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Resolution of a paradox: Hummingbird flight at high elevation does not come without a cost

Altshuler, Douglas L. and Dudley, Robert and McGuire, Jimmy A. (2004) Resolution of a paradox: Hummingbird flight at high elevation does not come without a cost. Proceedings of the National Academy of Sciences of the United States of America, 101 (51). pp. 17731-17736. ISSN 0027-8424. PMCID PMC539726.

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Flight at high elevation is energetically demanding because of parallel reductions in air density and oxygen availability. The hovering flight of hummingbirds is one of the most energetically expensive forms of animal locomotion, but hummingbirds are nonetheless abundant at high elevations throughout the Americas. Two mechanisms enhance aerodynamic performance in high-elevation hummingbirds: increase in wing size and wing stroke amplitude during hovering. How do these changes in morphology, kinematics, and physical properties of air combine to influence the aerodynamic power requirements of flight across elevations? Here, we present data on the flight performance of 43 Andean hummingbird species as well as a 76-taxon multilocus molecular phylogeny that served as the historical framework for comparative analyses. Along a 4,000-m elevational transect, hummingbird body mass increased systematically, placing further aerodynamic demands on high-elevation taxa. However, we found that the minimum power requirements for hovering flight remain constant with respect to elevation because hummingbirds compensate sufficiently through increases in wing size and stroke amplitude. Thus, high-elevation hummingbirds are not limited in their capacity for hovering flight despite the challenges imposed by hypobaric environments. Other flight modes including vertical ascent and fast forward flight are more mechanically and energetically demanding, and we accordingly also tested for the maximum power available to hummingbirds by using a load-lifting assay. In contrast to hovering, excess power availability decreased substantially across elevations, thereby reducing the biomechanical potential for more complex flight such as competitive and escape maneuvers.

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Altshuler, Douglas L.0000-0002-1364-3617
Additional Information:© 2004 by The National Academy of Sciences of the USA. Edited by David B. Wake, University of California, Berkeley, CA, and approved October 12, 2004 (received for review July 20, 2004). This paper was submitted directly (Track II) to the PNAS office. Published online before print December 14, 2004, 10.1073/pnas.0405260101 Data deposition: The sequences reported in this paper have been deposited in the GenBank database (accession nos. AY830455–AY830681). We thank C. Barber, R. Gibbons, and Earthwatch Institute (Maynard, MA) volunteers for assistance with fieldwork in Peru. Additional help was provided by P. Baik, M. Dillon, A. Gilbert, J. Goldbogen, W. Palomino, and V. Yabar. We thank M. Van Vlaardingen and Pantiacolla Tours (Peru), B. Gomez, C. Munn, R. Yabar, and B. Walker for logistical support. This work was supported by National Science Foundation Grants IBN 9817138 and DEB 0330750 and grants from the Earthwatch Institute.
Funding AgencyGrant Number
NSFIBN 9817138
NSFDEB 0330750
Earthwatch InstituteUNSPECIFIED
Subject Keywords:animal flight, aerodynamic power requirements, hummingbird phylogeny
PubMed Central ID:PMC539726
Record Number:CaltechAUTHORS:ALTpnas04
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:680
Deposited By: Archive Administrator
Deposited On:14 Sep 2005
Last Modified:24 Nov 2015 00:01

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