Woodpecker wars are intense and even draw a crowd

Acorn woodpecker battles over prized territory are serious business.

woodpeckers
Credit: Steve Byland/Shutterstock
  • Acorn woodpeckers are highly socialized birds who are, let's say, unusual.
  • Small teams of acorn woodpeckers battle for days over coveted territory.
  • Up to 30 spectators attend the battles, leaving their own territories unattended to do so.

Ornithologists already knew that acorn woodpeckers, Melanerpes formicivorus, were gonzo. They're major hoarders of acorns, females eat each other's eggs, and then there's the group sex. It turns out they're also committed, tenacious, and ferocious warriors when it comes to competition for high-quality territory. Small teams of acorn woodpeckers battle over abandoned "granaries," tree sections with thousands of holes dug into their bark by birds — the holes are ideal for storing acorns.

First author of a new study published in the journal Current Biology, Sahas Barve of the Smithsonian National Museum of Natural History, spoke to Phys.org. He sets the scene:

"When you're approaching a big tree with a power struggle from far away, you'll first hear a lot of acorn woodpeckers calling very distinctly, and see birds flying around like crazy. When you get closer, you can see that there are a dozen or more coalitions of three or four birds fighting and posturing on branches. One group has to beat all the others to win a spot in the territory, which is really, really rare in animals—even in fantasy novels it usually boils down to one army against the other."

The research also reveals that large numbers of acorn woodpeckers who are not themselves involved in the action watch the battle royal unfold as spectators.

Acorn woodpeckers

acorn woodpecker

Credit: Ondrej Prosicky/Shutterstock

Much of what's known about these birds, including the new research, comes from a long-running project at the Hastings Natural History Reservation in California's Monterey Country. Acorn woodpeckers first arrived at the sanctuary in 1968 and have been under observation since 1974. The birds are common in the oak woodlands of western North America.

Acorn woodpeckers have a polygynandrous mating system, something that's rarely seen in nature. A group will consist of as many as seven co-breeding males and four joint-nesting females. Breeding members of the group couple promiscuously within the group, and never outside it.

It's an incestuous arrangement by human standards, with father and son competing for and breeding with the same females. And though the females use the same nests, it's pretty competitive — one female will remove and eat another mother's eggs to make room for her own. Over time, according to Hastings, this results in a balance in the number of chicks among the females.

In addition, an acorn woodpecker group will also include other, non-breeding community "helper" members — they're the woodpeckers who go into battle for acorn granaries. Though the woodpeckers primarily feed on insects, acorns provide them with non-perishable nutrition for those colder months when bug meals are few and far between.

Fight Club

acorns embedded in tree holes

Credit: David A Litman/Shutterstock

A granary for which an acorn woodpecker will fight is reminiscent of a human wine rack: An array of vertical storage compartments for their precious winter food. And they're dead serious about acquiring this storage: "These birds often wait for years, and when there's the right time and they have the right coalition size, they'll go and give it their all to win a really good territory," says Barve.

The balls-to-the-wall action of acorn woodpecker battle have made it difficult for human researchers to keep track of what's going on, so Barve and his colleagues devised a solution: They outfitted woodpeckers with radio tags that allowed the researchers to tell when two birds were in the same location, and to track the origin of combatants, and also to make detailed observations of a melee.

While the researchers had thought that acorn woodpeckers living nearby would most fiercely make a play for a nearby granary, this turned out not to be the case. It's not yet known what prompts one group of woodpeckers to commit to battle, though the researchers suggest that a group's internal calculus somehow produces a decision whether to try and acquire a particular granary.

Yet commit they do. The researchers found that woodpecker teams will fight for as long as 10 hours straight, and will return day after day. This was something of a surprise to researchers, making them wonder how they even sustain themselves that long.

"Get ya acorns heayah, acorns, get ya acorns heayah!"

woodpeckers

Credit: Petr Simon/Shutterstock

Previous research missed the spectators because the brouhaha was so overwhelming and attention-grabbing. As many as 30 woodpeckers have been observed in the peanut gallery.

The researchers have seen birds coming from as far as three kilometers (1.9 miles) away. These onlookers may spend up to an hour each day in attendance. Among the spectators are woodpeckers who already have adequate granaries of their own — whatever they get out of watching has to be worth the time spent leaving their own granaries unattended. The researchers suggest the watchers may be curious about changes a battle could make to the local status quo.

These highly social birds may also actually be rooting for one fighting group over another. "They potentially have friendships," says Barve, "and they probably have enemies. The next step is to try and understand how their social networks are shaped, and how they vary across the year."

Iron Age discoveries uncovered outside London, including a ‘murder’ victim

A man's skeleton, found facedown with his hands bound, was unearthed near an ancient ceremonial circle during a high speed rail excavation project.

Photo Credit: HS2
Culture & Religion
  • A skeleton representing a man who was tossed face down into a ditch nearly 2,500 years ago with his hands bound in front of his hips was dug up during an excavation outside of London.
  • The discovery was made during a high speed rail project that has been a bonanza for archaeology, as the area is home to more than 60 ancient sites along the planned route.
  • An ornate grave of a high status individual from the Roman period and an ancient ceremonial circle were also discovered during the excavations.
Keep reading Show less

Skepticism: Why critical thinking makes you smarter

Being skeptical isn't just about being contrarian. It's about asking the right questions of ourselves and others to gain understanding.

Videos
  • It's not always easy to tell the difference between objective truth and what we believe to be true. Separating facts from opinions, according to skeptic Michael Shermer, theoretical physicist Lawrence Krauss, and others, requires research, self-reflection, and time.
  • Recognizing your own biases and those of others, avoiding echo chambers, actively seeking out opposing voices, and asking smart, testable questions are a few of the ways that skepticism can be a useful tool for learning and growth.
  • As Derren Brown points out, being "skeptical of skepticism" can also lead to interesting revelations and teach us new things about ourselves and our psychology.
Keep reading Show less

New study suggests placebo might be as powerful as psychedelics

New study suggests the placebo effect can be as powerful as microdosing LSD.

Credit: agsandrew / Adobe Stock
Mind & Brain
  • New research from Imperial College London investigated the psychological effects of microdosing LSD in 191 volunteers.
  • While microdosers experienced beneficial mental health effects, the placebo group performed statistically similar to those who took LSD.
  • Researchers believe the expectation of a trip could produce some of the same sensations as actually ingesting psychedelics.
Keep reading Show less
Quantcast