The sheathbills ( Chionis) is a genus of in the Monotypic taxon family Chionidae of the wader order Charadriiformes; the family consists of one genus with two species. They breed on subantarctic islands and the Antarctic Peninsula, and the snowy sheathbill Bird migration to the Falkland Islands and coastal southern South America in the southern winter; they are the only bird family endemic as breeders to the Antarctic region.
Taxonomy
The genus
Chionis was introduced in 1788 by the German naturalist Johann Reinhold Forster.
The
type species is the
snowy sheathbill,
Chionis albus.
The genus name is from the
Ancient Greek meaning snow.
Genetic studies of the order Charadriiformes show the sheathbills to be a sister group of the thick-knees of the family Burhinidae. These two groups together are in turn a sister group to the Recurvirostridae-Haematopodidae and Charadriidae.[Christidis and Boles, p. 128] Recent research on the Magellanic plover ( Pluvianellus socialis) of southern South America has indicated it too may be classified within the sheathbill family.[Christidis and Boles, p. 132]
Description
Sheathbills have white
plumage including a thick layer of
down feather, with only the face and leg colours distinguishing the two species. They appear plump and
dove-like, but are believed to be similar to the ancestors of the modern
and
. There is a rudimentary spur on the "wrist" or carpal joint, as in
. The skin around the eye is bare, as is the skin above the bill, which has swellings. They derive their
English language common name from the
Keratin (
rhamphotheca) which partially covers the upper mandible of their stout bills.
[ They are commonly known in the Antarctic as "Mutts" because of Bird call which is a soft "Mutt, mutt, mutt".
]
The two species are:
Behaviour
Sheathbills habitually walk on the ground, somewhat like rails. They fly only when alarmed or in migration, looking like .[
]
Food and feeding
The sheathbills are and opportunistic feeders, consuming invertebrates, faeces, and carrion—including the afterbirth of seals and their stillborn pups—between the tidelines. They also take chicks and eggs from and .
The bird has also been observed to directly pilfer milk from the teats of elephant seals.
Breeding
During the penguin breeding season, which is also the sheathbill breeding season, pairs of sheathbills in penguin colonies maintain territories covering a number of penguin nests. Breeding pair sheathbills often work together to harass adult penguins, nimbly avoiding their attempts to peck; they gain access to the eggs or chicks or kleptoparasitism the krill that the adult penguins regurgitate to feed their chicks. Near the few human settlements of the region, they boldly forage for offal. Because of this diet, they spend a good deal of time Self-grooming.[
]
They lay two or three blotchy white eggs in crevices or rock cavities.[
]
External links
