Effects of Photoperiod and Temperature on Postnuptial Molt in Captive White-Crowned Sparrows

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Abstract
Postnuptial molt was studied in 2 outdoor and 6 indoor groups of captive white-crowned sparrows (Zonotrichia leucophrys gambelii). Air temperature differed in 4 and photoperiod differed in 3 of the indoor groups. Molt occurred in all groups except birds at 12L [light]:12D [darkness]. The most typical post-nuptial molt was observed in groups at 16L:8D at 15.degree. or 20.degree. C. At 20L:4D photoperiod (20.degree. C) hastened molt onset compared to a 16L:8D photoperiod (20.degree. C), but resulted in lack of synchrony in molt onset in individuals (also occurring in birds at 16L:8D and 25.degree. C). No differences in molt duration among feather tracts studied were found between birds at 20L:4D or 16L:8D. Low air temperature (5.degree. C) reduced the overall duration of molt, but not the molt of any of the 6 feather tracts examined. This appeared to be the result of at least 2 processes: the shedding interval between adjacent primaries tended to be shorter in cold-acclimated birds; and the phasing of molt onset in secondary and body feathers relative to primary feather molt onset was significantly altered under low to moderate (5.degree.-15.degree. C) air temperature, favoring a shorter overall molt. Higher air temperatures had little or no effect upon molt tempo or chronology. Primary wing feathers of captives subjected to 16 and 20 h photoperiods grew at the same rate as those of captives at the natural breeding site. The calendar dates of molt onset of postnuptial molt as well as molt onset in various feather tracts observed in this study did not differ from those in a study conducted 10 yr earlier. Substantial differences were found in growth rates of individual feathers, perhaps reflecting the less exact methodology of earlier investigations in addition to differences in avian populations.