Diurnal constancy of feather growth rates in White-crowned Sparrows exposed to various photoperiods and feeding schedules during the postnuptial molt

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Abstract
To estimate the diurnal variation expenditure for feather synthesis during molt we measured the elongation of the primary remiges of White-crowned Sparrows (Zonotrichia leucophrys gambelii) through consecutive 12-h phases. All experimental birds (five groups) were illuminated and fed throughout the first 12-h phase of each cycle, but had various spans of illumination and feeding during the second 12-h phase. In spite of the differing schemes of illumination:feeding (12:12, 16:16, 16:12, 20:20, and 20:12), feather growth did not differ among groups in either 12-h phase. The grand average first-phase growth was 2.07 mm/12 h, compared with 2.05 mm/12 h in the second phase. These data suggest that nutrient expenditure for feather synthesis in White-crowned Sparrows is essentially constant throughout the 24-h cycle.