Ornithologists say birds have three methods of flight. The first is flapping--keeping their wings in constant motion to counteract gravity. Hummingbirds can flap up to seventy times per second. Flapping keeps you up in the air, but it is a lot of work.
A second flight method is gliding. Here the bird builds up enough speed, then coasts downward a while. It is much more graceful than flapping, but unfortunately it does not get the bird very far. Reality in the form of gravity sets in quickly. Gliding is nice, but it does not last.
Then there is the third way--soaring. Only a few birds, like eagles, are capable of this. Eagles' wings are so strong that they are capable of catching rising currents of warm air--thermal winds that go straight up from the earth--and without moving a feather can soar up to great heights. Eagles have been clocked at up to 80 miles per hour without flapping at all. They just soar on invisible columns of rising air.
- John Ortberg - If You Want to Walk on Water, You've Got to Get Out of the Boat
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