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Red-eyed Vireo

Vireo olivaceus ORDER: PASSERIFORMES FAMILY: VIREONIDAE

IUCN Conservation Status: Least Concern

A tireless songster, the Red-eyed Vireo is one of the most common summer residents of Eastern forests. These neat, olive-green and white songbirds have a crisp head pattern of gray, black, and white. Their brief but incessant songs—sometimes more than 20,000 per day by a single male—contribute to the characteristic sound of an Eastern forest in summer. When fall arrives, they head for the Amazon basin, fueled by a summer of plucking caterpillars from leaves in the treetops.

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At a GlanceHelp

Measurements
Both Sexes
Length
4.7–5.1 in
12–13 cm
Wingspan
9.1–9.8 in
23–25 cm
Weight
0.4–0.9 oz
12–26 g
Relative Size
Slightly larger than a Yellow Warbler; slightly smaller than a Tufted Titmouse.
Other Names
  • Viréo aux yeux rouges (French)
  • Vireo ojirrojo norteño, Vireo ojo rojo (Spanish)

Cool Facts

  • The red iris that gives the Red-eyed Vireo its name doesn't develop until the end of the birds' first winter. Then the brown iris the birds were born with becomes dull brick red to bright crimson in different individuals.
  • Some find the Red-eyed Vireo's song unending and monotonous. Bradford Torrey wrote in 1889, "I have always thought that whoever dubbed this vireo the 'preacher' could have had no very exalted opinion of the clergy." But each male sings 30 or more different songs, and neighbors have unique repertoires. Over 12,500 different Red-eyed Vireo song types have been recorded.
  • On May 27, 1952, Louise de Kiriline Lawrence counted the number of songs sung by a single Red-eyed Vireo seeking a mate on his territory 180 miles north of Toronto. He sang 22,197 songs in the 14 hours from just before dawn to evening, singing for 10 of those hours.
  • From the 1920s to the 1940s Red-eyed Vireos expanded west into Utah and Oregon and northeast into Newfoundland. The most likely cause is new shelterbelts and landscaping, particularly where eastern tree species were planted. Since the 1970s, however, numbers in the Big Basin region of the West seem to have fallen steadily.
  • Several subspecies of Red-eyed Vireos remain resident in South America or migrate only within that continent.
  • The Red-eyed Vireo's magnetic compass guides migration between continents. But fat stores seem to influence migration paths when the birds encounter the Gulf of Mexico. Fatter birds head across the Gulf, while leaner birds hug the coastline or travel inland around the Gulf. Cloud cover also makes routes near land more likely.
  • The oldest known Red-eyed Vireo was banded in its hatching year and then refound, and rereleased, when 10 years and 2 months old.

Habitat


Forest

Throughout their summer range, Red-eyed Vireos breed in deciduous and mixed forests with shrubby understories. Numbers are greatest away from forest edges and near small openings in the interior forest canopy. In the pine forests of the southeastern United States, they prefer stream and river edges supporting hardwood trees. In northern areas, breeding territories in alder thickets and aspen groves are common. Red-eyed Vireos can sometimes be found in residential areas, city parks, and cemeteries with enough large trees. During migrations, they use a larger variety of forest habitats. Still preferring broadleaf forests to conifers, they will make use of forest edges, citrus groves, city parks, suburban residential areas, and other areas with scattered trees. During fall migrations, they rest and feed in Gulf Coast pine forests with dense undergrowth. In their winter range in the Amazon basin, they inhabit a variety of habitats up to 10,000 feet elevation. Rainforest, mangroves, plantations, second-growth forests and forest edges, arid regions with adequate vegetation, and even gardens with scattered trees and shrubby clearings can serve as winter homes.

Food


Insects

Red-eyed Vireos eat invertebrates as well as seeds and fruits. Their diet changes substantially throughout the year: it’s mostly insects during summer, especially caterpillars which can account for 50 percent of their summer diet. Caterpillars make up only 15 percent of their spring diet, and 20 percent in fall. They also eat butterflies and moths, beetles, mosquitoes, flies, bugs, cicadas, wasps, ants, bees, and sawflies, to (less frequently) grasshoppers, crickets, dragonflies, and damselflies. They'll also eat spiders and small snails. Smaller prey are eaten whole. Caterpillars and other larger meals are trapped under a foot and plucked apart into bite-sized bits. Among plant foods, small wild fruits like blackberries, elderberries, spicebush, Virginia creeper, sassafras, dogwood, arrowwood, and bayberry outnumber the occasional flowers, leaf buds, and magnolia seeds. As fall migration approaches, the amount of fruit in their diet rises. During migration they eat both insects and fruit, but are almost entirely fruit-eaters on their over-wintering grounds in South America.

