The Zany, Swinging Lives of Acorn Woodpeckers

CC BY 2.0. Rennett Stove/Flickr

Welcome to some of the most bizarre social behavior on Earth.

You thought the swinging sixties and those key parties were crazy? You should see what the acorn woodpeckers have going on. The Cornell Lab of Ornithology gives it a prim spin, noting that "Acorn Woodpeckers are very unusual woodpeckers that live in large groups, hoard acorns, and breed cooperatively."

But a senior scientist at The Lab, Walter Koenig, makes it a bit more clear:

Acorn Woodpeckers exhibit some of the most bizarre social behavior on earth. Mate-sharing, group sex, infanticide, and acorn storing on a monumental scale.

Koenig has been studying the randy woodpeckers in central California’s Hastings Reserve since 1974. These birds would be remarkable enough just for their acorn hoarding alone. WIth thousands of cavities drilled into oak trees, the beehive-like storage system of acorns are a sight to see. Successive generations continue to add to the stash, sometimes comprising tens of thousands of holes – talk about a well-stocked pantry.

acorn woodpeckers

© Hayley Crews

But beyond that, things get even more interesting. As one of the world’s few polygynandrous mating systems, families of up to 15 birds watch over their turf, which includes one nest and a home tree filled with acorns.

"These birds waste no time courting, both sexes freely sharing mates within social groups. One to four related males form a coalition to nest with up to three females from a different group," notes The Lab.

And despite all the mate swapping, they have devised a clever way to avoid inbreeding. When the last breeder of one sex leaves or dies, a "reproductive vacancy" opens up. Auditions from birds from other groups begin, sometimes leading to more than 50 birds sparring for a chance to secure a spot. The victors join the family, allowing resources to be passed down, without the problems that come with in breeding.

And in a scene worthy of some sordid, dark soap opera, competition is fierce; when it comes to reproduction, especially. The Lab explains:

"Co-breeding females lay eggs slightly out of sync, and it doesn’t pay to go first. If a female finds an egg in the nest before she has laid her own, she will remove and begin to eat it. Soon the entire group, including the female that laid it, will feast on the egg. This abruptly stops once each female has laid at least one egg; then they all settle down to share the tasks of incubation and care."

Despite the zany-sounding antics, however, these birds have figured out some ingenious strategies for success ... even if they do sound like they've stolen the plot line from a Jerry Springer show. As Koenig says, "it’s all in a day’s work for these clown-faced denizens of the Southwest."