Of course, night time would be the perfect time to communicate in terms of coverage as the temperature on the surface of the ground would be at its coolest and sound would be conducted optimally. But, due to the prevalence of predators during the evening, elephants are wise to keep quiet, communicating rather when lions are asleep during the day. Elephants negotiate on the quality of their communication for the safety of the herd.
Infrasound communication allows for distress signals to be carried for many kilometres. This alerts fellow elephants to dangers or urgent pleas for assistance, or informs them of a female sending out estrus calls. This accounts for the sudden reaction in elephants when the human observers are unaware of any sort of sound. When an elephant has heard an infrasound call, it will immediately stop what it is doing in order to pay attention. Females make use of this ability in sending out estrus calls as the time in which they can mate is limited. Communicating their availability allows bulls from a far wider area to have the opportunity to mate with her, increasing her chances of bearing a strong, healthy calf (as she decides which bull she will accept).
This method of communication also strengthens bonds among the families and herds in a specific area, eliminating or reducing the need to travel vast areas to communicate and so reducing unnecessary energy expenditure. Such wise utilisation of natural abilities again demonstrates the intelligence that sets the magnificent elephant apart from its contemporaries.