Chimpanzees use certain grunts to refer to specific items of food, and their buddies understand exactly what they mean. Apples over here! When two separate chimp groups move in together, they can learn how to grunt in a different chimp language. The work, published in Current Biology this week, is the first non-human evidence for vocal learning of a referential call. 

Over the course of three years, a team led by Simon Townsend from University of Zurich observed two separate groups of adult chimpanzees after they moved in together at the Edinburgh Zoo. As the chimps got to know each other, the acoustic structure of their food grunts began to converge. "Our study shows that chimpanzee referential food calls are not fixed in their structure and that, when exposed to a new social group, chimpanzees can change their calls to sound more like their group mates," Katie Slocombe from the University of York says in a news release. 

In 2010, the team could hear the difference between how each group called for apples: The six local chimps used lower, softer grunts, while the seven newcomers made loud, high-pitched calls. “By 2013 the Dutch individuals changed their grunts to sound more like Edinburgh individuals," says University of York's Stuart Watson. You can listen to and compare their changing grunts here.

The peak frequencies of the Dutch chimps' calls dropped from 932 to 708 Hz, matching the calls of the Scottish host chimps, who altered slightly from 657 to 597 Hz over the same time, New Scientist reports. "It would be really exciting to try and find out why chimpanzees are motivated to sound more similar to their group mates," Townsend adds. "Is it so that they can be better understood? Or is it just to sound more similar to their friends?"

According to the authors, their findings represent the first evidence of non-human animals actively modifying and socially learning the structure of referential vocalizations from other members of their same species. This building block of language was likely also present in the common ancestor we share with chimps.