Though the various subspecies of Zonotrichia leucophrys differ in breeding sites and the dates of their arrival to breeding grounds, the basic system of breeding is very similar. The males are usually the first to arrive on the breeding grounds, and after the females have arrived it is only about one to three weeks before they make their first nests. Most pairs only produce one brood. This is done after an average of about 2 days from the time the cup-shaped nest was built (Morton 1997). The females incubate the eggs, and develop a brood patch during the nest construction to make this process more efficient. Incubation lasts about 12 days, throughout which the female is responsible for turning the eggs, as well as leaving during the day to forage for herself.
The male white-crowned sparrow finally begins to contribute to this effort once the eggs have hatched. He brings food, contributing more and more to feeding the young as they mature. But about halfway through their development (~day 5), his contribution steadily begins to decrease.
When first born, the young birds are naked except for a few down feathers along some tracks on their transparent pink body. Most of them fledge by the tenth day, and reach their adult weight by day 30-35.
Though not very common, brown-headed cowbirds have been known to be a brood parasite of the white-crowned sparrow. When this occurs, the cowbirds only lay about one egg per nest, and their young tend to be just as successful as those of the sparrow.
Average time to hatching: 13 days.
Average eggs per season: 4.
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