Science: Although ibirds and other animals have been known for some time to use low-frequency background noise, or infrasound, to get around, until recently no one knew exactly how it worked. Infrasound can be generated either from natural events, such as deep ocean waves or earthquakes, or from human-made events, such as the acceleration of a supersonic plane. The low-level sound waves created by these events travel long distances and reverberate off the land and the atmosphere. To try to understand how birds can use the sound waves to orient themselves, Jonathan Hagstrum of the US Geological Survey studied data on homing pigeons from three sites near Ithaca, New York, where researchers at Cornell University had conducted extensive releases between 1968 and 1987. Birds released from the Jersey Hill site almost always got lost, whereas birds released from the other two sites did not. Hagstrum concluded that Jersey Hill’s terrain interrupted sound transmission. He also found that short-term atmospheric conditions—a temperature inversion, for example—can temporarily affect infrasound transmittal in an area and thus interfere with animals’ ability to find their way.