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Intensity and Chronology of Postreproductive Molts in Male Canvasbacks

Jonathan E. Thompson and Ronald D. Drobney
The Wilson Bulletin
Vol. 107, No. 2 (Jun., 1995), pp. 338-358
Stable URL: http://www.jstor.org/stable/4163549
Page Count: 21
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Intensity and Chronology of Postreproductive Molts in Male Canvasbacks
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Abstract

We studied molt intensity and chronology in male Canvasbacks (Aythya valisineria) from termination of reproductive activities until fall migration (May-October) in 1989-1990. During this period, male Canvasbacks underwent prebasic, down, and partial prealternate molts. Males arrived on molting habitat already undergoing light prebasic molt. Total molt intensity increased to moderate levels in late preflightless birds and remained at this intensity through the postflightless period. Contour plumage molt intensity was reduced in staging birds concurrent with declining ambient temperatures and fall migration. Prebasic body molt was most intense in late preflightless birds, while peak prealternate molt occurred during the postflightless period. Remigial molt occurred from late July through August near completion of prebasic body molt. Prealternate molt began concurrent with late remigial molt and was not completed in male Canvasbacks before fall migration from central Alberta. Synchrony in the timing of remigial and prealternate molts suggests that these molts were probably under photoperiodic regulation in male Canvasbacks. Down replacement occurred throughout the postreproductive period but reached peak intensity in late preflightless, flightless, and postflightless birds. Only light down molt still occurred in staging Canvasbacks. All male Canvasbacks examined underwent the normal progression of postreproductive molts regardless of age; however, yearling males initiated prebasic molt earlier than birds ≥2 years old. Male Canvasbacks extended postreproductive molts over a period of six months which minimized the daily nutritional requirements for plumage growth.

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