The View from Sapsucker Woods

North American birders with life lists are being treated well by today's American Ornithologists' Union (AOU). For 20 years, many more bird names have been "split" into two or more component species than were "lumped." A generation ago the reverse was true, as birders howled when they lost life-list ground and mourned the passing of venerable names. Steadily those names have come back, however, so today we enjoy Baltimore and Bullock's orioles, Gray-crowned, Black, and Brown rosy-finches, Blue-headed, Cassin's, and Plumbeous vireos, and other familiar oldies. Two more names recently emerged from 60 years of obscurity, and the associated loss of "Blue Grouse" is exciting news even if its two daughter species (Sooty and Dusky grouse) recall far less engaging wavelengths.

Bird watchers (of which I am one) often accuse the AOU Committee on Classification and Nomenclature of making arbitrary calls and flip-flop decisions with our cherished bird names. But I spent 15 years on this committee and vouch that these decisions are made with painstaking care. Their purpose is to ensure that modern bird books, global scientific literature, and public policies accurately reflect up-to-date biological insights about the fundamental units of avian diversity—the species. The 20th century yielded spectacular new insights about what species are, how new ones are formed, and how they interact with one another both ecologically and genetically. Important examples of this bustling field of inquiry (including work in our own Fuller Laboratory of Evolutionary Biology) use birds as models, and the rate of new discoveries accelerated dramatically with the advent of DNA sequencing.

DNA technology often upholds interpretations made by classical taxonomists a century or more ago. Numerous old-school names were buried during the mid-1900s as evolutionary biology coalesced around two ideas about species: (1) across their current geographic ranges, many species contain several populations on their way toward becoming separate, daughter species, and (2) any evidence of interbreeding among these diverging forms proves that the single parent species still prevails. The first of these ideas is clearly true, and amply supported by new genetic data. The second explains why birders lost so many species names between 1940 and 1980, when presence of even a few hybrids between two different forms was treated by taxonomists as evidence that a single name should apply to both. Genetic studies show this second view to be biologically unsound.

Illustration by John W. Fitzpatrick

For more than a century, naturalists in western North America described two forms of "Blue Grouse." Darker birds of the Pacific mountains have a warty, yellow neck patch and 18 rounded tail feathers; males deliver a loud, 6-note hoot from high in trees, and the downy chicks are yellowish. Grayer birds of interior mountains have a smooth, purple neck patch and 20 square-tipped tail feathers; males deliver soft, low-pitched hoots from near the ground, and the downy chicks are grayish. Where these two forms encounter each other, in northern Washington and British Columbia, a few apparently hybridize. Big deal! A recent genetic study confirms that gene transfer is functionally absent between these two widespread forms.* These two grouse treat one another as separate species, and so should we.

The AOU committee knew of this scenario, but its policy is to refrain from formalizing a suspected "split" until a definitive, peer-reviewed study upholds the suspicion. Now that it's official, I doubt that Sooty Grouse and Dusky Grouse ever will be "lumped" again, and I rejoice that another fascinating evolutionary story will be reflected accurately in bird books. A final note to birders: keep your eyes on Yellow-rumped Warbler, and don't lose track of those old notes in which you separated Myrtle from Audubon's.

—John W. Fitzpatrick, Louis Agassiz Fuertes Director

* G. W. Barrowclough, J. G. Groth, L. A. Mertz, R. J. Gutierrez. 2004. Phylogeographic structure, gene flow, and species status in Blue Grouse (Dendragapus obscurus). Molecular Ecology 13:1911?1922.

For permission to reprint all or part of this article, please contact Laura Erickson, editor, Cornell Lab of Ornithology, 159 Sapsucker Woods Rd., Ithaca, NY, 14850. Phone: (607) 254-1114. email: lle24@cornell.edu