Birds & Birding

Acorn Woodpecker: The Fascinating Life of the Master Hoarder

April 24, 2017

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Acorn woodpecker on a black oak tree. Photo © Steve Ryan from Groveland, CA, USA (Acorn Woodpecker - Day 124) [CC BY-SA 2.0], via Wikimedia Commons

The acorn woodpecker displays some of the most interesting and complex feeding and social behavior among birds. A lot of its behavior may even seem completely at odds with what you know about “typical” woodpecker behavior.

Let’s take a look at the fascinating life history of these colorful, charismatic birds.

The first thing you’re likely to notice about acorn woodpeckers is that they’re in a flock. If you see one, you’ll probably soon see more. At least this is what I first noticed when I saw them around Santa Rita Lodge, located in the birding hotspot of Arizona’s Madera Canyon.

I’ve long enjoyed observing woodpeckers on my outdoor rambles. And mostly, you are seeing a solitary individual or perhaps a pair. I’ll be out snowshoeing and see a pileated woodpecker hammering away at a dead tree. Or perhaps a hairy woodpecker will show up at the backyard feeder. They’re always enjoyable birds to watch, but you often don’t see any of them.

With acorn woodpeckers, it’s like a riot of sound, color and flight acrobatics. The Cornell Lab of Ornithology, my trusted source for all things woodpecker, describes them aptly as “a troupe of wide-eyed clowns.”

Admittedly, other birders at Santa Rita Lodge seemed hardly to notice. They were looking for Southwest specialties and rarities. Acorn woodpeckers are entirely predictable and easily findable in their range. But look closer and there’s a whole lot going on.

Acorn woodpeckers at the Santa Rita Lodge. Photo © The Nature Conservancy (Lisa Feldkamp)

Acorn woodpeckers are indeed the most social of North American woodpeckers; they’re organized in family groups of up to twelve individuals (more on this relationship in a bit). All the activity happens around a most interesting tree and the territory surrounding it.

When you think of woodpecker behavior, chances are you picture a woodpecker drilling into a tree to access larvae or other invertebrates. The acorn woodpecker drills into trees to create storage holes. A family unit uses one tree to drill with thousands of holes, which they then fill with acorns.

These woodpeckers store acorns on a scale worthy of one of those cable hoarding reality television shows. A single granary tree, according to the Cornell Lab, can contain an astonishing 50,000 acorns and other nuts.

The acorn woodpecker plucks an acorn and sticks it in the tree hole. It then tamps it down – tap, tap, tap – with its beak to ensure a snug fit. As the acorn dries, it might loosen, so the acorn woodpeckers are constantly tending the tree, moving acorns around to appropriate-sized holes.

Why do the woodpeckers do this? It is an effective strategy for surviving cold weather without the need for migration. Acorns are rich in fat. If they were stockpiled together, they could be prone to getting mold or otherwise becoming inedible. Storing them on the ground would make them accessible to deer, rodents, turkeys and other acorn eaters.

Acorn woodpecker at granary tree. Photo © ALAN SCHMIERER / Flickr in the Public Domain
Acorn woodpecker at granary tree. Photo © ALAN SCHMIERER / Flickr in the Public Domain

The granary tree is easier to defend (and one acorn woodpecker is posted as a sentry against marauding ground squirrels and other woodpeckers).

Other birds stash food for the winter, of course. The Clark’s nutcracker is famous in this regard: it caches an astonishing number of pine seeds around the forest (and remembers where it hid them). But the acorn woodpecker is one of the champion food hoarders in the bird world.

Acorn woodpeckers eat a variety of other foods; like many woodpeckers, they eat plenty of insects. They just prefer to snatch flying insects from the sky rather than pecking them out of trees.

Photo © Tyler Karaszewski / Flickr through a Creative Commons license
Photo © Tyler Karaszewski / Flickr through a Creative Commons license

They are adaptable birds and will readily set up territories in suburbia. They are not picky about what they use as granaries: a telephone pole or even the side of a house will substitute for a tree. This makes them less-than-endearing to many living in their range.

The Cornell Lab of Ornithology reports that this sometimes leads to acorns stowed in places they can’t reach them. In one instance, researchers found 485 pounds of acorns in an Arizona water tank.

Photo © PEHart / Flickr through a Creative Commons license
Photo © PEHart / Flickr through a Creative Commons license

The social lives of these woodpeckers may be even more fascinating than their hoarding behavior. Walt Koenig’s lab at Cornell has been studying them since 1974; this long-term study continues to reveal the intricacies of an acorn woodpecker family unit.

Koenig writes:

“The mating system of this species is one of the most complex of any vertebrate, with social units consisting of up to seven related males competing for matings with up to three related females, all laying eggs in a single nest, and up to 10 nonbreeding helpers of both sexes (offspring from prior years).”

