The Chestnut-sided Warbler, (Setophaga pensylvanica), is a monotypic, (no sub-species), member of the genus Parulidae. Its relationships with other members of the genus is poorly understood and it is sometimes placed in the genus Dendroica with its close relative the Yellow Warbler. It was first described by Linnaeus in 1766. A summer visitor to the Eastern US, its breeding range runs up the East Coast and into South East Canada. In Texas it is typically seen during migration in the Eastern half of the State. It winters in Southern Mexico and the Central Americas as far South as Northern Venezuela.
The Chestnut-sided Warbler's preferred habitat is young deciduous secondary growth woodlands, thickets and abandoned farmlands. Originally, it was restricted to secondary growth woodland after fires or storms, but it has successfully adapted to human development and as such its numbers are increasing.
The Chestnut-sided Warbler typically feeds on insects (especially caterpillars) and spiders but will eat berries and seeds in the winter. It forages in the low to mid canopy and is a gleaner – pulling its prey from the underside of leaves while perched. When feeding these birds are highly active and fast-moving. In Winter these warblers often scavenge as part of a mixed flock.
Chestnut-sided Warblers lay 3-5 purple/brown eggs in a cup shaped nest made of grass lined with hair and roots. Typically, these are low to the ground, less than 10 feet, in small trees and bushes. Incubation is carried out by the female only. They are monogamous.
A medium-sized but stocky warbler, the male in breeding plumage has a distinctive yellow crown and white face with a thick black eye-stripe. The underparts are white but with a chestnut streak running from below the eye down onto its flanks. The upperparts are olive green with black streaks on the mantle and two white wing bars on grey-olive wings. Non-breeding plumage is vastly different, the upperparts being lime green and relatively un-streaked with underparts being gray/white. The female is similar in both plumages but much duller.
When singing, this warbler has 2 song types but both are musical with a distinct “pleased to meet ya” at the end. One song is a courtship song used before the eggs hatch, and the other is used once the chicks are born. This warbler is relatively common within its range and numbers are now increasing after a decline at the end of the last century due to its ability to interact with human habitats. It is therefore a species of least concern.
· A group of warblers is called a bouquet, a confusion, a fall or a wrench.
· Recent DNA studies show that the Chestnut-sided is closely related to the Yellow Warbler and likely the reason their songs are so similar.
· The oldest known individual was 6 years and 11 months.
· Climate change is pushing the Chestnut-sided Warblers breeding grounds further North and it may soon only breed in Canada.
· As a long distance migratory bird they are occasionally blown off course and this species has been recorded as a vagrant in Western Europe.