Cassin's Vireo
Vireo cassinii
Cassin's Vireo is a western woodland vireo that sits between its close relatives in coloring, showing a muted, intermediate blend of gray and olive tones.
- Feather type
- Grayish-olive head feathers; white spectacle feathers; two white wing-bar feathers
- Colours
- Grayish-olive head with muted contrast, white spectacles, faint yellowish flank wash
- Bird size
- Sparrow-sized, ~14 cm
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Overview
Overview
Cassin's Vireo breeds in mixed conifer and oak woodlands along the Pacific coast and interior mountains of the western United States, wintering mainly in Mexico. It was split from the Blue-headed and Plumbeous Vireos, which together formerly made up the single species known as the Solitary Vireo, and it shows plumage intermediate between those two relatives.
Distinguishing Cassin's from its close relatives requires attention to the degree of contrast between head and back and the intensity of yellow on the flanks.
Identifying the Feather
Recognizing the Feathers
- Head feathers: grayish-olive, showing only muted contrast with the back rather than the bold blue-gray of Blue-headed Vireo
- Back feathers: olive, slightly duller than in Blue-headed Vireo
- Face feathers: white spectacles, generally slightly less bold than in Blue-headed Vireo
- Underpart feathers: white with a faint yellowish wash on the flanks, less saturated than Blue-headed Vireo but more than Plumbeous Vireo
- Wing feathers: dark with two white wing bars
The muted, intermediate contrast between head and back, along with a faint (rather than absent or bold) yellow flank wash, helps place feathers as Cassin's Vireo rather than its two close relatives.
Plumage & Molt
Plumage
Sexes are similar, both showing grayish-olive head and back with muted contrast, white spectacles, and a faint yellowish flank wash. Immatures are similar to adults but slightly duller. There is no strong seasonal plumage variation, with a single complete molt after breeding.
Habitat & Range
Habitat & Range
This vireo breeds in mixed conifer and oak woodlands along the Pacific coast states and interior mountain ranges of the western United States. It winters mainly in Mexico, making it a medium-distance migrant.
Behavior & Field Notes
Behavior & Field Notes
Cassin's Vireo forages deliberately in mid-story and canopy foliage of mixed woodland, gleaning insects in the slow, methodical manner typical of vireos. Nests are cup-shaped and suspended from a forked branch. Its song consists of short, slow phrases with pauses, closely resembling those of Blue-headed and Plumbeous Vireos.
Frequently asked questions
How does Cassin's Vireo compare to Blue-headed and Plumbeous Vireos?
It shows an intermediate pattern: less contrast between head and back than Blue-headed Vireo, but more olive and yellow tones than the uniformly gray Plumbeous Vireo.
Were these three vireos once considered one species?
Yes, they were formerly lumped as the Solitary Vireo before being split into three species based on plumage and vocal differences.
What habitat does Cassin's Vireo prefer?
Mixed conifer and oak woodland along the Pacific coast and interior mountains of the western United States.
Is it easy to separate these three vireos by feathers alone?
It can be challenging, as the differences are subtle matters of contrast and color saturation rather than bold, unique markings.
Cassin's Vireo guides
In-depth guides for identifying and understanding Cassin's Vireo.
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