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An ultrasound image of a baby in the wombAn ultrasound image of a baby in the womb Some sounds are so high-pitched (those with frequencies above 20,000 Hz) that our ears cannot detect them. They are known as ultrasounds. Many animals, like dogs and bats, can hear some ultrasounds. Ultrasound is often used in medicine because, unlike X-rays, the sound waves do not damage the body's organs. An ultrasound scanner beams very high-pitched sound waves into the body. The echoes received from the bodies organs or a baby in the womb, are analysed by a computer to form an image.

A medical ultrasound examinationA medical ultrasound examination

Mouse-eared bat hunting a mothMouse-eared bat hunting a moth


Some animals, including bats, whales and dolphins, make calls and listen to the echoes of those calls that return from certain objects around them. They use these echoes to locate and identify the objects. This technique, called echolocation, is used by these animals both for getting around and for hunting—extremely useful in the darkness of the oceans (for whales and dolphins) or for flying at night (for bats). 

Echolocating animals include, among mammals, the bats (microbats), dolphins, toothed whales, shrews and two species of bird: the cave swiftlet and oilbird.

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