title: Vision impairs the abilities of bats to avoid colliding with stationary obstacles.
abstract: BACKGROUND
  Free-flying insectivorous bats occasionally collide with stationary objects they should easily detect by echolocation and avoid. Collisions often occur with lighted objects, suggesting ambient light may deleteriously affect obstacle avoidance capabilities. We tested the hypothesis that free-flying bats may orient by vision when they collide with some obstacles. We additionally tested whether acoustic distractions, such as "distress calls" of other bats, contributed to probabilities of collision.
  
  
  RESULTS
  To investigate the role of visual cues in the collisions of free-flying little brown bats (Myotis lucifugus) with stationary objects, we set up obstacles in an area of high bat traffic during swarming. We used combinations of light intensities and visually dissimilar obstacles to verify that bats orient by vision. In early August, bats collided more often in the light than the dark, and probabilities of collision varied with the visibility of obstacles. However, the probabilities of collisions altered in mid to late August, coincident with the start of behavioural, hormonal, and physiological changes occurring during swarming and mating. Distress calls did not distract bats and increase the incidence of collisions.
  
  
  CONCLUSIONS
  Our findings indicate that visual cues are more important for free-flying bats than previously recognized, suggesting integration of multi-sensory modalities during orientation. Furthermore, our study highlights differences between responses of captive and wild bats, indicating a need for more field experiments.
authors.affiliation: Department of Biology, University of Western Ontario, London, Ontario, Canada. dnorbach@gmail.com
authors.forename: Dara N
authors.initials: DN
authors.lastname: Orbach
authors.forename: Brock
authors.initials: B
authors.lastname: Fenton
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002685:Chiroptera / Q000502:physiology*; D055867:Cyclonic Storms; D004455:Echolocation / Q000502:physiology*; D005260:Female; D005426:Flight, Animal / Q000502:physiology*; D008027:Light; D008297:Male; D013028:Space Perception / Q000502:physiology / Q000528:radiation effects; D014785:Vision, Ocular / Q000502:physiology* / Q000528:radiation effects; D014828:Vocalization, Animal / Q000502:physiology