The topic of zoos is always one that is touchy for people, but if there’s one thing that’s often interesting to discuss, it’s how the animals seem to be evolving to live in captivity.

Zookeepers have found that captive gorillas use a unique vocalization when communicating with the humans who care for them – a sound like “snough!” – and they never use the same noise when interacting with other gorillas.

A new study on the matter concluded that the practice indicates gorillas are capable of vocal learning and innovation.

Scientists already knew that apes like chumps and orangutans invent knew sounds when they encounter completely novel situations – chimps, for example, blow raspberries at their human handles while orangutans prefer whistling.

In the case of the gorillas, researchers used an experiment to find out whether or not the ability shows up in the western gorillas housed at Zoo Atlanta, too. There, they observed six female and two male gorillas in three different scenarios.

In the first, the gorillas were within a meter of a familiar zookeeper. In the second, they were near a bucket of grapes. In the third, the zookeeper was holding the grapes.

To no one’s surprise they “spoke” most often when the trusted zookeeper was holding the food, and sure enough, made the attention-getting (AG) ‘snough’ sound.

Four of the right gorillas used the noise to get the zookeepers attention, and represented around 85% of all vocalizations during the experiment.

“In our study, the AG call was never used by captive gorillas when communicating with one another, 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.”

The same researchers reached out to facilities across the US and Canada, hoping to increase their pool of information. They received word back that the same call was being used by 33 gorillas at 11 different zoos, but after analyzing the sounds, it was determined that only around 40% of captive western gorillas are using the exact same vocalization.

“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.”

Interestingly, it’s also used most often by groups of related gorillas, suggesting the behavior may be learned or intentionally taught.

“Whether the AG call has emerged randomly or has been learnt/modelled by observing humans…remains unknown.”

Either way, this seems to be just one more example of how much these animals are like us – and perhaps one more argument against forcing them to live their lives on display.