I had a great month for vireos in September, seeing four species in my yard. Other birders saw yet another vireo species at the Fields Pond Audubon Center – a vireo never seen there before and the 133rd bird species found there.

Vireos are interesting little songbirds; their nearest relatives are the shrikes. Shrikes also are called butcher-birds because of their habit of impaling prey, such as mice and small songbirds, on thorns.

Vireos are considerably smaller than shrikes, but they have a hooked bill just as shrikes do. Vireos don’t impale their prey – small green caterpillars. They either eat them, or stuff the caterpillars down the throats of their young in the nest.

Vireos make a beautiful nest, the size of a tennis ball, and suspend it from a crotch at the end of a branch. Often the nest is made partly of narrow shreds of birch bark, held together by invisible threads of spider silk.

Fields Pond Audubon Center has federal permits to display bird nests. Visitors may stop by and ask a naturalist to show them a vireo nest.

The most abundant vireo in most of Maine is the red-eyed vireo. By now, these neo-tropical migrants are halfway to South America, as are the warbling vireos.

Blue-headed vireos, formerly called solitary vireos, are still coming through. They are short-distant migrants, spending the winter in the southern states.

The fourth species I saw in my yard in September was the Philadelphia vireo. I haven’t seen it there very often. That vireo nests in the northern half of Maine, and its song is very similar to that of the red-eyed vireo.

I should have mentioned that most people have never seen a vireo, despite the fact that they are quite common. They are hard to see, because they live in the tops of trees and live here only in the summer, when the leaves are green, and so are the vireos.

Advanced birders know the songs of the vireo species. It is possible to count vireos by hearing their songs all around, as when on a Breeding Bird Survey for the U.S. Geological Survey.

The fifth vireo species, the yellow-throated vireo, was seen by a couple from Connecticut. They were birding at the Fields Pond Audubon Center.

Later, I was delighted to hear of their sighting. I called them up and asked them about it. Their answers showed that they knew this species well, and they knew it was uncommon in this area.

The range of vireo species only comes slightly into the state of Maine. Only a few of the species nest east of Augusta. This individual yellow-throated vireo may have been dispersing, seeking to expand the species’ range.

For information on Fields Pond Audubon Center, call 989-2591.