Cassin’s Vireo
Vireo cassinii
The Cassin's Vireo is a common migratory breeder in Oregon, arriving in spring to set up territories in the state's forests. This species was formerly lumped with the Blue-headed and Plumbeous Vireos into the "Solitary Vireo" complex, but it is now recognized as its own distinct species in the West.
Like many vireos and small passerines, male and female Cassin's Vireos are virtually identical in their breeding plumage and size. Field identification of sex based on visual cues is generally not possible.
General Characteristics (Both Sexes)
Size & Shape: A medium-sized vireo, typically 4.3-5.3 inches (11-13.6 cm) long, with a relatively stout body and a short, thick, slightly hooked bill.
Coloration:
Upperparts: The back and wings are generally dull olive-green. The rump often appears a brighter olive-green than the mantle (back).
Head: The head is distinctly grayish-brown, contrasting somewhat with the olive-green back.
Underparts: The underparts are dingy white, with a yellowish-olive wash on the flanks and sides of the breast.
Spectacles: A key identifying feature is their prominent "spectacles", formed by a bold white eye-ring that connects to a white supraloral stripe (a stripe above the lores, between the eye and the bill). The eye-ring is often interrupted by a dusky loral streak (through the lores).
Wingbars: They have two broad, yellowish-white wingbars.
Bill: Black bill with a bluish-gray base to the lower mandible. Iris is brown. Legs are grayish-blue.
Behavior:
Foraging: Cassin's Vireos are deliberate foragers, moving slowly through the canopy of trees, gleaning insects and spiders from leaves and bark. They occasionally make short sallies to catch insects in mid-air.
Wing Flicking: Like Hutton's Vireos, they can sometimes exhibit a nervous wing-flicking behavior, though it's not as constant as a Ruby-crowned Kinglet.
Vocalization: This is a crucial ID feature. The song is a distinctive, halting, burry song of ascending and descending phrases, with each phrase typically having 2 to 4 notes. There can be a second or more of silence between phrases. It's often described as a "question and answer" song, with phrases like "chreu chree chooreet" or "chree ch-ri-chi-roo." Males sing persistently during the breeding season. Their calls are often harsh, raspy "cha-cha-cha" or "zhe-zhe-zhe" notes.
Male Cassin's Vireo in Oregon
Plumage: Visually indistinguishable from the female. While some sources might suggest females are "slightly duller," this difference is extremely subtle and not reliable for field identification.
Size: Males are generally similar in size to females.
Singing: Males are the primary singers, using their song extensively to establish and defend their breeding territory and attract a mate. They may engage in "countersinging" with rival males.
Female Cassin's Vireo in Oregon
Plumage: Visually indistinguishable from the male.
Size: Females are generally similar in size to males.
Nesting: Both male and female Cassin's Vireos participate in nest building, which is a bulky, cup-shaped nest suspended from a horizontal fork in a tree branch, often decorated with lichen and spider silk. Both parents share incubation duties (12-14 days) and feed the nestlings.
Habitat in Oregon
Cassin's Vireos are common summer residents throughout much of Oregon, particularly in the state's coniferous and mixed forests. They prefer relatively dry, open woodlands:
Mixed coniferous-deciduous forests: Especially common in areas with Douglas-fir, Ponderosa Pine, and various oaks.
Coniferous forests: Found in various conifer types, from low-elevation Ponderosa Pine to higher elevation mixed forests.
Oak woodlands: Can be found in oak-pine associations in southwestern and eastern Oregon.
They are widespread during migration, sometimes appearing in city parks and suburban areas with mature trees.
Key Distinctions from Similar Vireos in Oregon:
Blue-headed Vireo (*Vireo solitarius*): The Blue-headed Vireo is an eastern species but can be a vagrant in Oregon. It has a more distinctly blue-gray head, brighter white underparts, and often a more prominent yellow wash on the flanks. Its song is similar but often sounds more purely "musical" or "clearer" than the burry Cassin's song.
Plumbeous Vireo (*Vireo plumbeus*): Primarily an interior western species, occasionally found in eastern Oregon. It's much grayer overall, with less olive or yellowish tones. Its song is similar but generally less burry than Cassin's.
