Blackburnian warblers are around 11 to 13 cm (4.3 to 5.1 in) long, with a 20 to 22 cm (7.9 to 8.7 in) wingspan, and weigh 8 to 13 g (0.28 to 0.46 oz). The average mass of an adult bird is 9.7 g (0.34 oz). Among standard measurements, the wing chord is 6.3 to 7.3 cm (2.5 to 2.9 in), the tail is 4.2 to 5 cm (1.7 to 2.0 in), the bill is 0.9 to 1 cm (0.35 to 0.39 in) and the tarsus is 1.6 to 1.8 cm (0.63 to 0.71 in). In summer, male Blackburnian warblers 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. It is the only North American warbler with this striking plumage. 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. Basic plumages show weaker yellows and gray in place of black in the breeding male. Blackburnian warblers' songs are a simple series of high swi notes, which often ascend in pitch. Their call is a high sip. Blackburnian warblers are solitary during winter and highly territorial on their breeding grounds and do not mix with other passerine species outside of the migratory period. However, during migration, they often join local mixed foraging flocks of species such as chickadees, kinglets and nuthatches. These birds are basically insectivorous, but will include berries in their diets in wintertime. They usually forage by searching for insects or spiders in treetops. The breeding habitats of these birds are mature coniferous woodlands or mixed woodlands, especially ones containing spruce and hemlocks. It typically winters in tropical montane forests. Blackburnian warblers build a nest 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 that's placed near the end of a branch. Three to five whitish eggs are laid its nest which is usually placed 2–38 m (6.6–124.7 ft) above the ground, on a horizontal branch.