What's in a Name?

Science drives the often-bewildering changes to species check-lists

By Elizabeth Quill and Miyoko Chu

Last year, the solar system lost a planet—Pluto. Of course, Pluto is still there, traveling its far orbit around the sun as it has for eons. But after debating the meaning of "planet," scientists decided that Pluto didn't fit the bill. Now it's a "dwarf planet."

As astronomers scrutinize the status of planets, so too do ornithologists ponder and debate the status of birds. Every year the American Ornithologists' Union (AOU) Committee on Classification and Nomenclature meets to update North America's official bird list. As scientific knowledge continually changes, so do the names of the birds. Last year's check-list gained 9 species and lost 5, for a total of 2,041 species.

The check-list's scientific frontier is not in the actual discovery of new species (the last such addition was Gunnison Sage-Grouse in 2000) but in new evidence about already known birds. For example, the Black-bellied Storm-Petrel breeds on islands in the Southern Hemisphere but migrates north across the oceans in winter; it joined the list of North American birds for the first time last year after a new sighting off the coast of North Carolina.

Black-crested Titmouse (above) was lumped with Tufted Titmouse in 1983, but regained full species status in 2002.

James Giroux

Recent scientific information may also shift ornithologists' views of a bird, affirming its uniqueness—in which case it may be listed as a new species—or finding that it is too similar to another group to be called its own species. New methods for studying bird behavior and genetics are helping to redefine the relationships of birds, said Irby Lovette, director of the Cornell Lab of Ornithology's Fuller Evolutionary Biology Program and a new member of the AOU check-list committee. "We are getting a lot better at describing diversity," he said.

In 2006, the committee recognized five new species based on differences in behavior, vocalizations, morphology, and/or genetics that showed they were distinct from other birds with which they had formerly shared a species name (see sidebar).

Genetic evidence often overturns long-held assumptions about birds that were based on their appearance. "Things that look incredibly different aren't always genetically different," said Kevin McGowan, a research associate at the Lab. "Others that look almost exactly the same have a deep genetic divide." For example, Cordilleran and Pacific-Slope flycatchers look virtually identical and were once considered the same species but genetic data revealed they were more different than they had seemed.

What is a species, anyway?

Even with DNA analyses and other new techniques, however, defining a species can be daunting. To begin with, different ornithologists have different ideas about what a species is. Some use a "phylogenetic species concept," in which they classify species based on their positions in a phylogeny, essentially a family tree for birds. Others prefer the "biological species concept," which designates birds as belonging to the same species if they consistently interbreed.

Usually, the committee uses the biological species concept, Lovette said, but this sometimes raises questions. How should scientists deal with birds that don't interbreed since they live in different places? What about species that interbreed in just part of their range? What if scientists just can't tell?

For example, scientists recently compared DNA sequences of two subspecies of Ivory-billed Woodpecker—from Cuba and North America. The genetic evidence showed that the ivory-bills from these locations were as different from one another as either one is from the Imperial Woodpecker of Mexico. Under a phylogenetic species concept, Cuban and North American Ivory-billed Woodpeckers would be considered two species, according to Smithsonian scientist Robert Fleischer, who led the study.

One look through the lens of the biological species concept, however, quickly muddles the picture. Are ivory-bills in North America and Cuba difivory-bills in North America and Cuba different enough that they wouldn't breed with one another? No one knows, since the birds' ranges don't overlap. It's also unlikely that this criteron can be tested any time soon, since Ivory-billed Woodpeckers are extremely rare in North America and haven't been seen in Cuba since the 1980s.

Science behind the changes

Changes to bird check-lists don't alter what actually exists in nature. However, they can ruffle a few feathers when birders have to rework their life lists, and they can even have conservation implications. In 1989, the nomenclature committee recognized the species California Gnatcatcher, which had formerly been considered the same species as widespread Black-tailed Gnatcatcher. In 1993, the northernmost subspecies of California Gnatcatcher was listed as federally threatened, a status that raised the level of conservation attention.

The AOU renamed the Baltimore Oriole (left) and Bullock's Oriole (right) as one species, Northern Oriole, in 1973. The decision was reversed in 1995 because of limited hybridization and new genetic evidence showing that the Bullock's Oriole is more closely related to the Black-backed Oriole of Mexico than to the Baltimore Oriole.
Baltimore Oriole by Mike Hopiak	Bullock?s Oriole by B. B. Hall

J. V. Remsen, Jr., an AOU check-list committee member from Louisiana State University, said that the committee bases its decisions on data, not factors such as conservation. Last year, the committee considered a recent study pointing out differences in calls and bill size between populations of Brown-headed Nuthatches on the North American continent and those on the Bahamas. The nuthatches on the Bahamas are under serious threat, with a population of only 1,800. Still, the committee determined that more evidence was needed to grant full species status to nuthatches on the island.

Remsen said that when the committee decides it's premature to name a new species, it encourages researchers to get more evidence. That means if they come up with a convincing case, it's still possible that a new nuthatch will appear on the AOU check-list some day.

Even then, its place won't necessarily be assured. Consider what happened to juncos. Over the course of 60 years, ornithologists split Dark-eyed Juncos into as many as 7 species, then eventually lumped them all under one name. As birders keep up with the sometimes-bewildering changes to species check-lists, only one constant is a sure bet: whether in the complex and varied world of birds or among the seemingly ageless planets of the solar system—you can't take a name for granted.

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