Chimpanzees are able to alter their calls, with one group recently learning a new "word" for apple.

Chimps use a wide variety of grunts when they encounter various foods, such as palm nuts or figs. Wildlife researchers have long debated whether these calls represent individual foods, which would suggest the animals use the grunts like words. Until now, most biologists believed these sounds were fixed in the vocabulary of the animals, providing the animals no way to learn new sounds. Recordings of animals in captivity show this may not be the case, after all.

Seven chimpanzees from a safari park in Holland were placed into an enclosure at the Edinburgh Zoo in Scotland, alongside six adult chimps, in 2010. When caretakers placed apples in the cage, the new arrivals spoke with high-frequency shrieks. The chimps who were already living in Scotland emitted sounds with lower pitches. However, within three years, the newcomers were forming the same sound as their companions when apples were presented to the group.

"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, said.

Researchers are uncertain why the new arrivals changed their grunts to those matching their compatriots. The new sounds were only heard from the Dutch chimps after they established social bonds with the other chimpanzees. It is possible that social forces were at work, driving the animals to sound more like the others in their enclosure. Another possibility is that the chimps wanted to be better understood by others in their group.
 
This finding shows that chimpanzee grunts and calls are not fixed, as once theorized. This ability to adapt and adopt sounds is essential for human learning, and this talent appears to extend further back in the evolutionary tree than previously believed.

Chimpanzee calls were recorded and analyzed, in order to accurately measure the sounds made by the animals. However, researchers report the changes are easy to hear without the need for electronic equipment.

"These findings might shed some light on the evolutionary origins of these abilities. The fact that both humans and now chimpanzees possess this basic ability suggests that our shared common ancestor living over 6 million years ago may also [had this ability]," Simon Townsend, of the University of Zurich, said.

Discovery of the adaption of chimp calls in groups of the animals was presented in the journal Current Biology.