Skip to content

Acorn Woodpeckers Chose Storage Holes That Fit Individual Acorns

A male acorn woodpecker clinging to a granary tree drilled with acorn-storage holes
Research · Behaviour

Acorn Woodpeckers (Melanerpes formicivorus) in northern California, USA tended to store wider acorns in wider holes, rather than using openings at random. Researchers measured 126 acorn–hole pairs in Butte County during autumn 2024. The peer-reviewed study was published online on 21 July 2026 in The Wilson Journal of Ornithology.

Wider acorns were strongly associated with wider storage openings, although the relationship became weaker among the largest acorns. Acorn length also increased with hole depth, but this match was less consistent because many holes extended farther into the wood than the stored nut.

Video observations supported the measurements. Birds were filmed testing the fit of acorns, taking them back out and repositioning them before leaving them in a hole. The researchers therefore conclude that Acorn Woodpeckers show selectivity when placing stored food and generally choose openings suited to the individual nut.

Several oak species were producing acorns at the same time, yet every stored acorn examined belonged to valley oak (Quercus lobata). The authors suggest that the dimensions of the available holes may partly favour this species, although the study does not establish why the birds selected it exclusively. Most storage trees, known as granaries, were gray pines (Pinus sabiniana), which have been heavily affected by wildfire in the region. The authors note that losing these trees could reduce the supply of suitable storage sites.

Sources and image credit

  1. Stanford et al. (2026) — Granary hole selection by Acorn Woodpeckers (Melanerpes formicivorus): linking acorn and hole dimensionsPeer-reviewed primary research article in The Wilson Journal of Ornithology, published online 21 July 2026. Publisher metadata confirms the article, authors and publication date.
  2. Stanford et al. (2026) — Acorn size and granary hole selection by Acorn Woodpeckers (Melanerpes formicivorus)Primary 2026 conference abstract by the study authors. It reports the Butte County field period, 126 acorn–hole pairs, width and depth results, video-observed fit testing, exclusive use of Quercus lobata among sampled stored acorns, gray-pine granaries and the stated wildfire implication.

Image: Becky Matsubara / Wikimedia Commons — male Acorn Woodpecker (Melanerpes formicivorus) on a granary tree with visible acorn-storage holes at Lake Solano County Park, California, 7 March 2018. Representative image directly illustrating the granary behaviour studied; not a bird or tree from the Butte County study. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Behaviour

SPECIES IN THIS STORY

Species in this story

Acorn Woodpecker Melanerpes formicivorus Explore species

Independent research and conservation news archive

Did you find this information useful?

Wildlife Vagabond is independently built and maintained. Voluntary support helps cover source verification, hosting and continued work on research and conservation news.

Support Wildlife Vagabond

The news archive will remain freely available.