Cassin's Vireo

Overview

Cassin's vireo (Vireo cassinii) is a small North American songbird that breeds in the western United States and migrates to wintering grounds in Mexico and the southwestern US. It is the westernmost of three species formerly grouped as the 'solitary vireo' and is named after the nineteenth-century ornithologist John Cassin.

Identification

• A small bird measuring 11–14 cm in length with a grayish olive head, back, and flanks, and whitish underparts.
• Distinguished by solid white 'spectacles' around the eyes and white wing bars.
• Produces a persistent song of short, rough-whistled phrases separated by two-second intervals, often forming a 'question-and-answer' pattern or sounding like 'cha-cha-cha'.

Habitat

Breeds in open woodlands, western mountains, and foothills, typically occupying the middle to lower areas of the forest canopy. Its range extends from southern British Columbia through the US western coastal states, with wintering grounds spanning southern Arizona to southern Mexico.

Diet

The primary diet consists of insects such as true bugs, caterpillars, spiders, and ants, which are foraged in tree foliage. During autumn and winter, the bird also consumes fruits and berries to build up fat reserves for migration.

Did you know?

The species exhibits 'countersinging' behaviour, where males take turns singing to confront one another when asserting territorial boundaries.