Behavioral Ecology Advance Access published online on June 11, 2004
Behavioral Ecology, doi:10.1093/beheco/arh078
© 2004 by International Society for Behavioral Ecology
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1 Department of Zoology and Entomology, University of Queensland, St. Lucia 4072, Australia
* To whom correspondence should be addressed. E-mail: ekrebs{at}sfu.ca.
Competition over access to food has led to the evolution of a variety of exaggerated visual and vocal displays in altricial nestling birds. Precocial chicks that are fed by their parents also vary widely in appearance ranging from those with inconspicuous coloration to those with brightly colored bills, fleshy parts, and plumes. These ornaments are lost by the end of the period of parental dependence, suggesting they function in competition over parental care. We use a comparative approach to evaluate which ecological or life-history variables may have favored the evolution of conspicuous ornamentation in precocial chicks. We compiled data on chick morphology, ecology, and social organization of species in the Family Rallidae, a group with highly variable downy chicks. Chick ornamentation in the form of brightly colored bills, fleshy patches, or plumes is observed in 36 of 97 species for which downy chicks are described. Phylogenetic reconstructions suggest that nonornamentation is the ancestral state. Chick ornamentation has evolved multiple times within the Rallidae and is significantly associated with large clutch sizes and polygamous mating systems. Chick ornamentation was also weakly associated with adult ornamentation and adult dimorphism. We argue that these results support the hypothesis that lineages with higher levels of sibling competition are more likely to evolve ornamented chicks.
Revised September 8, 2003
Accepted October 1, 2003
Chic chicks: the evolution of chick ornamentation in rails
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