Years ago, biological anthropologist Roberta Salmi was at Zoo Atlanta when she noticed the gorillas were making a funny sound. The animals opened their mouths wide, then let out a theatrical noise somewhere between a cough and a sneeze—a “snough,” if you will.
At first, she and nearby zookeepers just chuckled. But like any good scientist, Salmi got curious and wondered what was going on behind the noise, which the gorillas only seemed to make when zookeepers came near them with food.
Now, after studying gorillas at Zoo Atlanta and surveying 19 other zoos in the United States and Canada, Salmi and her colleagues think they have a better understanding of why captive gorillas make the unusual utterance.
Zoo gorillas likely started “snoughing” to get their keepers’ attention, the researchers posit in a new paper published Wednesday in the journal Plos One. Scientists have never observed gorillas snoughing in the wild, which suggests apes kept in captivity can learn to make new sounds, a rare capability among animals.
Researchers suspect the animals caught on to the fact that sounds connected with illness got a response from the keepers.
“The snough will trigger the attention and the time of the keepers, because it’s their job to check the health of their animals, so any kind of signs of any disease, then the human goes to see what’s going on,” says Salmi, who leads the primate behavioral ecology lab at the University of Georgia, to Gizmodo’s Kevin Hurler.
To reach these conclusions, scientists designed an experiment involving eight western lowland gorillas (Gorilla gorilla gorilla) at Zoo Atlanta. In one scenario, they placed a bucket of fresh grapes outside the animals’ enclosure. In another, they had a keeper stand outside the cage. And in the third and final scenario, they had the keeper hold a bucket of grapes.
When researchers presented the animals with just the grapes or just the keeper, the gorillas mostly stayed quiet. But they snoughed—and made other attention-grabbing noises and motions, like clapping, beating their chests and banging on the enclosure—when the keeper held the food.
Half of the zoo’s gorillas snoughed during the experiment, and they kept making the noise until the zookeeper reacted. The gorillas never snoughed toward each other, which suggests the sound is reserved for humans.
“That’s quite decent evidence of the animals’ intention to request something from the keeper,” says Zanna Clay, a psychologist who studies primates at Durham University who was not involved in the study, to Science News’ Meghan Rosen.
To bolster their initial observations, the researchers also asked other zoos for photos, videos and observations via a survey. They found that 18 of 39 survey responses indicated snoughing.
“The interesting part is that since some of those gorillas outside of Zoo Atlanta didn’t have any interaction with these gorillas, it’s possible that this snough call has been invented multiple times and not only by the Zoo Atlanta gorillas,” Salmi tells Gizmodo.
The findings add to a growing body of evidence that suggests primates “may at least be limited or moderate vocal learners,” the researchers write in the paper. Scientists have also documented other apes in captivity learning to make new noises, including chimpanzees and orangutans.