With their sharp, powerful beaks, Acorn Woodpeckers excavate custom holes into trees that are the perfect size to hold an unusual food—acorns. Each Acorn Woodpecker group works together to maintain and defend its acorn collection. The same tree, called a “granary”, is reused over generations to store the winter food supply. As dependent as Acorn Woodpeckers are on this communal food resource, it is not surprising that they are also highly social birds. They live in stable groups of roughly a dozen individuals and have evolved an unusual polygynandrous mating system in which multiple males and females share a single nest cavity and communally raise chicks.