Chimpanzees have a sizable repertory of calls for the foods they love. Many of these sounds are grunts that the apes make when they’ve spotted, for example, figs or palm nuts, and that their fellow chimps understand. Scientists have debated whether the various grunts refer to specific foods, which would make the calls something like words in a human language. However, chimpanzees’ calls are considered to be largely fixed—meaning that unlike humans the apes are not vocal learners and cannot learn a new grunt by listening to the calls of others. Now, however, scientists recording the calls of two groups of captive adult chimpanzees have found that the apes can alter their sounds. The discovery occurred 3 years after seven adult chimpanzees (one shown in the photo above) from a safari park in the Netherlands were moved in with six other adults at Scotland’s Edinburgh Zoo in 2010. When given apples, the newcomers emitted loud, high-pitched calls (listen here). But the residents uttered softer grunts (listen here). Three years later, the immigrants’ calls had changed and sounded more like those of the Edinburgh apes (listen here). The altered grunts show that chimpanzee food calls are not as rigid as once thought, the scientists report online today in Current Biology. The researchers aren’t certain why the Dutch chimps changed their apple grunts, but they suspect that social forces were at play—either the arrivistes wanted to sound more like their new companions or to be better understood. The findings disprove the idea that chimpanzees cannot learn new sounds from their fellows, the scientists say. And that suggests that this ability—which is an important building block of human language—extends further back in time in our primate lineage than previously thought.