Antarctic shag
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The Antarctic shag (''Leucocarbo bransfieldensis''), sometimes referred to as the imperial cormorant, king cormorant, imperial shag, blue-eyed shag or Antarctic cormorant, is the only species of the
cormorant Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven ge ...
family found in the
Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...
. It is sometimes considered
conspecific Biological specificity is the tendency of a characteristic such as a behavior or a biochemical variation to occur in a particular species. Biochemist Linus Pauling stated that "Biological specificity is the set of characteristics of living organ ...
with the
Imperial shag The imperial shag or imperial cormorant (''Leucocarbo atriceps'') is a black and white cormorant native to southern South America, primarily in rocky coastal regions, but locally also at large inland lakes. Some taxonomic authorities, including ...
(''Leucocarbo atriceps'').


Description

The adult Antarctic shag is about 75–77 cm tall, has a wingspan of 124 cm, and weighs 1.5-3.5 kg. When looking at individuals within this species, the most defining characteristic is the warty yellow caruncle found on the forehead. Additionally, the blue "eye", which is actually blue skin surrounding the eye, is a distinct trait that stands out. The head, wings, and outside of the thighs are black. While the underparts and central back are white. White is also found on the wing bars that line the upper wing. The bill is dark ranging from brown to yellow. As the bill hooks, the lower mandible becomes lighter. The species has naked pink webbed feet and large black claws. The wings of this species are extremely strong and are powerful in flight with continuous wingbeats disrupted by some gliding. It is estimated that flight speed can reach 50 km per hour. Juveniles are duller and browner than adults. They don't usually have the warty caruncle or white patch on their back. Males and female look very similar but can be distinguished by size. Males are larger than females in size and are also larger-billed.


Taxonomy

The Antarctic shag is part of the order
Suliformes The order Suliformes (, dubbed "Phalacrocoraciformes" by ''Christidis & Boles 2008'') is an order recognised by the International Ornithological Congress, International Ornithologist's Union. In regard to the recent evidence that the traditional ...
and the family
Phalacrocoracidae Phalacrocoracidae is a family of approximately 40 species of aquatic birds commonly known as cormorants and shags. Several different classifications of the family have been proposed, but in 2021 the IOC adopted a consensus taxonomy of seven gen ...
, which includes all cormorants and shags. Still, there are some taxonomic issues regarding the species. The Antarctic shag is usually placed in genus ''
Phalacrocorax ''Phalacrocorax'' is a genus of fish-eating birds in the cormorant family Phalacrocoracidae. Members of this genus are also known as the Old World cormorants. Taxonomy The genus ''Phalacrocorax'' was introduced by the French zoologist Mathurin ...
'' or ''
Leucocarbo ''Leucocarbo'' is a genus of birds in the family Phalacrocoracidae with the members commonly known as blue-eyed shags. This is a group of closely related cormorant taxa. Many have a blue, purple or red ring around the eye (not a blue iris); other ...
''. This species is one of the
blue-eyed shag ''Leucocarbo'' is a genus of birds in the family Phalacrocoracidae with the members commonly known as blue-eyed shags. This is a group of closely related cormorant taxa. Many have a blue, purple or red ring around the eye (not a blue iris); othe ...
s, however its position within the group is debated. Some scientists lump the Antarctic shag with other species, such as the
imperial shag The imperial shag or imperial cormorant (''Leucocarbo atriceps'') is a black and white cormorant native to southern South America, primarily in rocky coastal regions, but locally also at large inland lakes. Some taxonomic authorities, including ...
. However, the
IOC World Bird List ''Birds of the World: Recommended English Names'' is a paperback book, written by Frank Gill and Minturn Wright on behalf of the International Ornithologists' Union. The book is an attempt to produce a standardized set of English names for all b ...
and the
Clements Checklist ''The Clements Checklist of Birds of the World'' is a book by Jim Clements which presents a list of the bird species of the world. The most recent printed version is the sixth edition (2007), but has been updated yearly, the last version in 202 ...
consider the Antarctic shag to be its own species.


