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. Their breeding season diet is dominated by the larvae of Lepidoptera, i.e. moths and butterflies. They may help control the spruce budworm (often considered a harmful pest) when breakouts occur, at the local if not at epidemic level. In one study from Ontario, 98% of the diet was made of insects, the remaining 2% being spiders. Among the migratory Setophaga warblers, it is considered one of the specialist at foraging in the micro-habitat of the tree’s top canopy.
The breeding habitats of these birds are mature coniferous woodlands, the central part of their breeding range being in the southeastern portion of Canada’s boreal forest. However, their distribution as a breeding species continues broadly down much of New England and the Appalachian Mountains, from New York to northernmost Georgia, in elevated mixed woodlands, especially ones containing spruce and hemlocks. Hemlocks in particular are most likely to host Blackburnian warblers in mixed forests.