Editor's Note: Phylogenetic analyses of sequences of mitochondrial and nuclear DNA indicate that all species formerly placed in Dendroica, one species formerly placed in Wilsonia (citrina), and two species formerly placed in Parula (americana and pitiayumi) form a clade with the single species traditionally placed in Setophaga (ruticilla). The generic name Setophaga has priority for this clade. See the 52nd Supplement to the AOU Checklist of North American Birds for details. Future revisions of this account will reflect these changes.
The Blackburnian Warbler is a brilliantly colored Neotropical migrant, one of a large group of Setophaga wood warblers that coexist during the breeding season in the northeastern coniferous forests of North America. Birds of this group are so similar structurally that early students of bird foraging and niche partitioning wondered how they coexisted. They are now known to separate ecologically by foraging areas ( Macarthur 1958 , Morse 1968a ), the Blackburnian exploiting a treetop niche.
Although the Blackburnian Warbler is morphologically similar to many of its congeners that share these forests, it differs strikingly from them in coloration. Breeding males are characterized by blazing orange plumage over much of the anterior part of their body, a color not shared by other members of this genus.
In common with some other Setophaga wood warblers, the range of the Blackburnian extends both to the northwest in Canada and to the southeast along the Appalachian Mountains. In the southern part of its breeding range, this species specializes on hemlock (Tsuga canadensis), although like the Black-throated Green Warbler (Setophaga virens) it sometimes inhabits deciduous forests as well. Throughout its breeding grounds, this insectivorous species appears to feed primarily on lepidopteran larvae, which it gleans from small branches high in trees. It nearly always builds its nest in conifers, on small limbs well out from the trunk.
Populations of this species are vulnerable owing to the loss of preferred winter forest habitat in northern South America, although Breeding Bird Survey data suggest that their numbers remain stable. Blackburnian Warblers are forest-interior species, and their numbers decline in forest fragments. Southerly populations breeding in eastern hemlock and Fraser fir are at risk as a result of wooly adelgids responsible for heavy mortality of these trees.
Some aspects of the Blackburnian Warbler's breeding biology are relatively well known, including foraging ( Macarthur 1958 , Morse 1968a ), population dynamics ( Morse 1976b ), interspecific interactions ( Morse 1976a ), habitat selection ( Morse 1976b ), and singing behavior ( Morse 1967c ). Some ecological studies have been performed on their wintering grounds in Colombia ( Chipley 1980 ; Lerner and Stauffer 1998 ). Recent studies have focused on the effect of silvicultural practices on this and other species (e. g., Hagen et al. 1996 , Meiklejohn and Hughes 1999 , Hobson and Bayne 2000b , Cumming and Diamond 2002 ). However, information on many aspects of the species' life cycle is rudimentary. Little is known of its migratory ecology. Many aspects of its breeding ecology remain largely or completely unknown, in part a consequence of its treetop existence in northern forests.