Different as night and day: wild bats modify echolocation in complex environments when visual cues are present

Many animals rely on the integration of senses to interact with their environment. While most studies on multisensory integration focus on animals that use passive sensing, fewer studies have investigated actively sensing animals, such as animals that use echolocation. Prior work has demonstrated that bats and dolphins have the ability to perceive objects through both echolocation and vision and may integrate information across senses to improve target identification. Less is known, however, about how these animals might modify their active sensing systems when additional sensory input, such as visual cues, is available. In this study, we examine how Brazilian free-tailed bats, Tadarida brasiliensis, in the wild use their echolocation calls during night compared to day under two different sensory challenges: ground detection in an open field and roost localization in a complex and cluttered environment at a cave edge. Both location and light condition had a significant effect on call frequency and call duration. Echolocation calls had shorter durations and wider bandwidths during night compared to day, and this effect was more pronounced during roost localization at the complex cave edge. These results suggest that bats may use vision to supplement echolocation, but modifications to their sensing systems may depend on environmental complexity and/or sensorimotor challenges.