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First published online October 17, 2008
Journal of Experimental Biology 211, ii (2008)
Copyright © 2008 The Company of Biologists Limited
doi: 10.1242/jeb.025668
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BATS TAKE TURNS BY BANKING AND CRABBING
kathryn{at}biologists.com
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Manoeuvring accurately through a complex environment can be a matter of life or death. Take a wrong turn and a crash could be fatal. José Iriarte-Díaz explains that quite a lot is known about the mechanisms that birds and insects use to negotiate turns, but virtually nothing was known about the mechanics of bat turns. Filming four Cynopterus brachyotis fruit bats as they flew along a corridor with a 90 deg. bend in the middle, Iriarte-Díaz and Sharon Swartz from Brown University found that the animals use a combination of banking and crabbing to make it round a bend (p. 3478).
According to Iriarte-Díaz and Swartz, it took between six and seven wing beats for the bats to take the 90 deg. turn. Analysing the animal's flight path and orientation, they found that as well as banking to generate corner-turning centripetal forces, the bats reoriented their bodies in the direction of the bend during each upstroke; they were crabbing too. The bats were using the net aerodynamic force to negotiate the turn during the upstroke by reorienting their bodies to direct the force around the corner, while using the forward component of the net aerodynamic force to move in the direction of travel during the down stroke.
Having found that C. brachyotis bats rely on two mechanisms to turn a corner, the team compared the mammal's manoeuvrability with bird and insect data from the literature and found that the bats are much more manoeuvrable than banking cockatiels, probably due to the bat's smaller size. However, they are not as manoeuvrable as microchiropteran bats, which H. Aldridge found could turn through 180 deg. in the 1980s. The team also compared their results with David Alexander's 1986 dragonfly data, where he found that crabbing insects were significantly more manoeuvrable than banking insects, and they suggest that combining crabbing with banking gives bats the edge when taking a turn.
References
Iriarte-Díaz, J. and Swartz, S. M.
(2008). Kinematics of slow turn maneuvering in the fruit bat
Cynopterus brachyotis. J. Exp. Biol.
211,3478
-3489.
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