the red-eyed vireo , vireo olivaceus , is a small american songbird , 1314 cm in length .
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 .
adults are mainly olive-green on the upperparts with white underparts; they have a red iris 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 (though this is faint in some populations) .
this bird , not always seen , may sing for long periods of time; it appears to be endlessly repeating the same question and answer .
it holds the record for most songs given in a single day among bird species .
more than 20,000 songs in one day .
the subspecies breeding in south america have a simpler song , a chestnut iris , and different remiges proportions .
they are sometimes split as the chivi vireo , v .
chivi .
some of the races concerned are v .
o .
chivi , v .
o .
vividior , and v .
o .
tobagoensis , the last being a relatively large subspecies endemic to tobago .
even within the chivi vireo , there are distinct variations in measurements , song and ecology , but the possible taxonomic significance of this remains unclear .
in the past , the yellow-green vireo (v .
flavoviridis) and the noronha vireo (v .
gracilirostris) have been considered as subspecies of the red-eyed vireo .
the breeding habitat is open wooded areas across canada and the eastern and northwestern united states .
these birds migrate to south america , where they spend the winter .
the latin american population occur in virtually any wooded habitat in their range .
most of these are residents , but the populations breeding in the far southern part of this species' range (e .
g .
most of its range in argentina , uruguay , paraguay and bolivia) migrate north as far as central america .
this vireo is one of the more frequent american passerine vagrants to western europe , with more than one hundred records , mainly in ireland and great britain .
in northern ohio , it seems to return to breed at about the same time as one century ago; but it may leave for winter quarters one or two weeks earlier at present than it did in the past .
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 .
the nest is a cup in a fork of a tree branch .
the red-eyed vireo suffers 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 trypanosomans might affect these birds not infrequently , 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 .
