Historically, studies concerning bat flight have focused primarily on the wings. By analyzing high-speed video taken on 48 individuals of five species of vespertilionid bats, we show that the capacity to flap the tail-membrane (uropatagium) in order to generate thrust and lift during takeoffs and minimal-speed flight (<1 m s−1) was largely underestimated. Indeed, bats flapped the tail-membrane by extensive dorso-ventral fanning motions covering as much as 135 degrees of arc consistent with thrust generation by air displacement. The degree of dorsal extension of the tail-membrane, and thus the potential amount of thrust generated during platform launches, was significantly correlated with body mass (P = 0.02). Adduction of the hind limbs during upstrokes collapsed the tail-membrane thereby reducing its surface area and minimizing negative lift forces. Abduction of the hind limbs during the downstroke fully expanded the tail-membrane as it was swept ventrally. The flapping kinematics of the tail-membrane is thus consistent with expectations for an airfoil. Timing offsets between the wings and tail-membrane during downstrokes was as much as 50%, suggesting that the tail-membrane was providing thrust and perhaps lift when the wings were retracting through the upstoke phase of the wing-beat cycle. The extent to which the tail-membrane was used during takeoffs differed significantly among four vespertilionid species (P = 0.01) and aligned with predictions derived from bat ecomorphology. The extensive fanning motion of the tail membrane by vespertilionid bats has not been reported for other flying vertebrates.

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 higherdensity 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.

Background: Almost nothing is known about the mating ecology and behavior of epauletted fruit bats (Epomophorus spp) of which eight species occur worldwide. Two species of epauletted fruits bats (Epomophorus wahlbergi and Epomophorus crypturus) overlap in their distributional ranges in Kruger National Park (KNP), South Africa. Morphologically, these two species are nearly identical to the human eye and field recognition is based upon the number and position of palatal rugae of captured individuals. In addition, the males of both species perform mating rituals during overlapping breeding seasons that appear quite similar and involve wing flapping and monotone vocalizations from calling stations in proximity to fruiting sycamore fig trees where females congregate to feed. The overlap in breeding seasons as well as physical and behavioral characteristics between these two species brings into question how species recognition occurs, and no research is available to understand how males are identified by the females of each species for mating purposes. We recorded vocalizations from calling males in local areas of KNP known to support both species and compared the sonograms to determine if the call structure of mating vocalizations between males of each species differs. Results: We recorded 25 mating vocalizations from seven male epauletted fruit bats near the Shingwedzi Research Camp and 31 mating vocalizations from nine individuals along the Sabie River near Skukuza. Analysis of calls showed significant distinctiveness of male mating vocalizations between the two species in terms of mean fundamental frequency, mean high frequency, mean low frequency, mean bandwidth, and mean call slope at the two sites. Conclusions: We hypothesize that differences in male mating vocalizations recorded at each of our study sites represent call structure differences that potentially may be used to avoid cross-mating between species.