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Black-throated Blue Warbler

(Dendroica caerulescens)
Banded 16 September, 2001
Carmel, Indiana

General Information

The Black-throated Blue Warbler is one of the 115 or so species of warblers that occur in the Americas. This species is a medium to long distance migrant that travels from its home range in Cuba, the Bahama Islands and other islands of the Caribbean to the eastern US and Canada to nest and raise one and sometimes two broods.

The male Black-throated Blue Warbler is an attractive bird about 4.5 to 5.5 inches long and with a wingspan of from 7 to 8 inches. Weights range from 7.5 to 13 grams depending on the amount of stored fat.

Figure 1 - Black-throated Blue Warbler - male

Figure 2 - Black-throated Blue Warbler - male

The male has a black face, throat and flanks, and white underparts. Females have brownish to greenish olive upperparts and buffy underparts.

The male’s song consists of 3 to 5, descending, buzzy notes sounding like zwee, zwee, zwee, zwee, zweeee. The last note is drawn out and ascending.

These birds are common spring migrants often seen in parks and yards. Two races are recognized. One race occurs in the Great Lakes area east to New England and Nova Scotia. The other, characterized by darker plumage, occurs in the Appalachian mountains.

Figure 3 - Black-throated Blue Warbler

Figure 4 - Black-throated Blue Warbler coverts

The age of the male can be determined based on plumage characteristics. On this young (HY) male, the tertials, greater alula and outer primary coverts are brownish, contrasting with the greater coverts that are black with blue edging (Pyle 1997). The primary coverts and alula of young males may have green edging as with the individual shown here.

The primary coverts and alula feathers on an older (AHY/ASY) male are black with blue edging, similar to the greater coverts shown in this photo.

Both the male and the female of this species have a white wing patch at the base of the primaries. The extent of this white patch varies with age and sex, and is more extensive in older birds (Pyle 1997).

Figure 5 - Black-throated Blue Warbler

Figure 6 - Black-throated Blue Warbler

The young male (shown here) has green tipping on the back feathers. Older birds lack the green tipping (Pyle 1997).

The flanks of this warbler are blackish.

Figure 7 - Black-throated Blue Warbler

Figure 8 - Black-throated Blue Warbler undertail

The undertail coverts are white. The outer four tail feathers have white spots.

Nesting Behavior

Black-throated Blue Warblers prefer to breed in deciduous or mixed woodlands where saplings, secondary growth and thick shrub layers occur. In the Appalachian Mountains, patches of rhododendron are often the preferred breeding habitat.

The female builds a cup nest of bark strips, dead leaves, spider webs and moss from 1 to 3 feet off the ground in a sapling, shrub or small tree. From 3 to 5 eggs, incubated by the female, hatch in about 12 days. Young, cared for by both parents, leave the nest in about 10 days. Cowbird parasitism is infrequent, but nest failures result from predation by Blue Jays and squirrels.

Banding Recoveries

According to the web page of the Bird Banding Lab, a total of 94,549 Black-throated Blue Warblers were banded between 1955 and 2000. As of 1998, 40 had been encountered. Since 1998, another 5 have been encountered, bringing the total encounters to 45, an encounter rate of 0.047%.

If you should recover a banded bird, please report the band number to the Bird Banding Lab by calling 1-800-327-BAND.

Conservation Status & Economic Importance

Extensive cutting of forests in eastern North America have no doubt impacted populations of Black-throated Blue Warblers, but regrowth of logged areas having thick understory provides suitable breeding habitat, and may be favoring recovery of these birds. These birds depend on thick understory. It is therefore important for property owners to allow understory to develop in wooded areas.

These birds feed on fruits, seeds, nectar and tree sap, especially in the winter, but in summer months, their diet will consist of insect pests such as moths, tent caterpillars, aphids, beetles and flies. Feeding behavior usually consists of gleaning of leaves low in the understory, and sallying forth to catch insects.

Literature Cited

Pyle, P. 1997. Identification Guide to North American Birds, Part I. Slate Creek Press, Bolinas, CA.

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