The Wilson's Warbler is 10 to 12 cm (3.9 to 4.7 in) in length, with a wingspan of 14-17 cm (5.5-6.7 in) and a mass of 5-10 g. It has a plain green-brown back and yellow underparts. The male has a small black cap. Males of the western race are greener above and brighter than males of the eastern, nominate race. Individuals from Alaska and the west-central portion of the species' range average slightly larger than those in eastern and Pacific coastal populations.


Habitat and Distribution

The breeding habitat is fairly open woodland with undergrowth or shrubs and thickets in moist areas with streams, ponds, bogs, and wet clearings. Wilson's Warbler breeds in northern Canada and the western US. It winters in overgrown clearings and coffee plantations, forest edges, deciduous forests, tropical evergreens, pine-oak forests, mangroves, thorn-scrub, riparian gallery forests, brushy fields. At all seasons, it prefers secondary growth, riparian habitats. It is a very rare vagrant to Western Europe.


Feeding

Wilson 's Warbler feeds primarily on insects gleaned from leaves and twigs, or caught by flycatching. Insects include beetles, bees, or caterpillars. The bird is an active forager, on shrubs, the ground, and tall trees during the winter.


Breeding

Nesting generally begins in early March in west coast populations, and extends into August in the northern range. The female does the majority of the nest building. The cup nest is typically constructed of vegetation and lined with grasses and hair. It is often sunken into moss or sedges at the base of shrubs. The clutch varies from 2 to 7 eggs, which are creamy or off-white with fine reddish spots. The eggs hatch at 11-15 days.


Calls and Songs

Its song is a chattering series of loud descending notes. The call is a flat chuff.