Chestnut-vented Warbler

The Chestnut-sided Warbler, Setophaga pensylvanica, is a captivating New World warbler, modest in size but striking in appearance. This species exhibits sexual dimorphism, particularly during the breeding season. Males are adorned with dark-streaked gray backs, black eyestripes, and a brilliant yellow crown. Their faces are a contrasting white, and their underparts are predominantly white with distinctive chestnut flanks. Two white wing bars add to their ornate plumage. Females, while similar, are more subdued in coloration and may lack the pronounced head pattern and chestnut coloring on their flanks. Outside of the breeding season, both sexes boast a bright yellow-green crown and a grey face with a white eye-ring, with their underparts remaining unstreaked.

Identification Tips

When identifying the Chestnut-sided Warbler, look for the summer males' unique combination of a white face, black eyestripe, and yellow crown. The chestnut flanks are a key feature, along with the two white wing bars present throughout the year. In non-breeding plumage, note the yellow-green crown and the lack of streaking on the pale grey breast. These characteristics help distinguish it from similar species, such as the larger Blackpoll Warbler in the fall.

Habitat

The Chestnut-sided Warbler thrives in second growth habitats, a landscape rich with young deciduous woodland and scrub. This preference has emerged as mature forests have been cleared, creating an environment where these warblers can flourish.

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, the Chestnut-sided Warbler is a migratory bird. It winters in Central America, reaching as far south as northern Colombia, with occasional sightings in Ecuador and rare vagrancies to western Europe.

Behaviour

These warblers are active foragers, often seen flitting through shrubs and small trees in search of insects. They may also engage in aerial sallies to catch insects in flight. During the breeding season, males can be observed singing both accented and unaccented songs, the former to attract females and the latter for territory defense.

Song & Calls

The Chestnut-sided Warbler's song is a cheerful high-pitched whistle, transcribed as "pleased, pleased, pleased to MEECHA." This song is particularly important during courtship, while a harsh chip call is used for communication at other times. Notably, the aggressive songs are highly localized, suggesting an adaptation for territory defense.

Breeding

Breeding habitats are typically low bushes in young deciduous woodlands or scrublands. The warbler's cup-shaped nest is woven from bark strips, weed stems, grasses, and plant down, often placed no more than 2 meters above the ground. They lay 3–5 creamy white or greenish eggs speckled with brown. Unfortunately, they are frequently targeted by brown-headed cowbirds for brood parasitism.

Diet and Feeding

The diet of the Chestnut-sided Warbler is primarily insectivorous, with a foraging behavior that involves actively searching through foliage. During 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 listed as Least Concern on the IUCN Red List. Its population experienced a rise with the increase of second growth forests in the late 19th century, although there has been a slight decline since then.