I encourage you to check out his lab’s page for detailed information, including a lot of published papers, on their behavior.

Basically, the acorn woodpeckers live as family units within a territory, nesting communally. Young woodpeckers remain with their parents for several years to help raise young. They eventually move off to check out other woodpecker territories, eventually settling into a new colony when they find one where an adult has recently died. This dispersal also helps reduce inbreeding, since there are multiple matings happening among a family group of birds.

Photo © Pablo Andrés Ortega Chávez (Flickr) [GFDL 1.2 or GFDL 1.2], via Wikimedia Commons
Photo © Pablo Andrés Ortega Chávez (Flickr) [GFDL 1.2 or GFDL 1.2], via Wikimedia Commons

In some acorn woodpecker family units, multiple females lay eggs in the same nest. This results in an intriguing (some might say disturbing) sequence of egg laying. When a female finds a clutch of eggs in the nest, she will remove all the eggs – and they’ll be eaten by other family members (including, quite probably, the mother).

As Bill Schutt, in his excellent recent book, Cannibalism: A Perfectly Natural History, writes, “Presumably this is because the oldest hatchling would be the most likely to survive. To eliminate this advantage, the birds will keep eating each other’s eggs until they both lay their eggs on the same day, a process that can take weeks.”

That’s a lot of potential egg eating, an unusual behavior in birds. Undoubtedly, as researchers continue investigating the complex lives of these birds, more surprises are in store.

Acorn woodpeckers are not difficult to see in many parts of their range, which includes coastal areas of Oregon and California, the U.S. Southwest, Mexico and Central America. Since they protect territories, they can reliably be found, year round, in many nature reserves and parks.

They were difficult to miss in Madera Canyon. That may make them less-than-exciting for the dedicated bird “ticker” but for a bird observer, their behavior provides endless fascination. Stake out a granary tree with a binocular, and let the show begin.

Matt Miller

Matt Miller is director of science communications for The Nature Conservancy and editor of the Cool Green Science blog. A lifelong naturalist and outdoor enthusiast, he has covered stories on science and nature around the globe. Matt has worked for the Conservancy for the past 14 years, previously serving as director of communications for the Idaho program. More from Matt

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13 comments

  1. Fascinating stuff Matt – always enjoy your section of Cool Green Science. I’ll never look at Acorn Woodpeckers the same again! It just goes to show you the folly in the numbers game of birdwatchers who are always looking for the next species to add to their list rather than watching the “same old birds” for long enough to understand how truly exceptional each one is in it’s survival strategies.

  2. I’m a great fa.n of Acorn Woodpeckers. They are very industrious. They once filled up a wall of my in-
    laws summer house in Cambria, CA. I remember seeing the grill of a pedestrian “walk sign” nearly full of acorns. The spaces were just the right size to hold an acorn.

  3. That is amazing to me I love birds and I’m so glad to learn about them Thank You for all the wonderful work you do Mary

  4. What an amazing bird. I had not heard of them until this article, and am not a birder in the sense that I feed our garden birds, and often stop to watch then where ever I see them.
    Thank you for this article and especially the beautiful photographs.
    Allan.

  5. I was in Ashland, Oregon last weekend and came across a family group of acorn woodpeckers. I was very curious since I was expecting to see pairs of woodpeckers during spring. This article explained that they live in family groups, and I came across a group of four males and two females. The males kept going into two separate holes in the tree, while the females observed. I have several pictures of their interactions.

  6. Very nice article we love woodpeckers we got all sizes in our yard

  7. Thank you for this interesting information on Acorn Woodpeckers. We live in an oak forest and enjoy watching the “family” of Acorn Woodpeckers that lives here. We have a feeder stocked with suet, wild bird seeds sunflower seeds etc. and the “Acorns” seem to enjoy all of that too. I will search for the granary tree.

  8. It’s interesting to discover that acorn woodpeckers don’t just live in oak trees. Recently a flock of the critters have moved into one of my eucs. Especially on sunny days, they twirl in the air, chase each other and squawk. I love woodpeckers.

  9. I am so fascinated by these birds! Amazing stuff. I love all birds and I’m on the Cornell web nearly 24/7 . Thank you Mr. Miller for all you do to educate all of us. Protect our birds. God bless. Mary

  10. Our local (Granite, Utah @ 5250 ft. msl) corvidae are also nut hoarders. Western scrub jays & magpies love to grab a nut & fly off to stash it somewhere. I’m told that they remember where…hm. They empty the peanut ring (2 lbs per ring full of raw peanuts. I buy 100 lbs per year.) in about 15 minutes. The results are a flock of great, glossy happy birds!