Evolutionary biologist from the University of Zurich, Simon Townsend, together with English researchers showed that chimpanzees are capable of referring to objects and socially learn meaningful calls.
The researchers found that chimpanzees living in captivity have special 'words' that they use for different types of food and can even learn the calls or grunts referring to specific food items used by strangers from foreign groups. So far researchers assumed that the acoustic structures of these calls are an expression of their excitement and cannot be controlled by the chimpanzees.
For their study the team recorded the grunt calls for apple before the integration in 2010. They then recorded the same grunt calls 1-year after integration and again in 2013. The research team 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. But in 2013, when analyses of the social network showed strong friendships between the two group members, a change in the call structure could be observed.