December 15, 2009

Arctic Skua

<em>Stercorarius parasiticus</em>

These aggressive seabirds are sometimes referred to as avian pirates. The name is well earned. Skuas steal much of their food from terns, puffins, and other birds that are carrying fish or other prizes back to their nests and young. Skuas strike by attacking in midair and forcing their victims to drop their kills in flight. The swashbuckling birds sometimes team up to overwhelm their victims, and they are relentless in chasing down their adversaries.

In North America, arctic skuas are known as parasitic jaegers. This mouthful of a moniker explains both aspects of the animal's feeding philosophy. "Kleptoparasitism" is the term for stealing food from other species, while "jaeger" is derived from the German "hunter."

Although some skuas make their living solely by piracy, others employ this tactic only part of the time. While breeding ashore in the Arctic, they put their own hunting skills to the test. Common quarry includes eggs and small birds, but skuas also feed on small mammals and fish.

Arctic skuas live most of their lives at sea, and come ashore only to breed in the Arctic summer. Once young jaegers leave the nest, they may not visit land for two years—until they have themselves reached breeding age.

Parasitic jaegers are great travelers and annually migrate to winter in the Southern Hemisphere. Both light- and dark-colored morphs of this bird occur, though scientists are not yet sure what natural advantages each color affords.

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