Chestnut-sided Warbler Identification Guide

Key Field Marks

• Small warbler, about 5 inches, often seen with its tail cocked upward while foraging in low-to-mid shrubs.
• Breeding male: bright yellow-green crown, black eyeline and black malar (mustache) streaking, white face and underparts, and a broad chestnut stripe running down each side from the shoulder.
• Two pale yellow wingbars on blackish-streaked wings; back streaked black over greenish-yellow.
• Breeding female: similar pattern but softer, less extensive chestnut and less black on the face.
• Fall/nonbreeding adults and immatures: lime-green crown and back, gray face, white eyering, whitish underparts, and yellow-green wingbars; chestnut on the sides is reduced or absent, especially in young birds.

Separating It From Similar Species

• Bay-breasted Warbler (fall): also greenish above, but Bay-breasted shows a faint buffy wash on the flanks/undertail coverts and dark legs, while Chestnut-sided has clean white undertail coverts and paler legs.
• Blackpoll Warbler (fall): streakier above with yellowish legs and feet ("wears yellow socks"), and lacks the clean gray face/white eyering combination of fall Chestnut-sided.
• Cape May Warbler (fall): shows fine breast streaking and often a hint of yellow on the neck sides; Chestnut-sided is plainer below.
• No other eastern warbler combines a plain gray face, white eyering, and lime-green back in fall plumage.

Habitat, Range & Season

• Breeds in second-growth habitat: shrubby old fields, regenerating clear-cuts, brushy woodland edges, and power-line corridors across the northeastern and north-central United States and southern Canada.
• A classic species that increased historically as forests were cleared, then logged and left to regrow into scrub.
• Present on breeding grounds roughly May through August; migrates through the eastern U.S. in spring (May) and fall (August–September).
• Winters in the understory and edges of forests in Central America, from southern Mexico to Panama.

Voice

• Song is a bright, whistled series often rendered as "pleased, pleased, pleased to MEETCHA", with an emphatic downslurred ending.
• Some males give an alternate, less accented song used mainly early in the breeding season.
• Call note is a flat, sharp chip.