Vocal learning is extremely rare in animals, but gorillas appear to have cracked it.
“Snough!” That’s apparently gorilla slang meaning “I say, old buddy, toss us a couple grapes, would you?” What’s most surprising about this unusual vocalization is that it appears to have been developed by caged gorillas specifically for the purpose of communicating with human zookeepers, and is never used while interacting with other gorillas. According to a new study, the creation of such a cry implies that gorillas, the intelligent sausages, are capable of vocal learning and inventiveness.
Previous study on other great apes has demonstrated that when exposed to fresh settings in captivity, both chimps and orangutans produce new sounds. Chimps, for example, have been observed blowing raspberry at humans, but orangutans prefer to whistle.
Researchers conducted an experiment to investigate whether this skill is shared by the western gorillas housed at Zoo Atlanta in the new article published in PLOS ONE. Six female and two male gorillas were observed in three experimental scenarios: the first had the apes being within a meter of a friendly zookeeper, the second a solo bucket of grapes, and the third the zookeeper carrying the food bucket.
“Gorillas vocalized most frequently under the human-food condition,” the research authors write, “with the most frequently utilized vocal signal being a species-atypical sound halfway between a sneeze and a cough… which we termed the attention-getting sound (AG) or’snough.’
This sound, which had never been documented in the species’ vocal repertoire, was employed by four of the eight gorillas in the investigation, accounting for 85 percent of all vocalizations observed throughout the trial. According to the researchers, the sound is acoustically unique from all other noises made by gorillas when feeding, such as grunts or hums.
“In our study, captive gorillas never used the AG call when communicating with one another, supporting the idea that it is a novel sound that is not part of the typical gorilla-gorilla communication repertoire and that it evolved to address the communicative need of attracting human attention in captive settings,” the authors write.
To broaden their inquiry, the researchers contacted handlers at additional institutions in the United States and Canada. They learned that the same cry is used by 33 different gorillas kept in 11 different zoos. However, after reviewing video footage of 15 of these gorillas, the researchers discovered just six animals “snoughing,” implying that the vocalization is used by around 40% of captive western gorillas.
“The AG cry is likely not as frequent as the more popular raspberry call made by caged chimps, which may imply that zoo gorillas just recently acquired this sound to attract human attention,” they write. Furthermore, the fact that the cry is frequently employed by gorillas who are closely connected to one another – such as siblings or parents and children – suggests that it may be handed down through social learning.
Sounds similar to this “snough” were previously attributed to Koko, the famed yet controversial “talking” gorilla who employed a variety of innovative utterances when engaging with human carers.
“These included a fake cough/sneeze followed by a hand motion and an open mouth that significantly mimicked our study’s AG sound,” the researchers write.
“It is uncertain if the AG (or snough) call evolved spontaneously or was learned/modeled by seeing people, as appears to be the case with Koko’s false cough and the orangutans’ whistle.”