groups.