Why might a particular bird be found in more than one habitat

Some birds are able to find food in more than one environment e. g gulls are usually associated with the sea shore where they eat aquatic and marine animals. However gulls can be found inland thousand of mile from seashore. Other birds such s rock pigeon now makes themselves equally at home in large urban areas and man made structures and also in rural areas. They are able to adapt their feeding habits to the environment