In Sweden the Black-legged Kittiwake breeds very rarely. At its regular breeding sites in the North Atlantic it builds the nest on narrow rock ledges on steep, often sheer sea cliffs, where the colonies can hold thousands of pairs. The nest is a compact cup of seaweed, grass and mud. The female normally lays 1–2 eggs, and both parents incubate and feed the young, which, unlike other gull chicks, stay put on the narrow rock ledge until they are able to fly.