Habitat and Distribution

Currently, the Antarctic shag is found on the
Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...
,
South Shetland Islands The South Shetland Islands are a group of Antarctic islands with a total area of . They lie about north of the Antarctic Peninsula, and between southwest of the nearest point of the South Orkney Islands. By the Antarctic Treaty of 195 ...
, and
Elephant Island Elephant Island is an ice-covered, mountainous island off the coast of Antarctica in the outer reaches of the South Shetland Islands, in the Southern Ocean. The island is situated north-northeast of the tip of the Antarctic Peninsula, west-so ...
. The Antarctic shag is described as a marine species staying near the shores of coastal regions and some islands. Additionally, colonies are usually found near packed ice. During the breeding season, breeding colonies are found on cliffs, rocky slopes, outcrops and sometimes even flat coasts or islets. This species is sedentary and doesn't migrate. However, a single Antarctic shag was found dead in Bahia, Brazil in 2002; it had previously been ringed in the South Shetland Islands. Colonies may move short distances to find waters that aren't frozen in order to feed. This short move most likely occurs during winter months when ice starts to spread and cover the ocean where the birds feed.


Population Status

The current population of the Antarctic shag is stable, with a estimated 20,000 individuals worldwide. Currently there is no particular threat that could hurt the community or population size. It is very hard to estimate the population of species in isolated areas, such as the Antarctic. Still, recent studies using Unmanned Aerial Vehicles (UAV) have allowed scientists to estimate Antarctic shag populations by taking images of colonies. Since this data is based on images, more can also be learned about topography, habitat selection and nesting. In the future, this might allow scientists to more precisely estimate population size. In 2018, a study found that 3.5% of the global Antarctic shag population breeds in
Ryder Bay Ryder System, Inc., commonly known as Ryder, is an American transportation and logistics company. It is especially known for its fleet of commercial rental trucks. Ryder specializes in fleet management, supply chain management, and transp ...
. The study also calls for greater protections of the area.


Behavior


Reproduction

Antarctic shags are
monogamous Monogamy ( ) is a form of Dyad (sociology), dyadic Intimate relationship, relationship in which an individual has only one Significant other, partner during their lifetime. Alternately, only one partner at any one time (Monogamy#Serial monogamy, ...
and only mate with one partner each nesting season. Still, partners may change between seasons. Males attract breeding partners with a greeting display. Typically, colonies breed on low rocky cliffs near the water. Sometimes, breeding colonies are shared with other
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
species such as the
rock shag The rock shag (''Leucocarbo magellanicus''), also known as the Magellanic cormorant, is a marine cormorant found around the southernmost coasts of South America. Its breeding range is from around Valdivia, Chile, south to Cape Horn and Tierra de ...
,
southern rockhopper penguin The southern rockhopper penguin group (''Eudyptes chrysocome''), is a species of rockhopper penguin, that is sometimes considered distinct from the northern rockhopper penguin. It occurs in subantarctic waters of the western Pacific and Indian O ...
, and
black-browed albatross The black-browed albatross (''Thalassarche melanophris''), also known as the black-browed mollymawk,Robertson, C. J. R. (2003) is a large seabird of the albatross family Diomedeidae; it is the most widespread and common member of its family. ...
es. This species usually forms smaller colonies of 20-40 pairs, but larger colonies of up to 800 pairs have been observed. Both genders build a nest from feathers, seaweed, and ocean debris. Materials are then connected with excreta, which is waste material, such as feces and urine. Shag mating pairs often steal nesting material from other couples. The final nest shape looks like a cone with the tip cut off, similar to a volcano. Nests are sometimes reused between years as many individuals return to the same breeding site. Antarctic shags lay their eggs between October and December. The female lays 2 or 3 eggs on average; but up to 5 eggs have been observed. Both parents help incubate the eggs for 28–31 days. Chicks hatch without a protective down making them vulnerable to the Antarctic conditions. Due to this lack of protection, parents must keep their chicks warm for the first few weeks. The naked chicks are fed by their parents for about 3 weeks with the male partner providing most of the food. After about 3 weeks, the chicks start to fledge. By age 4, the offspring will have reached sexual maturity. The Antarctic shag has an estimated life expectancy of 15–20 years in the wild. Breeding success can be directly affected by food availability and diving conditions.


