Signs of the Acorn Woodpecker are all over the park. Just look for trees that have numerous thumb-sized holes. These are called granary trees. The holes were made by Acorn Woodpeckers in order to store acorns. The birds hammer the acorns into the holes and when they want to eat the nut, they come back and peck the shell open. Wedging acorns into these holes deters crows, jays, squirrels, and others from burglarizing the acorn cache. Fresh acorns dry out and shrink, so the birds have to maintain the granary by moving the acorns to smaller holes. The birds will also eat tree sap and the insects attracted to it; they also sally out from a perch to catch flying insects in mid-air and forage for berries and seeds.
A medium-sized woodpecker, the adult is black on the back and wings and throat with a white underside and upper base of the tail. The adult male has a red cap with a creamy white forehead and throat. The female has a smaller red cap with a black forehead and white below.