Cassin’s Vireo is a somewhat drab ‘spectacled’ bird of the West.
It is however conspicuous in the forest due to its tireless, raspy
singing and harsh scolding call.
Cassin’s Vireo breeds from southern B.C. and southwest Alberta,
western Montana, northern Idaho, Washington, along the west coast to
southern California. It winters in areas of southern
California and Arizona and Mexico.
Medium sized Vireo with hooked bill and white ‘spectacles’. Length:
110-136mm. Weight: 13-18g.
Upperparts are dull olive-green becoming gray on crown and
auriculars. Face is brownish gray and the bold white
‘spectacles’ are formed by a supraloral stripe and eye-ring.
Wings and tail brownish black with 2 broad yellowish-white wing
bars. Remiges and rectrices finely edged olive-yellow or
grayish olive: outer rectrix finely edged in white. Throat and
underparts are dingy white with sides of breast olive green and
paler, yellowish-olive flanks. Legs are blue-gray. Bill
is black with hook. Seasonal variations in adult plumage
Sexes are monomorphic in plumage and size although females tend to
be slightly duller.
Similar to adults but upperparts brownish-gray; underparts entirely
dull white, the flanks and undertail coverts faintly tinged
Hutton’s Vireo is smaller with a narrower, incomplete eye-ring.
Underparts are drab olive and there is less contrast in plumage.
Bell’s Vireo lacks full eye ring and has a whitish supercilium.
Warbling Vireo, though similar in size, has indistinct supercilium
instead of eye ring.
Forages in a slow, deliberate manner, gleaning insects from foliage
in upper parts of trees. Sometimes flies out to catch insects
in midair or hovers to obtain insects from foliage tips. In
summer it feeds almost entirely on insects and also eats some
berries and small fruits, though especially in winter.
conspicuous and continuous raspy up and down song of the Cassin’s
Vireo sounds as if the bird is asking and answering questions.
Its call consists of short harsh scolding notes.
Occupies coniferous, mixed coniferous/deciduous and deciduous
forests in the mountains and foothills. In coastal British
Columbia, it is most numerous in open stands of Douglas fir, oak and
madrone on drier, rocky sites and in mixed woods of maple, alder,
cottonwood, Pacific dogwood, Douglas fir and western red cedar.
This vireo was named in honour of the nineteenth-century
ornithologist, John Cassin, who published the first comprehensive
work on the birds of western United States.
was formerly included as a “Solitary Vireo”, with the Plumbeous and
Blue-headed vireos however was recently split. The Cassin’s
Vireo includes two subspecies: V.c. cassinii, which
breeds along the west coast of North America and a non-migratory
Mexican subspecies V.c. lucasanus found only in the far
southern Cape District of Baja California Sur.
Three to five whitish eggs, lightly spotted with brown and black are
laid in a rather bulky open cup nest suspended by its rim, usually
three to twelve feet above ground. The nest consists of grass,
bark, plant fibers lined with plant down and hair.
Currently not listed as endangered, threatened or as a species of
special concern by any state, provincial or federal wildlife agency.
Cassin's Vireo breed in the dry, open forests of mountains
and foothills that are more indicative of the interior.
Therefore, Cassin's Vireo is a rare visitor to Colony Farm
as is reflected by the capture of only a few individuals in
April and zero capture rate for the remainder of the year.
Capture rates are standardized as birds captured per 100 net
hours from 2010 - 2012.