Delayed plumage maturation in Lazuli buntings: tests of the female mimicry and status signalling hypotheses |
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Authors: | Vincent R Muehter Erick Greene Laurene Ratcliffe |
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Institution: | (1) Department of Science, National Audubon Society, New York, NY 10003, USA Tel.: (212) 979-3150; Fax: (212) 473-1633; e-mail: vmuehter@audubon.org, US;(2) Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA, US;(3) Department of Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada, CA |
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Abstract: | The evolutionary importance of delayed plumage maturation (DPM) in passerines, the condition when more than 1 year is required
to achieve adult-like coloration, remains highly contentious. Adaptive hypotheses propose that aggression from after 2nd-year
(ASY) males or predation favors DPM in 2nd-year (SY) males, thereby increasing SY male survivorship or reproductive success.
However, each hypothesis suggests a distinct selective mechanism explaining “how” this is accomplished. Alternatively, DPM
may be a consequence of a nonadaptive molt constraint. We tested the female mimicry and status signalling hypotheses in territorial
ASY male lazuli buntings (Passerinaamoena) using three sets of model presentation experiments. The female mimicry hypothesis proposes that dull SY male plumage deceptively
mimics female plumage, and predicts that ASY males can not distinguish SY male from female plumage. The status signalling
hypothesis proposes that dull SY male plumage honestly signals low competitive threat, and predicts that ASY males respond
less aggressively to dull versus bright, ASY-like plumage. Contrary to the female mimicry hypothesis, ASY males distinguished
between SY male and female plumage, as they were aggressive to SY male models exclusively and attempted to copulate with female
models. Supporting the status signalling hypothesis, ASY males were significantly less aggressive to SY versus ASY male plumage.
While DPM may result from a physiological constraint on bright SY male plumage, our results support the idea that dull plumage
in an SY male's first breeding season may be maintained by selection to reduce aggression from ASY males, serving as a signal
of competitive status.
Received: 21 February 1997 / Accepted after revision: 16 June 1997 |
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Keywords: | Delayed plumage maturation Plumage Female mimicry Status signalling Passerinaamoena |
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