Since 1999, researchers with the Elephant Listening Project have used an acoustic monitoring system to record elephant sounds in the African rainforest.

They’ve learnt that elephants use infrasonic calls - calls too low in frequency to be heard by the human ear - for long-distance communication. Infrasound can travel farther than higher pitched sound. Elephant families separated by several kilometers use them to keep track of each other. Male elephants find fertile females by using these low frequency sounds.

Elephant populations in Africa are decreasing due to encroaching human civilization. But, even as we humans have become stewards to the elephants, it’s hard to know exactly how many elephants are left. Elephants in the dense forests of Africa are difficult to count. Sightings are rare. The Elephant Listening Project can use the elephant’s calls to determine the size and health of the herds. At least one such study was used to locate hotspots of elephant activity.

And it’s not just the elephants' sounds that get monitored. The recorders also pick up human sounds - gunshots, chainsaws and vehicle noise - which help to identify potential threats to forest elephant populations.

And for today that’s our show. We do hope you come to our website to let us know what you think at earthsky.org. We’re Block and Byrd for Earth and Sky.