Bats regulate biosonar based on the availability of visual information

The study of inter-sensory integration has focused largely on how different sensory modalities are weighted and combined in perception [1-3]. However, the extent to which information acquired through one sensory modality is modulated by another is yet unknown. We studied this problem in the Egyptian fruit bat (Rousettus aegyptiacus), an animal equipped with two modalities supporting high resolution distal sensing: biosonar and vision [4,5]. Egyptian fruit bats emit ultra-short, broad-band lingual echolocation clicks that enable accurate spatial orientation and landing [5]. They also rely heavily on vision, exhibiting high absolute sensitivity [4]. Here, we examine how visual information, regulated by altering ambient light level, influences biosonar sampling by Egyptian fruit bats. We tracked bats in the field and demonstrated that they routinely echolocate outdoors under a wide range of light levels. In the laboratory, under biologically relevant light levels, bats increased both echolocation click rate and intensity at lower light levels, where visual information was limited. These findings demonstrate how sensory information from one modality (vision) may influence sensory sampling of another (biosonar). Additionally, the bats adjusted biosonar sampling in a task-dependent manner, increasing click rate prior to landing. They did not cease echolocating under light conditions, which leads us to hypothesize that Egyptian fruit bats use echolocation to complement vision for accurate estimation of distance.