From Many, One: How Many Species of Redpolls Are There?

By Gustave Axelson
March 30, 2015
One species or two? Common Redpoll (left) by Sharon Watson via Birdshare, Hoary Redpoll (right) by Chris Wood.
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The Hoary Redpoll is one of those hard-to-get lifelist-adds that can turn birders into Captain Ahab seeking a little whitish bird. The allure of these little ghost finches has drawn many a lister to places like Minnesota’s Sax-Zim bog—in the dead of winter—just for a chance to lock into a Hoary.

But new research by two scientists at the Cornell Lab of Ornithology presents genetic evidence that reopens questions about the species status of the Hoary Redpoll, long thought to be the frosty cousin of the Common Redpoll. In a paper published this week in the journal Molecular Ecology, Nicholas Mason and Scott Taylor of the Cornell Lab’s Fuller Evolutionary Biology Program show that Hoary Redpolls and Common Redpolls have no differences at all across much of their genomes.

“Based on the samples of DNA we examined for Common and Hoary Redpoll, they’re probably best treated as a single species,” Mason says.

In other words, should this new evidence similarly sway the American Ornithologists’ Union’s checklist committee, all the heroic efforts birders have made to add a Hoary to their life lists may be for naught.

The division of redpolls into different species dates back to before the Civil War. In 1861, legendary ornithologist Elliot Coues (one of the founding fathers of the AOU) described eight separate redpoll species based on their visual appearances. Over time the AOU consolidated Coues’ list, but Hoary Redpoll, which has a snow-white breast, was still considered a separate species from Common Redpoll, which has a brown-streaked breast.

The researchers compared the DNA of 77 redpolls. The evolutionary tree they reconstructed shows that the three redpolls intermixed extensively in their evolutionary past. If they were separate species the branches of the tree would be much more distinct, as shown for their close relative, the White-winged Crossbill. Adapted with permission from Mason and Taylor 2015, Molecular Ecology; White-winged Crossbill by Nick Saunders via Birdshare.

Mason and Taylor looked beyond the plumage into strands of the birds’ DNA in the most extensive look ever at the redpoll genome. Whereas previous genetic analyses of redpolls looked at just 11 regions of the genome (at most), Mason and Taylor examined 235,000 regions. (That impressive number is a testament to the exponential advances in DNA-sequencing technology, but the researchers are quick to note it’s still less than 1% of the total genome.)

In all, the duo compared DNA from 77 redpolls, including specimens from museums around the world, from the Museum of Vertebrates at Cornell University to the Natural History Museum of Geneva in Switzerland. They found no DNA variation that distinguishes Hoary Redpolls from Common Redpolls. Furthermore, another redpoll species found in Europe—the Lesser Redpoll—also had extremely similar DNA sequences. This extreme similarity among all the redpolls stands in marked contrast to studies of other groups of birds—such as Black-capped and Carolina Chickadees—which show differences at many regions of the genome.

In nature, one of the key differentiators among distinct species is assortative mating, that is, members of a group breeding with each other more often than they breed with members of another group. According to Mason, when it comes to Hoary, Common, and Lesser Redpolls, “There are no clear-cut genetic differences, which is what we would expect to see if assortative mating had been occurring for a long time.”

The three current species of redpoll—Common, Hoary, and Lesser—stretch around the Arctic in a continuous swath that isn’t necessarily apparent from a normal map projection. Adapted with permission from Mason and Taylor 2015, Molecular Ecology.

Instead, Mason says the world’s three redpoll species seem to be “functioning as members of a single gene pool that wraps around the top of the globe.”

But how could it be that Hoary and Common Redpolls look so different given that their genetic makeup is basically the same? For that answer, Mason and Taylor delved into the birds’ RNA. (A quick flashback to high-school biology: If DNA is like the body’s blueprints, RNA is like the construction foreman communicating the instructions to build physical features, like hair or feathers.)

The physical differences among redpolls are associated with patterns in their RNA, not their DNA. In other words, the variation we see in plumage and size is probably not a matter of genetic variation, but of genetic expression. It’s kind of like how two humans might have the same gene for brown hair, but one person’s might be lighter than the other’s—that gene is being expressed differently. In the same way, Hoary and Common Redpolls have remarkably similar sets of genes, but those genes are expressed differently, causing the plumage and bill-shape differences we see.

