Why some woodpeckers imitate a neighbor’s appearance

A black back, a white belly, white spots on the wings, and a red spot on the back of the male’s crown are all field marks for Downy and Hairy Woodpeckers (as shown above). The Hairy is notably larger than the Downy, but size can be difficult to judge, making these woodpeckers challenging to differentiate, especially for new birders.

Other North American lookalikes are Black-backed and American Three-toed Woodpeckers of the northern and western forests. In Europe, Great and Lesser Spotted Woodpeckers bear a striking resemblance, as do the Lineated, Robust, and Helmeted Woodpeckers of South America.

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Recently, scientists published evidence that some woodpeckers have evolved to look like another species of woodpecker in the same neighborhood. The researchers say that this “plumage mimicry” isn’t a fluke — it happens among pairs of distantly related woodpeckers all over the world. The study, published in April 2019 in the journal Nature Communications, was conducted by researchers at the Cornell Lab of Ornithology, SUNY Buffalo State, the University of British Columbia, and Manchester University.

“Habitat, climate, and genetics play a huge role in the way feather color and pattern develop,” explains lead author Eliot Miller of the Cornell Lab. “Species in similar environments can look similar to one another. But in some cases, there’s another factor influencing the remarkable resemblance between two woodpecker species, and that’s mimicry. It’s the same phenomenon found in some butterflies that have evolved markings that make them look like a different bad-tasting or toxic species in order to ward off predators.”

Study authors combined data on feather color, DNA sequences, eBird reports, and NASA satellite measures of vegetation for all 230 of the world’s woodpecker species. It became clear, Miller says, that distantly related woodpeckers have come to closely resemble each other when they live in the same region of the globe.

The study didn’t specifically address the reason Downy Woodpeckers look like Hairies, but Miller speculates that the larger, more aggressive Hairies might make other birds, such as nuthatches and titmice, think twice about competing with Downies for food. Some evidence supporting this idea has been found in observational studies, but field experiments would be needed to more conclusively test the hypothesis.

Why a Downy Woodpecker might have red on its crown, not nape

A gallery of woodpeckers in Europe