Altshuler, Douglas L. and Dudley, Robert (2003) Kinematics of hovering hummingbird flight along simulated and natural elevational gradients. Journal of Experimental Biology, 206 (18). pp. 3139-3147. ISSN 0022-0949 http://resolver.caltech.edu/CaltechAUTHORS:20111005-090030062
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Hovering flight is one of the most energetically demanding forms of animal locomotion. Despite the cost, hummingbirds regularly hover at high elevations, where flight is doubly challenging because of reduced air density and oxygen availability. We performed three laboratory experiments to examine how air density and oxygen partial pressure influence wingbeat kinematics. In the first study, we experimentally lowered air density but maintained constant oxygen partial pressure. Under these hypodense but normoxic conditions, hummingbirds increased stroke amplitude substantially and increased wingbeat frequency slightly. In the second experiment, we maintained constant air density but decreased oxygen partial pressure. Under these normodense but hypoxic conditions, hummingbirds did not alter stroke amplitude but instead reduced wingbeat frequency until they could no longer generate enough vertical force to offset body weight. In a final combined experiment, we decreased air density but increased oxygen availability, and found that the wingbeat kinematics were unaffected by supplemental oxygen. We also studied hovering and maximally loaded flight performance for 43 hummingbird species distributed along a natural elevational gradient in Peru. During free hovering flight, hummingbirds showed increased stroke amplitude interspecifically at higher elevations, mirroring the intra-individual responses in our first laboratory experiment. During loaded flight, hummingbirds increased both wingbeat frequency and wing stroke amplitude by 19% relative to free-flight values at any given elevation. We conclude that modulation of wing stroke amplitude is a major compensatory mechanism for flight in hypodense or hypobaric environments. By contrast, increases in wingbeat frequency impose substantial metabolic demands, are only elicited transiently and anaerobically, and cannot be used to generate additional sustained lift at high elevations.
|Additional Information:||© 2003 The Company of Biologists Limited. Accepted 12 June 2003. We thank Peng Chai for deep insights into hummingbird flight performance. We also thank Peter Baik, Jeff Chen, Jeremy Goldbogen, Holly Hughes and Andrea Smith for assistance with video analysis. Laboratory and field experiments were supported by grants from the Earthwatch Institute, the Explorers Club, the Graduate Program in Zoology at the University of Texas, the Institute for Latin American Studies at the University of Texas, the National Science Foundation (IBN 9817138, IBN 992155 and DEB 0108555), Sigma Xi, and the Graduate School of the University of Texas at Austin.|
|Subject Keywords:||air density, elevation, flight, hummingbird, hyperoxia, hypoxia, kinematics, load lifting, oxygen concentration, wingbeat frequency, stroke amplitude|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||05 Oct 2011 16:37|
|Last Modified:||26 Dec 2012 14:00|
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