Skuas (family Stercorariidae) are robust seabirds recognized for their aggressive, predatory nature. Often nicknamed the “raptors of the seas,” these opportunistic feeders are found across nearly all the world’s oceans. Their distribution is circumpolar, thriving in both the Arctic and Antarctic regions. Skuas undertake some of the longest avian migrations known. A signature feeding strategy is kleptoparasitism, where they harass other seabirds, such as gulls and terns, to force them to drop or regurgitate their food. They spend the majority of their lives on the open ocean, only returning to land for the breeding season.
Southern Hemisphere Breeding Grounds
Southern Hemisphere skuas are typically larger species that nest around the Antarctic and Sub-Antarctic zones. They establish territories during the austral summer in locations like the Falkland Islands, South Georgia, and the Antarctic Peninsula. Preferred habitats include exposed rocky coastlines and patches of tussock grass or tundra on isolated islands. The breeding season is linked to the presence of massive colonies of other seabirds, which provide a reliable food source for the chicks.
Skuas become specialized predators and scavengers, with local diets reflecting the most abundant prey. For instance, near the Antarctic Peninsula, skuas frequently prey on penguin eggs and chicks. In places like South Georgia, their diet may incorporate seal carrion and afterbirth from Antarctic fur seals, alongside various petrels and prions. The presence of these concentrated food sources often leads to skuas nesting in dense colonies, vigorously defending their nests against intruders.
Arctic and Northern Hemisphere Breeding Habitats
The smaller skua species, often called jaegers in North America, breed exclusively across the northern reaches of the globe. Nesting sites are spread throughout the high Arctic tundra regions of North America, Greenland, and Eurasia. Unlike their southern relatives, these birds rely more heavily on terrestrial prey during the short Arctic summer, necessitating both inland and coastal nesting sites. They typically arrive between May and June, seeking territories in the open tundra and moorland.
The breeding success of northern skuas is closely tied to the cyclic populations of small rodents, primarily lemmings. When lemming numbers are high, skuas nest further inland, feeding their young almost exclusively on these mammals. If lemmings are scarce, many pairs forgo breeding entirely or rely instead on coastal resources, including the eggs and young of other shorebirds. They create a simple nest scrape on a slight rise, with both parents sharing incubation duties. The ability to switch between marine and terrestrial lifestyles defines the Arctic-breeding skuas.
Trans-Equatorial Migration and Pelagic Zones
When the breeding season ends, skuas largely abandon the land and become pelagic, living primarily over the open ocean. This non-breeding period involves some of the most extensive migrations known, with many species undertaking trans-equatorial journeys. Arctic-breeding species depart the far north around August and September, traveling thousands of miles to winter in the Southern Hemisphere.
Tracking studies show Arctic skuas may travel over 54,000 kilometers in a single year, reaching wintering grounds as far as the Benguela Upwelling off the southwest coast of Africa. Other common wintering areas include the Patagonian Shelf and the productive waters near New Zealand. During these movements, skuas maintain a high rate of travel, sometimes covering an average of 345 kilometers per day.
In the pelagic zones, kleptoparasitism becomes the dominant foraging method, sometimes accounting for over 95% of their diet. They chase gulls, terns, and other seabirds far from the coastline to steal catches of fish and squid. Southern Hemisphere skuas also exhibit migratory patterns; some populations, like Brown skuas, remain in the Southern Ocean, while others, such as the South Polar skua, cross the equator to forage in the Northern Hemisphere. The birds often use specific staging areas, such as the Grand Banks of Newfoundland, to feed and rest before continuing their journey across the tropics.