Postnuptial Molt in Harris' Sparrows

Abstract

We studied the postnuptial molt of captive male and female Harris' Sparrows (Zonotrichia querula) exposed to photoperiods simulating those on the breeding grounds and ambient temperatures of 22-250C. Postnuptial molt was completed in about 82 days in individual birds. It began with the loss of Pi and concluded with replacement of contour feathers in the dorsal and ventral body tracts. Peaks of molt intensity essentially coincided in all of the major feather tracts. Intensity was highest between days 28 and 59 of molt. Primaries were replaced in the sequence normal for other passerines, but secondaries exhibited considerable deviation from the typical passerine pattern. Rectrices were often molted centrifugally, from Ri through R6, but several were dropped and replaced simultaneously. Body molt, which is described in all tracts separately, began shortly after Pi was shed and continued until the end of the molt period. Postnuptial molt is protracted and lasts considerably longer in captive Harris' Sparrows than in other North American Zonotrichia which summer either at high northern latitudes or high altitudes. The time-course of molt in Harris' Sparrows suggests that (1) periods of breeding and postnuptial molt may overlap, and (2) postnuptial molt is completed during the fall migration.