The entire modem avian world is characterized by the absence of teeth. The upper and lower jaw bones become elongated to form a peculiar beak or bill covered by a horny sheath called as rhamphotheca. The modification of forelimbs into wings deprived birds of some of their normal functions. Beak serves both as mouth and hand. The diversity of form of beaks is mainly related to the type of food eaten and to the manner of feeding. Birds exhibit almost indefinite variations in shape, size and structure of beaks, of which only some of the most important and common types are described here.

  • Seed-eating beak :- Short, stout, peg-like and conical beaks are characteristic of small grainivorous or seed eating birds, such as sparrows, finches and cardinals. The weaker beaks are used for piercing up small seeds, while more powerful beaks are meant for crushing large and hard-shelled seeds and fruit stones.
  • Cutting beak : Birds such as jungle crows, possess long and slender beaks with cutting edges which can be used variously for cutting plants.
  • Fruit-eating beak :- In parrots, the beak is sharp, massive, deeply hooked and extremely strong. It is well adapted for gnawing or breaking open hard seeds and nuts, which form their staple diet. Enormous beak of hornbills, looking so heavy and cumbersome, is really quite light as its interior is of a cellular structure. It is suggested that these cells act as resonators, thus enabling the bird to produce its exceptionally loud cry.
  • Insectivorous beak :- In swallows Robin, Frog-mouth and swifts, the beak is small, wide and delicate to scoop up their living insect prey while on wing. In fly catchers, the beak is short but strong, with mandibles notched at the tip and beset with numerous rictal bristles at the base.
  • In hoopoe, the beak is long, slender and slightly curved and meant for turning the leaves or probing into the soil for insect grubs and pupae, etc. 
  • Wood-chiseling beak :- Woodpeckers have elongated, straight and stout chisel-like beaks for drilling into the barks or wood for insect larvae or for nest construction. They have thickened, shock-absorbent skull bones and strong neck muscles to make such pounding feasible.
  • Tearing and piercing beak :- Carrion-feeding and flesh-eating birds, such as vultures, hawks, eagles, owls and kites etc., have short, pointed, sharp-edged and powerful, hooked beaks for tearing flesh and operated by well-developed mandibular muscles.
  • Mud-probing beak :- Familiar examples of mud-probing beaks are found in snipe, stilt, sand-piper, Yellow leg, Kiwi jacana and lapwing, etc. Their beaks are extremely long and slender and are used as a probe for thrusting far down into water and mud in search of worms and larvae. Some of these birds are remarkable for the slenderness and extreme length of their beaks.
  • Water and mud straining beak :- In ducks:  teals and geese, the beak is broad and flat. The edges of the jaws are furnished with horny serrations or transverse lamellae, which act as a sieve or strainer, letting the water and mud pass out while retaining the food in the mouth. Such a beak enables the bird to avail itself of the rich store of food in the shape of insects and other organism. In flamingoes, the beak is distally curved downwards and likewise furnished with shifting lamellae. The two halves of lower jaw are considerably enlarged so that the comparatively narrow upper jaw closes upon a wide cavity. 
  • Fish catching beak :- Storks, herons and kingfishers have long, powerful and sharply pointed spearing beaks to capture fish, frogs, tadpoles and similar aquatic animals. Cormorants have long and narrow beaks, the edges of which are armed with sharp backwardly directed, tooth-like processes meant for capture of fish. In snake-birds or Indian darters, these serrations take the form of fine needle-like points.
  • Spatulate beak :- Spoonbill possesses a very specialized form of beak. It is flattened throughout its length but terminates in a broad, spatulate or spoon-like expansion meant for splashing in water and mud in search of insects, worms, fish, molluscs and other small animals upon which the bird feeds. 
  • Pouched beak :- Pelicans  consume enormous quantities of fish. Their beak is large, with a capacious gular pouch of extensile skin attached to the lower mandible and serving as a fishing net.
  • Flower-probing beak : Long, pointed and rapier-like probing beak of tropical humming birds dive down the corollas of flowers for sucking honey and insects. They suspend themselves in mid air before the flowers, while they extract their honey and insects. Their beaks are bent or so shaped so as to suit the particular shape of the flowers.

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