Quirks & Quarks

In lethally violent 'woodpecker wars' some birds fight, and some just come for the show

Coalitions of acorn woodpeckers battle for the opportunity to breed

Coalitions of acorn woodpeckers battle for the opportunity to breed

Acorn woodpeckers engage in wars in which up to fifty birds will fight in coalitions to take over vacant breeding territories (Bruce Lyon, UCSC)

To hear biologist Sahas Barve tell it, a woodpecker war is a sight to behold.

"It's a pretty entertaining and pretty awesome sight," he told Quirks & Quarks host Bob McDonald.  

"You come upon a big tree with probably forty or fifty birds flying around and you can see them bashing with their wings open, birds flying around, birds fighting each other, birds holding each other's legs."

These violent encounters turn out to be a struggle for succession, territory and breeding opportunities.

They can do a lot of damage — you can see birds with their eyes gouged out and blood on their plumage.- Sahas Barve, Smithsonian National Museum of Natural History

Research on this work was published in the journal Current Biology

Barve, from the Smithsonian National Museum of Natural History in Washington, DC, was part of a team that used location tracking tags on a species, called the acorn woodpecker, to untangle the complex story behind the woodpecker wars.

A family affair

The acorn woodpecker lives throughout southwestern North America, and Barve's work took place at the site of a long-term study of the birds — the Hastings Natural History Reservation in California.

Acorn woodpeckers have a fascinating family life, which proved critical to understanding their successional wars. A family of woodpeckers can include up to eight breeding males and several breeding females, as well as helper offspring of both sexes who do not breed. The family shares a nest and raises offspring co-operatively.

The trouble starts when the breeders die. If all the breeding males, for example, in a family die off, they can't be replaced by their helper offspring, as this would lead to incestuous interbreeding.

Nosy neighbours become fearsome fighters

So a vacancy exists in the family. And news of that vacancy circulates quickly among nearby unrelated acorn woodpeckers. Multiple coalitions of birds, usually helpers from other families, gather and begin a many-sided battle royale, with the winner taking the opportunity to fill the vacant breeding positions in the family. The same thing happens if the vacancy is caused by the death of the breeding females.

Sahas Barve and his colleagues were able to untangle the chaos of the woodpecker wars by precisely tracking the location of dozens of birds using using radio telemetry tags, as seen on this bird. (Sahas Barve)

And males or females, the fighting is fierce, said Barve. "These birds get really vicious and they're just going at it from dawn to dusk."

"Woodpeckers get especially violent because they have spears for mouths. They can do a lot of damage — you can see birds with their eyes gouged out and blood on their plumage. We know that some birds sustain really fatal injuries, like a broken wing, and you can't expect birds to live too long with a broken wing."

Some birds just like to watch

What really intrigued Barve and his colleagues, however, was not the fighters. It was the spectators.

"We were really surprised to find all these birds that you wouldn't expect to be at a power struggle still present and spending up to an hour every day, potentially, watching these fights."

It likely wasn't just to observe the violence, though.

"We feel that what these birds are getting from watching these power struggles is just to get a sense of which are the big coalitions in the area, who's coming from where, and how they are related."

It all contributes to the picture of a species that is extraordinarily socially aware and socially intelligent. Even if the occasional result of that intelligence is an outbreak of extreme violence. 

Produced and written by Jim Lebans

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