In the mating system of the bat Saccopteryx bilineata, bioacoustic constraints impede male eavesdropping on female echolocation calls for their surveillance

Abstract

At night, bats utter loud echolocation calls at high repetition rates that may reveal the location and current behaviour of callers to eavesdropping bats. Given the strong attenuation of echolocation calls, we predicted that territorial males of a harem-polygynous species ought to forage at close distance to females to survey their movements by social eavesdropping. We estimated a maximum detection distance of 38 m for echolocation calls of Saccopteryx bilineata (Temminck, 1838) (Chiroptera; Emballonuridae) broadcasted within the forest under the sound transmission conditions of our study site and for an assumed signal detection threshold of 20 dB SPL (50 m for a threshold of 0 dB SPL). We then simultaneously radio-tracked the nocturnal movements of eight male–female pairs that each rested in the same harem territory during the day and measured the distances at which dyads foraged. Male–female pairs foraged at a median distance of 139 m. In the case of 90% of simultaneous bearings, males foraged at distances that prevented eavesdropping on 44 kHz echolocation calls (>38 m; 87% of radio fixes >50 m). Males and females of the same daytime territory roosted, on average, 226 ± 194 m apart from each other at night. Thus, males were most likely unaware of where females foraged as a result of the strong attenuation of female echolocation calls. In general, such acoustic constraints on social eavesdropping may promote extra-harem group paternities, female choice, and sperm competition in bats, and may therefore present an important selective force in the evolution of bat mating systems.

Effects of tropical forest fragmentation on aerial insectivorous bats in a land-bridge island system

“…D. albus) were found roosting on small islands and also frequently used them as foraging grounds. The small home ranges that have been reported for some forest species such as S. bilineata in Costa Rica (95% kernel foraging areas averaging about 15 ha, mean 50% kernel core foraging areas of about 2 ha; Hoffmann et al, 2007) indicate that islands as small as the ones we sampled are likely to meet the roosting and foraging requirements of a range of forest species. More detailed knowledge of the roosting ecology, size of home ranges and mobility across habitats of other Neotropical aerial insectivorous bats, particularly in fragmented landscapes, could provide valuable information to better understand species-specific traits, requirements and their relation to forest fragmentation.…”

Climate, habitat, and species interactions at different scales determine the structure of a Neotropical bat community

“…The recording station and its surrounding plot represented the smallest scale and reflected the patch where bats fly and forage (Bradbury and Vehrencamp 1976). The respective transect represented the intermediate scale and reflected the array of patch heterogeneity within a habitat that an organism would experience in its foraging area (Hoffmann et al 2007). Sites represented the largest scale and reflected the forest life zones across the isthmus, which in turn are strongly defined by climate (Holdridge 1967).…”

The Relationship between Roosting Ecology and Degree of Polygyny in Harem-Forming Bats: Perspectives fromCynopterus

“…However, 2 main factors mitigate the potential for few males to monopolize most within-season breeding opportunities. First, unlike most harem-forming ungulates (e.g., Carranza et al 1996;Sánchez-Prieto et al 2004), and at least 1 species of bat (S. bilineata-Bradbury and Vehrencamp 1976; but see Hoffmann et al 2007), female harem members forage solitarily. Thus, although social interactions outside of the roost cannot be ruled out, cohesion of harem groups depends largely on the independent return of group members to the same roost.…”