Eared Grebes eat brine shrimp and aquatic insects for sustenance, but rigid exoskeletons make them hard to digest. So these grebes – along with their other grebe cousins – evolved to use their feathers as a way to slow down digestion. The feathers form dense balls in the digestive tract and appear to slow the passage of food long enough that the food can be safely liquified. The bird then regurgitates the tough bits within a ball of feathers. The Pied-billed Grebe shown here is feeding feathers to her chicks.

More info and transcript at BirdNote.org. 

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