To look simultaneously at both DNA and RNA, Mason and Taylor sampled birds—some with highly streaked plumage, some with white plumage, and some with in-between markings— from a large flock that had gathered in a fellow Cornell Lab employee’s backyard in Cortland, New York. If Hoary and Common Redpolls had long been separate species, then the birds sampled should have mostly fit neatly into two categories, both by visual appearance and genetically. Instead, there were a few birds that definitely fit the visual description of what we call a Common Redpoll, a few birds that definitely fit the pattern for a Hoary Redpoll, and a lot of birds in the middle—with varying degrees of whitish breast and faint brown streaks.

The bird on the left is a classic dark, streaky Common Redpoll, while the bird on the far right is a snowy, small-billed Hoary Redpoll. But many birds lie in between these two extremes. The new research suggests all the Common–Hoary confusion over the years may have been justified. Photos, from left to right, by Sharon Watson, newfoundlander61, Guy Lichter, Stuart Oikawa, and Chris Wood.

“We didn’t find distinct characteristics to separate the redpoll types, but rather a continuum, or a progression, of physical traits,” Mason says. “And many redpolls were somewhere in the middle.”

Next, Mason and Taylor are planning to work their research into an official proposal for the AOU to lump Hoary, Common, and Lesser Redpolls into a single species, based on the genetic evidence. If accepted by the AOU’s Nomenclature Committee, the end result may sting for birders who see a Hoary Redpoll subtracted from their life list. But Taylor hopes his research will change the way people look at redpolls altogether.

“I think this makes them a more interesting bird,” he says. “It means they’re part of an exciting, complicated system that can make a single species look different across different parts of its range.”

For more on redpolls and phylogeny:

Comments

  • Josephine Lloyd

    We live on the south east shore of Lake Winnipeg, near Beaconea. We have had a flock (maybe 10-12) of redpolls at our feeder all winter. Some are paler than others, but we figured it was males and females. Lovley little guys!

  • Josephine Lloyd

    sorry…spelled “Beaconia” wrong!

  • frederic gutknecht

    more info should come…

  • Tim Flook

    I am north of Beaconia at Albert Beach – Here I also have a small flock of this beautiful Bird. They do not come every day but perhaps once per week. This tells me they likely have a route they take for feeding stations. They are able to share space with Chickadees but not with some other birds. I place sunflower seeds along the Veranda hand rail. Two or three are of the Classic dark streaky common Redpoll but most are of the photo of the central location. Many have just the Red Cap which made me think of a Chipping Sparrow, but hard to tell if they are the same type or not.
    Just an enjoyment to watch.

  • Gene McGarry

    I just shared a series of photos of Common Redpolls that includes one that might arguably be a Hoary. It is no surprise and perhaps welcomed to read that these two specie may, in fact, be one species. Love the challenge of birding!

  • Laurence Thomson

    I am a somewhat new “birder”, but it seems to me that even if the Hoary Redpoll is a “morph” of the Common Redpoll, it is still a great thing to find this more rare version of the bird.

  • Laurie

    It seems as though the birds are making the same adjustments to their environment that all living things do. Color is especially important for survival.

  • The redpolls are a great story of evolution in itsef. Imagine if beings from outer space attempeted to classify the various forms of humans – maybe as different species, but later found out that they could interbreed and produce fertile young even though they look so different. They are just varieties or perhaps subspecies of Homo sapiens.
    So the best answer that a politician can give to the stupid question: “Do you believe in evolution?” It is this – evolution is just something we study and to look at the redpolls as an example or a more familiar species, the human population.

  • Bernadine Brown

    We live in Rossburn, MB & we seldom see Redpolls at our feeders. Last winter was the first time in 10 years that we had the pleasure of their delightful company. I enjoyed this article very much & hopefully we’ll get to see the Redpolls again. We aren’t fussy about the choices…anyone will do.

  • Pat Downey

    Then I guess this would be the same deal as w/ snow geese. From white to “blue” and everything in between.

  • Judy Joerger

    We live in New Hampshire and on the Connecticut River. This year we have had and still do, tons of Redpolls, along with tons of Pine Siskins. They always seem to be together on my thistle feeder and on the ground. Haven’t seen either of those two species for about 4 years. So happy to have them here. Some Redpolls looked paler than others, but I figured also that the pale ones were females. We always have goldfinches and before they started turning yellow, a quick look at the 3 species, all looked so similar. Then you notice the red crown and begin to see other differences among these small birds. I’ve been taking pictures and really enjoying seeing them for so long this winter (and now spring). It has been an extremely snowy and cold winter here and that my account for having so many birds. I am faithful to always keeping the feeders full!

