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Flight Performance and Competitive Displacement of Hummingbirds across Elevational Gradients

Altshuler, Douglas L. (2006) Flight Performance and Competitive Displacement of Hummingbirds across Elevational Gradients. American Naturalist, 167 (2). pp. 216-229. ISSN 0003-0147.

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Hummingbirds, with their impressive flight ability and competitive aerial contests, make ideal candidates for applying a mechanistic approach to studying community structure. Because flight costs are influenced by abiotic factors that change systematically with altitude, elevational gradients provide natural experiments for hummingbird flight ecology. Prior attempts relied on wing disc loading (WDL) as a morphological surrogate for flight performance, but recent analyses indicate this variable does not influence either territorial behavior or competitive ability. Aerodynamic power, by contrast, can be derived from direct measurements of performance and, like WDL, declines across elevations. Here, I demonstrate for a diverse community of Andean hummingbirds that burst aerodynamic power is associated with territorial behavior. Along a second elevational gradient in Colorado, I tested for correlated changes in aerodynamic power and competitive ability in two territorial hummingbirds. This behavioral analysis revealed that short-winged Selasphorus rufus males are dominant over long-winged Selasphorus platycercus males at low elevations but that the roles are reversed at higher elevations. Several lines of evidence support the hypothesis that the burst rather than sustained aerodynamic performance mediates competitive ability at high elevation. A minimum value for burst power may be required for successful competition, but other maneuverability features gain importance when all competitors have sufficient muscle power, as occurs at low elevations.

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Altshuler, Douglas L.0000-0002-1364-3617
Additional Information:© 2006 by The University of Chicago. Submitted September 24, 2004; Accepted September 15, 2005; Electronically published December 12, 2005 I thank P. Chai and R. Dudley for advice and support throughout all phases of this research. Comments on earlier drafts of this manuscript were also provided by C. J. Clark, M. H. Dickinson, S. Heredia, and F. G. Stiles. I gratefully acknowledge P. Baik, C. Barber, R. Gibbons, A. Gilbert, B. Holmes-Stanciu, C. Lewis, C. Shohet, O. Starry, D. Stephens, and the Earthwatch volunteers for field assistance; the Starsmore Discovery Center and the Rocky Mountain Biological Laboratory for logistical support; and the Colorado Springs School for hospitality. Fieldwork was supported by grants from the National Science Foundation (IBN-9817138 and IBN-992155), the Earthwatch Institute, Sigma Xi, and the University of Texas at Austin.
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Earthwatch InstituteUNSPECIFIED
University of Texas at AustinUNSPECIFIED
Subject Keywords:aerodynamic power requirements, burst performance, community structure, elevation, flight behavior, mechanistic approach
Issue or Number:2
Record Number:CaltechAUTHORS:ALTamnat06
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4138
Deposited By: Archive Administrator
Deposited On:28 Jul 2006
Last Modified:02 Oct 2019 23:10

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