Elephants are intelligent, so they're aware people can be dangerous. And according to a new study, some African elephants may even have a specific "word" to warn each other about nearby humans.

To conduct the study, researchers from Oxford University, Save the Elephants and Disney's Animal Kingdom tested the reactions of wild Kenyan elephants to audio recordings of human voices, specifically the Samburu tribe of North Kenya. When they played these voices to resting elephants, the animals quickly became more vigilant, ran away and emitted a low, distinctive rumble.

Having recorded this rumble, the team then played it back to another group of elephants. They also reacted as if they'd just heard the Samburu voices, erupting with alertness as they ran and rumbled.

These findings build on previous Oxford research showing African elephants have a distinct warning call for bees, which prompts fellow elephants to flee while shaking their heads, an apparent attempt to prevent beestings. The alarm calls for "bees!" and "humans!" might sound similar to us, the researchers say, but they contain key low-frequency distinctions that elephant ears can detect.

"Elephants appear to be able to manipulate their vocal tract to shape the sounds of their rumbles to make different alarm calls," Oxford zoologist and study co-author Lucy King says in a statement. "We concede the possibility that these alarm calls are simply ... an emotional response to the threat that other elephants pick up on. On the other hand, we think it is also possible that the rumble alarms are akin to words in human language, and that elephants voluntarily and purposefully make those alarm calls to warn others about specific threats. Our research results here show that African elephant alarm calls can differentiate between two types of threat and reflect the level of urgency of that threat."

While elephants fled both human and bee sounds (or warnings thereof by other elephants), there are two significant differences in their reactions, the researchers say. For one, the elephants didn't shake their heads when warned of humans, instead displaying vigilance that may be intended to locate the threat. And second, a closer listen to their alarm calls reveals a sort of linguistic subtlety.

"Interestingly, the acoustic analysis done by Joseph Soltis at his Disney laboratory showed that the difference between the 'bee alarm rumble' and the 'human alarm rumble' is the same as a vowel-change in human language, which can change the meaning of words (think of 'boo' and 'bee')," King explains. "Elephants use similar vowel-like changes in their rumbles to differentiate the type of threat they experience, and so give specific warnings to other elephants who can decipher the sounds."

African elephants are a vulnerable species, according to the International Union for Conservation of Nature (IUCN), meaning they're likely to become endangered unless the conditions threatening their survival and reproduction improve. Poaching for ivory and meat is still a major threat, but the IUCN says the worst danger is "loss and fragmentation of habitat caused by ongoing human population expansion and rapid land conversion," adding that conflict with people "further aggravates the threat."

By learning what scares elephants and how they react to danger, the researchers are working to reduce the animals' conflicts with humans in Kenya. Since elephants are afraid of bees, for example, King and her colleagues have built beehive fences — made of either real or dummy hives — around local farms to stop elephants from raiding crops. Beehive fences cost only $150 to $500 per 100 meters (328 feet), and they've already had an 85 percent success rate in three Kenyan villages.

"In this way, local farmers can protect their families and livelihoods without direct conflict with elephants, and they can harvest the honey too for extra income," King says. "Learning more about how elephants react to threats such as bees and humans will help us design strategies to reduce human-elephant conflict and protect people and elephants."

Russell McLendon is science editor at MNN. Follow him on Twitter and Google+.

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