It is likely the birds that Wilson spotted were adults. In this species the juvenile birds tend to migrate along the coast while the adult birds choose a more inland route. There are two distinct and separate subspecies of Nashville warblers. The ruficapilla subspecies is found in the eastern half of North America. The ridgwayi subspecies breeds along the west coast of North America from northern California to southern British Columbia. This subspecies is a little brighter and used to be considered a separate species, the Calavaras warbler. Both species prefer deciduous forest or bog habitat. They eat insects which they glean from low branches and shrubs.