The Wilson’s warbler is a small wood warbler at about 10-12 cm in length. Adult males have yellowish, olive-green unmarked underparts in their breeding plumage. They also have a clearly defined black cap on top of their head and black eyes that stand out in contrast to their yellow face. Females are duller overall and have a yellow-olive cap, yellow eyebrow, and plain yellow face. The back is olive-yellow in both sexes and the tail is dark and unmarked. Wilson warblers flutter rapidly in mid-air and have rapid body movements including tail flicking and waving.
Song is a loud, ringing series of harsh chips dropping in tone and speed toward the end: chi-chi-chi-chi-CHETCHETCHET. Call note is a loud CHET!
The Wilson’s warbler is more common in the West than in the East. They are typically found low to the ground in thick, brushy woods and alder and willow thickets, especially along streams and near other water. This species is an abundant spring migrant in the West.
Most commonly, the Wilson’s warbler consumes adult and larval insects like bees, mayflies, beetles, and caterpillars, as well as spiders. They rarely forage on the ground but instead pick from foliage and twigs higher up. The Wilson’s warbler uses several methods to capture its food including gleaning, hovering, and sallying.
Nesting sites are selected by the female and are usually placed at or below ground level—at the base of a tree, under bunches of grass, moss, or other ground vegetation. They use material such as leaves, stems, moss, and hair to construct their nests. They usually have 2 to 7 eggs and incubate them for a maximum of 13 days. Male Wilson’s warblers rarely help with brooding and incubating. Young Wilson’s warblers fledge 9 to 11 days after hatching.
The Wilson’s warbler is named for Alexander Wilson (1766–1813), one of North America’s first ornithologists.