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Question: How can owls fly without their predators or prey hearing them?
Owls are a nocturnal bird of prey, which means that they hunt at night. If you've ever been in the woods at night, you may remember how quiet it is and how frightening any noise that you hear can be. For this reason, an animal that hunts at night must be silent in order to be able to sneak up on its prey.
However, this is not the only way an owl benefits from silent flight. One of the most noticeable features of an owl is the large eyes, located directly on the front of the face. Nocturnal animals typically have large eyes to help them collect the little bit of light available to them. Having eyes on the front of the face means that owls see like us, using both eyes to create one picture (referred to as binocular vision). This allows the owl to judge how far away its prey is. As useful as this wonderful eyesight is, the owl also depends greatly on its hearing for hunting. The owl's ears are located on either side of the face, but unlike our ears they are not symmetrical. One ear is slightly higher and farther forward than the other. This means that the owl can hear in three dimensions also. So the owl is able to pinpoint the exact location even of an animal that it can't see (for example a mouse scurrying underneath snow). Since the owl relies on both eyesight and hearing for locating prey, you can understand that making a lot of noise when flying would not be good for the owl.
Now to answer your question, an owl's flight is silent because of its feathers. All birds have several kinds of feathers, but we are only interested in a couple of types. The long, stiff feathers on a bird's wing are known as flight feathers. These stiff feathers beating against air creates the sound you hear when a bird flies. Owl's flight feathers are soft and tattered along the edges, which greatly reduces the amount of sound created. Hold your hand out flat with your fingers held tightly together and flap it up and down by your ear. You can hear the sound of moving air. Now spread your fingers apart and do the same thing. You will notice a big reduction in sound. A soft pile on some of the flight feathers keeps them from making noise when rubbing together. In addition to this, owl's wings, legs and feet are covered with down feathers. (Down feathers are what give baby chicks their fuzzy appearance). Any noise that is created by the wings is absorbed by these soft fluffy feathers.
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