Where do Egyptian fruit bats fly when auditory and visual spatial information conflicts?

Abstract

Egyptian fruit bats, Rousettus aegyptiacus, present a distinct opportunity to unravel the relative contributions of auditory and visual stimuli for navigation. This species has evolved lingual echolocation, but also uses rod vision to navigate. Echolocation and visual gaze are anchored to the head, but the bat's active control over sonar beam aim, ear, and eye position can influence sampling of sensory space. We investigated the relative weighting of echolocation and vision in free-flying Egyptian fruit bats. In this experiment, we used stereo IR video and microphone array recordings to quantify the bat’s trajectory, head direction and sonar beam as it flew to a landing perch. We introduced sensory conflict by equipping the bats with goggles fit with prisms that shifted visual images by 23 degrees to the left or right. In control trials, prisms were replaced with clear or light-blocking lenses. When bats were presented with conflicting visual and echolocation information, they flew in the direction of the prism shift and often missed the perch. Preliminary analyses of sonar beam aim suggests that their navigation is largely guided by vision. These findings underscore the dominant role of vision in bats that have also evolved auditory specializations to operate in darkness.