From the Spring 2021 issue of Living Bird magazine. Subscribe now.

When John James Audubon happened upon a nest hole containing a mix of red-shafted and yellow-shafted North­ern Flickers in 1843, he wrote in his journal that he wasn’t sure what to make of it: “[it was] the most curious set of five birds that I ever saw, and which I think will puzzle all naturalists in the world.”

Audubon was traveling along the Missouri River, and little did he know that he was in the hybrid zone where the eastern yellow-shafted forms of the Northern Flicker intermingle and inter­breed with the western red-shafted forms. To confuse matters even more, hybrid offspring of the two forms can show a mix of traits from both parents, resulting in birds with varying shades of orange.

Color variation in flickers is caused by differences in just a few genes out of tens of thousands. Northern Flicker illustrations by Megan Bishop.Color variation in flickers is caused by differences in just a few genes out of tens of thousands. Northern Flicker illustrations by Megan Bishop.

Now 178 years later, scientist Step­fanie Aguillon—a PhD candidate in the Fuller Evolutionary Biology program at the Cornell Lab of Ornithology—has solved Audubon’s puzzle, identifying the genes that cause the coloration dif­ferences in flicker wing and tail feathers. For her dissertation, Aguillon sequenced the entire flicker genome and found that yellow- and red-shafted flick­ers completely differ at only 0.01% of the genome. But that tiny difference—a few genes out of tens of thousands—accounts for the red or yellow shaft.

One of those genes (abbreviated CYP2J19) is the same driver of yellow-to-red coloration differences in canaries and Zebra Finches.

“It’s so exciting to think that I’ve answered a question that has gone unanswered for so long,” said Aguillon, who added that scientists have been studying the genetics of flicker color­ation since the 1980s. “I’m definitely lucky to be working during the age of genomic sequencing because it turns out it would be impossible to under­stand flicker coloration without looking at the entire flicker genome. It’s a true honor to be included in the long list of biologists that have thought about flicker coloration.”

Aguillon’s research was published in the January 2021 issue of the jour­nal Proceedings of the Royal Society B.

Cornell Lab of Ornithology

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