owever, by living where two or more oak also live, the acorn woodpeckers almost always find food. If one species of oak has a dismal acorn year, it is highly unlikely that the other oak species there would also have a complete crop failure that year. It takes many generations of woodpeckers to build a granary capable of supporting a stable population, and these are often focused on large, old oaks with plenty of dead branches for storing acorns. Their lives and social systems revolved around these granaries.
Acorn woodpeckers have a very complex social system. If you compared it to that of humans, it appears to include group sex, infanticide, communal living, and incest avoidance.
Acorn woodpeckers depend on acorns for survival. So, the variation in the abundance of acorns has occupied Dr. Koenig for the last 20 years as well. Acorn crops appear to be synchronous over wide areas of California. If it is a mast year for the valley oak in your back yard, it is probably a mast year for valley oaks at Hastings. Conversely, if there are very few acorns on your blue oak, there are probably very few acorns on blue oaks at Hastings as well. Walt and his colleague Jean Knops tell the story of how oaks, across long distances, have highly synchronous years of abundance.
Woodpeckers are not the only animal that depends on the acorns. Over 1,000 species of insects live in oak trees. Some wasps are specialized predators on them! It is a myth that the acorn woodpecker is choosing acorns occupied by larval insects. Acorn woodpeckers would eat those insects as a little bonus, if they found them, but woodpeckers depend on acorns for carbohydrates- "junk food" for fast energy.