Acorn Woodpeckers (Melanerpes formicivorus) are larder hoarders. Breeding groups create a granary by drilling holes in a dead tree, and stuffing acorns into them. The acorns are visible, and the group defends the tree against potential cache robbers. The acorns represent a significant part of their diet; they also eat insects, fruit, seeds and sometimes tree sap. Madera Canyon, Arizona.