Birds have more or less developed wings; the only known groups without wings are the extinct moa and elephant birds | Birds also have digestive and respiratory systems that are uniquely adapted for flight |
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Wings are evolved forelimbs, and most bird species can fly |
Some species of birds, particularly penguins and members of the duck family, are adapted for swimming.
22Flightless birds include ratites, penguins, and diverse endemic island species | |
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