Chestnut-sided Warbler

The Chestnut-sided Warbler is a handsome bird of shrubby, regenerating woodland, with breeding males showing a crisp combination of a bright yellow crown, black eye-line and mustache stripe, white face and underparts, and a bold chestnut stripe running down each flank. The back is streaked black on a yellow-green background, and the wings show two yellowish wingbars.

Non-breeding and immature birds look quite different, appearing plain lime-green above and clean white below with little or no chestnut on the flanks, sometimes causing confusion during fall migration. Historically rare, this species expanded dramatically as forests across the Northeast were cleared and then abandoned to grow back as brushy second-growth habitat, which it favors.

Key Field Marks

• Breeding male: bright yellow crown, black eye-line and malar (mustache) stripe, white face and underparts, bold chestnut stripe down the flanks
• Streaked black-and-yellow-green back
• Two yellowish wingbars
• Fall/immature: plain lime-green above, clean white below, little or no chestnut visible

Similar Species

Fall Chestnut-sided Warblers can resemble Bay-breasted or Blackpoll Warblers in nonbreeding plumage, but Chestnut-sided shows a distinctly bright lime-green back and crown, whiter underparts, and a plain white eye-ring, whereas those species show more streaking and duller tones overall. Breeding males are unmistakable due to the chestnut flank stripe.

Habitat

This species favors young second-growth deciduous woodland, brushy fields, overgrown clear-cuts, and shrubby forest edges, generally avoiding mature closed-canopy forest.

Range

Chestnut-sided Warblers breed across the northeastern and north-central United States and southeastern Canada, south through the Appalachians. They winter primarily in Central America.

Migration

This species is a medium- to long-distance Neotropical migrant, and its breeding range and abundance expanded significantly following widespread historical deforestation and subsequent forest regrowth in eastern North America.

Behavior

Chestnut-sided Warblers forage actively in shrubs and low trees, often holding the tail cocked up and wings slightly drooped while gleaning through dense brushy vegetation.

Voice

The song is a bright, cheerful series often rendered as 'pleased-pleased-pleased-to-MEETCHA.' The call is a sharp 'chip.'

Feeding

It gleans caterpillars and other insects and spiders from leaves and twigs in shrubs and small trees, typically at low to middle heights.

Nesting & Breeding

The female builds a loosely woven cup nest low in a shrub or sapling, usually less than a meter or two above the ground. She lays 3-5 eggs, and this species is a frequent host of Brown-headed Cowbird parasitism in fragmented habitat.