In a fascinating discovery, gorillas at Zoo Atlanta were caught calling their keepers using a strange hybrid of coughing and snoring.

Only two other species have shown this ability to create new vocalizations to get our attention: chimpanzees and orangutans housed in zoos. Now, we can add gorillas to that list.

As many of us know, Koko put the spotlight on gorilla intelligence in the 80s and 90s with her incredible ability to communicate with humans using sign language. She has been trained, but now it seems the gorillas have taken it upon themselves to establish unique communication with us on their terms.

Biological anthropologist Roberta Salmi of the University of Georgia and her colleagues conducted an experiment to confirm the purpose of “snough” by putting eight zoo gorillas in three different situations.

Only two other species have shown this ability

In the first, only the caregiver was present, in the second only the food was present, and in the last, the caregiver was holding the food. When they were present, the food and the caretaker were in sight but out of reach.

The gorillas involved used the ahem-like “snough” vocalization most often when a human with food was present, indicating that the call is likely an attempt to attract the attention of the caretaker.

Interestingly, the same call has been discovered in other US zoos. As many as 33 gorillas housed in 11 different zoos in the US and Canada reportedly make a similar call, although so far only six gorillas in four different facilities have been confirmed to use this sound.

Salmi and his team aren’t sure whether different groups independently discovered that this sound is effective, or whether it spread through intelligent primates (who are more than capable of learning from each other) who passed their knowledge on to each other.

Gorillas can recognize and distinguish human voices

Most components of language appear in the communication systems of other animals, such as vocal learning, syntax, and semantics. It was once thought that primates lacked the proper equipment to vocalize as we do, but this has since been shown not to be true, he writes ScienceAlert.

The novelty of this cry adds to a growing body of evidence showing that primates can indeed make new sounds for new contexts.

“Evidence for vocal learning and innovation, although sparse, is slowly accumulating for captive monkeys,” the team wrote in the paper published in PLOS One.

“Orangutans can learn to produce vocal utterances and whistles, chimpanzees adopt novel referential food calls through vocal convergence as part of social integration, and apes such as Koko the gorilla and Vicky the chimpanzee are capable of producing a limited number of novel utterances.”

Previous research has also shown that gorillas can recognize and distinguish between different human voices.

The ability to produce unique calls, rare in the animal kingdom

Examples of complex vocal learning – the ability to produce unique calls – are rare in the animal kingdom and only confirmed in some species of birds, bats, cetaceans and elephants. But they do all this by imitation.

Acoustic analysis has shown that gorilla snoring is a unique sound, not an imitation – although these cheeky apes are certainly capable of mimicking us in other ways.

“These results demonstrate that gorillas can modify their calls to produce a novel sound, and further confirm that they can intentionally produce their calls and gestures to change their caregiver’s attention,” the team concluded in the paper.

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