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| | Info Health - Birds |
 | | Birds are bipedal, warm-blooded, oviparous vertebrate animals characterized primarily by feathers, forelimbs modified as wings, and (in most) hollow bones. |
 | | Depending on the taxonomic viewpoint, there are about 8,800—10,200 living bird species (and about 120—130 that have become extinct in the span of human history) in the world, making them the most diverse class of terrestrial vertebrates. |
 | | Most birds are diurnal, or active during the day, but some birds, such as the owls and nightjars, are nocturnal or crepuscular (active during twilight hours), and many coastal waders feed when the tides are appropriate, by day or night. |
| www.infohealth.info /modules.php?name=Birds-MM (385 words) |
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