The chestnut-sided warbler (Setophaga pensylvanica) is a New World warbler. They breed in eastern North America and in southern Canada westwards to the Canadian Prairies. They also breed in the Great Lakes region and in the eastern USA.
The chestnut-sided warbler has benefited from the clearing of mature forests. They make use of the abundant second growth habitats. In the tropics where they winter however, the species occurs mostly in mature tropical rainforests. Their cup-shaped nests are placed in a low bush, which is usually located in young deciduous woodland or scrub. These birds lay 3–5 eggs that are creamy white or greenish with brown speckles in color. The nest is a small cup woven of bark strips, weed stems, grasses, and plant down. The nest is usually placed in a small crotch of a shrub or vertical tangle of vines no more than 2 m (6.6 ft) above the ground. This species is frequently parasitized by brown-headed cowbirds. source