[5] The genus name Cardellina is a diminutive of the Italian dialect Cardella, a name for the European goldfinch, and the specific epithet pusilla means "very small".

The population of the subspecies has declined sharply in the 21st century because it migrates preferentially to the southern end of the Baja Peninsula in Mexico,[9] where luxury resort and residential developments have replaced the bird's habitat.

Individuals from Alaska and the west-central portion of the species' range average slightly larger than those found in eastern and Pacific coastal populations.

[13] The breeding habitat is fairly open woodland with undergrowth or shrubs and thickets in moist areas with streams, ponds, bogs, and wet clearings.

At all seasons, it prefers secondary growth, riparian habitats, lakes, montane and boreal forests with overgrown clearcuts.

[11] Nesting generally begins in early March in west coast populations, and extends into August in the northern range.

[12] Wilson's warbler is an insectivore, feeding primarily on insects gleaned from leaves and twigs, or caught by flycatching.

Wilson's warbler is an active forager, moving rapidly through shrubs, on the ground, and sometimes in taller trees during the winter.