The Chestnut-sided Warbler (Setophaga pensylvanica) is just five inches long and highly mobile. Luckily for birders, it is distinguished by bright colors in the spring and changing their costume for their fall migration.
Males have a black facemask topped with a bright yellow crown and reddish-brown flanks in May. The mask disappears in August, replaced by a bright white eye-ring and olive-green feathers on its back.
Females have muted face and head colors, with a smaller patch of chestnut on their sides in spring. In the fall, their flank colors are gone, and their bright green backs and eye-ring help identify them from most other migratory warblers. If you have clear views and quick eyes, you might notice a cocked tail and two wing bars as you bend your neck to keep this bird in sight.
Not thought to nest in Carver County, but breeding has occurred across the Minnesota River in Scott County and in second-growth deciduous trees and shrubs found in the counties north of Mille Lacs.
Some reference books point to a declining population in Minnesota — 0.6% per year in the past 60 years. Other sources indicate their status depends on the presence of young trees and shrubs in areas that have been cleared of forest, then left to regenerate. The species was considered rare before the original forests were cleared in the expansion of European settlement in the 1800s.
Crossing north across the Gulf, males arrive from southern Mexico, Central America and Columbia in early May. Nocturnal migrants, they precede the females by five to seven days. These warblers come back through our county in the weeks after mid-August.
During their migratory presence here, they will feed off insects hiding (unsuccessfully) on the underside of leaves. Hopping quickly between the small branches, they change their position and perspective to continually nourish themselves for their nighttime journeys north and south.
In their breeding season, males singing will peak at dawn and decrease through the day. Typically, the song will consist of four notes, transliterated as “Pleased, pleased, pleased to meetcha.” The recording in the species’ description in the website “All About Birds” may help you point your eyes towards this fast-moving bird LINK.
The Chestnut-sided Warbler is a treat to see and hear during its few days in Carver County. The bright colors in May and then the change of clothes in September mark migration high points for birders.
For more information:
The Sibley Guide to Birds, David Allen Sibley
Birds of Minnesota and Wisconsin, Janssen, Tessen, and Kennedy
Birds of Minnesota, Robert B. Janssen
The Audubon Society’s Encyclopedia of North American Birds, John K. Terres
Birds of the World, Cornell Lab of Ornithology
Online: All About Birds, Cornell Lab of Ornithology LINK
Online: Minnesota Breeding Bird Atlas
