Acorn woodpeckers

Vivek Khanzode
August 17, 2021
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Two woodpeckers on a branch
Vivek Khanzode

Male (left) and female (right) acorn woodpeckers.

Researchers had traditionally explained the evolution of acorn woodpeckers’ polygamous co-breeding with a concept known as kin selection. In this view, cooperative breeding could have arisen and perpetuated itself among the woodpeckers despite reducing the number of offspring an individual bird parented because even if a male loses out on a breeding opportunity to one of his brothers, the resulting chicks will still carry a portion of that lonely male’s shared DNA. Also, if the unmated male helps raise and support his nieces and nephews, he also increases the chances that they survive and reproduce, passing on a portion of his DNA to the next generation.

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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