Demography of straw-colored fruit bats in Ghana.

Abstract

Eidolon helvum is widely distributed across sub-Saharan Africa where it forms large, dense colonies. The species is migratory and satellite telemetry studies have demonstrated that individuals can migrate over 2,500 km. It is a common source of bush meat in West Africa and evidence of infection with potentially zoonotic viruses has been found in West African colonies. The species, therefore, is of interest to both ecologists and those interested in public health. Despite this, demographic parameters of the species are unknown. We focused our study primarily on a colony of up to 1,000,000 bats that roost in trees in Accra, Ghana to obtain estimates of birth rate and survival probability. Aging of bats by examination of tooth cementum annuli allowed use of life tables to indicate an annual survival probability for juveniles of 0.43 (95% confidence interval [CI] 0.16-0.77) and for adults of 0.83 (95% CI 0.73-0.93). Additionally, an annual adult survival probability of 0.63 (95% CI 0.27-0.88) was estimated by following 98 radiocollared bats over a year; capture-recapture data were analyzed using multistate models to address the confounding factor of emigration. True survival probabilities may be in between the 2 estimates, because permanent emigration may lead to underestimation in the capture-recapture study, and population decline may lead to overestimation in the life table analysis. Birth rates (0.96 young per female per year, 95% CI 0.92-0.98) and colony size changes were also estimated. Estimation of these key parameters will allow future analyses of both infection dynamics within, and harvest sustainability of, E. helvum populations.