Common (left) and Hoary (right) Redpolls may look like two different species, but their genes say otherwise. Photo: Seabrooke Leckie/Flickr Creative Commons

Common Redpoll or Hoary Redpoll: It’s a familiar riddle for even the most experienced birders. “Every time there is a big redpoll flight,” Audubon field editor and bird expert Kenn Kaufman says, “there are endless arguments about the identity of certain individual birds.”

Those arguments, however, may soon be moot. A study published in Molecular Ecology by a team from the Cornell Lab of Ornithology examined DNA from 77 redpolls and found essentially no genetic differences between the Common, Hoary, and Lesser Redpoll.

Scientists have been debating the number of redpoll species since before the Civil War. Some have documented as many as eight varieties, while others have argued that there is only one. Currently, most ornithological groups recognize three: the Common and the Hoary, which reside in North America, and the Lesser, which lives in Europe.

Since the ‘80s, several studies have documented the genetic similarities between Common and Hoary Redpolls. Yet no one has studied more than 11 regions of the redpoll genome, making ornithologists wonder whether they were missing the true differentiating genetic markers, says Kaufman. The Cornell study contradicts that idea: With the help of cutting-edge DNA technology, the researchers examined 235,000 regions of the genome (still less than 1 percent of the entire sequence) and still found very few differences.

The study goes on to suggest that physical disparities among individual redpolls are due to varying degrees of gene expression. This phenomenon can be seen in humans as well. “Two people may have the exact same gene, but if one gene is expressed at a far lower level than that of another individual, then that can have a pretty profound effect on appearance,” says lead author Nicholas A. Mason, a Ph.D. candidate at the Cornell Lab of Ornithology. “Hair color is a good example of that.”

Mason and his co-author, Scott A. Taylor, said they will soon propose combining the Hoary and Common Redpoll to the American Ornithologists’ Union’s checklist committee. They might also reach out to the British Ornithologists’ Union to get approval to include the Lesser Redpoll in the same species.

The Hoary Redpoll is a particularly difficult bird to see for those who don’t live in northern Canada and Alaska; some hardcore birders have gone well out of their way to add it to their life lists. Nonetheless, Kaufman can’t imagine there being too much conflict over consolidating the redpolls. “In recent years there have been more ‘splits’ than ‘lumps,’” he says, citing the splitting of the Winter Wren into three species as a modern example. “So if continuing taxonomic work occasionally takes one away, it’s not that big a deal.”

But it’s far from a done deal. Canadian finch expert Ron Pittaway notes that the AOU recently rejected a similar proposal, also based on genetic evidence, to lump the three North American species of rosy-finches.

For now, here are some ways to identify between the Common and Hoary pseudo-species:

Common Redpolls

live slightly further south; might venture to the mid-Atlantic and lower Midwest regions in some winters

are heavily streaked

have a longer bill

Hoary Redpolls

breed in the high Arctic; are sometimes found at the extreme northern edge of the Lower 48 in winter

have frosty, whitish plumage with fewer streaks

have a stubby bill

Here’s the twist: Redpolls with intermediate plumage are common in certain areas, like north-central Alaska, and are often impossible to ID. But fear not—Pittaway has a great guide here.