Feather-Eating In Grebes: A 500-Year Conundrum

Abstract

ABSTRACT Grebes are unique among birds in ingesting their own feathers. This behavior and the subsequent ejection of feathers as pellets have long puzzled ornithologists, who have tended to treat feather-eating and pellet-casting as independent behaviors rather than as complementary components of the digestive process. The diet of many grebes, including those with the most ancestral traits, is dominated by small invertebrates whose exoskeletons are resistant to digestion. Most birds eat grit to mechanically break down hard foods. Not so with grebes, which are chemical digesters. Feather-eating performs two main functions. The first is to retain food until it is fully digested; this is accomplished by a large feather bolus in the gizzard. The second, provided by a distinct group of feathers in the pyloric pouch, is to filter undigested or indigestible items from entering the intestine. Some of the gizzard bolus is probably regurgitated nightly, but the process is incomplete and undigested food can persist ...