The almost invisible vireos

There are at least four, and probably five, vireos which you can see in Northwestern Ontario. All of these birds are similar in appearance.
But unless you are very persistent, and have a good set of field glasses, you will find it hard to tell them apart.
The word “vireo” comes from Latin and refers to the colour green. The basic colour of all of these birds is green, olive-green, with bits of yellow or white added in various places.
Some people say the Red-eyed Vireo is the most numerous bird in North America—numbering in the hundreds of millions.
Vireos are birds of the tree-tops, which is why they are not very noticeable. A green bird, among green leaves, high up in the trees, is not likely to come to your attention easily.
All vireos eat insects as their main diet. They are very methodical, moving through the trees in deliberate fashion, picking up grubs, eggs, caterpillars, and any kind of insect which walks, hops, or flies.
Almost all vireos build the same kind of nest, too. It is a basket very carefully hung in the fork of a branch.
It is not solid, like a robin’s nest, nor is it a hanging bag like the oriole’s, but is a very sturdy cup—soundly attached to the twigs.
The Red-eyed Vireo (Vireo olivaceous) is the most common of the lot. As its name says, it has bright red eyes. It also has a grey cap with a dark line through the eye.
It is olive-green above and white below, and probably is the easiest one to identify.
If you can’t see it, you can surely hear it. The most boring song in the woods, it is something like a robin’s, but with a pause after each phrase. It is repeated endlessly all day—even through the hottest weather.
The Philadelphia Vireo (Vireo philadelphus) looks much like the first, but without any outstanding marks on its head. And its breast is yellow instead of white.
Its song is much like that of the Red-eye, but with longer pauses and higher pitched. It is equally monotonous.
The Warbling Vireo (Vireo gilvus) is similar to the first two. The breast is white, and again it has no distinguishing head marks. Its song is not like the others, but is a continuous warble—usually going up in pitch and with not too much energy.
The Solitary Vireo (Vireo solitarius) is a fairly easy one to spot. It has a very prominent white ring around its eye, as well as two quite distinct white wing bars.
Also its sides are yellow. Its voice is something like the Red-eye, but with long pauses.
The Yellow-throated Vireo is likely to be found only in Rainy River District of Northern Ontario, though it is quite common further south. It also has white wing bars, but its throat is bright yellow—its trademark.
It also has that song with deliberate, spaced phrases. This is Vireo flavifrons.
So there are our vireos. Extremely common, extremely useful, and very hard to tell apart. In the fall, they all look alike—like plain green warblers.
So unless you are very keen and very patient, wait until spring comes and then try to tell which is which.

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