Small, active, bright yellow warbler. Most birds (adults of both sexes and young males) have a black cap; young females lack this feature. Also note the rather long, narrow tail that is actively flipped around while foraging. Extensive breeding range across northern and western North America; more common in the west than east. Prefers dense thickets, especially with willows and alders. Winters primarily in Mexico, extending as far south as Panama. Migrants and wintering birds are found in any brushy wooded habitat. Listen for husky chip notes. Compare with Yellow Warbler, but note Wilson’s is smaller, smaller-billed, and has a relatively longer, thinner tail.