Short answer: Yes! Long answer: Well, it's very complicated so let me explain it in this post...
Oh man, this is it, this is the blog post. I've been talking about and putting off writing a blog post on this subject that people have both been hoping for and others have been dreading my Darwin Day special on Nicholas Mason and Scott Taylor of the Cornell Lab’s Fuller Evolutionary Biology Program's paper on redpoll speciation in Molecular Ecology. This paper basically says that Common, Lesser, and Hoary Redpolls are all the same species based on their genetic evidence. I'm writing this post not because I'm a sadistic lumper that wants to steal lifers, but because I want to increase knowledge about a question that has plagued birders and ornithologists since the Civil war, but now we finally have an answer. For some reason with these three animals in particular, an annoying phenomena has occured and it's people being stubborn with how many species there are based on the scientific evidence, so to make it up to the dissenting party, I'm going to talk about some antitheses to the "one to rule them all" doctrine many have claimed over the question of how many species redpolls are in order to appease that part of my audience. I will be presenting my unbiased scientific opinion, without bringing any of my personal feelings into this discussion whatsoever.
Before I go into depth about redpolls, it's helpful to define the major species concepts that taxonomists use:
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.
According to Kenn Kaufman several studies have documented the genetic similarities between Common and Hoary Redpolls since the 1980s. No study has examined more than 11 regions of the redpoll genome, making ornithologists wonder whether they were missing the true differentiating genetic markers. Until now...
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, comparing DNA from 77 redpolls, including specimens from museums around the world. 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. One of the key differing factors among distinct species is assortative mating, or members of a group breeding with each other more than another group. According to Mason, “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.” 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. Mason has said “We didn’t find distinct characteristics to separate the redpoll types, but rather a continuum, or a progression, of physical traits, and many redpolls were somewhere in the middle.” Interesting indeed, considering that Redpolls with intermediate plumage are common in certain areas, like north-central Alaska, and are often impossible to ID.
Redpolls follow a gradient of streaking on the flanks from the most streaks on flammea to the least on hornemannii. Then you have intermediate birds like the one in the center which can be real nightmares to ID. This could be either a dark HORE, a light CORE, or a hybrid, which if we use the Biological Species Concept to define a species, would support lumping them. Photos, from left to right, by Sharon Watson, newfoundlander61, Guy Lichter, Stuart Oikawa, and Chris Wood via Flickr.
While the evidence supporting Redpolls as a single species is convincing, it was not mentioned in the 2016 AOS Check-list supplement and rejected in the 2017 supplement (the same tragic year that Thayer's Gull was lumped), to the relief of many listers whom were already annoyed that they lost one tick with Thayer's gone and Yellow-rumped Warbler and Willet not being split. Kenn Kaufman can’t imagine there being too much conflict over consolidating the redpolls. “In recent years there have been more ‘splits’ than ‘lumps,’ so if continuing taxonomic work occasionally takes one away, it’s not that big a deal.” Johanna Beam, a young birder studying at St. Olaf university in Minnesota, has actually spoken to Scott Taylor, one of the authors of the paper, and on the topic of the lump, she has said: "but sadly he (Scott Taylor) thinks they're not going to accept it until they get actual breeding data from the arctic, which is some nasty work because of funding, mosquitoes, lodging etc up there."
It's not over yet, 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, which breed in high mountain areas of western North America,.
To summarize, the consensus on if Common, Lesser, and Hoary Redpolls are all the same species is yes simply based on the Phylogenetic Species Concept I talked about earlier and DNA analysis conducted by Mason and Taylor. I have asked multiple respected people in the birding community for their thoughts and they mostly agree with me. You can choose whether you agree or disagree with me, but for now I offer this quote on the study by Scott Taylor himself: “I think this makes them a more interesting bird, it means they’re part of an exciting, complicated system that can make a single species look different across different parts of its range." Keep in mind that if you do disagree with me, this is opinion purely based on evidence.
I would like to thank Tessa Rhinehart and William Von Herff for giving me and supporting the idea to write about this complex subject, as well as Sam Bressler and Ethan Gyllenhaal for helping me find access to the original Mason and Taylor paper (which was unfortunately behind a paywall); this post couldn't exist without your help. I also would like to acknowledge the amount of work Nicholas Mason and Scott Taylor put into their study, as well as Gustave Axelson and Jesse Greenspan for writing concise summaries of the study on the Cornell Lab and Audubon websites respectively. I lastly want to thank Kenn Kaufman, Ron Pittaway, Lindsey Duval, John Puschock, Ryan Zucker, Ethan M, Johanna Beam, Nathan Martineau, Jerald Reb, Jared Gorrell, Ben Sanders, Alex Sundvall, Joseph Kurtz, Greg Neise, Dominic Garcia-Hall, TIm Swain, Ise Varghese Mac, Sharon Steitler, Aidan Place, Alberto Lobato, Brian C. Johnson, Alvaro Jaramillo, and many other birders for offering their diverse opinions on this subject.
Thanks for reading and have a happy Darwin Day!
All copyrighted images belong to their respected owners. Please notify me if I neglected to credit your work. All copyrighted images in this post are protected under FAIR USE for reasons of Commentary, Education, Criticism, Parody, and Social Satire.
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