Southern giant petrel

Macronectes giganteus is a seabird of the family Procellariidae described by Gmelin in 1789 ^[1]. It is known in Peru as «petrel gigante sureño» ^[2]. It is one of the two giant petrels, the only species in their genus ^[3], and together with the northern giant petrel it ranks among the main scavengers of the Southern Ocean; it breeds right around the Southern Ocean, with colonies reaching north to the Falkland Islands, Isla Noir in Chile and Chubut in Argentina ^[4]. The IUCN Red List classifies it as Least Concern in its 2018 assessment ^[5], and Peru's official list of threatened wildlife, approved in 2014, places it in the Near Threatened category ^[2].

It is a large petrel, the size of a small albatross ^[6]. It has two plumage phases: in the white phase the bird is entirely white apart from a few black feathers scattered at random, and in the dark phase the colour runs from uniform blackish brown to greyish brown with a greyish-white head, neck and upper breast; 3 authors writing between 1936 and 1962 held that the head and neck of dark birds grow paler with age ^[7]. In 208 families studied on Macquarie Island in the 1967-1968 season, and setting aside 2 anomalous families, the inheritance of the two phases fitted a single pair of autosomal genes with white dominant over dark ^[7].

The horny plate at the bill tip, called the nail or unguis, is pale green ^[3] and at a distance does not usually contrast with the rest of the bill ^[8]. Males have a larger and deeper bill than females, a difference used to sex breeding adults ^[3].

Similar species

• Macronectes halli: The northern giant petrel has a dark red bill nail at every age, against the pale green of Macronectes giganteus, and has no white phase, which exists only in Macronectes giganteus ^[3],[8].

It breeds right around the Southern Ocean and is most abundant at high latitudes, although it has colonies as far north as the Falkland Islands, Isla Noir (Chile) and Chubut Province (Argentina) ^[4]. It breeds both further north and further south than the northern giant petrel, and is more widespread than that species in the South Atlantic ^[3].

In Chile the best-known colony is on Isla Noir (54° 30′ S), in Magallanes, where counts from 2003 to 2013 added up to about 1756 breeding pairs; the author concludes that the figure of 290 pairs given in 2008 for all of Chile underestimated the population about 6 times ^[6]. Along the channels and fjords between Puerto Montt and Cape Horn, from October to April between 2001 and 2016, nobody saw or photographed the northern giant petrel there, only this species ^[6].

At sea it ranges from Antarctic to temperate waters and, in the Pacific Ocean, goes well into tropical latitudes ^[6]. In ship-based surveys made between 1980 and 1995 off Peru and Chile, between 3° S and 50° S and up to 370 km from the coast, 106 individuals were logged, treated as migrants that breed in the southern hemisphere ^[9].

Young birds disperse very far. Of 7503 chicks banded in Antarctica by the Brazilian Antarctic programme between the 1983-1984 and 1992-1993 seasons, 68 were recovered outside Antarctica, at a mean distance of 8030 km from their colony, mostly in Australia (57.3 %) and South America (17.6 %) ^[10].

It lays a single egg a year, and on average about 30 % of the adults that could breed do not do so in a given season ^[4]. It can breed for the first time at 4 years old, but normally starts between 6 and 10 years of age ^[10].

The northern giant petrel lays about 6 weeks earlier than this species ^[3], and that difference in timing, together with breeding behaviour, is what mainly keeps the two species apart where they breed on the same islands ^[4]. Even so, mixed pairs and hybrids have been documented on Bird Island, South Georgia, along with a hybrid male that bred with a female northern giant petrel ^[3].

In the Chilean fjord region laying begins in late October or November and continues through December, and hatching and chick-rearing run from late January to May ^[6]. On Isla Noir the nests were concentrated on the highest ground, and the area with most empty nests bordered territories of caracaras and skuas, both known predators of giant petrel eggs and chicks; in 2013 a pair of caracaras was seen distracting an incubating petrel while the other bird pushed the egg out of the nest ^[6].

