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鳥類世界
早於三千年前，中國古籍《爾雅》對鳥類作出的定義為：「二足而羽謂之禽」，指凡具有兩隻腳，而身體覆蓋著羽毛的便稱之為鳥類。為了適應環境，鳥類進化出各種不同的體型和特徵，例如企鵝為了在嚴寒的南極中生存，全身會長出重疊密接和呈鱗片狀的羽毛；各種水鳥為了適應水棲的生活，亦會演化出有蹼的腳。目前為人所知的鳥類共有九千多種，體型卻差距極大。現存最大的鴕鳥身高可達兩米半，而最小的蜂鳥卻僅僅只有六厘米的身長。
Birds World
Earlier than three thousand years ago, the Chinese ancient "ELEGANCE" definition of birds made as follows: "Two feet and feathers that the birds" refers Where have two feet, and the body covered with feathers will be called birds. In order to adapt to the environment, birds have evolved a variety of different size and features, such as penguins in order to survive in the cold of Antarctica, overlapping body president of adhesion and scaly feathers; variety of waterfowl in order to adapt to aquatic life will evolve webbed feet. Currently there are more than nine thousand kinds of birds known, but the gap between great shape. Existing maximum height of up to two meters ostrich and a half, while the smallest hummingbird but with only six centimeters in length.