Flickers: The Closer You Look, The Less Different They Are

By Hugh Powell
June 6, 2018
Red-shafted and Yellow-shafted Flicker woodpeckersTwo kinds of Northern Flicker: “Red-shafted” of western North America by Todd Steckel; “Yellow-shafted” of eastern North America by Bill McMullen, via Birdshare.

For birders, one of the many small delights of traveling cross-country is that moment when the flickers change. These pretty and common woodpeckers flash bright colors in their wings and tail—salmon-red in western North America and lemon-yellow in the East.

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It’s such a noticeable difference that for decades the two were regarded as separate species, Red-shafted and Yellow-shafted Flickers. But in 1982, the two forms were officially lumped and considered a single species, the Northern Flicker.

In the years since, scientists have wondered whether a closer look at the two birds’ genomes might reveal differences too small to have been detected with earlier technology. Now, a new study published this week in Auk: Ornithological Advances, by Stepfanie Aguillon and colleagues at the Cornell Lab of Ornithology, presents an answer.

The original studies of the 1980s compared the flickers’ DNA using protein molecules as a proxy, and they were unable to discover any differences between the two forms at all. In the new study, Aguillon and her collaborators directly compared more than 16,000 DNA locations, and for the first time found clear evidence of genetic differences between Red-shafted and Yellow-shafted forms. At the same time, those differences were very small, indicating that the two lineages diverged only recently. 

As with Blue-winged and Golden-winged Warblers, the flickers are an example of two forms that physically look very different but genetically are nearly identical. 

“I find Northern Flickers to be really interesting because up until this point, we couldn’t find any differences at all, even though the two forms look so different.” Aguillon says. “Now that we have these results, it seems likely that only a few small parts of their genomes differ—the ones that are related to their plumage differences.”

But by the same token, Aguillon says, those small differences shouldn’t be interpreted as confirmation that the two forms are a single species. That decision would be better answered through studies of ecology, mating behavior, and hybridization than by a simple tabulation of genetic differences, she says. 

Nevertheless, the study showcases today’s exquisitely sensitive genetic sequencing tools—enabling Aguillon to see the slightest of differences between two close relatives, and to begin to reconstruct the evolutionary pathways that brought them into being. 

Reference

Aguillon, S. M., L. Campagna, R. G. Harrison, and I. J. Lovette. 2018. A flicker of hope: genomic data distinguish Northern Flicker taxa despite low levels of divergence. Auk 135:738–756 doi: 10.1642/AUK-18-7.1.