Attacked by pygmy nuthatches - unusual behavior in the ponderosas

It's common to see mixed-species flocks in the fall and winter in the ponderosa pine forest. Nuthatches, chickadees and woodpeckers travel together, helping each other watch for predators as they forage. But this was something different. On this late October day, we watched the pygmy nuthatches attacking a hairy woodpecker, driving him off. Why were they attacking their supposed flock collaborator? Listen to this episode to find out!