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Breeding adult male. Photo: OHFalcon72/Flickr (CC BY NC ND 2.0)

Bay-breasted Warbler

Setophaga 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."

Conservation status	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.
Family	Wood Warblers
Habitat	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 open woodland.

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Feeding Behavior

Appears more sluggish in foraging than do other Dendroica warblers feeding in the same spruce forests. Forages in and out along branches, mostly at mid-levels in trees. Rarely catches flying insects in mid-air. In winter in the tropics, joins mixed foraging flocks in the forest canopy.

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.

Young

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

Diet

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

Nesting

Males may not arrive on breeding grounds until early June. 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.

Illustration © David Allen Sibley.
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Text © Kenn Kaufman, adapted from
Lives of North American Birds

Migration

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.

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Migration

All Seasons - Common
All Seasons - Uncommon
Breeding - Common
Breeding - Uncommon
Winter - Common
Winter - Uncommon
Migration - Common
Migration - Uncommon

Songs and Calls

A high thin teesi-teesi-teesi-teesi, without change in pitch or volume.

Audio © Lang Elliott, Bob McGuire, Kevin Colver, Martyn Stewart and others.
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How Climate Change Will Reshape the Range of the Bay-breasted Warbler

Audubon’s scientists have used 140 million bird observations and sophisticated climate models to project how climate change will affect this bird’s range in the future.

Zoom in to see how this species’s current range will shift, expand, and contract under increased global temperatures.

Climate threats facing the Bay-breasted Warbler

Choose a temperature scenario below to see which threats will affect this species as warming increases. The same climate change-driven threats that put birds at risk will affect other wildlife and people, too.