If the stores are eaten, the woodpecker will move to another area, even going from Arizona to Mexico to spend the winter. The acorn woodpecker ( Melanerpes formicivorus) is a medium-sized woodpecker, 21 cm (8.3 in) long, with an average weight of 85 g (3.0 oz). The Acorn woodpecker (Melanerpes formicivorus) is a medium-sized. In parts of its range the acorn woodpecker does not construct a 'granary tree', but instead stores acorns in natural holes and cracks in bark. When any protective group of woodpeckers experiences a death or disruption to the hierarchy, nearby birds rush to the area and fight for access to the trove these fights also attract woodpecker audiences who leave their own territories to witness the battles. The acorns are visible, and a group defends its granary against potential cache robbers like Steller's jays and western scrub jays. As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird's time. The woodpeckers then collect acorns and find a hole that is just the right size for the acorn.

These holes, always above the snow line so that the acorns can be retrieved in winter, can be observed in the hundreds on large trees. They also drill holes in the thick bark of mature living trees, notably the Ponderosa Pine in California. In some parts of their range, such as California, the woodpeckers create granaries or 'acorn trees' by drilling holes in dead trees, dead branches, telephone poles, and wooden buildings. They can be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap. Acorn woodpeckers also feed on insects, sap, and fruit. Acorns are such an important resource to the California populations that acorn woodpeckers may nest in the fall to take advantage of the fall acorn crop, a rare behavior in birds. Acorn woodpeckers, as their name implies, depend heavily on acorns for food.

Acorn woodpecker e.g