GCBO Bird of the Month
Wilson's Warbler
by Mike Williams

Wilson’s Warbler, (Cardellina pusilla), is a new world warbler found in Western and Central North America with at least 3 subspecies. It is a member of the order Parulidae. (Note: it is placed in the order Wilsonia not Cardinella by some authorities). Originally described by Alexander Wilson, a Scottish American naturalist and poet in 1811 and after whom the species is named. Wilson is often called the Godfather of American ornithology.

Wilson’s Warblers are migratory and breed in South and Central Canada from Newfoundland in the East to British Columbia in the West. They also breed in the Western US as far South as Northern California, Arizona and New Mexico. It winters primarily in Western Mexico and Central America but also in smaller numbers on the Gulf Coast from Southern Texas to Eastern Louisiana. 

It is typically found in open wooded areas as well as scrubby riverbanks. Undisturbed understory is its primary habitat requirement especially for breeding. Usually found at low altitudes, certainly not over 3000 ft. During migration and wintering any wooded areas are used. 

Wilsons Warblers are insectivores, feeding on all manner of bugs and spiders. They will eat berries when food is scarce and will often form part of mixed songbird flocks looking for food in winter. 

Breeding season is April to July with the peak at end May. Wilson’s Warblers are not strictly monogamous and sometimes form small breeding groups or harems. Occasionally they produce 2 broods in a season. The nest is a cup of grasses and leaves lined with hair and moss. Nests are low to the ground often in dense clumps of weed. 4-6 white eggs are laid, and incubation is for 11-12 days, and the young fledge around 13 days after hatching. Incubation is carried out solely by the female. Wilson’s Warblers are a favored victim of the parasitic Brown-headed Cowbird. 


A small warbler with a long tail which it often raises and flips, with olive green upperparts and darker green to almost black wings. Its head is yellow with a distinctive small black cap. Note the face around the eye and including the forehead is yellow. Underparts are yellow to yellowish green including the undertail coverts. The bill is dark but often has a fleshy colored base and its legs are pinkish brown. The females and young are similar to the males but duller, with no black cap on the juveniles. 

Its call is a rapidly repeated loud chip and its song is a repeated chee-chee-chee-chee.

Interesting Facts:

·        A group of warblers is known as a fall, a bouquet, a confusion or a wrench.

·    Wilson’s Warblers show some regional variation and are typically much brighter in the West.

·    One of the smallest North American warblers, Wilson’s Warblers weigh less than half an ounce.

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