South Georgia Shag Leucocarbo georgianus Scientific name definitions

c. 75 cm (calculated); 2883 g. Has crest on crown ; cap to just above gape and upperparts including outer sides of thighs black with blue gloss, or more bronzy green on scapulars and upperwing, can have some hair-like white filoplumes on head and upperparts, usually has white bar formed by variable number of lesser wing-coverts and can have white patch on central back; underwing blackish, but greater coverts and remiges have grey-brown sheen, and variable amount of white at base of leading edge; tail duller blackish with whitish shafts at base; white on throat and head-sides from just above gape over most of ear-coverts, most of neck-sides, entire breast and rest of underparts ; crest much reduced or lost as breeding season progresses, white filoplumes also lost and worn plumage is less glossy. Iris dark brown; very prominent buffy-yellow to orange-yellow warty caruncles on sides of forehead, blackish bare skin from lores to gape and on gular pouch, eyering blue , greyer bluish in non-breeding season ; bill blackish grey, often with variable horn-brown tinge at sides, especially paler tip to mandible; legs pink . Sexes similar, but male heavier and larger-billed. Juvenile lacks or or has just hint of crest, dull brown with slight greenish sheen instead of black, white on sides of head more restricted and sometimes does not reach ear-coverts, lacks white on central back, wing-coverts pointed and have paler brownish tips (most obvious on greater coverts), fringes whiter and complete on many lesser coverts, no caruncles, eyering and bare facial skin initially dull brownish rather than blackish, base of bill and skin below gape pale; subsequent immature plumages intermediate, with new blacker feathers admixed. Very like other “blue-eyed” pied shags, from which should be carefully separated using overall size, amount of black on head-sides, white markings on upperparts, bill length and often subtle variation in caruncles and colour of bare facial skin; in present species, amount of black on head-sides is roughly intermediate between that of larger-billed P. atriceps atriceps and P. a. albiventer; most similar to near-identical P. bransfieldensis and some birds have identical pattern on head-sides, but bill typically smaller, while georgianus often has slightly more black on anterior ear-coverts thus division between black and white on head-sides is more diagonal than horizontal. Also very like P. purpurascens, but relatively small bill again useful, facial skin below gape blacker, the legs typically brighter pink, while pattern on head-sides can be very similar but in present species ear-coverts tend to be mostly white or usually 50% white, whereas in purpurascens they are usually mostly dark because the black starts at gape or just below it and runs backwards in a straight line. P. melanogenis and P. verrucosus have largely black head-sides, and latter also has yellower skin below gape and often even more prominent caruncles.

Species sometimes placed in genus Notocarbo or Leucocarbo. Often treated as conspecific with P. atriceps, P. bransfieldensis and P. nivalis, and sometimes also including P. melanogenis, P. verrucosus and P. purpurascens; South Orkney and South Sandwich populations of present species frequently ascribed to P. bransfieldensis. Monotypic.

South Georgia, South Orkney Is, South Sandwich Is and Shag Rocks (Scotia Sea).

Marine; inshore feeder. Breeds on islets and rocky zones, including ledges and terraces of sea cliffs and stacks; also on flat or gently sloping ground, sometimes covered in tussock grass.

Benthic prey, mainly fish (Nototheniidae), up to 27 cm long. Feeds mainly by pursuit-diving. Generally feeds alone or in small flocks. Analyses of stable isotope ratios in blood and feathers have been used to infer trophic and habitat specializations in this species. Males forage at a higher trophic level than females and sex-related dietary differences persist for long periods. It is suggested that the trophic differences are driven by differences in physiological performance, with males tending to dive deeper than females because of their larger size, and hence able to access higher trophic-level prey. The sexes tend to forage at different times of day. Analyses revealed highly significant relationships between stable isotope signatures in blood (representing breeding season diet) and those in feathers (mostly representing previous non-breeding season diet) in both this species and P. verrucosus. This strongly suggests individuals have distinct foraging specializations (and most probably foraging locations) that are maintained over long periods (1 Bearhop, S., Phillips, R. A., McGill, R., Chere, Y., Dawson, D. A. and Croxhall, J. P. (2006). Stable isotopes indicate sex-specific and long-term individual foraging specialisation in diving seabirds. Marine Ecology Progress Series. 311: 157–164. Close ).

Male gives barking and moaning calls, female hisses; voice very like that of P. bransfieldensis.

Season short; laying Oct–Dec. Generally forms small colonies, but sometimes hundreds of pairs and sometimes very dense. Nest a truncated cone of seaweed, grass, mud and excreta, or sometimes consisting almost entirely of penguin tail feathers, placed on ground, even on snow; nest-site often reused, but partners usually different, perhaps normally as result of one bird dying. Clutch 2–3 eggs; incubation period 27–31 days; chick naked, grows dark grey down; fledging period c. 56–65 days. Hatching success 85–91%; both hatching and fledging success lower with later laying. Sexual maturity at three years of age. Known to have lived to at least 12 years old.

Not globally threatened. Total population of c. 7500 pairs, including almost 4000 at South Georgia, c. 2000 in South Orkney Is (including 830 on Signy I), 1000 at Shag Rocks and 100–1000 in South Sandwich Is. Surveys of ice-free areas of Laurie I (in South Orkneys) revealed total of 668 breeding pairs in seven colonies in Dec 1994, nests concentrated on rocky islets, mostly off N & W coasts, with largest at Pirie Peninsula, Wilton Bay and Watson Peninsula; counts in 2005–2006 indicated that a decline had occurred, with 80 occupied nests on W coast (31% decrease) and 85 on E coast (26% down) of Pirie Peninsula, while 181 at Cape Davidson in 2003–2004 also represented a reduction (of 16%) (2 Coria, N. R., D. Montalti, E. F. Rombola, M. M. Santos, M. I. Garcia Betoño, and M. A. Juares (2011). Birds at Laurie Island, South Orkney Islands, Antarctica: breeding species and their distribution. Marine Ornithology 39(2):207–213. Close ). Frequently taken for food in the past as it habitually flew very close over whaling ships, where easily knocked down. Not subject to any particular threats at present.