About Vireo olivaceus chivi (Vieillot, 1817)
This taxon is the subspecies Vireo olivaceus chivi, first described by Vieillot in 1817. For adult red-eyed vireos, the upper body is primarily olive-green, with white underparts, a red iris, and a grey crown bordered by black. A dark blackish stripe runs through the eye, with a wide white stripe directly above this dark line. Adults have thick blue-grey legs and a thick, strong bill. Yellowish coloring appears on the flanks and undertail coverts, and this yellowish tone is faint in some populations. Historically, the yellow-green vireo (V. flavoviridis), chivi vireo (V. chivi), and Noronha vireo (V. gracilirostris) were classified as the same species as the red-eyed vireo. The chivi vireo was the most recent of these to be split into a separate species. Other close relatives of the red-eyed vireo include the black-whiskered vireo (V. altiloquus) and the Yucatan vireo (V. magister). For both sexes of red-eyed vireo, measurements fall in the following ranges: length 12–13 cm (4.7–5.1 in), weight 12–26 g (0.4–0.9 oz), and wingspan 23–25 cm (9.1–9.8 in). The breeding habitat of red-eyed vireos is open wooded areas across Canada, and the eastern and northwestern United States. Most northern breeding populations migrate to South America to spend the winter. Latin American resident populations occupy nearly any wooded habitat within their range. Only populations that breed in the far southern part of the species' range, including most of the range within Argentina, Uruguay, Paraguay, and Bolivia, migrate north as far as Central America. In northern Ohio, red-eyed vireos currently return to breeding grounds around the same time they did one century ago, but they now depart for wintering grounds one to two weeks earlier than they did in the past. Red-eyed vireos glean insects from tree foliage, preferring caterpillars and aphids, and sometimes hover while foraging. In some tropical regions, they regularly join mixed-species feeding flocks, and travel through the upper levels of the forest higher than most members of these flocks. They also eat berries, especially before migration and when they are in their winter quarters. Fruit-bearing trees such as tamanqueiro (Alchornea glandulosa) or gumbo-limbo (Bursera simaruba) will draw red-eyed vireos into parks and gardens in wintering areas. They do not typically pick fruit while hovering, instead they often reach for fruit acrobatically, sometimes even hanging upside down. The red-eyed vireo builds a cup-shaped nest in the fork of a tree branch. Red-eyed vireos experience nest parasitism from the brown-headed cowbird (Molothrus ater) in the northern part of their range, and from the shiny cowbird (M. bonariensis) further south. Studies of birds captured in Parque Nacional de La Macarena and near Turbo, Colombia, noted that infection by Haemoproteus and trypanosoma is not uncommon in these birds; even though only three red-eyed vireos were examined in this study, all three were infected with at least one of these parasites.
