It increases with temperature. Using this information, it is possible to measure one's distance from a lightning bolt. Begin counting immediately after you see the flash. Every five seconds counted is roughly equivalent to one mile of distance. Many animals are able to hear sounds that humans cannot.
Some migratory birds are able to hear the infrasonic sounds produced when ocean waves break.
This allows them to orient themselves with coastlines. Elephants, whales, hippos, rhinoceros, giraffe, okapi, and alligator are just a few examples of animals that create infrasound. Elephant's hearing range between 1 and 20,000 Hz. Humans cannot hear sounds in the infrasound range. Typically, an elephant's numerous different rumbles will span between 14 and 35 Hertz.