Nesting

Nesting Facts
Clutch Size
1–5 eggs
Number of Broods
1-2 broods
Egg Length
0.8–0.9 in
2–2.4 cm
Egg Width
0.5–0.9 in
1.2–2.4 cm
Incubation Period
11–15 days
Nestling Period
10–12 days
Egg Description
Dull white with sparse, sepia speckling.
Condition at Hatching
Born helpless, with eyes closed and sparse down on the pinkish orange skin of their heads, backs, and wings.
Nest Description

The female spends 4 to 5 days constructing a nest of bark strips, grasses, pine needles, wasp-nest paper, twigs, and plant fibers that hangs below the branch. She glues the materials (some of which are provided by the male) together and to the branch fork with spider-web adhesive, occasionally supplemented with spider egg cases and sticky plant fibers. The open cup is usually just over 2 inches across and an inch and a half deep, surrounded by half-inch walls and supported by an inch-thick floor.

Nest Placement

Tree

The female chooses a fork in a branch of a midstory to understory tree or shrub. The fork is typically shaded, concealed from above by vegetation, and far enough from the trunk to provide an unobstructed 360 degree view. Most nests are in deciduous trees, at an average height of 10 to 15 feet.

Behavior


Foliage Gleaner

Breeding males sing incessantly from before sunrise until well into the afternoon, usually from treetops around the periphery of their territories. Challenges provoke posturing, chasing, pecking, grappling, and displacing rivals from perches. Females and males indicate threats by raising crown feathers, fanning tails, and opening the bill while pecking and calling. Males also threaten by tilting their bodies forward and thrusting their heads out. The female aggressively defends the nest. She and the male will swoop, snap, and peck at intruding jays, crows, squirrels, and chipmunks. Both chase, scold, and strike intruding cowbirds with their wings. But once cowbird eggs are in the nest they are generally tolerated, though the vireo parents sometimes cover the intruder’s eggs with additional nesting material. Red-eyed Vireos hop along and flit between branches when foraging. They glean most of their invertebrate food from the underside of leaves. Pairs are seasonally monogamous. The female builds the nest, incubates the eggs, and broods the young. The male offers nest materials and feeds the female, especially during incubation. The female begs for food away from the nest, quivering her wings, opening and closing her mouth, and calling, much like a begging chick. She solicits copulation by calling and crouching with wings quivering and tail spread and lowered. Both mates vibrate wings and twitter during copulation. Both may join large mixed flocks during migrations and on wintering grounds.

Conservation

status via IUCN

Least Concern

Red-eyed Vireos are numerous and populations have been growing slowly but steadily in most of their range since 1966, according to the North American Breeding Bird Survey. However, in the western United States, numbers fell by nearly 75 percent (3 percent per year, on average) over the same period. Partners in Flight estimates the global breeding population at 180 million, with 48 percent breeding in Canada, 27 percent in the U.S., and the remainder breeding in South America. Populations are sensitive to disturbances such as clearcut logging, stripmining, and forest fragmentation. Logging practices that leave smaller canopy openings are less disruptive. Red-eyed Vireos are among the most common hosts to Brown-headed Cowbird eggs. Nest parasitism is more frequent near forest edges. Local populations show growth during the breeding season after large caterpillar outbreaks. Like many nocturnal migrants, Red-eyed Vireos are killed in collisions with buildings and other tall structures, sometimes in large numbers.

Credits

Range Map Help

Red-eyed Vireo Range Map
View dynamic map of eBird sightings

Migration

Long-distance migrant. Red-eyed Vireos leave the U.S. and Canada each fall to spend winters in the Amazon basin of South America. Western populations typically swing east before joining common flight paths south.

Find This Bird

Red-eyed Vireos are very common in Eastern forests during summer. They can be hard to see in the treetops, particularly after the trees leaf out, but this is one bird that really highlights the value of learning bird songs. Their short, rising-and-falling song is fairly easy to recognize and the birds give it almost all day long, including during the mid-afternoon doldrums when few other species are singing. Learning this song helps in two ways: it makes it easier to find the species, and it gives you a familiar song against which to compare other songs and perhaps find additional species. On migration, look for the species in nearly any patch of trees. On the species’ South American winter range, it retains its fondness for forest canopy and trees with large leaves.