| Sheathbills | |
|---|---|
 | |
| Snowy sheathbill (C. albus) | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Charadriiformes |
| Suborder: | Charadrii |
| Family: | Chionidae Bonaparte, 1832 |
| Genus: | Chionis J.R. Forster, 1788[1] |
| Type species | |
| Vaginalis alba Gmelin, JF, 1789 | |
| Species | |
Thesheathbills are afamily ofbirds,Chionidae. Classified in the wader orderCharadriiformes, the family consists of one genus,Chionis with two species. They breed onsubantarctic islands and theAntarctic Peninsula, and thesnowy sheathbillmigrates to theFalkland Islands and coastal southernSouth America in the southern winter; they are the only bird familyendemic as breeders to the Antarctic region.[2] They are also the only Antarctic birds withoutwebbed feet.
Sheathbills have whiteplumage including a thick layer ofdown, with only the face and leg colours distinguishing the two species. They appear plump anddove-like, but are believed to be similar to the ancestors of the moderngulls andterns.[citation needed] There is a rudimentaryspur on the "wrist" orcarpal joint, as inplovers. The skin around the eye is bare, as is the skin above the bill, which hascarbuncular swellings. They derive theirEnglish name from thehorny sheath which partially covers the upper mandible of their stout bills.[2] They are commonly known in the Antarctic as "Mutts" because of theircall which is a soft "Mutt, mutt, mutt".[citation needed]
The genusChionis was introduced in 1788 by the German naturalistJohann Reinhold Forster.[3] Thetype species is thesnowy sheathbill,Chionis albus.[4] The genus name is from theAncient Greekkhiōn meaning snow.[5]
Genetic studies of the order Charadriiformes show the sheathbills to be asister group of the thick-knees of the familyBurhinidae. These two groups together are in turn a sister group to theRecurvirostridae-Haematopodidae andCharadriidae.[6] Recent research on theMagellanic plover (Pluvianellus socialis) of southern South America has indicated it too may be classified within the sheathbill family.[7][8][9]
The two species are:
| Common name | Scientific name and subspecies | Range | Size and ecology | IUCN status and estimated population |
|---|---|---|---|---|
| snowy sheathbill
| Chionis albus (Gmelin, JF, 1789) | Antarctica, theScotia Arc, theSouth Orkneys, andSouth Georgia | Size: Habitat: Diet: | LC |
| black-faced sheathbill
| Chionis minor Hartlaub, 1841 | South African territory of thePrince Edward Islands, the French territories of theCrozet Islands andKerguelen Islands, and the Australian territory ofHeard Island. | Size: Habitat: Diet: | LC |
Sheathbills habitually walk on the ground, somewhat likerails. They fly only when alarmed or in migration, looking likepigeons.[2]
The sheathbills arescavengers and opportunistic feeders, consuming invertebrates,faeces, and carrion—including sealafterbirth andstillbornseal pups—between the tidelines. They also take chicks andeggs frompenguins andcormorants.[citation needed]
The bird has also been observed to directly pilfer milk from theelephant seals’ teats.[10][11][12]
During the penguinbreeding season, which is also the sheathbill breeding season, pairs of sheathbills in penguin colonies maintainterritories covering a number of penguin nests.Two mated sheathbills often work together to harass adult penguins, nimbly avoiding their attempts to peck; they gain access to the eggs or chicks orsteal thekrill that the adult penguins regurgitate to feed their chicks. Near the few human settlements of the region, they boldly forage foroffal. Because of this diet, they spend a good deal of timecleaning themselves.[2]
They lay two or three blotchy white eggs in crevices or rock cavities.[13] Thenests are lined messily withseaweed, stones, feathers,guano, bones, and occasionallyplastic trash; even dead chicks may not be removed.Incubation lasts 28 to 32 days, and the young fledge 50 to 60 days later.[2]
Genera ofshorebirds and their extinct allies | |||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| |||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||
| |||||||||||||||||||||||||||||||||||||||||||||
_svg-element.svg)
