Wild Facts about the Black-throated Blue Warbler
PIF Priority Bird for Southern Blue Ridge
This species is our most distinctively different looking wood warbler when comparing the male and female. Males are a striking deep blue, black and white, while females are quite drab. Nearly all plumages show a white flash at the base of the primaries that is quite visible from a distance. The males and females differ so much in appearance that early ornithologists like Audubon considered them separate species. The Black-throated Blue Warbler is a fairly common bird of hardwood and mixed deciduous-coniferous woodlands in the northeastern United States and southern Canada, as well as the Appalachian Mountains all the way south to northern Georgia. Considered a forest-interior species, large-scale clearing of forests over the last 300 years likely has impacted population levels, although Breeding Bird Survey data shows stable population trends for the last thirty years. Future deforestation on its Caribbean wintering grounds will likely impact this species.
This was likely a very common bird of the extensive forest of the northeastern United States and southern Canada. Clearing of these forests in the 17th and 18th centuries reduced suitable breeding habitat for this species. However, abandonment of farms and reforestation starting in the mid-19th century and still continuing has increased forested habitat again. It is possible that breeding habitat for this species is more extensive now than 150 years ago. This bird is a neotropical migrant that winters mainly in the Caribbean and parts of Central America. Neotropical (New World) migratory birds breed during summer in temperate North America, migrating north each spring from wintering areas, then fly back to spend the bulk of the year in Mexico, Central or South America, or the Caribbean.
Breeding density seems to be linked to the thickness of the shrub layer. Thick shrub layers typically have more breeding pairs. Breeding Bird Survey (BBS) data show populations are basically stable since 1966 to the mid-1990’s. Decreases by region seem to show at the margins of the breeding range, while increases occurred in the central parts of its range. Overall there is no major decline for this bird within suitable habitat.
The male has a dark blue back, black face, throat and flanks, whitish underparts and a large white wing patch. Females are much drabber birds. They are greenish-gray in color, usually with a small white wing spot. Age can produce some plumage variation in this species. This species does not molt into a different looking (called confusing by birders!) fall plumage, so individuals can be identified with confidence year-round.
This species breeds mainly in large, mostly continuous tracts of deciduous or mixed deciduous-coniferous woodlands. In the mountains of North Carolina, this species occurs mostly above 3,000 feet in elevation. Forests most suitable as breeding habitat contain a rather thick undergrowth of deciduous or broad-leaved evergreen shrubs. Selection of habitats with a dense shrub layer seems to be related to nesting requirements and not foraging needs.
Many of the vocalizations of Dendroica warblers have been studied extensively, but those of the Black-throated Blue Warbler have received scant attention. Typically males do most of the singing, and they have several song types. These songs vary a great deal within and among individuals in speed, pitch and numbers of notes. A commonly heard song is a buzzy zee-zee-zee-zreeeee, and another sounds like zreee-zhrurrr. Most singing is done during the breeding season from May through early August, and singing usually occurs from perches in the mid- to lower levels in the canopy.
This species can have more than one brood per season. Females chose the nest sites and do most of the nest building. The nest is usually located in dense shrub layers of deciduous or mixed deciduous-coniferous woods, and is frequently found in broad-leaved evergreen shrubs like laurel or rhododendron in the mountains of North Carolina. Nests are usually found low (often no more then three feet off the ground) in a fork of a low shrub, sapling or herb like blue cohosh. The nest is constructed mainly of bark strips glued together by cobwebs and saliva, with an inner wall of shredded bark fibers that is lined with rootlets, moss and animal hair.
Black-throated Blue Warblers feed on insects and other small invertebrates. During the breeding season they forage from the ground to high in the forest canopy, with males often foraging higher than females. This bird seems to locate a high percentage of prey from the lower surfaces of leaves. Small fruits are often eaten during the winter. Major foods eaten during the breeding season include larval Lepidoptera and beetles, adult fly species and spiders.
This is a bird of the northeastern United States and southern Canada that also inhabits all parts of the Appalachian Mountains south to Georgia. It breeds in the North Carolina mountains usually above 3,000 feet in elevation. Most individuals winter in the Caribbean and parts of mid-Central America.
Migrants collide with man-made structures like TV towers and buildings. Evidently, this species will tolerate frequent human visits to its nest once eggs are laid and incubation begins. Large-scale clearing of forests likely impacts breeding and wintering birds. In the northern parts of its range, it is quite common in managed and unmanaged northern hardwood forests. On the wintering grounds, this species is often seen in shade coffee plantations. In general, more detailed population studies need to be done in the southern part of its breeding range, where landscape scale habitat changes are rapidly occurring.
American Warblers, by Morse, 1989, Harvard University Press
Peterson Field Guides: Warblers, by Dunn and Garrett, 1997, Houghton Mifflin Co.