People who've been humbled, it's said, eat their words. By the same token, certain birds eat their own feathers, though not because they've suffered a defeat. Rather, these birds consume feathers in order to survive.
The birds in question are grebes, aquatic birds with a diet that consists of insects, crustaceans, and sometimes fish. But fish-eating grebes like the Horned Grebe and the Red-necked Grebe can't readily digest the bones inside fish. That's why they pluck and eat large quantities of their own feathers. The feathers create a filter of sorts within the grebe that traps the bones in the bird's stomach before they can enter the intestine. Thus trapped, the bones slowly dissolve until they can more easily be passed.