Chick regurgitations were analysed at colonies in northern Argentine Patagonia: almost all of them (90.8 %) held carrion of penguins, sea lions and birds; 65.1 %, cephalopods; 43.7 %, crustaceans; and 19.4 %, fish ^[11]. Penguins were the most frequent food in all 4 seasons studied (over 74 %) and 72.7 % of samples held items of human origin; to the authors, finding species that vessels catch or throw back, along with so much marine litter, suggests that these birds feed heavily on discards over the Patagonian Shelf ^[11].

It hunts as well as scavenges, mainly penguins in the Magallanes region: on Isla Noir in 2010, about 20 petrels were seen swimming as one of them caught a penguin, of which nothing was left within a few minutes because all of them joined the feast ^[6].

It also dives. In Antarctica, 10 adults were filmed making 113 dives onto a Weddell seal carcass sunk in about 3 m of water; successful dives lasted on average 4.48 seconds, between 3 and 7, and the authors think the birds found the carcass again by smell, guided by the film of grease floating above it ^[12].

Carrion is an important food at some localities and seasons, and in some places giant petrels are also significant predators on land ^[4]. On Heard Island, a 43 % drop in this species' fledgling production was put down in part to a 60 % fall in the pup production of southern elephant seals ^[4].

Its global category is Least Concern ^[5]. In Peru it is classified as Near Threatened on the official list of threatened wildlife species ^[2]. It has also been listed in Appendix II of the Bonn Convention on migratory species (CMS) since 1999 ^[13].

A worldwide compilation of censuses up to the 1999-2000 season estimated 30575 breeding pairs, almost 20 % fewer than the estimate of 38000 pairs published in 1985, with marked declines on Heard, Macquarie, Marion, King George, Penguin and Signy islands and increases at other localities ^[4]. A later estimate, cited in 2015, puts the world population at 50170 breeding pairs ^[3].

It is very sensitive to human disturbance: its colonies have declined near research stations, and some pairs move to breed elsewhere, where often only part of them arrive ^[4]. It follows ships more than the northern giant petrel does, which may expose it more to commercial fishing; according to band recoveries, around 10 % of the reported fledgling mortality of giant petrels came directly from interactions with fisheries, and near Palmer Station, on the Antarctic Peninsula, hooks found beside nests or embedded in adults rose sharply over 10 years ^[4].

In Peruvian waters, the IMARPE observer programme on board the artisanal jumbo squid fishery of the south of the country, between 2015 and 2017, saw a single bird of this species and no catches of giant petrels; the only bird hooked in 16 trips was an albatross, which was released ^[14].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In 25 adults from a colony in Chubut, Argentina, sampled in the 1999-2000 and 2000-2001 seasons, no antibodies were found against avian influenza virus or several other avian viruses tested, but they were found against avian adenovirus, in 14 % of birds in the first season and in 60 % in the second ^[15].

A Macronectes giganteus sample taken in the South Shetland Islands during the 2024-2025 austral summer yielded the full genome of a highly pathogenic H5N1 avian influenza virus of clade 2.3.4.4b, a close relative of the viruses then circulating in South America ^[16]. On Bird Island, South Georgia, a bird showing loss of coordination, twitching and lethargy was found on 17 September 2023, shortly before the virus was confirmed in dead skuas on the same island ^[17].

At Paloma, a preceramic village in the Chilca Valley on Peru's central coast, occupied between 7800 and 4700 years before present according to uncorrected radiocarbon dates, the animal remains include a giant petrel of this species, which the author takes, together with guanacos and deer, as a sign that the village was also lived in during the austral winter ^[18].

Outside Peru, on Tristan da Cunha, where this species no longer breeds, giant petrel eggs and chicks were taken for subsistence, causing steep declines and local extinctions, and in the Falklands many eggs were collected in the early 1950s for their reputation of fine flavour; there, giant petrels were also killed because they attacked sheep stuck on their backs ^[4].

The IMARPE observer programme in the artisanal jumbo squid fishery sailing from Lomas, Atico, La Planchada, Quilca and Matarani between October 2015 and April 2017 recorded a single bird among 300 albatrosses and petrels of 11 species, over the continental slope and not over the shelf; 4 northern giant petrels were seen on the same trips, so the colour of the bill tip is worth checking ^[14],[8].