Guide to Boreal Birds
Perching Birds Overview
This vireo has been one of the most abundant birds in North America, although its numbers seem to have declined recently, possibly as a result of the destruction of wintering habitat in the neotropics, fragmentation of northern breeding forests, or other causes. Its principal habitat, broad-leaved forests, often supports one pair per acre. A persistent singer during the breeding season, the Red-eyed Vireo utters its endless series of short phrases from dawn till dusk, even on the hottest days when other birds are silent, and may even sing while grappling with the large insects it captures. The Red-eyed Vireo is a fierce fighter around its nest and can intimidate even the large Pileated Woodpecker. Its horizontal posture and slow movement through the understory of broad-leaved woods make it an easy bird to study.
Description
5 1/2 -6 1/2" (14-17 cm). Sparrow-sized. Olive green above, whitish below, with a narrow white eyebrow bordered above with black. Gray crown; red eye (eye dark in immature); no wing bars. Warbling Vireo similar, but lacks gray crown and black border over bold white eyebrow.
Voice
A series of short, musical, robin-like phrases endlessly repeated; like that of Solitary Vireo but faster and not so musical.
Nesting
3 or 4 white eggs, sparsely marked with dark brown, in a thin-walled pendant cup of bark strips and plant fibers, decorated with lichen and attached to a forked twig.
Habitat
Broad-leaved forests; shade trees in residential areas.
Range/Migration
During winter, Red-eyed Vireos are most numerous in the northern Amazon basin where they feed primarily on fruits. As the time of migration approaches, they begin to consume more insects. Whether or not a bird crosses the Gulf may be diet-related. Birds with substantial fat reserves are more likely to attempt a crossing; individuals lacking adequate reserves tend to orient northwestward and follow the coast. This species seldom stays for more than a day along the U.S. Gulf coast; most individuals continue their migration at first nightfall. This may be an adaptation that allows Red-eyed Vireos to avoid the intense competition for foraging habitat that is in such short supply in this area. This is one of the more common "eastern" species to appear as a vagrant along the California coast in late May and early June.
Breeds from British Columbia, Ontario, and Gulf of Saint Lawrence south to Oregon, Colorado, Gulf Coast, and Florida. Winters in tropics.