Visually aided biosonar in bats

It is currently unclear to what extent bats rely on vision and how they weigh and integrate visual and acoustic (sonar-based) information. In a recent joint project we studied how the Egyptian fruit bat (Rousettus aegyptiacus), an animal equipped with both high resolution vision and echolocation, adjusts sensory acquisition for the two senses.

HFSP Program Grant holders Cynthia Moss and Yossi Yovel and colleagues
authored on Thu, 31 March 2016

Egyptian fruit bats emit ultra-short, broad-band lingual echolocation clicks that enable accurate spatial orientation and landing. They also rely heavily on vision, exhibiting high absolute sensitivity. We examined how the availability of visual information, which we regulated by altering ambient light level, influenced biosonar sampling by Egyptian fruit bats.

Our study was composed of two parts. We first tracked bats in the field using miniature GPS to document in which light levels these bats typically operate and to demonstrate that they routinely use echolocation when foraging outdoors. In the laboratory, we then flew the bats in a flight corridor under a range of biologically relevant light levels. We found that bats increased both echolocation click rate and intensity at lower light levels, where visual information was limited.

These findings show how sensory information from one modality (vision) may influence sensory sampling of another (biosonar). We believe the discovery that information available through one modality alters sampling of another is probably relevant to other animals and other sensory systems. Interestingly, the bats did not cease echolocating even under high illumination conditions, which leads us to hypothesize that Egyptian fruit bats use echolocation to complement vision for accurate estimation of distance.

Reference

Bats regulate biosonar based on the availability of visual information. Danilovich, S, Krishnan, A. Lee,  W-J, Borrisov, I, Eitan, O., Kosa, G. Moss, C.F. and Yovel,  Y.  Current Biology, Volume 25, Issue 23, pR1124–R1125, 2015.

Pubmed link

Echolocating bats foraging in a cocktail party (by Cynthia Moss)