Tobalske, Bret W. and Altshuler, Douglas L. and Powers, Donald R. (2004) Take-off mechanics in hummingbirds (Trochilidae). Journal of Experimental Biology, 207 (8). pp. 1345-1352. ISSN 0022-0949 http://resolver.caltech.edu/CaltechAUTHORS:20110822-111151857
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Initiating flight is challenging, and considerable effort has focused on understanding the energetics and aerodynamics of take-off for both machines and animals. For animal flight, the available evidence suggests that birds maximize their initial flight velocity using leg thrust rather than wing flapping. The smallest birds, hummingbirds (Order Apodiformes), are unique in their ability to perform sustained hovering but have proportionally small hindlimbs that could hinder generation of high leg thrust. Understanding the take-off flight of hummingbirds can provide novel insight into the take-off mechanics that will be required for micro-air vehicles. During take-off by hummingbirds, we measured hindlimb forces on a perch mounted with strain gauges and filmed wingbeat kinematics with high-speed video. Whereas other birds obtain 80–90% of their initial flight velocity using leg thrust, the leg contribution in hummingbirds was 59% during autonomous take-off. Unlike other species, hummingbirds beat their wings several times as they thrust using their hindlimbs. In a phylogenetic context, our results show that reduced body and hindlimb size in hummingbirds limits their peak acceleration during leg thrust and, ultimately, their take-off velocity. Previously, the influence of motivational state on take-off flight performance has not been investigated for any one organism. We studied the full range of motivational states by testing performance as the birds took off: (1) to initiate flight autonomously, (2) to escape a startling stimulus or (3) to aggressively chase a conspecific away from a feeder. Motivation affected performance. Escape and aggressive take-off featured decreased hindlimb contribution (46% and 47%, respectively) and increased flight velocity. When escaping, hummingbirds foreshortened their body movement prior to onset of leg thrust and began beating their wings earlier and at higher frequency. Thus, hummingbirds are capable of modulating their leg and wingbeat kinetics to increase take-off velocity.
|Additional Information:||© 2004 The Company of Biologists Limited. Accepted 21 January 2004. We thank Ben Zimmerman and Brenna Brandsma for their assistance in collecting comparative data on take-off velocity, and anonymous referees for their helpful comments on a previous draft of this manuscript. This study was supported by grants from the M. J. Murdock Charitable Trust (99153 and 2001208) and National Science Foundation (DUE 9952346) to B.W.T.|
|Subject Keywords:||rufous hummingbird, Selasphorus rufus, force, perch, velocity, kinematics, flight|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||13 Sep 2011 17:14|
|Last Modified:||26 Dec 2012 13:29|
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