One of the continent's best-studied and most familiar songbirds, the White-throated Sparrow is found at some season throughout much of North America south of the tree line and principally east of the Rocky Mountains. To many its distinctive whistled song is synonymous with the northern wilderness. During migration and throughout its winter range, this species is a common visitor at feeding stations. It breeds primarily in the boreal coniferous and mixed forest and, a short-distance migrant, winters mainly in the southeastern U.S. A habitat generalist, it tends to occur in shrubby edges or early successional stages or openings in the forest, nesting and foraging for seeds and insects on or near the ground.
Throughout its extensive range the White-throated Sparrow shows no subspecific variation. However, it exhibits plumage polymorphism (white-striped and tan-striped morphs – see color photos) in both sexes, most obvious in the breeding season, associated with a difference in an autosome. These differences in plumage and karyotype are maintained by negative assortative (disassortative) mating – each morph mates with its opposite. Plumage differences are paralleled by differences in behavior and breeding strategy. White-striped (WS) males sing more, are more aggressive and more likely to engage in extra-pair copulation than their tan-striped (TS) counterparts. TS birds of both sexes provide more parental care than WS birds. This unusual combination of attributes has made the White-throated Sparrow an attractive subject for studies of genetic, neural, and endocrine control of life-history characteristics. It also provides a rare example of a non-recombining autosomal segment of the genome and may be useful as a model for the early stages of sex chromosome evolution ( Thomas et al. 2008 ). See Behavior (sexual behavior) for details of polymorphism and assortative mating.
In many respects the natural history of the White-throated Sparrow is much like that of other North American sparrows. Because of its abundance, accessibility on both breeding and wintering grounds, and the relative ease with which it can be maintained in captivity, it has been used in many types of biological investigation, in addition to studies related to polymorphism, e.g. breeding biology, physiology in relation to the annual cycle, circadian rhythms, migration, dominance and territoriality, functions of song, and the effects of pesticides and forestry practices.