Mlaika is a 10-year-old female African elephant living in semicaptivity with other orphaned pachyderms in Tsavo, Kenya. The stockade that she sleeps in is located three kilometers from a busy highway. Peter L. Tyack of Woods Hole Oceanographic Institution and his colleagues analyzed Mlaika's calls and were surprised to discover that they were unlike any of the normal calls made by African elephants. Rather, they sounded like moving trucks. Mlaika did not directly copy the sounds she heard, however. The team reports that her trucklike calls shared characteristics both with the sounds she was exposed to and other truck sounds recorded at other times, which suggests "that Mlaika used the general features of truck sounds as a model."
The researchers also studied the vocalizations of Calimero, a 23-year-old male African elephant living for the past 18 years in a zoo in Switzerland. Calimero's companions are two female Asian elephants. In the wild, Asian and African elephants use different calling systems, with Asian elephants relying mainly on chirping sounds. The researchers analyzed Calimero's calls and found that they were significantly different from any standard calls used by African elephants. Instead they sound like the chirps of female Asian elephants. "To our knowledge," the authors write, "this discovery in elephants is the first example of vocal imitation in a nonprimate terrestrial mammal."