Beak

The beak, bill, and/or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs, and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, courtship, and feeding young. The terms beak and rostrum are also used to refer to a similar mouth part in some ornithischians, pterosaurs, cetaceans, dicynodonts, anuran tadpoles, monotremes (i.e. echidnas and platypuses, which have a beak-like structure), sirens, pufferfish, billfishes and cephalopods.

Comparison of bird beaks, displaying different shapes adapted to different feeding methods. Not to scale.

Although beaks vary significantly in size, shape, color and texture, they share a similar underlying structure. Two bony projections – the upper and lower mandibles – are covered with a thin keratinized layer of epidermis known as the rhamphotheca. In most species, two holes called nares lead to the respiratory system.