Entries in bats (1)

Tuesday
Nov072017

Vertical limits of bat echolocation

Contrary to popular belief, bats are not actually blind—this misconception stems from the fact that more than half of the 900 species do rely upon echolocation to navigate during their nocturnal activities. Echolocation, the use of sonar (sound navigation and ranging) with special morphological and physiological adaptations, enables bats to “see” with sound! Bats emit high-frequency calls and listen for the returning echoes, which provide them with the information they need to negotiate complex terrain and track moving prey in the dark. This echolocation is so precise they can discriminate differences of less than one millimeter in surface textures [1]!

I was surprised to learn that this impressive capability has a big flaw. In a recently published paper [2], scientists found that bat echolocation has a tough time with some environmental features. Specifically, smooth, vertical surfaces (think metal or glass plates on a building) provide a false environmental cue to the bat, tricking the animal into sensing that it is actually flying into open air! As you can imagine, this does not end well for the bats. Sadly, bats are often found dead or injured near buildings and other smooth structures, and the false cues the bats pick up from the buildings may be a major culprit. 

The sensory trap that a smooth building may create is not the only one that bats can fall prey to. In fact, Dr. Stefan Grief demonstrated in a previous study [3] that smooth metal or plastic plates also act as a sensory trap when laid on the ground; bats mistook these surfaces for water. In his recent study [3] at the Max Planck Institute for Ornithology, Dr. Grief and his colleagues flew greater mouse-eared bats around a dark, rectangular flight tunnel. Near one of the tunnel’s corners, the researches placed a metal plate either on the ground or against the wall. The result? All but two of the bats out of 21 hit the vertical plate at least once, but none of the bats ever hit the horizontal plate of any other part of the tunnel.

However, as noted previously, bats are not blind and they do integrate echolocation and vision to navigate. Why then do smooth, vertical structures pose such a navigational hazard to bats? That is still a question pondered by bat biologists, and one that Dr. Greif aims to explore in the future.

BGH

  1. Simmons, J. A., Ferragamo, M. J., & Moss, C. F. (1998). Echo-delay resolution in sonar images of the big brown bat, Eptesicus fuscusProceedings of the National Academy of Sciences of the United States of America95(21), 12647–12652.
  2. Greif, S., Zsebok, S., Schmieder, D., & Siemers, BM. (2017). Acoustic mirrors as sensory traps for bats. Science, 357(6355), 1045-1047.
  3. Greif, S., & Siemers, B. M. (2010). Innate recognition of water bodies in echolocating bats. Nature Communications1, 107–. http://doi.org/10.1038/ncomms1110.