The southern giant petrel (Macronectes giganteus) is a formidable seabird with a powerful presence across the Southern Ocean’s vast, cold waters. Its role in the ecosystem has earned it nicknames like “stinker” and “glutton,” hinting at its unique survival strategies.
Identification and Appearance
The southern giant petrel is a large seabird, recognized by its size and a massive, pale, horn-colored bill with a greenish tip. This bill is topped with a prominent nasal tube, a characteristic of petrels, which functions to excrete excess salt absorbed from their marine diet. This physiological adaptation allows them to thrive in a saltwater environment.
Two distinct color morphs exist within the species. The most common is a dark morph, appearing as a mottled grey-brown with a lighter head, neck, and upper breast in older birds. A much rarer light morph is almost entirely white with only a few black speckles. Younger birds of the dark morph are a uniform sooty blackish-brown and become paler as they mature. The species is distinguished from the northern giant petrel by its bill tip, which is reddish in the northern species.
Distribution and Habitat
The southern giant petrel has a circumpolar distribution across the Southern Hemisphere, with a range extending from the Antarctic continent to the subtropical coasts of Australia, Africa, and Chile. It is an oceanic species that spends most of its time foraging over cold southern seas. While at sea, some foraging trips can cover up to 4,000 km.
Breeding occurs on numerous subantarctic islands, including the Falkland Islands, South Georgia, and Macquarie Island, as well as on the Antarctic Peninsula. They form nesting colonies on bare or grassy ground. These colonies are typically loose and dispersed, though some in the Falkland Islands can be larger and more densely populated.
Diet and Foraging Strategies
As an apex scavenger and predator, the southern giant petrel has a varied and opportunistic diet. Its food sources include krill, squid, and fish gathered from the ocean surface. They are also powerful predators, preying on the eggs and chicks of other seabirds, such as penguins and albatrosses.
A substantial portion of their diet consists of carrion, particularly the carcasses of seals and whales. Their strong legs allow them to move effectively on land, where they aggressively dominate other seabirds at feeding sites, earning them the moniker “vulture of the seas.” Males tend to forage in coastal areas, while females often travel further offshore.
Breeding and Defense
Southern giant petrels typically reach sexual maturity around six or seven years old but often don’t begin breeding until they are ten. They form monogamous pair bonds and return to loose colonies to breed, with the season starting in October. The nest is a mound of moss, grass, and stones on open ground, where a single white egg is laid. Both parents share the incubation period, which lasts between 55 and 66 days.
When threatened near the nest, adults and chicks will spit a foul-smelling, oily stomach substance at intruders. This substance is an effective deterrent for predators and also serves as a high-energy food source for chicks and for adults during long flights. After hatching, the chick is guarded by its parents in the nest until it fledges.