While ducks, geese, and shorebirds return to the north as early as possible in order to breed quickly, other arctic birds delay their arrival until the weather warms. This allows them to feed for longer in the south, and means that when they do arrive in the North, food is readily available. Marine birds such as the alcids must wait until openings in the sea ice have formed, in order to be able to catch fish. Razorbills, in particular, take advantage of the extra food available in their Atlantic wintering grounds in the spring, before heading north to breed.