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The Winter Private Granaries of Acorn Woodpeckers

Are they the ultimate hoarders of the bird world? Probably.


Acon woodpecker at a tree granary peppered with acorns
Credit: Lorraine Bruno / FWS

These industrious birds busily prepare for winter by collecting acorns and then “tattoo” them into thousands of tiny holes they drill in dead trees. Known as granaries, these trees serve as massive storage units for their precious winter food supply.


Over generations, acorn woodpeckers reuse the same trees, which can hold thousands of acorns. Even as many as 50,000.


This clever food storage system has captured the attention of scientists for decades. Walt Koenig, a Senior Scientist at the Cornell Lab of Ornithology, has been studying acorn woodpeckers since 1972. “They’re one of the most interesting birds in North America,” Koenig told Atlas Obscura. “In fact, I can’t think of any others that even come close.”


Each acorn is meticulously placed into a hole, forming an elaborate pattern of dots across the tree trunks. It’s a sight to behold - one that reminds us of how wonderfully intricate nature can be. Furthermore, these birds have built a remarkable culture around their granaries, passing them down through generations like prized family heirlooms.


When finding good granary tree candidates, the birds seek out dead limbs, snags, and trunks with nice, thick bark, selecting for areas of dead tree tissue to avoid drilling into the sap. In more urban habitats, they’ll use other forms of dead wood, often leaving people’s homes or sheds completely pockmarked.


If you ever see a tree filled with rows of acorns carefully packed into holes, know that you’re witnessing the handiwork of one of North America’s most remarkable birds.

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