| This Warbling Vireo is a sparrow sized bird, olive-gray above and whitish below. The western birds tend to be a little greener than their eastern relatives and immature birds may have a yellow tinge to their underparts. The absence of wing bars help to separate it from similar species. It is similar in general appearance to the Red-eyed Vireo, but lacks the bold facial patterns and the red eyes. The narrow white eyebrow is faint and less prominent than that of the Red-eye. They are a furtive, secretive bird without conspicuous field marks. They can be difficult to locate, and if they are to be seen at all, you must learn the song well. The languid voice is similar to the melodious warble of the Purple Finch but slower and ending in rising accented notes. The male will sing throughout the day, even while sitting on the nest.
The habitat consists of the streamside deciduous woodlands and isolated groves and shade trees throughout most of the United States and western Canada usually arriving north in April. They are especially fond of elm trees for nesting and their numbers have declined recently, especially in urban areas because of the extensive spraying of these trees. During the winter the Warbling Vireo heads for the tropics of Central America and South America leaving their breeding grounds in October.
During courtship the male struts around the female with wings and tail spread while singing. The female quivers her wings in response to the courtship song. These courtship displays usually occur within 30 feet of the nest.
The clutch consists of 3 or 4 white eggs spotted with brown and placed in a well made hanging basket constructed of bark strips, leaves, grass, spider silk, and plant fibers and fastened to a fork high in a tree away from the trunk. The nest is selected by the female and does most of the building though the male does help build the nest as well as defend it from intruders. The eggs are incubated by both parents for 12 days, and are able to fly about 16 days later. The nest is often parasitized by the Brown-headed Cowbird and the vireo has little defense against the intruder which completely crowd the nest as they mature quickly. Despite this parasitism the numbers of Warbling Vireos has increased especially in the west.
The diet consists almost entirely of insects, especially caterpillars which it gleans from the foliage and bark while hovering near the treetops. Spiders and berries make up a lesser part of their diet.
Length: 5 to 6 inches.
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