Behavioral Ecology and Sociobiology

, Volume 7, Issue 4, pp 273–279 | Cite as

Age, coloration and dominance in nonbreeding hummingbirds: A test of the asymmetry hypothesis

  • Paul W. Ewald
  • Sievert Rohwer


During the nonbreeding season, adult Anna and black-chinned hummingbirds (Calypte anna and Archilochus alexandri) have lower defense costs and more exclusive territories than juveniles. Adult C. anna are victorious over juveniles in aggressive encounters, and tend to monopolize the most temporally predictable resources.

Juveniles are more successful than adults at stealing food from territories (the primary alternative to territoriality), presumably because juveniles are less brightly colored. Juveniles have lighter wing disc loading than adults, and consequently should have lower rates of energy expenditure during flight. Reduced flight expenditures may be more important for juveniles because their foraging strategy requires large amounts of flight time. These results support the contention of the asymmetry hypothesis that dominance can result from a contested resource being more valuable to one contestant than to the other.

Among juveniles, defence costs are also negatively correlated with age and coloration; amount of conspicucus coloration is negatively correlated with the number of bill striations, an inverse measure of age.


Energy Expenditure Flight Time Lower Defense Wing Disc Defence Cost 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag 1980

Authors and Affiliations

  • Paul W. Ewald
    • 1
  • Sievert Rohwer
    • 1
  1. 1.Department of Zoology and Washington State MuseumUniversity of WashingtonSeattleUSA

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