(Rissa tridactyla), oceanic gull, a white bird with pearl-gray mantle, black-tipped wings, black feet, and yellow bill. It nests on the North and South Atlantic coasts. Kittiwakes have evolved a number of behavioral and structural modifications for nesting on narrow cliff ledges. A close relative, with red bill and feet, is the red-legged kittiwake (R. brevirostris), which inhabits the region of the Bering Sea.