Cassin's Vireo

Vireo cassinii

Order PASSERIFORMES - Family VIREONIDAE

Menu

1. Cool Facts
2. Description
3. Similar Species
4. Sound
5. Range
6. Habitat
7. Food
8. Behavior
9. Reproduction
10. Conservation Status
11. Other Names

A common bird of the far western forests, the Cassin's Vireo is conspicuous for its constant singing. Formerly lumped as a "Solitary Vireo" with the Plumbeous and Blue-headed vireos, it is now considered a separate species.

Cool Facts

• The Cassin's Vireo is the western-most form in the "Solitary Vireo" complex. Formerly considered one species, three species now are recognized. In appearance it is intermediate between the brightly colored Blue-headed Vireo and the dull gray Plumbeous Vireo. Its song also is intermediate between the other two species, being much hoarser than Blue-headed Vireo, but slightly higher and with more clear phrases than Plumbeous Vireo.

• Two subspecies of Cassin's Vireo are recognized. One is widespread in western North America from Canada to the northern part of Baja California. The other form is found only on the very southern tip of Baja California more than 800 km (500 mi) away.

• The Cassin's Vireo is a fearless defender of its nest. Both the male and female will vigorously scold a predator and dive at it. The female often will not leave her nest and sometimes can be picked up off of it by a human observer.

Description

• Size: 11-14 cm (4-6 in)
• Wingspan: 24 cm (9 in)
• Weight: 13-18 g (0.46-0.64 ounces)

• Small songbird, medium-sized vireo.
• Brownish-gray head with white spectacles.
• Two whitish wingbars.
• Belly white, flanks yellowish.

• Back olive-green to gray, becoming gray on the head; rump brightest green.
• Wings and tail brownish black.
• Wingbars yellowish-white.
• Wing and tail feathers edged with olive-yellow or grayish-olive.
• Outer tail feather with fine white edge.
• Underparts dingy white.
• Side of chest smudged dull olive-green.
• Eyes brown.
• Bill black with gray base.
• Legs grayish blue.

Sex Differences

Sexes alike, but female slightly duller.

Immature

Immatures similar to adults, but crown and sides of head more olive.

Similar Species

• Blue-headed Vireo is very similar, but has blue-gray crown contrasting more sharply with throat and the back; very limited overlap in range.
• Plumbeous Vireo is gray over all upperparts, with only the rump having any greenish, the edging of flight feathers are not yellow, and the flanks have little or no yellow.
• Hutton's Vireo is smaller, eyering is incomplete, has dingier underparts, and less contrasting plumage.
• Bell's Vireo lacks a full eyering so does not appear spectacled, has weaker wingbars, and does not appear so contrasting.

Sound

Song a broken series of slightly burry whistled notes, inflected upwardly and then downwardly. Calls a series of short harsh notes.

»listen to songs of this species

Range

Summer Range

Breeds along Pacific Coast from British Columbia and extreme southwestern Alberta, southward to Baja California. Also in parts of Idaho and western Montana.

Winter Range

Winters in southern Mexico. A few in extreme southern California and lower Colorado River valley.

Habitat

Breeds in dry, open forests of mountains and foothills.

Food

Arthropods.

Behavior

Foraging

Forages in middle and lower levels of forest. Gleans insects from outer twigs and foliage. Forages in slow and deliberate manner.

Displays

Male performs nest-building display while slightly crouched with body horizontal, usually without nest material in bill.

Reproduction

Nest Type

Open cup suspended by rim from a fork of a branch of a tree or sapling. Woven of grasses, dead leaves, moss, and hair, decorated with lichen, spider egg cases, cocoons, pieces of wasp nest and paper. Inner lining of grasses, plant fibers, and hair.

Egg Description

Whitish with a few brown spots around large end.

Clutch Size

Usually 4 eggs. Range: 2-5.

Condition at Hatching

Helpless.

Conservation Status

Populations increasing slightly.

Other Names

Viréo de Cassin (French)
Vireo de Cassin (Spanish)
Solitary Vireo (western form) (English)

Sources used to construct this page:

Goguen, C. B., and D. R. Curson. 2002. Cassin's Vireo (Vireo cassinii). In The Birds of North America, No. 615 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.