A '''woodpecker''' is a [[bird]] that pounds its [[beak]] into a [[tree]]'s surface to find [[food]].<ref>http://www.defenders.org/wildlife_and_habitat/wildlife/woodpeckers.php</ref> There are 21 species of woodpeckers in the United States. <ref>Internet Center for Wildlife Damage Management, ''WOODPECKERS'', by Rex E. Marsh, 2005 [http://icwdm.org/handbook/birds/woodpeckers.asp]</ref>
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'''Woodpeckers''' consist of 180 species of tree-clinging birds of the family Picidae, characterized by the use of their beaks as a hammer on trees,<ref>http://www.defenders.org/wildlife_and_habitat/wildlife/woodpeckers.php</ref> either probing for food or chiseling out cavities to make nests. With the exception of Australia and New Guinea, woodpeckers are found world-wide, with twenty-one species in the United States<ref>Internet Center for Wildlife Damage Management, ''WOODPECKERS'', by Rex E. Marsh, 2005 [http://icwdm.org/handbook/birds/woodpeckers.asp]</ref>.
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==Description==
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Woodpeckers vary in size from three inches in the piculets (''Picumnus sp.'') of South America to twenty-four inches for the (possibly extinct) [[imperial woodpecker]] (''Campephilus imperialis'') of Mexico. All bear "zygodactyl" feet - two toes in front, two behind - as an aid in clinging to tree bark; in addition, stiffened tail feathers on most species help to prop the bird in a tripod stance when clinging vertically.
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Woodpeckers are generally colored dark above, with light underbellies. Sexual dimorphism is present, with males displaying distinctive colors and patterns versus females. Most species feed on insects; some feed on fruits, and a few feed on the sap of trees. All woodpeckers have a long, sticky tongue, which is used to gather insects or sap after drilling into trees.