Beak
Encyclopedia : B : BE : BEA : Beak
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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.
Anatomy
The beak is composed of an upper jaw called the maxilla, and a lower jaw called a 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 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 structure at the base of the beak called the cere.
On some birds, the tip of the beak is hard dead tissue 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 full of nerve-endings for locating things by touch. The beak is constantly worn down by use, and so grows continuously the bird's whole life.
Unlike jaws with teeth, beaks are not used for chewing. Birds swallow their food whole, which is broken up in the gizzard.
Diversity
Beaks can vary significantly in size and shape from species to species. Examples of birds with unusual beaks include the hummingbird, the toucan and the spoonbill.See also
References
- Gilbertson, Lance; Zoology Lab Manual; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)
External links
- http://www.peteducation.com/article.cfm?cls=15&cat=1829&articleid=2752
- http://www.birdsnways.com/wisdom/ww53eiv.htm
- http://qp-society.com/qpserc/beak.html
- http://www.archive.org/search.php?query=creator:%22Beak%22 - an electronic musician using the name "Beak"
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