Hutton's Vireo (*Vireo huttoni*): A resident in western Oregon, also dull olive-gray. Hutton's Vireo is smaller, has a more incomplete (often broken) eye-ring, and its song is a much simpler, monotonous repetition of a single note ("too-weep...").
Like many vireos and small passerines, male and female Cassin's Vireos are virtually identical in their breeding plumage and size. Field identification of sex based on visual cues is generally not possible.
General Characteristics (Both Sexes)
Size & Shape: A medium-sized vireo, typically 4.3-5.3 inches (11-13.6 cm) long, with a relatively stout body and a short, thick, slightly hooked bill.
Coloration:
Upperparts: The back and wings are generally dull olive-green. The rump often appears a brighter olive-green than the mantle (back).
Head: The head is distinctly grayish-brown, contrasting somewhat with the olive-green back.
Underparts: The underparts are dingy white, with a yellowish-olive wash on the flanks and sides of the breast.
Spectacles: A key identifying feature is their prominent "spectacles", formed by a bold white eye-ring that connects to a white supraloral stripe (a stripe above the lores, between the eye and the bill). The eye-ring is often interrupted by a dusky loral streak (through the lores).
Wingbars: They have two broad, yellowish-white wingbars.
Bill: Black bill with a bluish-gray base to the lower mandible. Iris is brown. Legs are grayish-blue.
Behavior:
Foraging: Cassin's Vireos are deliberate foragers, moving slowly through the canopy of trees, gleaning insects and spiders from leaves and bark. They occasionally make short sallies to catch insects in mid-air.
Wing Flicking: Like Hutton's Vireos, they can sometimes exhibit a nervous wing-flicking behavior, though it's not as constant as a Ruby-crowned Kinglet.
Vocalization: This is a crucial ID feature. The song is a distinctive, halting, burry song of ascending and descending phrases, with each phrase typically having 2 to 4 notes. There can be a second or more of silence between phrases. It's often described as a "question and answer" song, with phrases like "chreu chree chooreet" or "chree ch-ri-chi-roo." Males sing persistently during the breeding season. Their calls are often harsh, raspy "cha-cha-cha" or "zhe-zhe-zhe" notes.
Male Cassin's Vireo in Oregon
Plumage: Visually indistinguishable from the female. While some sources might suggest females are "slightly duller," this difference is extremely subtle and not reliable for field identification.
Size: Males are generally similar in size to females.
Singing: Males are the primary singers, using their song extensively to establish and defend their breeding territory and attract a mate. They may engage in "countersinging" with rival males.
Female Cassin's Vireo in Oregon
Plumage: Visually indistinguishable from the male.
Size: Females are generally similar in size to males.
Nesting: Both male and female Cassin's Vireos participate in nest building, which is a bulky, cup-shaped nest suspended from a horizontal fork in a tree branch, often decorated with lichen and spider silk. Both parents share incubation duties (12-14 days) and feed the nestlings.
Habitat in Oregon
Cassin's Vireos are common summer residents throughout much of Oregon, particularly in the state's coniferous and mixed forests. They prefer relatively dry, open woodlands:
Mixed coniferous-deciduous forests: Especially common in areas with Douglas-fir, Ponderosa Pine, and various oaks.
Coniferous forests: Found in various conifer types, from low-elevation Ponderosa Pine to higher elevation mixed forests.
Oak woodlands: Can be found in oak-pine associations in southwestern and eastern Oregon.
They are widespread during migration, sometimes appearing in city parks and suburban areas with mature trees.
Key Distinctions from Similar Vireos in Oregon:
Blue-headed Vireo (*Vireo solitarius*): The Blue-headed Vireo is an eastern species but can be a vagrant in Oregon. It has a more distinctly blue-gray head, brighter white underparts, and often a more prominent yellow wash on the flanks. Its song is similar but often sounds more purely "musical" or "clearer" than the burry Cassin's song.
Plumbeous Vireo (*Vireo plumbeus*): Primarily an interior western species, occasionally found in eastern Oregon. It's much grayer overall, with less olive or yellowish tones. Its song is similar but generally less burry than Cassin's.
Hutton's Vireo (*Vireo huttoni*): A resident in western Oregon, also dull olive-gray. Hutton's Vireo is smaller, has a more incomplete (often broken) eye-ring, and its song is a much simpler, monotonous repetition of a single note ("too-weep...").