Bay-breasted Warbler, Setophaga castanea

Bay-breasted Warbler, Setophaga castanea, female. Photograph taken within a residential community in Alamos, Sonora, November 2022. This is the first eBird report for Sonora that is now also documented photographically. Photograph, identification, and related information courtesy of David F Smith, Alamos, Sonora.

Background and Identification

The Bay-breasted Warbler, scientifically known as Setophaga castanea, is a small songbird renowned for its striking plumage and migratory behavior. These warblers are known for their high-pitched songs and are often observed foraging actively in the upper canopy of trees. In Mexico, bay-breasted Warblers are called Chipe Castaño.

The Bay-breasted Warbler is fairly large, about 14 cm (5.5 inches) in length with an average mass of 13 grams (0.46 oz). This species has striking plumage. In the breeding season, males differ significantly in appearance from females. During this season (breeding), males have rich chestnut-colored throats, breasts, and flanks that contrast with a black face and dark grey back. They have very prominent white wing bars and a streaked back. Females and non-breeding males during this time have more subdued colors, displaying mixes of olive-green, yellowish, and buff tones. There are sometimes small hints of chestnut red colors on their flanks. Juvenile males resemble females in the breeding season from the time they hatch to when they are about one year old. When the breeding season is over, males are dull in color and look more similar to female and juvenile males.

Habitat and Geographical Range

Boreal forests are the most common landscape to find this species. They favor coniferous forests, especially those dominated by spruce and fir trees, which provide ample food and nesting sites.

Bay-breasted Warblers are migratory, spending their winters in Panama and northern South America. They breed in boreal forests of North America, mostly in Canada and the northeastern United States. During their migrations, these warblers travel long distances through the eastern United States and the Caribbean to reach their wintering grounds. They often migrate in mixed-species flocks.

Common Misidentifications

In breeding season plumage, Bay-breasted Warblers of both sexes are unlikely to be confused with other warbler species. Drab females in their first spring and summer can be easily misidentified from Blackpoll and Pine Warblers. Male Blackpoll and Pine Warblers do not have any chestnut coloring, which can help distinguish the two species from one another.

Conservation Status

From a conservation perspective, the Bay-breasted Warbler is currently considered to be of Least Concern, with abundant populations in their geographical range. Recently, they have been placed on the Partners in Flight Watch List in the category of moderately abundant or widespread but with declines in their populations or high threats. In Canada, which contains over 90% of the Bay-breasted Warbler’s range, they have experienced population declines of 5% annually (on average) from 1989 to 2009.