An interesting table showing the hearing ranges for some animals [from Animal Behavior Online]

I am impressed by the incredible hearing range of the rodents.

The infrasonic communications of the elephants is well known. African elephants have a social structure best described as fluid; animals move freely over wide areas, sometimes affiliating with other animals. Female members of a family tend to stay together, and of course their juveniles travel with them. These female-centered groups may merge with other such groups periodically. Adult males are less likely to join groups.

Female African elephants use “contact calls” to communicate with other elephants in their bands (usually a family group). These infrasonic calls, with a frequency of about 21 Hz and a normal duration of 4-5 seconds, carry for long distances (several kilometers), and help elephants to determine the location of other individuals. Calls vary among individual elephants, so that others respond differently to familiar calls than to unfamiliar calls. Perhaps elephants can recognize the identity of the caller.

Perception of infrasounds, however, presents some specific problems. An object smaller than the distance between waves is a poor receiver for those waves. Thus infrasonic receivers need to be large. This is probably the reason that infrasonic communication is used by only a few animals, and the best understood infrasonic communication system is the African elephant’s.

The large pinnae (external portion of the ear; trad.: il padiglione auricolare) in the African elephant may play an important role in the elephant’s perception of low frequency sounds, which are significant in communication among elephants. Receiving structures whose size is matched to the wavelength of the sound perform better.