Imperial cormorant, King cormorant, Imperial shag, Blue-eyed shag, Antarctic cormorant
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 family found in the Antarctic. It is sometimes considered conspecific with the Imperial shag (Leucocarbo atriceps ).
Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
Gliding flight is heavier-than-air flight without the use of thrust and is employed by gliding animals. Birds in particular use gliding flight to m...
Monogamy is a form of relationship in which both the male and the female has only one partner. This pair may cohabitate in an area or territory for...
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starts withThe 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.
Currently, the Antarctic shag is found on the Antarctic Peninsula, South Shetland Islands, and Elephant Island.
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.
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, but can also include crustaceans, octopuses, snails, worms, slugs 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.
Antarctic shags are monogamous 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 species such as the rock shag, southern rockhopper penguin, and black-browed albatrosses. 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.
