NOTES ON THE YELLOW WARBLER

Yellow Warbler on American Pokeweed - Photo courtesy Sharon Milligan
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   For a few glorious moments this morning I watched an adult female Yellow Warbler glean its way through the topmost branches of my back yard oaks. It was the first transient species that I have seen on my home grounds since fall migration got off to its usual slow start in mid July. Transient species merely pass through an area, and they are of great interest to birders who measure the seasons in terms of what birds are seen on any given day.

    The Yellow Warbler is a common spring migrant and a sometimes abundant fall migrant here. Ordinarily, one would be alert for it in wet deciduous thickets, especially swamp willows, where this species occurs in greatest numbers. But migrants do occur in any woodlands, or indeed in places where only a few scrawny bushes, such as those found in salt marsh scrub, prevail. Virtually all the Yellow Warblers seen in flight during this period of fall movement are heard calling. Once learned, the short and slightly vibratory “zreep” that seems unfailingly to accompany fall birds, is an excellent clue to their presence.

    As a breeding species, this is one of the most widespread wood-warblers in North America. I think it fair to say that I've seen it, provided the season was a warm one, everywhere I've ever birded, and that includes Alaska, the Northwest Territories, Maine, Oregon, Montana, Arizona, Colorado, Florida, Mexico and so on and so on.

    Since we here in Mississippi know the Yellow Warbler only as a transient, I've always been a bit fascinated by its breeding distribution. The fact is that there are only a few southern states and the northernmost reaches of the Canadian provinces where it does NOT breed.

    Out of curiosity, I went on a research spree, and found much generally obscure information in "Warblers," by Jon Dunn and Kimball Garrett; that guide is part of the Peterson Field Guide series and well worth owning if your interest in birds spills over from the whats to the hows, whens, and wheres of it all.

    This is amazing! Dunn and Garret wrote that there are 43 subspecies in three main groups of the Yellow Warbler! The species name is Setophaga petechia. Relax now; only members of one of those groups, called the Northern Yellow Warbler, which is highly migratory, occurs in continental North America. But, if you happen to be birding the Florida Keys, you could see a member of the Caribbean group, called the "Golden Warbler," or, if you bird in Mexico south to northern South America, you could see a chestnut-headed bird of the group called "Mangrove Warbler." (These constitute groups of subspecies). It is possible to identify members of these three groups, helped along by a field guide and where you happen to be when you see your bird.

    I recall that I saw my first "mangrove" subspecies of the Yellow Warbler, in Sonora, Mexico, just a skip from the Sea of Cortez. It was an adult male and absolutely breathtaking; it appeared so decidedly different from any bird I had ever seen, I felt sure that it was a full species.

    As a matter of fact, these three groups of subspecies were indeed once treated as separate species; in 1942 they were lumped as one, and all fall under the species name Yellow Warbler, or Dendroica petetchia. Given increased knowledge and DNA research, who knows if they may again be given the status of separate species.

    The lumping and splitting of species is a fascinating part of bird study; we often don't think of it until it affects us. I lost one when it was declared that the Myrtle and western Audubon's races of the Yellow-rumped Warbler accounted for just one species; I gained one when the American Ornithologists' Union recently declared that the Black-crested Titmouse (of south Texas) deserved its own genus. And so it goes.

    Our trees, bushes and shrubs are about to be well populated with Yellow Warblers of the northern group of subspecies; aside from adult males and females, which differ from each other enough to allow for separation of mature birds, we will be seeing many more immatures of both sexes, and it is well to remember that. There are several ways to identify a Yellow Warbler; adults are more an "all yellow" species than other warblers; most have yellow wing bars, bright yellow faces, black beady eyes. Adults males have reddish-brown streaks. In just about all but the palest young females, keep in mind that the Yellow Warbler is the only wood-warbler that has this unique field mark: yellow tail spots!

This article was published in August 2003