Many types of animals—including bats, dogs, moths, dolphins, whales, and some species of fish—can hear sound at much higher frequencies than humans can detect, and thus we refer to them as being able to detect ultrasound. Many animals which can detect ultrasound use these higher frequency sounds as hunting tools. Whales, for example, use ultrasound as a navigation aid (they are, in fact, thought to have their own natural sonar system), and as a tool when hunting.
Bats also use ultrasonic techniques to detect prey, by emitting high-frequency sounds and using echoes to detect the location of the prey animal. Interestingly enough, there is evidence that the ultrasonic frequencies emitted by bats trigger evasive maneuvers in moths, many species of which are preyed upon by bats.