"Vocal learning enables a flexible and open communication system in which animals may learn to imitate signals that are not typical of the species," the researchers wrote.
They say this is the first time vocal learning has been recorded in a nonprimate land mammal.
In the wild, elephants often need to communicate over long distances, using low frequency calls to keep tabs on other members of their group. Experiments have shown that elephants can recognize the voices of particular individuals at distances of up to one and a half miles (two and a half kilometers).
So having a uniquely recognizable call, like Mlaika's low truck-rumble sound, could be a very useful.
"Elephants may well be able to produce unique calls, like a vocal signature, that are particular to that individual or to its family or to very closely bonded individuals," Poole said.
"Vocal learning could be used to maintain individual-specific social bonds in the complex and fluid society of elephants, where members of a social group come and go, keeping in contact over long distances and maintaining close social bonds over lifetimes."
Studies suggest some other group-living mammals may mimic unusual sounds for similar reasons. For instance, sperm whales have been found to match the click repetition rates of submarines' sonar signals. And captive bottlenose dolphins have shown themselves to be skilled at replicating computer-generated sounds.
The best known mimics in the animal world are birds. Pet parrots and mynah birds, in particular, are famous for their ability to copy words and expressions taught to them by their owners.
Birds also have a tendency to pick up on mechanical sounds. Elephants might be good at truck noises, but Australia's lyre bird can imitate motorcycles, chain saws, and clicking cameras. Other Australian birds are including cell phone ring tones in their repertoire.
The ring-tone phenomenon has also been noted among songbirds in Britain, another country with high numbers of cell phones per capita.
According to the Royal Society for the Protection of Birds, Europe's largest wildlife conservation charity, mimicry accounts for around 10 percent of the songs of the European starling. Ring tones, car alarms, and other electronic noises feature in its hit parade.
Similarly, song thrushes, blackbirds, and marsh warblers in the U.K. are incorporating such sounds into their songs.
Studies indicate that, for birds, vocal copying may improve a male's ability to attract mates and defend its territory from rivals.
Yet the elephant's reputation as a mimic is set to grow. "I know someone who owns an elephant that makes a humming sound that he thinks it learned from listening to a lawn mower," Poole said. The researcher also knows of "croaking" elephants that might possibly be imitating frogs.
She added, "We are due for some more surprises from elephantsa species that continues to surprise!"
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