  • Bob Holbrook

    An example of why I keep my own list that shows what I have seen, where and when and don’t have to rely on others to determine what I see or didn’t see, what counts or doesn’t count. My list is my list. Period. Sure do enjoy those little rascals and the little Hoary was a beaut on a late spring trip up to Churchill, Canada.

  • Michael Cordero

    This is the second time in the last 3 years we have redpolls all winter. First year there was between 200 or 300 on a good day. This year we stopped counting at 500 or 600.Not all the time but a little more frequency in the last two weeks in March. Today we had about 25 siskins and around 70 or so redpolls still. They do appear to be different sizes and some have a little coloring difference. They ate at least 120 lbs of thistle before switching over to sunflower seeds. They like to spread seed all over. we have about 14 feeders and platforms and we they come they are all over everyone of them. Have thousands of photos and a couple of movies. Search for backyard redpolls on face book to see one of them.

  • Thomas Thorn

    I live in the middle of Rimouski, a city in eastern Quebec.
    I have been feeding 100 to 200 Redpolls and Pine Siskin since the beginning of February.
    They arrive each morning about 6:30. I have photos of feeding these small birds from my hand.
    The count is about 50 % Pine Siskin and 50 % Redpolls with some color variation.
    I place some sun flower seeds on the inside of an open window and they actually come inside the house.
    If I had a bird tagging kit, I could have tagged many of these birds this winter.
    Among the flock I spotted a yellow finch that also comes each day.
    Winter bird watching is a very delightful way of passing the cold winter !

  • Lawry Sager

    Interesting work. But I daresay that I’m not the only reader to be amused by reference to DNA and RNA discussed in high school biology. Yes, Meselson and Stahl were working out the implications of Crick and Watson’s discovery, but neither that nor Rosalind Franklin’s photograph that originally suggested the double helical structure, had appeared in our texts in those ancient times.

    Has bird watching really “progressed” to a point where someone might actually be upset that science has deprived them of a number on their lifelist? I admit that I find the concept of a lifelist interesting. Perhaps it’s time to dig out the checklists from 1953 to the present, the scraps of paper and notes scribbled on page margins, and worn field guides, and start counting. It would probaly be of more use to note the changes over time: of arrival and departure dates, relative abundance, and range expansions (and contractions). But, as I can still see in my mind’s eye individual birds and locales crowd out the importance of counting, and I’d just pick up my binoculars and head out.

    One of those mind-pictures is the last group of redpolls seen in the brittle sunlit birches of western Maine, all too many years ago. Perhaps you could steer some my way during the next irruption….

  • Richard M. Gage

    I am still observing Cassins Finch here in Prescott, Arizona and wondered if that finch is seperated from the House Finch and Purple Finch by major differences in their DNA. And is the Cassins Finch a closer relative to the Purple Finch because the females really resemble each other in my opinion. That question could also be aimed at scientists lumping most of our Juncos under the same moniker…..The Oregon Junco as well as the red backed junco and a third similar bird are all considered relative to the Junco of those living in eastern North America. I am just asking. Thanks for taking the time to read and answer this question. Dick Gage

  • Richard Tafel

    I live near North Bay, Ontario, 200 miles north of Toronto. About every other year many redpolls come to my feeders. This year – and indeed even this week, over 200 of them have dotted the ground and areas about the feeders, daily. And, that could be during many days of well below zero degrees F. Some are, indeed a bit whiter, and I presumed they would be deemed the Hoarys. However, they do mix so consistently, and have such identical other habits, that I always wondered whether really they were distinct species. Glad to read the updated science. Now I can enjoy their energies without worrying about whether some may be deemed different species.

  • Elizabeth Miller

    As a newcomer to birding, I very much enjoyed the picture you paint of your bird resort! Would appreciate knowing where you are located.

  • Michael Cordero

    We are located in Warren NH On facebook Search for backyard redpolls Have Many hundreds of photo’s too.

  • Mike Mlodinow

    They are not even morphs–morphs have genetic differences.

    [This comment has been migrated from an earlier post version by Cornell Lab staff.]