Bay-breasted Warbler - Field Marks

Migration has slowed down in the southern U.S. by now, but in the northern states the boreal breeding warblers are still passing through. This is the time to see Bay-breasted Warblers as they head north to their breeding grounds.

Bay-breasted Warbler
Dendroica castanea

This is a characteristic warbler of spruce forest in eastern Canada in summer. Its numbers vary from year to year, and are likely to increase quickly during population explosions of the spruce budworm or other forest pests. This species forages rather slowly compared to most warblers, moving deliberately among the branches. The male Bay-breasted Warbler is unmistakable in spring but goes through a striking transformation in fall, becoming a greenish "confusing fall warbler."

Field Marks
Male, spring: Dark-looking, with a chestnut throat, upper breast, and sides. Note the large spot of pale buff on the neck. Female, spring: Paler, more washed out. Autumn: Olive green above; two white wing bars; dull buff-white below. May have trace of bay on sides. Buff undertail coverts, dark legs.

5-6" (13-15 cm)

Similar Species
See fall Blackpoll Warbler (usually has pale legs).

A high, sibilant tees teesi teesi; resembles song of Black-and-white Warbler; thinner, shorter, more on one pitch.

Canada, northeastern edge of United States. Winters Panama to Venezuela.

Bay-breasted Warbler - Range Map

In spring, most apparently move north through Central America and then fly north across the Gulf of Mexico, continuing to Canada and the Northeast. In fall, evidently moves south on a broader front. Some may linger quite late in fall.

Woodlands, conifers in summer. Usually breeds in northern coniferous forest, in thick stands of spruce and fir. Where spruce is not found, will nest in deciduous or mixed second-growth woods of birches, maples, firs, and pines. In winter, in the tropics, occurs in forest edge, second growth, and lighter woodland up to 3,600' elevation.

Diet: Mostly insects, berries. In breeding season, eats a variety of insects, including beetles, flies, moths, caterpillars, leafhoppers, and grasshoppers; also berries. May eat many spruce budworms when that insect is at epidemic numbers. In winter in the tropics, eats many berries.

Behavior: Appears more sluggish in its foraging than do other Dendroica warblers in same spruce forests. Forages along branches, mostly at mid-levels in trees. Rarely flies out to catch flying insects in midair. In winter in the tropics, joins mixed foraging flocks in treetops.

Males may not arrive on breeding grounds until early June; establish nesting territories and defend them by singing.

Nest: Site is on a horizontal branch of a dense spruce, hemlock, birch, or other tree, 4-40' above the ground. Nest is a large, open cup, either loosely built or compact, made of grasses, lichens, roots, mosses, and protruding conifer twigs; lined with bark strips and hair.

Eggs: 4-5, sometimes 3-7. Off-white, with brown or black marks at larger end. Incubated by female, 12-13 days. Female is fed on the nest by the male during incubation. Tends to lay more eggs in years of spruce budworm outbreaks when food is abundant. Rarely parasitized by cowbirds.

Young: Both parents feed the nestlings. Young leave the nest 11-12 days after hatching.

Numbers may rise and fall, increasing after big outbreaks of spruce budworm or other insects. Could be vulnerable to loss of habitat on wintering grounds.

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