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Arctic Skua
last update: Mar 04, 2009 12:42 PM
Also known as the Parasitic Jaeger
Latin name: Stercorarius parasiticus
Longevity: the oldest found was 31 years old
Population: 500,000-1,000,000
Cites classified: Least Concern
Where found: This species breeds in the north of Eurasia and North America, completely encircling the North Pole, with significant populations as far south as northern Scotland. They then migrate to the Southern Hemisphere over the southern oceans and are common in eastern Australia.
Wingspan: 110 to 125 cm
Length: 44 cm
Weight: 450 g
Mating/Breeding: Parasitic jaegers usually breed every year, but about 3% of experienced breeders will not breed in a given year. Parasitic jaegers are monogamous, and no polygamy has been recorded. Parasitic jaegers breed in the Arctic tundra between May and September, after migrating there from the Southern Hemisphere. They demonstrate site fidelity, with pairs returning year after year to the same territory. Parasitic jaegers exhibit reversed sexual dimorphism, in which females are larger than males. Larger females produce larger eggs and they have more body heat and surface area for incubating eggs. Females lose weight after their chicks hatch, so larger females are better adapted to stresses encountered post-hatching. Larger females can also defend better defend nests from predators and compete better for mates than smaller females. Smaller males, on the other hand, are more efficient at foraging. Kleptoparasitism requires agile flight, which is easier for birds with shorter wings and less momentum. Long distance foraging is more efficient for smaller birds. Smaller, more agile males are also better at territorial displays and courtship rituals. Parasitic jaegers invest heavily in raising offspring. Males forage more than females during courtship and incubation. Females do most of the incubation, though males do help with incubation. After hatching, females begin to help with foraging to provision hatchlings. Near the end of the breeding season both males and females forage for their young equally. Parasitic jaegers defend territories and young vigorously; hatchlings are almost constantly watched by at least one parent.
Hibernation: Migrate to the Southern Hemisphere in the winter months
Aggressive?: Males defend nests more than females, but females grow more aggressive after the eggs are laid. Sometimes an extra-pair jaeger will assist with defence.
Hunting Habits: Parasitic jaegers also search for and capture their own prey. They prey on the nests of waterfowl, including snow geese, and eat the eggs and young they find. They eat small mammals, including lemmings. They also eat small birds and occasional insects and berries.
Feed on: This bird will feed on lemmings and other rodents on the breeding grounds, but also robs gulls and terns of their catches. Like the larger skua species, it continues this piratical behaviour throughout the year, showing great agility as it harasses its victims.
Predators: Parasitic jaegers are preyed on by other birds, including ravens and great skuas. Because parasitic jaegers are rare in the United Kingdom, some people are debating whether or not to control great skua populations by culling individuals that specialize on seabirds, presumably including parasitic jaegers. Parasitic jaegers are also eaten by mammals, including American mink. Efforts to reduce feral mink populations in the United Kingdom have improved the breeding success of parasitic skuas.
Colour: Light phase adults have a brown back, mainly white underparts and dark primary wing feathers with a white "flash". The head and neck are yellowish-white with a black cap and there is a pointed central tail projection. Dark phase adults are dark brown, and intermediate phase birds are dark with somewhat paler underparts, head and neck. All phases have the white wing flash.
Interesting Trivia:
- Only adults return to breeding territories, juveniles are rarely seen. It is believed that parasitic jaegers spend the first two years of their lives at sea before returning to breeding areas.
