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either of two species of shorebirds comprising the genus Chionis, family Chionididae, the only bird family confined to South Polar regions. It is named for the rough, horny sheath around the base of its bill shielding its nostrils. The sheathbill is an aggressive predator on the eggs and young of penguins, petrels, and terns; otherwise it scavenges the feces and afterbirths of seals and the offal around whaling stations. The short, stout bill has pimply skin at the base, the eyes are pink rimmed, and the short, thick legs and unwebbed feet are blue gray. The snowy sheathbill (C. alba), 40 centimetres (16 inches) long, has a yellow bill. The lesser sheathbill (C. minor) is black billed and slightly smaller. Sheathbills may be seen hundreds of miles at sea but are usually encountered along shore, in small parties. Fearless of man, they fight among themselves with their wings, which are equipped with sharp spurs. Two or three eggs are laid in a rock crevice. Usually only one chick survives.