 This tendency, known as philopatry, is so strong that a study of Laysan albatrosses found that the average distance between hatching site and the site where a bird established its own territory was 22 m; another study, this time on Cory's shearwaters nesting near Corsica, found that of nine out of 61 male chicks that returned to breed at their natal colony bred in the burrow they were raised in, and two actually bred with their own mother.Colonies are usually situated on islands, cliffs or headlands, which land mammals have difficulty accessing.This is thought to provide protection to seabirds, which are often very clumsy on land.