Description:

About 10 or 11 subspecies of Red-eyed Vireo are divided into two groups: North American breeders called olivaceus group and South American breeders consisting of resident and migratory populations known as chivi group.

Red-eyed Vireos migrate long-distances between the breeding grounds in the U.S. and Canada and the wintering areas in the Amazon basin of South America.  In North America, the Red-eyed Vireo’s breeding range extends from Southeastern Alaska, Northeastern and West-central British Columbia south to Northern US.  It then extends across central/Southern Canada and Northern US down through central and Eastern US.  Summering individuals (breeding not verified) also have been observed in other portions of the western US from Oregon and Idaho to central Texas and extreme Northeastern Mexico.  In winter they are seen in Northern South America, including Colombia, Venezuela, Guyana, Suriname, Ecuador, Peru, and Western Brazil.

Historically, from 1920s through 1940s, Red-eyed Vireo breeding range expanded into Oregon, Utah, and Newfoundland.  The planting of trees, particularly eastern species, for shelterbelts and landscaping may have facilitated this expansion.  Today, these vireos have become most abundant in the eastern as well as the northern portions of their range.

Identification:

General: At a length of 12 to 13 centimetres and a mass ranging from 12 to 26 grams, the Red-eyed Vireo is a fairly large species of vireo.  It has a relatively long bill and a long, flat crown accentuated by a distinct supercilium.  The sexes are weakly dimorphic.

Adult Male: Adults have a blue-gray crown that contrasts with the plain, grayish olive-green upperparts. The lateral edges of the crown bordering the upper edge of the supercilium form a distinct blackish border.  The dusky eye-line extends from the lores to behind the eye, where it gradually becomes less prominent. Adult Red-eyed Vireos have white underparts with pale yellow flanks and undertail coverts. Their signature iris is usually bright red, but some adults appear a slightly brownish red.

Adult female: Sexes are alike in appearance, but the female is typically smaller and lighter than the male.

Juvenile: Juveniles are most distinguishable from adults through the fall and early winter of their first year by their grayish-brown (not red) iris.  As with the adults, undertail coverts are washed with pale yellow, but the flanks appear washed with olive.

Similar Species: Red-eyed Vireos are similar to Yellow-green Vireos (Vireo flavoviridis) but their ranges mainly overlap during the winter in South America with the exception of both species’ rare visits to coastal California (fall and winter) and the Gulf Coast (spring) and as, in the also rare case as breeders in the Lower Rio Grande Valley of Texas.  Yellow-green Vireos are bright green above, with yellowish edges to the wing and tail feathers.  They have a bright yellow-green rump and upper tail-coverts, as well as extensive and brighter yellow on the underparts. The gray of the crown blends rather smoothly with the rest of upperparts and has less prominant dark lateral edges.  Comparatively, the Yellow-green Vireo’s supercilium is very indistinct especially behind the eye or at the postocular area.

Black-whiskered Vireo (V. altiloquus) can co-occur with Red-eyed Vireo in coastal portions of central Florida as well as during migration and summer along U.S. Gulf Coast as far west as Louisiana.  Their main distinguishing characteristics from Red-eyed Vireos are the blackish malar stripe, duller green/brownish green upperparts, indistinct lateral edges of the crown, and a shorter, more abrupt song.

Philadelphia Vireo (V. philadelphicus) and Warbling Vireo (V. gilvus), also have plumage patterns similar to that of Red-eyed Vireo, but they also lack black edging to the crown above the supercilium.  Their foreheads and crowns appear paler, less bluish, and less strongly patterned than in Red-eyed Vireo. Additionally, Philadelphia Vireo typically has more yellow on its underparts and Warbling Vireo has much grayer upperparts.

Behavior: In North America during the breeding season, Red-eyed Vireos are mainly insectivorous.  They forage from ground level to the treetops, but activity is usually concentrated in the canopy where they search small areas for prey while hopping along branches, then make short flights to new areas.  During the nonbreeding season, Red-eyed Vireo diet consists largely of fruit.

Red-eyed Vireos are more often heard than seen. Their persistent song consists of simple and whistled phrases: cherr-o-wit, cheree, sissy-a-wit, tee-oo and continues, averaging one phrase every two seconds.  Their call is a nasal mewing: myaah, meeyaen; or a longer, more whining descending: ye-annnnnn when agitated.  Red-eyed Vireos may occasionally mimic other species.

Habitat: Rangewide, Red-eyed Vireo breeds in deciduous and mixed deciduous-coniferous forests, but stay away from areas where understory is lacking.  Most often found in riparian areas, they are more abundant in the forest interior rather than at the edge.  However, Red-eyed Vireos can occur in residential areas, city parks, and cemeteries where large trees grow.

Information:

Red-eyed Vireo males arrive to the breeding grounds and establish territories, singing from the edges and throughout.  Pairs form soon after the females arrive and selection of the nest site then begins solely by the female.  The nest is open cup constructed mainly of bark strips, grasses, pine needles, wasp-nest paper, twigs, and plant fibres.  Clutch sizes range from one to five eggs.  The female incubates the eggs and generally spends more time than the male brooding and feeding young.

Conservation Status:

Red-eyed Vireo populations are not threatened in any part of their range and in fact are currently abundant and widespread, showing increasing population trends in many areas.

There are however, a few threats that can affect Red-eyed Vireo populations.  Like all vireo species, they are particularly susceptible to cowbird parasitism both in the chivi (South American) and olivaceus (North American) groups.  These vireos are also sensitive to large clear-cuts and forest fragmentation as well as the isolation of forest fragments.  Lastly, Red-eyed vireos are quite commonly killed during nocturnal migration by colliding with tall structures.