Moulting

Birds can lose individual feathers at any time of year through, for example, sustaining an injury. However, when a bird moults, it is a complete and systematic replacement of its plumage. It begins through changes in the environment and the bird’s metabolism. In Britain the moult from breeding plumage occurs during the late summer and early autumn. This is shown by the abnormally large amount of feathers laying on the floor in open areas of concentrated bird population, such as the shores and surrounding edges of reservoirs. Birds which show distinct summer and winter plumages also prove that a moult has taken place. One of the most obvious species to highlight this fact is the black-headed gull. Its summer plumage has the bird’s distinctive ‘black’ hood (below, top). This is actually a dark chocolate-brown colour, but looks black from a distance. By winter, the black-headed gull’s appearance has changed following its autumn moult. It now has two small black dots on an otherwise white head (below, bottom). It will regain its black hood before the next breeding season.