Diet

The most common way to study the Antarctic shag's diet is by analyzing its pellets. Their pellets are often composed of bones, fur and feathers. Antarctic shags usually forage alone or in small groups. Most of the Antarctic shag's diet is composed of
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, but can also include
crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...
s,
octopus An octopus ( : octopuses or octopodes, see below for variants) is a soft-bodied, eight- limbed mollusc of the order Octopoda (, ). The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttle ...
es,
snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
s,
worm Worms are many different distantly related bilateral animals that typically have a long cylindrical tube-like body, no limbs, and no eyes (though not always). Worms vary in size from microscopic to over in length for marine polychaete wor ...
s,
slug Slug, or land slug, is a common name for any apparently shell-less terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced shell, or only a smal ...
s and other invertebrates. The fish diet is mostly composed of humphead notothen (''Gobionotothen gibberifrons''), gaudy notothen (''Lepidonotothen nudifrons''), bullhead notothen (''Notothenia coriiceps''), and Antarctic spiny plunderfish (''Harpagifer antarcticus''). Typically, the females consume more invertebrates while the males consume more fish. This difference in diet is most likely due to the difference in size of each gender.


Role in the food web

Antarctic shags are rarely prey for other species. There have been a few documented cases, including
leopard seal The leopard seal (''Hydrurga leptonyx''), also referred to as the sea leopard, is the second largest species of seal in the Antarctic (after the southern elephant seal). Its only natural predator is the orca. It feeds on a wide range of prey incl ...
s and
brown skua The brown skua (''Stercorarius antarcticus''), also known as the Antarctic skua, subantarctic skua, southern great skua, southern skua, or hākoakoa (Māori), is a large seabird that breeds in the subantarctic and Antarctic zones and moves furth ...
s killing Antarctic shags. However, other
bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
species prey on their eggs and chicks as well. Unlike other birds, the Antarctic shag consumes
demersal fish Demersal fish, also known as groundfish, live and feed on or near the bottom of seas or lakes (the demersal zone).Walrond Carl . "Coastal fish - Fish of the open sea floor"Te Ara - the Encyclopedia of New Zealand. Updated 2 March 2009 They occ ...
. In fact, this species can reach extreme depths when diving for their food. Since demersal fish are found on the ocean floor, these fish feed on other benthic species. Thus, the Antarctic shag links the benthic and pelagic zones of the food web. Despite linking these two areas of the ocean, the Antarctic shag has a limited population. Therefore, the amount of demersal species consumed doesn't impact the entire ecosystem.


Diving

On average, the Antarctic shag dives 25 meters to feed on fish. Their maximum dive depth is around 60 meters. The number of dives and depth of each dive is related to foraging conditions. They most likely ingest smaller fish and invertebrates while underwater. In contrast, larger fish, 15 cm or longer, are brought to land to eat. Shags can't predict how much time is required to dive and capture prey. Once underwater, the bird looks for prey, and reacts based on the situation. If a fish is found but the shag doesn't have enough oxygen, it will come back up to the surface, take in the largest amount of air possible, and dive again to capture the prey. This shows that the Antarctic shag changes its diving strategy based on the situation. Many birds can't fly with wet feathers and diving in the water can cause feathers to become waterlogged (fully saturated). Often, you see waterbirds standing with their wings spread to dry off their feathers after diving. Antarctic shags are unique in this respect and due to their dense inner plumage, this species doesn't need to dry off via wing-spreading like other diving bird species. These dense feathers close to the skin also prevent icy waters from hitting the skin. Additionally, birds having to spread their wings to dry could have further reduced their body temperature in an already extremely harsh climate. Therefore, both the cold water and cold air could have caused this species to develop over time.


Vocalization

Shags are known to be quiet but often vocalize at breeding sites or when vulnerable. When threatened, the male makes a "aaark" call while the female will make a hissing call. In contrast, during breeding, males makes a "honk" call.


References


External links

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Images
{{Taxonbar, from=Q1264549 Leucocarbo Birds described in 1936 Taxa named by Robert Cushman Murphy