The red-eyed vireo (Vireo olivaceus) is a small American songbird. It is somewhat warbler-like but not closely related to the New World warblers (Parulidae). Common across its vast range, this species is not considered threatened by the IUCN.
is a Latin word referring to a green migratory bird, perhaps the female golden oriole, possibly the European greenfinch. The specific is Neo-Latin for 'olive-green', from Latin ('olive').
Adults are mainly olive-green on the upper parts with white underparts; they have a red iris which may appear dark from a distance and a grey crown edged with black. There is a dark blackish line through the eyes and a wide white stripe just above that line. They have thick blue-grey legs and a stout bill. They are yellowish on the flanks and undertail coverts.
In the past, the yellow-green vireo (V. flavoviridis), the chivi vireo (V. chivi), and the Noronha vireo (V. gracilirostris) have been considered to be conspecific with the red-eyed vireo; the chivi vireo was split most recently. Other closely related species include the black-whiskered vireo (V. altiloquus) and the Yucatan vireo (V. magister).
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Red-eyed vireos are one of the most prolific singers in the bird world. They usually sing high up in trees for long periods of time in a question-and-answer rhythm. This species holds the record for most songs given in a single day among bird species, with more than 20,000 songs in one day.
Songs generally consist of 1âÂÂ5 syllables between 2 and 6 kHz. Songs are usually spaced apart by 0.8âÂÂ1 seconds although at times vireos may sing at a slower or faster rate. Red-eyed vireos have a large repertoire size with one study finding an average of 31.4 song types per bird with one individual singing 73 different song types. Individuals may tend not to duplicate the songs of nearby conspecifics (members of the same species).
The red-eyed vireo's breeding habitat covers deciduous and mixed conifer-deciduous forests with shrubby understories across eastern North America, northern United States, and across Canada. These birds migrate to South America, where they spend the winter primarily in the Amazon River Basin. In northern Ohio, they seem to return to breed at about the same time as one century ago; but they may leave for winter quarters one or two weeks earlier at present than they did in the past.
Red-eyed vireos frequently nest farther from forest edges and near openings in the interior forest canopy, such as near river edges. When migrating, however, they will utilize a wider variety of habitats, including forest edges, city parks, and suburban residential areas.
Female red-eyed vireos tend to build cup-shaped nests in the forks of branches, usually far enough from the trunk of the host tree to have a minimally-obstructed view. Most nests are built 10-15 feet (3-4.6 meters) from the ground. Nests generally take 4-5 days to complete, consisting largely of bark strips, grasses, pine needles, and other paper-like or fibrous materials. Female red-eyed vireos often use spider silk and sticky plant fibers to bind nest materials. Nests are two inches (5 cm) across and one and a half inches (3.8 cm) deep. While the nest floor is often one inch (2.5 cm) thick, walls tend to be half of an inch (1.3 cm) thick.
Red-eyed vireos glean insects from tree foliage, favouring caterpillars and aphids and sometimes hovering while foraging. In some tropical regions, they are commonly seen to attend mixed-species feeding flocks, moving through the forest higher up in the trees than the bulk of such flocks.
They also eat berries, especially before migration, and in the winter quarters, where trees bearing popular fruit like tamanqueiro (Alchornea glandulosa) or gumbo-limbo (Bursera simaruba) will even attract them to parks and gardens. Fruit are typically not picked up from a hover, but the birds often quite acrobatically reach for them, even hanging upside down.
Red-eyed vireos suffer from nest parasitism by the brown-headed cowbird (Molothrus ater) in the north of its range, and by the shiny cowbird (M. bonariensis) further south. Parasitism by Haemoproteus and trypanosoma may commonly affect these birds, as was noted in studies of birds caught in Parque Nacional de La Macarena and near Turbo (Colombia): though only three red-eyed vireos were examined, all were infected with at least one of these parasites.
The red-eyed vireo is a visitor to some western states, especially California. This vireo is one of the more frequent American passerine vagrants to Europe, with more than one hundred records, mainly in Ireland and Great Britain.
The red-eyed vireo is listed as a least concern species by the IUCN. The last assessment of the species was in 2019, prior to the taxonomic split of the red-eyed vireo and the chivi vireo. However, the IUCN considers the population to be both considerably large and relatively stable.