Red-eyed Vireo (Vireo olivaceus)

Red-eyed vireo
In Wisconsin, North America
Conservation status
Least Concern (IUCN 3.1)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Passeriformes
Family:	Vireonidae
Genus:	Vireo
Species:	V. olivaceus
Binomial name
Vireo olivaceus (Linnaeus, 1766)
Non-Breeding   Breeding   Migration
Synonyms
Muscicapa olivacea Linnaeus, 1766

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.

Vireo is a Latin word referring to a green migratory bird, perhaps the female golden oriole, possibly the European greenfinch. The specific olivaceus is Neo-Latin for 'olive-green', from Latin oliva ('olive').^[2][3]

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.^[4]

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).^[4]

Measurements:^[4]

Both sexes:

• Length: 4.7–5.1 in (12–13 cm)
• Weight: 0.4–0.9 oz (12–26 g)
• Wingspan: 9.1-9.8 in (23–25 cm)

Eggs:^[4]

• Clutch size: 1-5
• Number of broods: 1-2
• Length: 0.8-0.9 inches (2-2.3 cm)
• Width: 0.5-0.9 inches (1.3-2.3 cm)
• Incubation period: 11-15 days
• Nestling period: 10-12 days
• Color: dull white with sparse sepia speckling

Song

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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.^[5]

Songs generally consist of 1–5 syllables between 2 and 6 kHz. Songs are usually spaced apart by 0.8–1 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.^[6] Individuals may tend not to duplicate the songs of nearby conspecifics (members of the same species).^[7]

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.^[5] These birds migrate to South America, where they spend the winter primarily in the Amazon River Basin.^[5] 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.^[8]

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.^[4]

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.^[4]

Red-eyed vireos glean insects from tree foliage, favouring caterpillars and aphids and sometimes hovering while foraging.^[9] 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.^[10]

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.^[11] Fruit are typically not picked up from a hover, but the birds often quite acrobatically reach for them, even hanging upside down.^[12]

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^[13] 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.^[14]

The red-eyed vireo is a visitor to some western states, especially California.^[15] 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.^[16]

• Basto, Natalia; Rodríguez, Oscar A.; Marinkelle, Cornelis J.; Gutierrez, Rafael & Matta, Nubia Estela (2006). "Haematozoa in birds from la Macarena National Natural Park (Colombia)". Caldasia 28(2): 371–377 [English with Spanish abstract].
• Foster, Mercedes S. (2007). The potential of fruiting trees to enhance converted habitats for migrating birds in southern Mexico. Bird Conservation International 17(1): 45–61. doi:10.1017/S0959270906000554
• Henninger, W.F. (1906). "A preliminary list of the birds of Seneca County, Ohio." Wilson Bull. 18(2): 47–60. DjVu fulltext
• Londono, Aurora; Pulgarin-R., Paulo C. & Blair, Silva (2007). "Blood Parasites in Birds From the Lowlands of Northern Colombia." Caribb. J. Sci. 43(1): 87–93.
• Machado, C.G. (1999). "A composição dos bandos mistos de aves na Mata Atlântica da Serra de Paranapiacaba, no sudeste brasileiro [Mixed flocks of birds in Atlantic Rain Forest in Serra de Paranapiacaba, southeastern Brazil]." Revista Brasileira de Biologia 59(1): 75–85 [Portuguese with English abstract]. doi:10.1590/S0034-71081999000100010
• Ohio Ornithological Society (OOS) (2004). "Annotated Ohio state checklist. Version of April 2004"
• Pascotto, Márcia Cristina (2006). Avifauna dispersora de sementes de Alchornea glandulosa (Euphorbiaceae) em uma área de mata ciliar no estado de São Paulo [Seed dispersal of Alchornea glandulosa (Euphorbiaceae) by birds in a gallery forest in São Paulo, southeastern Brazil]." Revista Brasileira de Ornitologia 14(3): 291–296 [Portuguese with English abstract].

Wikimedia Commons has media related to Vireo olivaceus.

• Red-eyed Vireo - Vireo olivaceus - USGS Patuxent Bird Identification InfoCenter
• Red-eyed Vireo Species Account - Cornell Lab of Ornithology
• Stamps (for Saint Vincent and the Grenadines, Venezuela) with RangeMap at bird-stamps.org
• "red-eyed vireo media". Internet Bird Collection.
• Red-eyed vireo photo gallery at VIREO (Drexel University)
• "Vireo olivaceus". Avibase.
• Red-eyed Vireo Bird Sound at Florida Museum of Natural History
• Interactive range map of Vireo olivaceus at IUCN Red List