Flexible use of visual and acoustic cues during roost finding in Spix’s disc-winged bat (Thyroptera tricolor)

Abstract The ability of an animal to detect environmental cues is crucial for its survival and fitness. In bats, sound certainly plays a significant role in the search for food, spatial navigation, and social communication. Yet, the efficiency of bat’s echolocation could be limited by atmospheric attenuation and background clutter. In this context, sound can be complemented by other sensory modalities, like smell or vision. Spix’s disc-winged bat (Thyroptera tricolor) uses acoustic cues from other group members to locate the roost (tubular unfurled leaves of plants in the order Zingiberales). Our research focused on how individuals find a roost that has not been yet occupied, considering the urge to find a suitable leaf approximately every day, during nighttime or in daylight. We observed the process of roost finding in T. tricolor in a flight cage, manipulating the audio/visual sensory input available for each trial. A broadband noise was broadcast in order to mask echolocation, while experiments conducted at night reduced significantly the amount of light. We measured the time needed to locate the roost under these different conditions. Results show that with limited visual and acoustic cues, search time increases significantly. In contrast bats seemed capable of using acoustic and visual cues in a similarly efficient manner, since roost search showed no strong differences in duration when bats could use only sound, only vision, or both senses at the same time. Our results show that non-acoustic inputs can still be an important source of information for finding critical resources in bats. Switching home frequently is a real challenge for highly specialized bats. Our study shows how the bat, Thyroptera tricolor, flexibly uses both acoustic and visual cues to find a roost that has not been previously occupied by other bats. This ability to switch sensory modality depending on environmental conditions is crucial for a bat that may be evicted from the roost during the day, when the risk of predation is higher.