Berries of an Invasive Plant are Dying Woodpecker Feathers Red

Researchers discover the origin of the red pigment that has been popping up in yellow-shafted Northern flickers.

Across eastern North America, yellow-shafted Northern flickers, which normally sport bright yellow lines running up their feathers, have been mysteriously gaining a reddish-orange hue.

According to a new study published in The Auk: Ornithological Advances, the red coloration does not reflect genes acquired from their western relatives, the red-shafted Northern flicker. Rather, it appears the woodpeckers have been gorging on the juicy red berries of the invasive honeysuckle plant.

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Where the western and eastern flickers meet, interbreeding often produces birds with a blend of yellow and red. However, orange-red wing feathers have been appearing much farther east, smack in the middle of the yellow-shafted Northern flicker’s range, for years.

Scientists measured the chemical composition of the pigment in these unusually colored birds and discovered that their red coloration comes from a pigment known as rhodoxanthin, which is found in a variety of plants including honeysuckle berries. The red-shafted flickers, on the other hand, get their reddish hue from carotenoid pigments.

Another line of evidence supporting the berry origin of the red pigment came from data collected at a bird-banding station, which showed that the rosy color appears during the fall moult — precisely the time when the berries become ripe.

The honeysuckles were introduced decades ago with the hopes of creating valuable wildlife habitat, study lead author Jocelyn Hudon of the Royal Alberta Museum explains in a press release.

But aberrant coloration arising from ingestion of the honeysuckle berries may end up having negative consequences for these birds. "The ready availability of a pigment that can alter the coloration of birds with carotenoids in their plumages could have major implications for mate selection if plumage coloration no longer signaled a bird's body condition," he says.

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