Acorn Woodpeckers & Granary Trees

The Acorn Woodpeckers (Melanerpes formicivorus) that live along the rivers in our area are busy this time of year!  Acorns are ripe and ready for collecting, and these busy woodpeckers are capitalizing on an abundant crop.

Male Acorn Woodpecker (Melanerpes formicivorus) dining on a favorite: a flying insect.

Acorn woodpeckers are a rather rowdy bunch, living and breeding in large community groups.  Though famous for their acorn gathering, they also feed on sap, fruit, grass seeds and other nuts, as well as flying insects when they are abundant during the warm season.  They may stash uneaten insects in crevices.  Acorns are stored in communal granary trees, thousands at a time.  According to Cornell's All About Birds site, acorn woodpeckers can store up to 50,000 acorns in one granary tree, each snuggly wedged in its own hole. 

Granary Tree

I've read that when stashing an acorn, a woodpecker will poke an acorn into a hole, pull it out, poke it into another hole, pull it out again and try another, testing different holes for the perfect fit for that particular acorn.  As stored acorns dry out, they become loose in their holes and woodpeckers will move them into a better-fitting hole.  Acorn woodpeckers drill holes in the thick bark of dead limbs, doing no harm to living trees.

Acorn Woodpecker, checking out the communal granary tree.

Acorn woodpeckers are dependent on acorns and the oak woodlands that produce them.  In the highly agricultural Great Central Valley, most of our oak woodland remnants are scattered along the rivers, hugging the banks of the Tuolumne, Stanislaus, and Merced.  They range widely across much of California, wherever suitable oaks are found.

Granary Tree



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