It's a Family Affair

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Right now acorn woodpeckers are preparing for the coming winter. These birds, like nearly all woodpeckers, are black and white with a splotch of red on their head. They are usually described as having a clown's face. This, coupled with their raucous laugh, makes them easy to find throughout California.

As the name indicates they are closely associated with oak trees. Extended family groups of them are busy now stocking collective granaries. The birds gather acorns and stuff them into holes they have drilled into the bark of large trees, providing food for later in the season.

But their unique claim to fame -- to quote Walt Koenig, the researcher who studied them for 30 years -- is their bizarre sexual behavior. In a granary group, there can be up to six males cobreeders with three female cobreeders and six or more non-breeding helpers. The six males are all related, as either brothers or fathers and sons but they compete for sexual access to the three females, who are also related to each other. The females lay eggs all in one nest. After the eggs hatch not only do the breeding males and females help provision the young but the helpers also help. And just who are these helpers? They are the young, both male and female, from previous years. Sure sounds like one big happy family -- but not so fast.

To prevent incest, the non-breeders must leave their family of origin and join another nearby family group. This only happens when a vacancy occurs due to death of a breeder. A pair of same-sex birds from one group fights another pair of same-sex birds for dominance and therefore entrance into the new family. These are very intense brawls Dr. Koenig calls "power struggles." The losers have to return to their natal group as helpers until another opportunity arises. Koenig has also found that joint-nesting females will sometimes destroy each other's eggs.

Who knew about this ongoing soap opera in the woodpecker world?


This is Michael Ellis with a Perspective.