Flight

Birds of prey need to fly so that they can find prey. The shape of a bird’s body allows air to easily pass over it so that they can fly easily and not be using up huge amounts of energy. Sometimes birds, like vultures, need to fly a really long time before they can find their prey. Their bones don’t weigh much because they are hollow [see diagram on the left.] but it still takes lots of muscles and energy to get them up in the air and keep them there. For example: Vultures look for dead animals and they might fly for hours and hours before they find one. This means that they would use a whole lot of their energy and strength to flap their wings for that long. It takes 15 times more energy to fly and flap as it does to just sit still.
Most birds of prey use a combination of ways to fly. They fly by using:

	Flapping. This way uses the most energy. When they flap down, their feathers close up and they push against the air which makes them rise. When they flap up, they open up their feathers to let the air through so that they can get in the right position to push down against the air again.
	Gliding. The birds fly with air currents and don’t flap their wings very much. Just like a toy glider, they travel through the air using wind and gravity. They will ride the wind until their weight makes them drop lower.
	Soaring. The birds will stay level or rise higher by riding thermals or air currents. They don’t have to flap their wings and that saves lots of energy.
		Riding thermals: The sun heats up the earth and causes warm air currents to rise. Thermals happen later in the morning, after the sun has had time to warm up the land. The birds will fly until they find the thermal, and glide in circles as the warm air pushes them up in the sky. One of our sources called it an “elevator” [Krautwurst] which is exactly the way to imagine it. Heavy birds like buzzards will fly to the top of one thermal “elevator” and then go looking for another. In that way, the bird can fly longer because he doesn’t get as tired as he would if he flapped his wings all the time.

		Riding updrafts: Imagine a wind current traveling through a valley or through a city. The wind current will hit a mountain or a building and have to go somewhere. It follows the surface it meets and rises along it until it reaches the top. If a raptor flies into the current, the wind will push him up a mountain or a building without having to flap his wings and use energy. He can fly longer distances if he rides updrafts and thermals.

	Hovering. Birds can use kiting or vertical hovering to stay in the air.
		Kiting: If you see a bird that looks like it is flying in one place and not moving forward in the air, it is probably kiting. The wings are stretched out and only very small wing flapping is done. Birds called kites do this and others like Red-tailed Hawks and Rough-legged Hawks will, too.
		Vertical hovering. This is where the bird is flying in one place, straight up in the air, beating its wings very quickly. Wind helps the bird stay up. American Kestrels do this.

Birds of prey will generally use more than one kind of flying. A bird might use flapping, then glide up a thermal current, and then begin flapping again.