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If bird bones were solid, like human bones, flying would be very difficult because birds would be too heavy. Instead, most birds have hollow bones. But that's not the only reason their skeletons are so light. Since the days of their dinosaur ancestors, birds have evolved to have fewer bones.
A bird's skeleton is strong enough for flight because many of its bones are fused (joined together solidly instead of jointed).
A bird's skull is extremely light in proportion to the rest of its body. The skull usually represents less than one percent of a bird's total body weight. That's because birds have eliminated some of heavy structures such as the jaw, jaw muscles, and teeth. (A bird doesn't need teeth to chew its food because it has a specialized stomach called a gizzard that grinds the food up after it's swallowed.)
If you weighed all the bones in a bird's body, that total would be less than the weight of all the feathers on that's bird's body. A pelican about five feet long and weighing nearly 20 pounds has a skeleton that weighs only 23 ounces. That tells you just how perfectly a bird's skeleton is adapted to its capacity for flight.
Thanks to its lighter skeleton, a bird is better at walking, jumping, taking off, perching, soaring, diving, catching prey, and landing.
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