In autumn, Acorn Woodpeckers spend large amounts of time storing acorns in holes drilled into a single tree, called a granary tree. One granary tree may have up to 50,000 holes in it. These images of Acorn Woodpeckers were taken at granary trees in the Arastradero Preserve in Palo Alto and San Antonio Open Space Preserve in Los Altos.


More information regarding Acorn Woodpeckers, including it's call, may be found at the link below.
Cornell Lab of Ornithology
http://www.birds.cornell.edu/AllAboutBirds/BirdGuide/Acorn_Woodpecker_dtl.html#fig1