Sheathbill
Encyclopedia
The sheathbills are a family
of bird
s, Chionidae. Classified in the wader order Charadriiformes
, the family contains one genus, Chionis, with only two species. They breed on subantarctic
islands and the Antarctic Peninsula
, and the Snowy Sheathbill
migrates 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. They are also the only Antarctic birds without webbed feet.
including a thick layer of down, with only the face and leg colours distinguishing the two species. They look plump and dove
-like, but are believed to be similar to the ancestors of the modern gull
s and tern
s. There is a rudimentary spur on the "wrist" (carpal) joint, as in plover
s. The skin around the eye is bare, as is the skin above the bill, which has carbuncular swellings. They derive their English
name from the horny sheath which partially covers the upper mandible of their stout bills.
s from cormorant
s or penguin
s.
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 cleaning themselves.
They lay 2 or 3 blotchy white eggs in crevices or rock cavities. The nests are lined messily with seaweed, stones, feathers, guano, bones, and occasionally plastic trash; even dead chicks may not be removed. Incubation lasts 28 to 32 days, and the young fledge 50 to 60 days later.
(Pluvianellus socialis) of southern South America has indicated it too may be classified within the sheathbill family.
The two species are the Snowy Sheathbill
(Chionis albus) and the Black-faced Sheathbill
(C. minor).
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, Chionidae. Classified in the wader order Charadriiformes
Charadriiformes
Charadriiformes is a diverse order of small to medium-large birds. It includes about 350 species and has members in all parts of the world. Most Charadriiformes live near water and eat invertebrates or other small animals; however, some are pelagic , some occupy deserts and a few are found in thick...
, the family contains one genus, Chionis, with only two species. They breed on subantarctic
Subantarctic
The Subantarctic is a region in the southern hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° – 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Indian Ocean, Atlantic Ocean and...
islands and the Antarctic Peninsula
Antarctic Peninsula
The Antarctic Peninsula is the northernmost part of the mainland of Antarctica. It extends from a line between Cape Adams and a point on the mainland south of Eklund Islands....
, and the Snowy Sheathbill
Snowy Sheathbill
The Snowy Sheathbill also known as a Pale-faced sheathbill or Paddy is one of two species of sheathbill. It is usually found on the ground. It is Antarctica's only permanently land-based bird.- Description :...
migrates to the Falkland Islands
Falkland Islands
The Falkland Islands are an archipelago in the South Atlantic Ocean, located about from the coast of mainland South America. The archipelago consists of East Falkland, West Falkland and 776 lesser islands. The capital, Stanley, is on East Falkland...
and coastal southern South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
in the southern winter; they are the only bird family endemic
Endemism in birds
An endemic bird area is a region of the world that contains two or more restricted-range species, while a "secondary area" contains one or more restricted-range species. Both terms were devised by Birdlife International....
as breeders to the Antarctic region. They are also the only Antarctic birds without webbed feet.
Description
They have white plumageFeather
Feathers are one of the epidermal growths that form the distinctive outer covering, or plumage, on birds and some non-avian theropod dinosaurs. They are considered the most complex integumentary structures found in vertebrates, and indeed a premier example of a complex evolutionary novelty. They...
including a thick layer of down, with only the face and leg colours distinguishing the two species. They look plump and dove
Dove
Pigeons and doves constitute the bird family Columbidae within the order Columbiformes, which include some 300 species of near passerines. In general terms "dove" and "pigeon" are used somewhat interchangeably...
-like, but are believed to be similar to the ancestors of the modern gull
Gull
Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s and tern
Tern
Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...
s. There is a rudimentary spur on the "wrist" (carpal) joint, as in plover
Plover
Plovers are a widely distributed group of wading birds belonging to the subfamily Charadriinae. There are about 40 species in the subfamily, most of them called "plover" or "dotterel". The closely related lapwing subfamily, Vanellinae, comprises another 20-odd species.Plovers are found throughout...
s. The skin around the eye is bare, as is the skin above the bill, which has carbuncular swellings. They derive their English
English language
English is a West Germanic language that arose in the Anglo-Saxon kingdoms of England and spread into what was to become south-east Scotland under the influence of the Anglian medieval kingdom of Northumbria...
name from the horny sheath which partially covers the upper mandible of their stout bills.
Behaviour
They habitually walk on the ground, somewhat like rails. They fly only when alarmed or in migration, looking like pigeons.Food and feeding
The sheathbills are opportunistic feeders, consuming invertebrates, faeces, and carrion—including seal afterbirths and stillborn seal pups—between the tidelines. They will take chicks and eggEgg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
s from cormorant
Cormorant
The bird family Phalacrocoracidae is represented by some 40 species of cormorants and shags. Several different classifications of the family have been proposed recently, and the number of genera is disputed.- Names :...
s or penguin
Penguin
Penguins are a group of aquatic, flightless birds living almost exclusively in the southern hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have countershaded dark and white plumage, and their wings have become flippers...
s.
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. Two mated sheathbills often work together to harass adult penguins, nimbly avoiding their attempts to peck; they gain access to the eggs or chicks or stealKleptoparasitism
Kleptoparasitism or cleptoparasitism is a form of feeding in which one animal takes prey or other food from another that has caught, collected, or otherwise prepared the food, including stored food...
the krill
Krill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
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 cleaning themselves.
They lay 2 or 3 blotchy white eggs in crevices or rock cavities. The nests are lined messily with seaweed, stones, feathers, guano, bones, and occasionally plastic trash; even dead chicks may not be removed. Incubation lasts 28 to 32 days, and the young fledge 50 to 60 days later.
Taxonomy
Genetic studies of the order Charadriiformes show the sheathbills to be a sister group of the thicknees of the family Burhinidae. These two groups together are a sister group to Recurvostridae-Haematopodidae and Charadriidae. Recent research on the Magellanic PloverMagellanic Plover
The Magellanic Plover is a rare and unique wader found only in southernmost South America. It was long placed in with the other plovers in the family Charadriidae, however behavioural evidence suggested they were distinct, and molecular studies confirmed this, suggesting that they are actually...
(Pluvianellus socialis) of southern South America has indicated it too may be classified within the sheathbill family.
The two species are the Snowy Sheathbill
Snowy Sheathbill
The Snowy Sheathbill also known as a Pale-faced sheathbill or Paddy is one of two species of sheathbill. It is usually found on the ground. It is Antarctica's only permanently land-based bird.- Description :...
(Chionis albus) and the Black-faced Sheathbill
Black-faced Sheathbill
The Black-faced Sheathbill , also known as the Lesser Sheathbill or Paddy bird, is one of only two species of sheathbills, aberrant shorebirds which are terrestrial scavengers of subantarctic islands.-Description:...
(C. minor).
External links
- Sheathbill videos on the Internet Bird Collection
- Sheathbill sounds on xeno-canto.org