Blackburnian warblers are small colorful songbirds that breed in eastern North America. In summer, males display dark gray backs and double white wing bars, with yellowish rumps and dark brown crowns. The underparts of these birds are white and are tinged with yellow and streaked black. The head is strongly patterned in yellow and black, with a flaming-orange throat. Other plumages, including the fall male and adult female, are washed-out versions of the summer male, and in particular lack the bright colors and strong head pattern. Blackburnian warblers are practically unmistakable if seen well, even the females due to their dull-yellow supercilium, contrasting with greyish cheeks and yellow throat contrasting with the dark streaky sides and back.
Blackburnian warblers breed from southern Canada, westwards to the southern Canadian Prairies, the Great Lakes region, and New England, to North Carolina. They are migratory, wintering in southern Central America and in South America, and are very rare vagrants to western Europe. The breeding habitats of these birds are mature coniferous woodlands, the southeastern portion of Canada's boreal forest, and mixed woodlands, especially ones containing spruce and hemlocks. Blackburnian warblers typically winter in tropical humid montane forests.
Blackburnian warblers are solitary during winter and highly territorial on their breeding grounds and do not mix with other birds outside of the migratory period. However, during migration, they often join local mixed foraging flocks of chickadees, kinglets, and nuthatches. Similarly, in the tropics, they are fairly social while engaging in migration but solitary from other birds while wintering. Blackburnian warblers are active during the day and usually forage by searching for insects or spiders in treetops. Blackburnian warblers generally sing at dusk and dawn. Their songs are a simple series of high 'swi' notes, which often ascend in pitch; these include 'zip zip zip zip zip zip zip zip', 'titititi tseeeeee' or 'teetsa teetsa teetsa teetsa'. Their common call is a high 'sip'.
Blackburnian warblers form monogamous pairs. The breeding season begins in mid-May to early June in the contiguous United States and about 1 to 2 weeks later in Quebec. Pairs build a nest near the end of a branch consisting of an open cup of twigs, bark, plant fibers, and rootlets held to branch with spider web and lined with lichens, moss, hair, and dead pine needles. Blackburnian warblers typically lay only one brood per year, but if a nest is destroyed they may produce a second or even third brood. The female lays 3 to 5 whitish eggs and incubates them for 12-13 days. Only the female broods and spends about 80% day actively brooding, while the male usually helps bring food to the nest. The chicks hatch altricial (helpless); they remain in the nest about 2-4 weeks and become independent from their parents 2-3 months later. Females usually start to breed at 2 years of age while males become reproductively mature when they are between 1 and 2 years old.
The greatest threat to Blackburnian warblers is the destruction of forest habitat, which could cause the birds to lose up to more than 30% of their wintering or breeding habitat.
According to Partners in Flight resource, the total population size of the Blackburnian warbler is 13,000,000 breeding individuals. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are increasing.