The acorn woodpecker’s main food source is insects, but acorns and tree sap serve as key nutritional backup. Acorn woodpeckers, as their name implies, depend heavily on acorns for food. Acorns are a critical resource, allowing the birds to make it through the winter. Acorn woodpeckers … 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. They live in extended family groups and engage in many communal activities, including territory defense, feeding of the group's chicks at the cavity nest, and specialized acorn storage structures termed "granaries." Acorn woodpeckers (Melanerpes formicivorus) are a common sight in the oak woodlands of western North America.