[CLIP: Acorn woodpeckers fight]What you’re hearing is war—among woodpeckers, a species called acorn woodpeckers. The birds fight long, bloody battles over access to trees, where these woodpeckers nest and store their food: you guessed it, acorns. “In bark and in dead parts of trees, they make individual holes in which they store one acorn at a time. They put in a lot of effort in the short term for this big long-term prize.”Barve and his colleagues tracked acorn woodpeckers during these power struggles. [Sahas Barve et al., Tracking the warriors and spectators of acorn woodpecker wars]The scientists say these battles reveal a lot about animal social behavior.