The first thing to do when trying to understand the vocal communication system of another species is to figure out how many different types of vocalizations there are. We have found 8 basic types of vocalization in the adult African elephant vocal repertoire. In that process, we discovered two new vocalizations not previously described by scientists, the ‘croak’ and the ‘rev’. The croak is often heard when elephants are exploring the environment with their trunks,and the rev often occurs when elephants are startled by something such as an approaching animal. Although trumpets are the most well known elephant vocalization, ‘rumbles’ are the most common and we know most about them. |
Although it is difficult for us to detect with our limited hearing, we have shown that our elephants have distinctive sounding voices. We know that voice activated phone systems can understand our voices when we respond to a command such as “say or press one”. Using the same “human speech recognition technology”, our colleagues at Marquette University have developed special software to accurately identify individual elephant rumbles, showing that they have unique voices just as humans do. So not only do best friends talk to each other by exchanging rumbles, they probably can also recognize each other by their voices alone. What a great way to keep track of everyone when they are out of sight. It’s the elephant version of a cell phone. 
There is a lot more information in a rumble besides the differences between individuals. Females appear to have ‘mate attraction’ rumbles that signal their reproductive state to distant males. In the wild, males are solitary and usually only visit females for mating, so it could help everyone if female rumbles indicated something about their current fertility. We found that the cycling females in our herd start rumbling much more than usual just before ovulation. Together with researchers at Marquette University, we have shown that these “pre-ovulatory” rumbles are distinct from “normal” rumbles, involving a lowering of the pitch of the call. Males may listen for these rumbles so they can find females who will soon become ready to mate. But what happens when the male gets into the female herd? When we introduced a male into our herd containing cycling females, the females became less vocal, and males switched to using olfactory cues to determine female fertility.
