How do birds fly? is a classic question. And one that, when asked by a child, stumps many parents. It's tempting to answer: because they have wings! And feathers! But what if your child wants a more informative answer? What if your child wants to know the actual mechanics of how birds' bodies are built to lift off the ground and coast through the air?
Then, my friend, you need hard facts.
Facts like: Birds' bones are much less dense than mammals' bones. This lessens birds' weight, making them light enough to defy gravity.
Birds have digestive and respiratory systems, as well as very high metabolic rates, that work in tandem to make them perfect flying machines.
Birds have an essential bone in their chests (the wishbone) that provides the strength and skeletal support needed to flap their wings.
Most birds also have around 175 muscles, the largest of which are the pectorals, or chest muscles, which are integral for take off, reaching altitude and landing.
Much like an airplane, in fact, birds' wings are curved from front to back in a shape called an airfoil. Air slides quickly over the top of an airfoil and more slowly underneath. When air moves slowly, there is more pressure than with fast moving air. The slower air and greater pressure underneath the wing is called lift and is what elevates the bird up into the sky.
Other factors, too, such as weight, thrust, and drag all come into play with a birds' flight.
And feathers? They do play a crucial role. A bird can open them fully, close them completely or any one of dozens of incremental positions in between that helps steer the bird where he wants to go.
So next time you see a gull or a swallow swooping, gliding or soaring above you, take some time to think about the physiology of a birds' body, of all the muscles, bones and feathers working together to get, and keep, that bird flapping into the horizon.
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