It’s become a summertime ritual.

Starting with the Forty-third Supplement in 2003, the American Ornithologists’ Union Committee on Classification and Nomenclature has published an annual update to its authoritative (and oddly spelled) Check-list of North American Birds. Since no new edition of the Check-list has appeared since 1998—the average span between editions has run to 16 years—keen birders and ornithologists wait eagerly each July for the new issue of the Auk, where the wise men and women of the committee pronounce on matters of, well, classification and nomenclature. Most notoriously, the committee’s report notifies us of “splits” and “lumps,” recognizing species as distinct or not; but the careful reader will find much more, from rearrangements at levels beyond the species to name changes reflecting relationships with taxa outside the area covered by the Check-list.

In recent years, our wait has been eased by the publication on line (aou.org) of the committee’s votes some weeks in advance of the appearance of the formal Supplement. Nothing is “official,” of course, until the printed pages of the Auk hit the mailbox, and the preliminary online votes at times leave some questions unanswered, but this preview both allays birderly impatience and gives us insights into the deliberations behind those magisterial paragraphs to come.

This year’s Supplement is likely to be of particular interest to birders here in the Southwest, both for what it does and for what it does not do.

The AOU committee is not in the first instance a records committee, but among its tasks is the determination of a species’ rightful place on the various North American lists. This year’s Supplement will add no fewer than seven new birds to the tally of those legitimately recorded in the United States. Three of them join the country’s avifauna thanks to strays detected here in the Southwest. New Mexico’s astonishing Sungrebe from November 2008 was unanimously admitted to the list, as were the somewhat less startling records of Gray-collared Becard and Brown-backed Solitaire from Arizona in June and July, 2009, respectively. Texas contributes an additional two species, Bare-throated Tiger-Heron and Amazon Kingfisher, both of which (especially, I think, the former) are not entirely unexpected strays to Arizona—eyes open, minds alert!

Another potential vagrant to our area has been assigned to a new family. Masked Tityra, which breeds as close to the Arizona border as southern Sonora, had inhabited that taxonomic no-bird’s-land assigned to “genera incertae sedis,” but now, along with a number of tropical relatives including Gray-collared and Rose-throated Becard, it is given its own family, Tityridae, in keeping with an action taken by the AOU’s South American Checklist Committee as early as 2007. The name perpetuates one of birding’s great mysteries, namely, the origin of the word “tityra,” which was, unfortunately, given no etymology when Vieillot created the genus almost 200 years ago.

The most closely scrutinized of the committee’s decisions are always the “splits,” where a single erstwhile species is recognized as in fact comprising two or more distinct species. This time around, the splits will produce no additions to the Arizona list, but birders who have ventured farther afield will be interested to know that the Snowy Plover we know from the American Southwest is now distinguished from the Kentish Plovers of the Old World, and that “our” Mexican Jays are now treated as distinct from the Transvolcanic Jay of Mexico. The red-nosed rallid known variously over the years in North America as the Florida Gallinule or the Common Gallinule or the Common Moorhen is once again split from “the” Moorhen of Europe; the revived species is likely to bear the English name American Gallinule, a decidedly lackluster alternative to such eloquent options as Laughing Moorhen or Helmeted Gallinule.

English names have not been the committee’s strong suit lately. Blandness can be forgiven, but the practice of assigning the same name to a “new,” more narrowly defined species as that borne by the old taxon more broadly construed is logically sloppy and confusing. This time around, the committee rejected a proposal to rectify the English names of the small, stub-tailed North American Troglodytes wrens; how much better it would be to have called the eastern and northern representative “Eastern Wren” (in clear contradistinction to “Pacific Wren”) than to burden it with the old name “Winter Wren”—an ambiguous term that now requires us, annoyingly, to add “sensu stricto” if we want to make clear that we are talking about just the newly redefined species. “Canada Goose” is another such name, and now the committee has done it again with “Mexican Jay”; not only is the name ambiguous (does it in any given instance refer to the “new” species or to the “old” Mexican Jay?), but it is also profoundly misleading in that the Mexican Jay sensu stricto has a broad range extending, as Arizona and Texas birders well know, north of the border, while the Transvolcanic Jay is in fact a Mexican endemic. We all know that names are the abritrariest of arbitrary signifiers, and the committee has repeatedly insisted that English names are not the appropriate vehicle for indicating taxonomic relationships or geographic peculiarities, but one could almost be excused the impression that the committee has gone out of its way of late to avoid clarity.

Many birders may be surprised by the committee’s rejection or deferral of some proposed splits. The evidence for the existence of two species of Mountain Chickadee—with “Gambel’s Chickadee” the resident species in Arizona—is deemed unconvincing. The members’ comments are somewhat more encouraging on the restoration of Myrtle and Audubon’s Warblers to full species status (and, to some extent, the elevation of the west Mexican and the Guatemalan breeding populations). Though the proposed split has not passed, several of the committee members voting “no” appear to indicate a willingess to approve the change once more information has been published. Like juncos or fox sparrows, these are birds whose reproductive behavior and evolutionary history will continue to bedevil any attempt at classification, whatever the species concept behind it.

The committee also rejects the proposed re-split of Mexican Duck and Mallard. There are multiple lines of evidence suggesting that the taxon diazi, Mexican Duck, is more closely allied to Mottled and American Black Ducks than it is to Mallard, which would seem to require either a lumping of all four taxa or a realignment that removes Mexican Duck from Mallard. Half of the committee, though, finds the genetic evidence unconvincing and the frequency of hybridization and introgression between this taxon and Mallard too great to allow the split. Here we have yet another case where taxonomic determinations have political consequences: once restored to species status, Mexican Duck would have been a good candidate for protection as a threatened or endangered species.

The most far-reaching of the changes approved in this year’s Supplement are certainly those to the classification of the wood warblers. A thorough new analysis including nearly every species and subspecies in the family Parulidae has produced some entirely new groupings and some surprising name changes to go with them. Geothlypis, the venerable yellowthroat genus, now also includes Kentucky, Mourning, and MacGillivray’s Warblers (but not Connecticut, which remains in a monotypic Oporornis). Canada and Wilson’s Warblers move over to join Red-faced Warbler in Cardellina. Hooded Warbler, American and Tropical Parulas, and all of the warblers formerly known as Dendroica belong with American Redstart—and thanks to priority, are henceforth to be known under that species’ genus name, Setophaga. All this is going to take some getting used to for those of us who grew up with the old warbler genera, but the majority of the committee finds the evidence presented in support of the proposal complete and compelling, “and too bad about Dendroica.” Yellow-breasted Chat will probably be left in the family for the time being, but the analysis tends to support the suspicion that this odd bird belongs elsewhere, a change to watch for in future Supplements. But beware: once you start reading them, your summers will never be the same.