Document Detail


Transient hovering performance of hummingbirds under conditions of maximal loading.
MedLine Citation:
PMID:  9100364     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Maximal load-lifting capacities of six ruby-throated hummingbirds (Archilochus colubris) were determined under conditions of burst performance. Mechanical power output under maximal loading was then compared with maximal hovering performance in hypodense gas mixtures of normodense air and heliox. The maximal load lifted was similar at air temperatures of 5 and 25 degrees C, and averaged 80% of body mass. The duration of load-lifting was brief, of the order of 1 s, and was probably sustained via phosphagen substrates. Under maximal loading, estimates of muscle mass-specific mechanical power output assuming perfect elastic energy storage averaged 206 W kg-1, compared with 94 W kg-1 during free hovering without loading. Under conditions of limiting performance in hypodense mixtures, maximal mechanical power output was much lower (131 W kg-1, five birds) but was sustained for longer (4 s), demonstrating an inverse relationship between the magnitude and duration of maximum power output. In free hovering flight, stroke amplitude and wingbeat frequency varied in inverse proportion between 5 and 25 degrees C, suggesting thermoregulatory contributions by the flight muscles. Stroke amplitude under conditions of maximal loading reached a geometrical limit at slightly greater than 180 degrees. Previous studies of maximum performance in flying animals have estimated mechanical power output using a simplified actuator disk model without a detailed knowledge of wingbeat frequency and stroke amplitude. The present load-lifting results, together with actuator disc estimates of induced power derived from hypodense heliox experiments, are congruent with previous load-lifting studies of maximum flight performance. For ruby-throated hummingbirds, the inclusion of wingbeat frequency and stroke amplitude in a more detailed aerodynamic model of hovering yields values of mechanical power output 34% higher than previous estimates. More generally, the study of performance limits in flying animals necessitates careful specification of behavioral context as well as quantitative determination of wing and body kinematics.
Authors:
P Chai; J S Chen; R Dudley
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of experimental biology     Volume:  200     ISSN:  0022-0949     ISO Abbreviation:  J. Exp. Biol.     Publication Date:  1997 Mar 
Date Detail:
Created Date:  1997-05-02     Completed Date:  1997-05-02     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0243705     Medline TA:  J Exp Biol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  921-9     Citation Subset:  IM; S    
Affiliation:
Department of Zoology, University of Texas, Austin 78712, USA. pengchai@utxvms.cc.utexas.edu
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MeSH Terms
Descriptor/Qualifier:
Animals
Biomechanics
Birds / physiology*
Flight, Animal / physiology*
Muscles / physiology
Physical Exertion

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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