Investigations of delayed plumage maturation in the orchard oriole
Enstrom, David A.
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Permalink
https://hdl.handle.net/2142/22856
Description
Title
Investigations of delayed plumage maturation in the orchard oriole
Author(s)
Enstrom, David A.
Issue Date
1990
Doctoral Committee Chair(s)
Robinson, Scott K.
Burley, Nancy
Department of Study
Biology
Discipline
Biology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, General
Biology, Ecology
Biology, Zoology
Language
eng
Abstract
I investigated delayed plumage maturation (DPM) in the orchard oriole Icterus spurius), a dichromatic neo-tropical migrant in which first year males possess a distinct non-definitive plumage. I used model/playback experiments to test predictions of alternative breeding season signaling hypotheses for DPM. I found that, contrary to the results of several previous studies, subadult plumage in the orchard oriole does not reduce intra-sexual aggression directed toward subadults during the breeding season. I attribute these different results to differences among species in the reliability of plumage cues of sex and age. In a second study, I examined winter adaptation hypotheses for DPM. I conducted focal animal observations of foraging orioles during the non-breeding season in Panama in order to evaluate predictions of the winter status signaling hypothesis, and I found that, contrary to this hypothesis, subadult male plumage reduced neither the frequency or intensity of adult male aggression during the winter. While in Panama, I also examined the molt characteristics of orioles in order to test predictions of the molt constraint hypothesis. I found that the majority of feathers grown by subadult males during the presumed per-alternate molt were of non-definitive coloration, contrary to predictions of molt constraint hypothesis. Finally, I tested female preference for age specific plumage characteristics. I found that females preferred adult males to subadult males in choice experiments with both live and model males.
These results suggest that subadult plumage may not be advantageous in any context and demonstrate that subadult plumage in the orchard oriole is costly in the context of intrasexual aggression and female mate choice. I suggest that DPM may be the result of age specific constraints on plumage development in subadult males.
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