The Red-legged Kittiwake is a small gull found breeding on remote oceanic islands at only four locations in the world, all in the Bering Sea. Over 75% of the known population breeds on St. George Island, in the Pribilof Islands group. Nesting colonies occur on vertical sea cliffs up to 300 m high, where this species builds its nests on small ledges along with several other species of seabirds, including the Black-legged Kittiwake (R. tridactyla)-a common, widespread, and more-studied relative of the Red-legged Kittiwake.
The Red-legged Kittiwake feeds in surface waters, sometimes forming melees over dense schools of fish with flocks of Black-legged Kittiwakes. Both species feed day or night, but the Red-legged has a larger eye, a possible adaptation to night feeding when vertically migrating prey, like lampfish (Myctophidae) and squid, become available. In summer, the highest concentrations of Red-legged Kittiwake are found over deep water, from the edge of the continental shelf (200 m) to water 2,000 m deep. In winter, this species apparently feeds in even deeper water if, as reported, it scatters over the North Pacific ocean.
During the 1980s, both species of kittiwake in the Bering Sea suffered frequent reproductive failure and population declines at some sites, possibly due to inadequate food supplies near colonies. These gulls live in a marine environment where food resources fluctuate with oceanographic conditions, but reasons for changes in the Bering Sea and their effects on these species are not well understood. Little is known about the Red-legged Kittiwake away from its breeding sites, so other, unknown, factors may also have influenced its population trends.