Two African elephants in the wild.
Credit: Copyright Julie Larsen Maher/WCS.
African elephants belt out distinct alarm calls to specify which kind of threat is approaching in the wild, be it humans or bees, a new study shows.
As the largest land animals on Earth, elephants face relatively few predators in the wild, but these threats include people, who poach the animals for their ivory, and swarms of angry bees, which can inflict painful stings around the eyes and trunks of elephants. A powerful swarm of bees could even kill a thin-skinned calf.
Researchers had already discovered that elephants produce a "rumble" — like a gravelly baritone growl — in response to the threat of bees. What's more, elephants will flee when they hear a recording of this rumble, even when there's no sign of bees around, according to that 2010 study in PLOS ONE. [Elephant Images: The Biggest Beasts on Land]
The same team of scientists wanted to figure out if elephants had special calls for other types of threats. In the new study, published in the journal PLOS ONE on Feb. 26, they tested how elephants reacted to the voices of Samburu tribesmen in northern Kenya.
Compared with a white noise control, both the sounds of tribesmen and the sounds of angry bees triggered uneasy and vigilant behavior in the elephants; the animals started sniffing, they lifted their heads up and scanned the landscape and they hightailed it out of the area. The elephants also started shaking their heads but only in response to the noises of angry bees, likely to knock any insects away from their face.
The suggestion of these threats also elicited vocal responses from the elephants, known as rumbles.
There were slight differences in the formant frequencies of the rumbles in response to bees and the rumbles associated with humans, the researchers said. Unlike differences in pitch, differences in formant frequencies produce subtle differences in sound, which, for example, allow humans to distinguish between vowels and the meaning of words.
Humans create those subtle frequency chances by manipulating their mouth and tongue. The authors say it's not clear to what extent the subtle differences in elephant alarm calls are the result of intentional sound manipulation or the simple byproducts of different distressed states.
However, they write that the "parallels between elephant vocal behavior and human linguistic abilities are suggestive."