Guide to Boreal Birds
Perching Birds Overview
The bird formerly known as the Solitary Vireo was recently split into three separate species by American ornithologists: Cassin's, Plumbeous, and Blue-headed Vireos. Cassin's Vireo occupies the westernmost part of the former Solitary Vireo's range.
Description
5-6" (13-15 cm). Very similar to both Blue-headed and Plumbeous Vireos, with plumage roughly intermediate between the two. Duller and grayer overall than Blue-headed but shares that species' yellow sides and flanks, olive back, white wing-bars, and bold white "spectacles."
Voice
Song a series of phrases; intermediate between clear notes of Blue-headed Vireo and rough, husky notes of Plumbeous Vireo. Call a husky chatter.
Nesting
3-5 white eggs, lightly spotted with brown, in a pendant cup of bark strips and down, placed in a forked twig of a small forest tree.
Habitat
Coniferous and mixed forests.
Range/Migration
Breeds from British Columbia, and southwestern Alberta south to central Idaho and along the West Coast to southern California. Most leave the U.S. in the fall but a small number overwinter in southeastern Arizona.