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First published online August 8, 2003

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Kinematics of hovering hummingbird flight along simulated and natural elevational gradients

Douglas L. Altshuler^1,* and Robert Dudley^1,2,

¹ Section of Integrative Biology, University of Texas at Austin, Austin, Texas 78712, USA
² Smithsonian Tropical Research Institute, PO Box 2072, Balboa, Republic of Panama

View larger version (18K): [in a new window]   Fig. 1. Hovering kinematics in hypodense air. As ambient air was replaced with normoxic heliox, air density decreased but the partial pressure of oxygen remained constant. The data depicted here were from the experiments performed at 1875 m, although the same trends were evident at 2900 m. (A) Wingbeat frequency increased slightly with decreasing air density. (B) Stroke amplitude increased substantially with decreasing density to a limit near 180°. Values are means ± S.E.M.

View larger version (18K): [in a new window]   Fig. 2. Hovering kinematics in hypoxic air. As ambient air was replaced with pure nitrogen, the partial pressure of oxygen declined but the air density varied only slightly. Otherwise, conditions were identical to that of the first experiment described in Fig. 1. (A) The wingbeat frequency decreased slightly but significantly as oxygen partial pressure decreased (see text). (B) Stroke amplitude varied considerably but exhibited no clear pattern with changing partial pressure of oxygen. Values are means ± S.E.M. All symbols as in Fig. 1. 1 mmHg=133.3 Pa.

View larger version (22K): [in a new window]   Fig. 3. Kinematics in hyperoxic air. As ambient air was replaced with hyperoxic heliox, air density decreased and oxygen concentration increased simultaneously. During normoxia trials, ambient air was replaced with normoxic heliox so that air density decreased but oxygen concentration remained at 21%. Hummingbird kinematics in hyperoxia were equivalent to those in normoxia. Values are means ± S.E.M. See text for details. %O2 is the oxygen concentration at each density under hyperoxia.

View larger version (18K): [in a new window]   Fig. 4. Wingbeat kinematics during hovering across a natural elevational gradient in the Peruvian Andes. Data are species mean for 43 species of hummingbirds. (A) Wingbeat frequency decreased with increasing body mass. The largest hummingbird is the giant hummingbird Patagona gigas, which is substantially larger than all other trochilid taxa and is considered an outlier. However, the decrease in wingbeat frequency with body mass is found even if P. gigas is removed from the analysis (inset; all P<0.001; see text). (B) Stroke amplitude increased with increasing elevation, mirroring the results of experiment 1 (Fig. 1). See text for regression equations.

View larger version (26K): [in a new window]   Fig. 5. Wingbeat kinematics during free hovering and load-lifting in Peruvian hummingbirds. (A,B) Raw species data, (C,D) phylogenetically corrected independent contrast data. Solid lines, free flight; broken lines, load-lifting. Wingbeat frequency decreased with increasing body mass during both load-lifting and free hovering flight. Stroke amplitude increased with increasing elevation during free flight, but not with elevation during load-lifting, because all hummingbirds reached a maximum stroke amplitude of approximately 180° at the point of maximum lifting. See text for regression equations.