This morning, I spent the morning banding migratory passerines with Dr. Christopher Heckscher of Delaware State University. We captured several beautiful White-throated Sparrows (Zonotrichia albicollis), which come in two distinct color morphs that are not dependent on age or sex.
“Tan-striped” birds (left) have a tan crown stripe and supercilium, whereas these features are bright white on “white-striped” birds (right). Notice also the streaking on the breast of the tan-striped, whereas the white-striped has a clean gray breast. The tan and white phenotypes are genetically inherited (Thorneycroft 1966, 1976), and white-striped birds of both sexes are typically more aggressive than their tan counterparts (Kopachena & Falls 1993). The species breeds across Canada and New England, where breeding pairs typically feature one of each morph, and migrate to wintering sites in the southern and eastern United States and northern Mexico. There is also a disjunct wintering population on the Pacific coast of the US.
These two birds were captured in White Clay Creek State Park, Delaware, on 10 May 2013. They may have been either (1) transients from southern wintering sites, moving northward toward their boreal breeding grounds, or (2) birds that wintered in Delaware, but have yet to leave for their breeding grounds. We may never know….but since we banded the birds with unique serial numbers, there is always the remote possibility that they will be captured again by other researchers!
Thorneycroft, H. B. 1966. Chromosomal polymorphism in the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Science 154:1571-1572.
Thorneycroft, H. B. 1976. A cytogenetic study of the White-throated Sparrow, Zonotrichia albicollis (Gmelin). Evolution 29:611-621.
Kopachena, J. G. and J. B. Falls. 1993. Aggressive performance as a behavioral correlate of plumage polymorphism in the White-throated Sparrow (Zonotrichia albicollis). Behaviour 124:249-266.