“Snough!” Apparently, that’s gorilla speak for “I say, old boy, chuck us a few grapes would you?”. What’s particularly striking about this unique vocalization, though, is that it seems to have been devised by captive gorillas for the specific purpose of communicating with human zookeepers, and is never used when interacting with other gorillas. According to a new study, the invention of such a call indicates that gorillas are capable of vocal learning and innovation, the clever sausages.
Previous research on other great apes has revealed that both chimpanzees and orangutans come up with new sounds when encountering novel situations in captivity. Chimps, for example, have been known to blow raspberries at their human handlers, while orangutans prefer to whistle.
In the new study published in PLOS ONE, researchers devised an experiment to determine whether this ability is shared by the western gorillas housed at Zoo Atlanta. Six female and two male gorillas were observed in three experimental scenarios, the first of which placed the apes within a meter of a familiar zookeeper, the second involved a solitary bucket of grapes, and the third included the zookeeper holding the food bucket.
According to the study authors, “gorillas vocalized most often during the human-food condition, with the most frequently used vocal signal being a species-atypical sound somewhere between a sneeze and a cough... which we named the attention-getting sound (AG) or 'snough'.”
This call, which has never previously been described in the species’ vocal repertoire, was used by four of the eight gorillas involved in the study, and represented 85 percent of all vocalizations observed during the experiment. The researchers explain that the sound is acoustically distinct from all other calls that gorillas usually produce during feeding, such as grunts or hums.
“In our study, the AG call was never used by captive gorillas when communicating with one other, supporting the idea that it is a novel sound not part of the typical gorilla-gorilla communication repertoire and that it emerged to address the communicative need of attracting human attention in captive settings,” write the authors.
Widening their investigation, the researchers reached out to handlers at other facilities across the US and Canada. They received confirmation that the same call is employed by 33 different gorillas housed at 11 different zoos. However, after examining video footage of 15 of these gorillas, the study authors only observed six individuals “snoughing”, suggesting that the vocalization may be employed by around 40 percent of captive western gorillas.
“The AG call is likely not as common as the more prominent raspberry call used by captive chimpanzees, which may indicate that zoo gorillas only recently adopted this sound for the purpose of getting the attention of humans,” they write. Moreover, the fact that the call is often used by gorillas that are directly related to each other – such as siblings or parents and children – indicates that it may be passed on by social learning.
Previously, sounds resembling this “snough” had been attributed to the famous yet controversial “talking” gorilla Koko, who used a range of novel utterances when interacting with human caregivers. “These included a fake cough/sneeze, which was accompanied by a hand gesture and an open mouth and strongly resembled our study’s AG sound,” say the study authors.
“Whether the AG (or snough) call has emerged randomly or has been learnt/modelled by observing humans, as seems to be the case for Koko’s fake cough and the orangutans’ whistle, remains unknown.”