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Beak

Birds Guide

Beak

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The bill of a scavenger—the vulture.
The bill of a scavenger—the vulture.
The bill and knob of a Swan Goose.
The bill and knob of a Swan Goose.
Northern Gannets billing.
Northern Gannets billing.
The bill of the Greater Flamingo
The bill of the Greater Flamingo

The beak—otherwise known as the bill or rostrum—is an external anatomical structure which serves as the mouth in some animals. It is a distinctive feature of birds and, in addition to eating, is used by them for grooming, manipulating objects, killing prey, probing for food, courtship, and feeding their young.

Contents

Anatomy

Beaks can vary significantly in size and shape from species to species. The beak is composed of an upper jaw called the maxilla, and a lower jaw called the mandible. The jaw is made of bone, typically hollow or porous to conserve weight for flying. The outside surface of the beak is covered by a thin horny sheath of keratin called the rhamphotheca. Between the hard outer layer and the bone is a vascular layer containing blood vessels and nerve endings. The rhamphotheca also includes the knob which is found above the beak of some swans, such as the Mute Swan and some Swan Geese (pictured).

The beak has two holes called nares which connect to the hollow inner beak and thence to the respiratory system. In some birds, these are located in a fleshy, often waxy structure at the base of the beak called the cere (from Latin cera. Hawks, parrots, doves, and skuas are among the birds that have ceres. Budgerigars are dimorphic because the males' ceres turn bright blue upon maturity, while the females' ceres turn tan. The female budgies' ceres also appear wrinkled, to a greater extent during periods of fertility. Immature budgies have pale pinkish ceres which are smooth and shiny.

Nares are bird nostrils. The nares of birds are usually located directly above the beak. On some birds, such as the budgerigar, the nares are situated within the cere.

Beak
External naris labeled at left; internal naris labeled at right.
Gray's subject #223 994
Dorlands/Elsevier n_01/12558781

Nares can also refer to nostrils on other animals, such as sharks, rays, and sawfishes. Nares is a medical term from Latin that describes human nostrils.

On some birds, the tip of the beak is hard, dead tissue used for heavy-duty tasks such as cracking nuts or killing prey. On other birds, such as ducks, the tip of the bill is sensitive and contains nerves, for locating things by touch. The beak is worn down by use, so it grows continuously throughout the bird's life.

Unlike jaws with teeth, beaks are not used for chewing. Birds swallow their food whole, which is broken up in the gizzard.

Examples of birds with unusual beaks include the hummingbird, the toucan and the spoonbill.

Billing

During courtship, mated pairs of a variety of bird species touch and clasp each other's bills. This is called billing, and appears to strengthen the pair bond (Terres, 1980). Gannets raise their bills high and repeatedly clatter them (pictured); the male puffin nibbles at the female's beak; the male waxwing puts his bill in the female's mouth; and ravens hold each other's beaks in a prolonged "kiss".

See also

References

  • Gilbertson, Lance; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)
  • Terres, John. K. The Audubon Society Encyclopedia of North American Birds, New York: Alfred A. Knopf, 1980. ISBN 0394466519

External links


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This guide is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.


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