Sand martins are common summer visitors, arriving in March and leaving in October. They nest in colonies, digging burrows in steep, sandy cliffs, usually around water, so are commonly found on wetland sites. The tunnels they bore can be up to a metre in length. At a chamber at the end of the burrow, four or five eggs are laid on collected straw and feathers. Sand martins are sociable birds and will nest together in summer and gather to roost in large numbers in autumn; eventually they migrate to Africa to spend the winter.