Bay-Breasted Warbler

Setophaga castanea (formerly Dendroica castanea)

bay-breasted_warbler.jpg

Photo of a bay-breasted warbler
Non-breeding and female bay-breasted warblers can be difficult to identify. Look for the two white wing bars, cinnamon cast on the flanks, unstreaked breast, and buffy undertail feathers.
MDC Staff
Family

Parulidae (wood-warblers) in the order Passeriformes

Description

Adult breeding male has a black head with a chestnut crown, throat, and sides; the sides of neck and underparts are buffy. The adult female is similar but lacks the black head and is paler. Both have 2 white wing bars and dark legs. Song is a rapid series of double notes, all on the same, high pitch: tseetsy-tseetsy-tseetsy-stee, or sweeswee-sweeswee-sweeswee-swee.

Similar species: Although adult bay-breasted warblers in breeding plumage are easy to identify, nonbreeding males, breeding and nonbreeding females, and immature males present an identification challenge. Blackpoll warblers have streaking on their breasts. Pine warblers show a stark border between yellow throat and dark cheeks; also, the lower belly and undertail coverts on pine warblers are white and not buffy. A discussion of all the fine points is beyond the scope of this introductory field guide. Keep in mind the key features below.

Key Identifiers

 

  • Two white wingbars in all plumages
  • No distinct streaking on breast in all plumages
  • Female, immature, and nonbreeding plumages show some yellowish or olive above, especially in head and nape area
  • Many plumages show faint chestnut or cinnamon color on flanks
  • Rather large, for a warbler
  • Learn the song and listen for it
  • Unlikely to see in Missouri except during migration: late April through the end of May, and early August through early October
Size

Length: 5½ inches (tip of bill to tip of tail).

Habitat and conservation

This is one of more than 300 North American bird species threatened by global climate change. Climate models indicate that the zone of favorable weather conditions for this species' breeding territory is moving northward from the current, long-established breeding territory. It is unknown if the birds, the spruce forests, and their budworm food can all move northward, too.

Foods

The bay-breasted warbler moves through the trees, hopping from branch to branch, feeding on insects. The spruce budworm is a vital food in their breeding territory; during outbreaks of that caterpillar, bay-breasted warbler populations boom. Then, when the insect population drops, the warbler populations decline. Overall declines in this warbler's numbers may be due to pesticide spraying to control their favorite food on their breeding grounds.

image of Bay-Breasted Warbler Distribution Map
Distribution in Missouri

Statewide, as a migrant.

Status

Uncommon transient. Genus name: This and nearly 30 other wood-warblers used to be in the genus Dendroica, but evidence from genetic research showed that the genus could not logically be kept separate from genus Setophaga. Today, all the Dendroica warblers are now in genus Setophaga.

Life cycle

This warbler migrates from Panama, Venezuela, and Colombia through the entire eastern United States to nest in spruce-fir forests in Canada and the far northern United States. It is present in Missouri from late April through the end of May, and from early August through early October. Cup nests are built in spruce trees, made of twigs, grasses, rootlets, hairs, spider web, mosses, and other fine materials. A clutch comprises 4–7 eggs, which are incubated 12–13 days. The young start leaving the nest 11–12 days after hatching.

Human connections

Difficult-to-identify fall warblers present a challenge to birders, but it's part of our human nature to rise to challenges! A thornier problem involves long-term conservation challenges, which involve education, foresight, and economic and political willpower. Humans have a voice in public policy, but warblers do not.

Ecosystem connections

The close relationships among the spruce forests, the spruces' budworm pests, and the bay-breasted warbler's budworm diet and spruce-tree nesting sites, beautifully demonstrate the interconnections of nature.