Almost two centuries have elapsed since Alexander Wilson ( Wilson 1808 ) clarified the taxonomic status of the songbird known then as the Blue-winged Yellow Warbler (Sylvia solitaria). More than 30 years before, George Edwards ( Edwards 1760 ) confused the first specimen of this species with the Pine Creeper (Pine Warbler [Dendroica pinus]), illustrated by Mark Catesby ( Catesby 1731 ). Known by Wilson at the beginning of the nineteenth century as a summer species of sequestered woods, the Blue-winged Warbler benefited later from widespread agricultural uses of the land. Now the species is common in overgrown old fields and brushy swamps throughout its range in eastern North America. The bright-yellow, but easily overlooked, territorial male sings a high-pitched, insectlike Beeee Buzzzz. The duller-colored female skulks in thick undergrowth, except when feeding young.
Prior to the colonization of eastern North America by early European settlers, Blue-wings commuted each spring from Middle America to their primary range in North America, the Ozark Mountains east through the wooded savannas of Tennessee and Kentucky. Blue-wing populations swelled in numbers and expanded in distribution as settlers changed the landscape: cut forests and abandoned fields progressed into habitats that favored this shrubland specialist. In recent years, however, Blue-wing populations have declined in the northeastern United States, along with other shrubland birds, due to regrowth of forests and loss of habitat to urban sprawl.
Pioneering Blue-wings attracted the attention of ornithologists eager to add rare species to their collections and birders eager to add new species to their local lists. Adding to the anticipation was the prospect of finding the attractive hybrids between this species and Golden-winged Warbler (V. chrysoptera)—the rare Brewster's and even rarer Lawrence's warblers. Wilson and his eminent successor, John James Audubon, encountered no Brewster's or Lawrence's warblers. Initial descriptions in 1874 of these hybrid phenotypes sparked great debates as to their identity. Almost 40 years later, a Massachusetts banker, Walter Faxon ( Faxon 1911 , Faxon 1913 ), published the first clues to the riddle of hybridization between Blue-winged and Golden-winged warblers. Eager studies of hybridization then advanced from Faxon's novel application of Mendelian genetics to the plumage-color patterns of wild birds to behavioral and ecological interactions and recently to applications of the latest techniques of molecular genetics ( Parkes 1951 ; Short 1963 ; Ficken and Ficken Ficken and Ficken 1968b , Ficken and Ficken 1968a , Ficken and Ficken 1968d , Ficken and Ficken 1968c , Ficken and Ficken 1969 ; Gill and Murray 1972a ; Confer and Knapp Confer and Knapp 1977 , Confer and Knapp 1981 ; Gill Gill 1980 , Gill 1997a ; Confer and Larkin 1998 ). Still challenging us, however, is how, or even whether, invading Blue-wings directly cause the extinction of local populations of Golden-winged Warblers.
Supplementing the above studies of interactions with Golden-winged Warblers are important studies of vocalizations ( Lanyon and Gill 1964 , Gill and Murray 1972b , Kroodsma et al. 1984 , Kroodsma 1988 , Highsmith 1989a ), population ecology (Canterbury et al. Canterbury et al. 1995a , Canterbury et al. 1995b ), and breeding biology ( Canterbury 1997 ).