Which bird is it?

Black-legged Kittiwake
tridactyla

This kittiwake is a widely distributed breeder across the northern parts of the Northern Hemisphere. It builds nests of grasses, seaweeds, mosses, and mud on small ledges on vertical cliffs, usually on the lower sections of the Cliff face. Clutch size varies from one to three eggs, depending on availability of food resources. When conditions are unfavorable, kittiwakes may fail to lay eggs, even in several consecutive years. If food resources are poor after hatching, larger chicks will kill smaller, competitive siblings.

Black-legged Kittiwakes feed on a wide variety of prey, especially fishes but also amphipods and euphausiids. They feed mainly by plunge-diving in the top 0.5 meter (1.5 feet) of the water column, frequently near their colonies. Birds disperse widely for feeding, but will gather in small feeding flocks at local concentrations of food, such as about fishing vessels, feeding whales, and oceanic upwelling.