Chestnut-sided Warbler

The Chestnut-sided Warbler, Setophaga pensylvanica, is a captivating New World warbler, modest in size but striking in appearance. It is closely related to the Yellow Warbler and exhibits a range of plumage variations across seasons. Adult males in summer are particularly distinctive with their dark-streaked gray backs, white faces, and black eyestripes, crowned with a splash of yellow. Their underparts are white, set off by rich chestnut flanks, and they sport two white wing bars. Females and non-breeding individuals present a more subdued coloration, with less pronounced head patterns and minimal chestnut on the flanks.

Identification Tips

In summer, look for the male's bold face pattern and chestnut sides. Females and non-breeding birds can be identified by their bright yellow-green crowns, white eye-rings on a grey face, and pale, unstreaked underparts. The consistent presence of wing bars throughout the year aids in identification, as does the lack of streaking and yellowish back, which distinguishes them from the larger Blackpoll Warbler during the fall.

Habitat

The Chestnut-sided Warbler thrives in second growth habitats, a testament to its adaptability and the changing American landscape. It nests in low bushes within young deciduous woodlands or scrublands, often taking advantage of the regrowth following forest clearings.

Distribution

Breeding primarily in eastern North America and southern Canada, extending west to the Canadian Prairies, the Great Lakes region, and the eastern United States, this warbler is a migratory species. It winters in Central America, reaching as far south as northern Colombia, and has been recorded as a rare vagrant in western Europe.

Behaviour

These warblers are active foragers, flitting through shrubs and small trees in search of insects. They may occasionally sally forth to catch insects mid-flight, but they predominantly glean their prey from foliage. During the winter, they can be enticed into gardens with berry-bearing trees.

Song & Calls

The male's song is a cheerful whistle, often transcribed as "pleased, pleased, pleased to MEECHA," with the accented version primarily serving to attract females. Unaccented songs are associated with territory defense and are more localized, reflecting the long-distance dispersal of females. Their calls are characterized by harsh chips.

Breeding

The Chestnut-sided Warbler's cup-shaped nest is artfully woven from bark strips, weed stems, grasses, and plant down, typically situated no more than 2 meters above the ground in a shrub or vine tangle. They lay 3-5 creamy white or greenish eggs speckled with brown. This species is known to be parasitized by the Brown-headed Cowbird.

Similar Species

While similar to the Blackpoll Warbler in size, the Chestnut-sided Warbler can be distinguished by its lack of streaking and the presence of yellowish tones on its back during the fall.

Diet and Feeding

Insectivorous by nature, the Chestnut-sided Warbler's diet consists mainly of insects gleaned from foliage. In the winter months, they supplement their diet with berries, such as those from the Cymbopetalum mayanum tree.

Conservation status

The Chestnut-sided Warbler is currently classified as Least Concern by the IUCN, with population trends reflecting an initial increase due to the proliferation of second growth forests, followed by a slight decline.