In the early summer, male black-throated blue warblers establish territories and pair with females. Territories are advertised with singing and are aggressively defended, and females are closely guarded from other males. Although the black-throated blue warbler is generally monogamous during the breeding season, extra-pair copulations are common among both sexes (3).
Mated pairs of black-throated blue warblers can produce one to three broods per season, with clutch size ranging from two to five eggs (3). Incubation is performed by the female and lasts 12 to 13 days. The nest, constructed from bark, dried grasses and twigs and lined with fur, mosses or rootlets, is typically situated less than 1.5 metres above the ground (2), in dense foliage (6). Both the male and female black-throated blue warbler contribute to nest-building and to feeding the young, which fledge eight or nine days after hatching (3).
In the winter, the black-throated blue warbler is typically solitary and may occupy the same territory from one year to the next (2). Both males and females are generally intolerant of other warblers of the same sex. As this species does not sing during the winter months, exclusive territories are maintained through visual contact and avoidance, as well as chasing and calls (3).
The black-throated blue warbler is insectivorous, with flies, beetles, and insect larvae comprising most of its diet, although it also occasionally feeds on fruits, berries and seeds (2) (3). This species tends to forage in middle-level trees and underbrush (2), remaining within the boundaries of its territory (3). During its autumn migration, the black-throated blue warbler may be drawn to peanut butter or suet at bird feeders (2).