Postnuptial and Postjuvenal Molt in White-Crowned Sparrows in Central Alaska

Morton, Martin; King, James; Farner, Donald

The phenology of the postnuptial and postjuvenal molts in the White-crowned Sparrow was ascertained from examination of 500 free-living birds near Fairbanks, Alaska, during 1962. At the same time, the pattern of postnuptial molt was studied in 17 captive adults exposed to natural temperature and photo-period. There were no conspicuous differences between free-living and captive birds, and the data from these groups were combined in the general analysis. Postnuptial molt began in the population in the first week of July and ended by 25 August. In individual birds, the complete postnuptial molt required about 48 days. Renewal of the primary remiges required 37 days in the average individual; all nine primaries grew concurrently during the last 11 days of this period. Renewal of the secondary remiges required 26 days in the average individual, and a maximum of six secondaries grew concurrently. The renewal of the rectrices required about 25 days, all 12 growing concurrently. Molt of the contour plumage usually began with the shedding of the first primary and continued for about one week after the completion of growth in the flight feathers. Postjuvenal molt began in the population in the last few days of June and was essentially ended by 20 August. The duration of molt in an individual bird was about 34 days. Midsummer flock-formation began in immature White-crowned Sparrows in the third week of July, when the postjuvenal molt was well advanced. Adults initially remained apart, but began to join the immatures in flocks in the first week of August during the declining phase of the postnuptial molt. Migration, or premigratory gathering, of the local population began soon after 15 August, and White-crowned Sparrows were absent from the region after 1 September. A few of them must have begun the southward movement before body molt was finished. The summer molt of White-crowned Sparrows in central Alaska is characterized by its brevity, intensity of flight-fe

Postnuptial and Postjuvenal Molt in White-Crowned Sparrows in Central Alaska

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