Male acorn woodpecker on an acorn granary.
Scientists once though these polygamous birds were trading the relative certainty of parenting offspring in a couple for the increased odds of controlling a territory chock-full of acorns afforded to them by teaming up with their brothers or sisters. Strength in numbers is important for these woodpeckers because of the vicious, bloody battles they must fight to win territories with the best granaries. These granaries are trees, usually dead, that have been plugged full of thousands of acorns over many years by the woodpeckers living in their vicinity. Presiding over a granary that is well-stocked can make or break a group’s ability to reproduce during lean years when acorns are less abundant.
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.