Woodpeckers: Spread-wing display

Steve Zamek
August 17, 2021
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Three woodpeckers on a branch
Steve Zamek

Acorn woodpeckers doing the spread-wing display.

Researchers had long assumed that acorn woodpeckers opting for a rare form of polygamy, in which co-breeding siblings are forced to compete to mate, were making an evolutionary compromise. To researchers, this sibling rivalry seemed likely to result in individual woodpeckers leaving behind fewer offspring each year than if they had opted for a more traditional coupled pairing with a guaranteed opportunity to mate. To balance out this short-term loss of evolutionary fitness, researchers hypothesized that the woodpeckers’ polygamy must confer some indirect or long-term advantages but quantifying those benefits in wild populations before this study had proven extremely challenging.

But now, a new study published today in the journal Proceedings of the Royal Society B suggests that even complex cooperative breeding strategies may offer direct evolutionary benefits over an animal’s lifetime, and perhaps offers clues into how social behavior first evolved in humans and other animals. The study finds that male acorn woodpeckers breeding polygamously in duos or trios of males actually fathered more offspring than males breeding alone with a single female, contrary to conventional thinking among biologists that monogamous males necessarily produce more offspring than those in polygamous groups.

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