WASHINGTON, Feb. 5 (Xinhua) -- Chimpanzees are capable of learning calls that refer to specific food items such as apple to communicate better with other members of their species, according to a study of two separate groups that were merged together at Britain's Edinburgh Zoo.
The findings, published Thursday in the U.S. journal Current Biology, suggested that human language isn't as unique as we thought in its ability to reference external objects with socially learned symbols.
Chimpanzees are known to produce alarm and food calls that refer to objects in their environment. However, so far researchers assumed that these calls are just an expression of their excitement and cannot be controlled by the chimpanzees.
In 2010, a group of adult chimpanzees from Beekse Bergen Safari Park in the Netherlands were introduced to a group of chimpanzees at the Edinburgh Zoo, and that provided researchers an opportunity to study whether chimpanzees are capable of changing their calls to sound more like their new neighbors.
The researchers observed that before the integration the two groups produced acoustically different grunt calls for apple and furthermore had different preferences for apple.
After the integration of the two groups, the researchers discovered that the acoustic structure of the grunt calls of the new group members had been adapted to the ones produced by the chimpanzees already living there.
"Three years after the integration, the grunt calls of the new chimpanzees very much resembled the grunt calls produced by the Edinburgh chimpanzees," said study author Simon Townsend of the University of Zurich in Switzerland. "The preferences for apple in these chimpanzees stayed the same during this period, but the grunt calls changed."
The researchers found that the fact that they lived together for a year and heard the different grunt call for apple from the other group members was not sufficient to cause the changes in their call structure.
Only in 2013, when analyses of the social network showed strong friendships between the two group members were formed, a change in the call structure could be observed, they said.
The findings "represent the first evidence of non-human animals actively modifying and socially learning the structure of a meaningful referential vocalization" from other members of their species, the researchers wrote.
"The fact, that not only humans, but also chimpanzees learn object-specific calls suggests that our common ancestor that lived more than 7 million years ago also possessed this ability," Townsend added.