Although the terns and skimmers are sometimes split off into separate families (Sternidae and Rynchopidae respectively), the gulls, terns and skimmers share an evolutionary ancestry and many visual and behavioural characteristics. They are mostly white and/or grey seabirds, often with raucous or chattering calls. Many feed on fish but some of the gulls, in particular, have become generalists and have adapted to inland, terrestrial habitats and are often found on cultivated land and associating with human beings. They are usually colonial nesters.