Vision in echolocating bats - Fladdermus.net

Submitted manuscript
Vision complements echolocation in an aerial-hawking bat
Jens Rydell and Johan Eklöf
Zoology Department, Göteborg University, Box 463, SE 405 30 Göteborg,
Sweden.
Corresponding author:
Johan Eklöf, address as above
Tel. +46-317733666
Fax. +46-31416729
E-mail: johan.eklof@zool.gu.se
Abstract
The northern bat Eptesicus nilssonii hawks flying insects in the air using
frequency-modulated echolocation calls. It is known to detect and catch visually
conspicuous prey (white moths) hovering low among grass stalks. To overcome
the problem with acoustic clutter from the grass that interferes with target echo
detection, the bats made use of visual cues in addition to those of echolocation.
However, vision increased the chance of detection only when the moths were at
least 5 cm in wingspan. Smaller targets were detected using echolocation alone.
The mean detection range was 3.5 m, which suggests a visual acuity of 49´ of
arc. This is consistent with results of optomotor response tests and counts of
retinal ganglion cells in closely related species. The results suggest that vision in
Eptesicus bats is not sufficiently sharp for prey detection under normal
conditions but only when the prey is unusually large and conspicuous.
Nevertheless, the northern bat shows flexibility in prey-detection techniques not
previously recognised among aerial-hawking bats.
Key words: acoustic clutter, Hepialidae, insectivorous bats, nocturnality,
ultrasound, visual acuity.
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