It’s 2010, and the world now has three kinds of winter wren, two species of whip-poor-will, and three black scoters. Boobies are no longer relatives of pelicans, but herons have taken their place. And although common names have been left unmolested, there has been some major hokey-pokey in several dozen scientiﬁc names, including sparrows, longspurs, towhees, warblers, and waterthrushes (which have left the Ovenbird and are now in their own new genus, Parkesia).
They join the ranks of familiar birds (the Solitary Vireo, juncos, New World vultures, etc.) whose relationships, not to mention their locations in ﬁeld guides, birders have had to reimagine over the years. All because of the decisions of the American Ornithologists’ Union’s North American Classiﬁcation Committee (NACC).
Of course, it’s not hokey-pokey at all. It’s a never-ending quest to piece together evolutionary relationships, presided over by 12 ornithologists and evolutionary biologists, all of whom donate their spare time to the cause. It is their task to decide on these changes, thereby giving bird watchers a luxury few other naturalists have: a single, codiﬁed set of names and relationships. This year, to keep birders in the loop on why names changed, the NACC began posting their deliberations as well as the changes themselves; explore at www.bit.ly/aouchanges.
It’s as if the committee is a group of librarians charged with organizing some 10,000 books. They have to make sure the books in each shelf, stack, and room have more in common with each other than with books in any other part of the library. And there’s a catch—they don’t know exactly what’s inside most of the books. To look inside, they have to study things like the birds’ skeletal structure, vocalizations, behavior, and DNA.
“One advantage with DNA-type data is simply that there’s a lot of it,” says Irby Lovette, director of the Fuller Evolutionary Biology Program at the Cornell Lab and a member of the NACC. He points to a 2008 paper published in Science as one that used DNA to redraw the entire lineage of birds at the level of orders.
The team compared 19 places along the genomes of 171 species of birds. This approach yields conﬁdence; it’s as if, to compare two book copies, someone ﬂipped to 19 different pages to check how similar the words were. Their results included some surprises: swifts regained a diurnal lifestyle after splitting from nightjars; tropical tinamous re-evolved ﬂight after their ostrich-like ancestors had lost it.
The Science study was also a main source for the NACC’s changes at the order level, including making new orders for the boobies (Suliformes), tropicbirds (Phaethontiformes), and hawks (Acciptriformes; falcons may be more closely related to parrots); and merging the herons with the pelicans, in the Pelecaniformes.
Though DNA evidence is voluminous, it isn’t enough on its own. The committee insists on having at least two separate lines of evidence, particularly when deciding whether to split a species. “DNA is good at telling you what happened in the past,” Lovette said. “It’s not so good at telling you what’s happening now.”
A prime example is the Western Scrub-Jay, one of this year’s proposed changes that didn’t make the cut. The Western Scrub-Jay is probably at least two species—an inland and a coastal form, with different bill shapes and voices, and DNA differences that show the populations are isolated. But it’s not clear that the two forms remain separate in a narrow zone in Nevada. The committee decided to wait for evidence from ﬁeld studies in the overlap zone.
Still, don’t hold your breath for another “armchair tick” on your life list. Should behavioral data support splitting the Western Scrub-Jay, it’ll need to be published, and then a proposal will have to be made to the NACC.
Science moves slowly, but that’s as it should be. “When we’re uncertain whether to lump or split a species, that’s a natural outcome of the fact speciation is a natural process that happens over time,” Lovette said. “Rather than seeing that uncertainty as a problem, I think it’s a very honest and natural reﬂection of the way biology works.”
How long might that take? “Somewhere under a million years,” he said.
Chesser, R. T., et al. 2010. Fifty-ﬁrst supplement to the American Ornithologists’ Union Check-list of North American Birds. Auk 127:726–744.
Hackett, S. J., et al. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320:1763–1768.