Bay-breasted warblers breed in the boreal spruce-fir forests of eastern and central Canada, as well as the extreme northern United States.

[4] In the breeding season, bay-breasted warblers feed primarily on insects and spiders, especially the spruce budworm (Choristoneura fumiferana).

To avoid competition with similar species, bay-breasted warblers concentrate their foraging on the breeding grounds to the interior middle portions of coniferous trees.

[4] Adult males in breeding plumage are primarily grayish above, with two white wing bars, dark streaks on the back, and a creamy neck patch.

Chestnut-sided warblers also have a bright yellow crown, dark mask, and white cheek and throat in breeding plumage.

[9] The genus name Setophaga is from Ancient Greek ses, "moth", and phagos, "eating", and the specific castanea is Latin for chestnut-coloured.