Beak
The beak - otherwise known as the bill - is the only device a bird has for consuming food. It is composed of an upper jaw called the maxilla, and the lower jaw called a mandible. Birds have no teeth so they must swallow their food whole. A bird's beak can vary in size and shape depending on the nature of their diet. Some birds such as the falcons have evolved to have a cutting type beak which allows them to tear through flesh, whereas the hummingbird has a probe like beak which allows them to drink the nectar from certain flowers. Bird beaks are useful in otherways, e.g. woodpeckers use theirs to cut wood, parrots have sharp swivelled beaks to tear fruits. Herons have long beaks to pull out fish from the water and ducks have flat beaks that allow them to retain all the fish and plants while draining out the water.
ReferencesGilbertson, Lance; Zoology Lab Manuel; McGraw Hill Companies, New York; ISBN 0-07-237716-X (fourth edition, 1999)
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