The Kerguelen shag (''Leucocarbo verrucosus'') is a species of cormorant

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to the Kerguelen Islands in the southern Indian Ocean, one of the most isolated places on Earth. Many authorities consider it a subspecies of 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 ...

Range and habitat

This species

nests A nest is a structure built for certain animals to hold eggs or young. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic materi ...

on the coast of Grande Terre (the main island of the archipelago), on offshore islands, and on islands in the Golfe du Morbihan. It forages at sea throughout the archipelago, usually within of shore and especially in bays and inlets, though immatures have been seen rarely as far as . Reports from

Heard Island The Territory of Heard Island and McDonald Islands (HIMI) is an Australian external territory comprising a volcanic group of mostly barren Antarctic islands, about two-thirds of the way from Madagascar to Antarctica. The group's overall size ...

and western Australia may be of ship-assisted birds. In the austral summer it feeds among

kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwa ...

, sometimes at the bottom.

Description

The Kerguelen shag is long with a wingspan of , making it the smallest

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 ...

. The adult's upperparts, tail, and thighs are metallic greenish black; the underbody to the throat is white; and the wing linings are brown. Some individuals have white patches on the back and wings. The head and the back of the neck are deep blue or purple, except that a black cap reaches below the eye to the chin and ear coverts. The face and throat pouch are dark brown, ornamented with yellow-orange tubercles. The bill is horn-colored or brown; the eyes are hazel. The legs and feet vary from dark brown to dark-blotched bright pink. Breeding adults have a little black erectile crest on the forehead, yellow or orange caruncles (large warts) above the base of the bill, and a bright blue ring around the eye. After the breeding season, the plumage fades, the eye-ring becomes lead-blue, and the caruncles become smaller and duller-colored. Juveniles are dark brown with varying amounts of white underneath and brown iris, bill, and feet. They have no caruncles, and their eye-rings are lead-blue. They acquire adult plumage gradually. Unlike many cormorants, this species does not spread its wings when it is perched.

Feeding

Kerguelen shags presumably eat mostly fish and such invertebrates as

echinoderm An echinoderm () is any member of the phylum Echinodermata (). The adults are recognisable by their (usually five-point) radial symmetry, and include starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers, as well as the s ...

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 can ...

s, and

polychaete Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made ...

worms. In summer they mostly forage alone, but from May to October they form linear flocks of several hundred, diving and surfacing sequentially down the line.

Reproduction

This species breeds in colonies, usually of 3 to 30 pairs but occasionally up to 400. Colonies may be near those of

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 ...

s. There is a period of nest-building and displaying in late March and early April—an unusual time for a subantarctic cormorant. Advertising males display by throwing the head back till the nape touches the tail. Nests are cones of seaweed, twigs, and grass held together with mud and guano, up to 1 meter tall and 33 cm across, with a cup averaging 20 cm across and 8 cm deep. Nests that survive may be reused, perhaps not by the same pair. Breeding activity starts as early as September, but laying usually starts at some point from late October to late November and lasts till mid January; the times vary considerably among colonies. The clutch comprises two to four eggs, about 6.2 cm long and 3.9 cm wide. The second egg is laid 2 or 3 days after the first. Both parents incubate for an average of 29 days. Both protect the chicks from predation by

skua The skuas are a group of predatory seabirds with seven species forming the genus ''Stercorarius'', the only genus in the family Stercorariidae. The three smaller skuas, the long-tailed skua, the Arctic skua, and the pomarine skua are called ...

gull Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. They are most closely related to the terns and skimmers and only distantly related to auks, and even more distantly to waders. Until the 21st century ...

s, and

sheathbill The sheathbills are a family of birds, Chionidae. Classified in the wader order Charadriiformes, the family consists of one genus, ''Chionis'' with two species. They breed on subantarctic islands and the Antarctic Peninsula, and the snowy sheath ...

s, which nevertheless take some chicks. Chicks hatch black with a pink throat and develop blackish-brown down with greyish-white tufts. Other aspects of reproductive behavior and success are unknown. The population was about 6,000 to 7,000 pairs in 1984–1987. Interactions with human beings and introduced mammals do not appear to be damaging the population.

Classification

This species has been placed in genera ''Halieus'', ''Hypoleucos'', ''Notocarbo'', and ''Leucocarbo''. Others place it in the genus Phalacrocorax. It has been considered conspecific with some other blue-eyed shags under the name

. Here it is considered a separate species following the '' Handbook of the Birds of the World'' and other authorities It has been suggested that Heard shags may visit the Kerguelens and that Kerguelen shags with white wing or back patches are the result of hybridization.

Etymology

The epithet ''verrucosus'' means "full of warts", referring to the facial ornaments.

References

{{Taxonbar, from=Q1269577 Kerguelen shag Birds of the Indian Ocean Birds of subantarctic islands Fauna of the Kerguelen Islands Kerguelen shag