(noun) The exterior, projecting part of a bird's mouth, composed of bone covered with a hard keratin shell. A bird's bill wears away with use and grows continually through the bird's life, and it may change color seasonally, such as the dark bill of the summer snow bunting that turns yellow in the winter. The size, shape and structure of the bill will vary by species, and most birds' bills are specialized for the type of food they eat, such as thick, conical bills for cracking seeds, hooked bills for dismembering prey or spatulate bills for filtering water for aquatic plants and insects.
In addition to feeding, birds also use their bills to carry items such as nesting materials or food to cache, and the bill is essential for preening. Some birds will also use their bills in courtship rituals or to carve out cavities for nesting.
To identify a bird based on its bill, note the length, shape, color and markings on the bill, such as a different colored tip, a subterminal band, a fleshy cere or a distinct nail. Also note how the bird uses its bill for feeding or other activities.
Photo – Gull Bill © David Friel