The Arctic skua, also known as the parasitic jaeger, is a seabird that inhabits the northern latitudes. It is widespread across the Arctic and subarctic regions. This avian predator has earned a reputation as a bold and aggressive bird, evident in its interactions. This tenacity allows the Arctic skua to thrive in challenging polar ecosystems.
Physical Characteristics
The Arctic skua is a medium-sized bird, comparable to a gull. It measures 41 to 46 centimeters in length, with a wingspan ranging from 110 to 125 centimeters. Its weight ranges from 330 to 570 grams, with females often being slightly larger than males. A distinguishing feature of breeding adults is their elongated central tail feathers, called streamers, which can extend up to three inches beyond the main tail.
This species displays distinct color morphs: pale, dark, and an intermediate form. The dark morph has blackish-brown plumage, sometimes with a paler wash on the sides of the neck. The pale morph has a dark head, a yellowish wash on the neck, and white underparts often marked by a dark breast band. The intermediate morph blends these characteristics.
Habitat and Migration
The Arctic skua breeds in the tundra and moorlands of the Arctic and subarctic regions. Breeding grounds are found along coastlines, though some populations nest further inland. Nests are simple scrapes on dry ground, often on a slight rise for an unobstructed view.
Beyond the breeding season, the Arctic skua undertakes a trans-equatorial migration to warmer waters. They spend non-breeding months in the oceans of the Southern Hemisphere, demonstrating one of the longest migratory journeys among seabirds. They can be found off the southwest coast of Africa, particularly in areas like the productive Benguela upwelling, and their range extends into the southwest Indian Ocean. Individual skuas can cover 43,900 to 54,200 kilometers annually.
Autumn migration begins between early August and early September as they depart northern breeding sites. Spring migration begins around late April, with birds arriving back at their breeding grounds by mid-May. This extensive journey highlights the species’ endurance and adaptability to diverse oceanic environments.
Diet and Foraging Behavior
The Arctic skua has a varied diet. During the breeding season, their diet can include small mammals like lemmings and voles, as well as insects, the eggs of other birds, and even their chicks. Their primary foraging strategy is kleptoparasitism.
This involves pursuing other seabirds to steal their freshly caught food. The skua chases host birds such as puffins, terns, kittiwakes, gulls, and auks, until they are forced to regurgitate or drop their catch. The Arctic skua then snatches the dislodged fish or other prey mid-air.
The success of these aerial pirating attempts can depend on factors such as the proximity of the interaction to cliffs or the open ocean, where the host birds might seek refuge. Skuas often target puffins carrying larger fish loads, maximizing the energy return for their effort. While kleptoparasitism can account for a significant portion of their diet, its reliance can decrease when terrestrial prey like lemmings are abundant on their breeding grounds.
Breeding and Nesting Habits
Arctic skuas are monogamous birds, forming pair bonds and exhibiting strong fidelity to their nest sites. Their nest is a simple scrape on the ground. It is often lined with plant material.
Nests are frequently situated on a slight rise or mound within the tundra, providing the pair with an elevated vantage point for observing their territory. A typical clutch consists of one to two eggs, which are usually dark olive-brown with distinctive speckles. Both parents share the responsibility of incubation, which lasts for approximately 26 days.
The chicks are precocial, meaning they are relatively well-developed and mobile shortly after hatching, allowing them to leave the nest quickly. The Arctic skua is known for its fierce defense of its nest and young. Both adults will fearlessly dive-bomb and attack any perceived threats, including larger predators or even humans, that venture too close to their breeding territory. They employ strikes with their feet, bill, or wings to deter intruders and and may also engage in distraction displays, such as feigning injury, to draw attention away from their vulnerable offspring.