Systematics

Figure 2. The first 4 pairs of chromosomes in the 2 commonest karyotypes of the White-throated Sparrow.

Geographic Variation

No geographic variation in plumage or size described, surprising for a species with so large a range. The species is dimorphic in color of the supercilium and breast; see Behavior: sexual.

Subspecies

Monotypic; no subspecies described. Note, however, that Fringilla pennsylvanica Latham, 1790, is a synonym of Zonotrichia albicollis (Gmelin, 1788). In either case, the type specimen is from Pennsylvania.

Related Species

On basis of morphological and genetic evidence, the genus Zonotrichia is most closely related to genera Junco and, perhaps, Spizella, Melospiza, and Passerella (Dickerman 1961, Paynter 1964, Short and Simon 1965, Zink 1982, Patten and Fugate 1998, Carson and Spicer 2003). Breeding ranges of four of the five species of Zonotrichia overlap substantially; the breeding range of these four species is >2500 km from the more distantly related fifth species, the Rufous-collared Sparrow (Z. capensis) of the montane Neotropics. Mitochondrial DNA evidence suggests that the White-throated Sparrow is sister to a clade of both the White-crowned (Z. leucophrys) and Golden-crowned (Z. atricapilla) sparrows (Zink et al. 1991, Zink and Blackwell 1996). These two species diverged from the White-throated Sparrow ~750,000 ybp, and the three together diverged from Harris's Sparrow (Z. querula) ~1.2 million ybp.

Hybrids reported with the Golden-crowned Sparrow (Payne 1979), White-crowned Sparrow (Abbott 1959, disputed by Banks 1970), and Dark-eyed Junco (Junco hyemalis), of which there are at least 14 records (Dickerman 1961, Short and Simon 1965, Blem 1981, Jung et al. 1994). There is even a report of a White-throated Sparrow fostering two fledgling Dark-eyed Juncos (Greenlaw 1977), although the fledglings did not appear to be hybrids. The White-throated Sparrow has hybridized with the Song Sparrow (Melospiza melodia) in captivity (McCarthy 2006).