Unique Insights into Dispersion Distances Among Calling Males of Wahlberg's Epauletted Fruit Bat in Kruger National Park, South Africa

Abstract

In June 2009, we used a novel technique to quantify dispersion patterns among a large group of calling male Epomophorus wahlbergi congregated around five neighboring and synchronously fruiting sycamore fig trees (Ficus sycomorus) in Kruger National Park, South Africa by using the physics of sound attenuation over distance to monitor and map positions of calling males without disturbing their mating behavior. The lack of fruiting sycamore fig trees across the area concentrated males among five fruiting trees along a 10 km stretch of riverine corridor that paralleled the river road. We hypothesized that the patterns of dispersion among calling males would be clumped in relation to fruiting fig trees that attract foraging females. Results show that the distribution of calling perches were clumped (R = 0.75) as opposed to randomly or equally dispersed. In addition, we found that a 2 km section of the corridor contained the majority of calling males and in this area calling males were more tightly clumped (R = 0.58) than across the other 6 kms of corridor. In addition, distances among calling males and their nearest neighbor were significantly less on average (25m) in the higher- density area, than in the lower density areas (315m)(P < 0.001). Although most males were near fruiting figs, they maintained a minimum dispersion and never were observed calling from the same tree. In addition, some males appeared dominant over others and consistently positioned themselves closest to ripe fig trees where females were foraging. Our data give previously unobserved insights into how male Wahlberg's epauletted fruit bats position their calling roosts in relation to one another and fruiting fig trees under conditions of extreme drought and limited local food availability.