If you have a pet, you know your buddy knows your voice. Whether you’re calling them for dinner or just in greeting, companion animals like dogs, cats, and horses are able to distinguish between familiar and unfamiliar people talking.
New research finds that gorillas are also able to discriminate between the people they know and like and strangers or humans they don’t particularly care for.
Researchers found that captive gorillas at Zoo Atlanta responded negatively when they heard the voices of people they didn’t know or those they had negative interactions with. The findings suggest they likely recognized who was talking and possibly were aware of the relationship they had with the speaker.
“While conducting another project at the Zoo Atlanta we observed some of the gorillas having consistent negative reactions to the presence of particular humans,” lead author Roberta Salmi, director of the Primate Behavioral Ecology Lab at the University of Georgia, tells Treehugger.
They designed an experiment to test whether gorillas were able to tell the difference between familiar and unfamiliar voices. Within the familiar voices, they made sure to include those people with whom gorillas have repeated positive interactions, such as keepers, and those with whom they usually have negative interactions, such as veterinarians.
Over a period of about six months, the researchers played audio recordings to the apes of three groups of people: long-term keepers who had worked with the great apes for at least four years and had positive relationships with them; people the apes were familiar with but had negative interactions with, such as veterinarians and maintenance workers; and people the animals didn’t know. All the recordings had the people saying the same phrase, “Good morning. Hello.” That’s how keepers usually greet the gorillas.
The gorillas had very few reactions to their keepers, but they responded with signs of stress to those who were unfamiliar or those with whom they had negative exchanges.
“Interestingly, even if our sample size was small, all variables we tested, gazing frequency, duration, latency, and stress responses showed a similar pattern,” Salmi says.
“When gorillas hear the voice of a caregiver they generally ignore it, but if they hear the voice of a stranger or of those familiar humans with whom they have negative interactions, the reaction was strikingly different, with increased vigilant behavior and for few subjects, high level of stress, immediately following the playback of those human voices.”
The findings were published in the journal Animal Cognition.
Why Voice Recognition Matters
Many animals can recognize the voices of members of the same species. That capacity is often key to survival.
“The ability to recognize conspecific individuals by hearing only their calls is of extreme importance for social animals since it allows them, among other functions, to avoid potential competitors and associate with friends, monitor the behaviors of group members, and regulate inter-individual and inter-group spacing, even when visibility is reduced,” Salmi says.
“Species however do not live in a vacuum and individuals may benefit from understanding information exchanged by other species, for example, many species are able to correctly interpret the alarm calls of other species, with obvious positive consequences.”
The lifesaving alerts from other species can help them avoid predators.
Researchers have been unsure, however, whether undomesticated animals can recognize the difference in human voices.
Science has shown that dogs can distinguish between an owner’s voice and a stranger’s. Scientists have proposed that domestication may explain these abilities in some species, but this doesn’t explain why captive gorillas can make the same distinctions. Instead, this study suggests that individual experience may be an alternative method that animals use to understand voices that aren’t from within their own species, Salmi says.
Researchers were relieved to see that when the gorillas in the study heard the voices of people they didn’t know or with whom they had negative interactions, they stopped whatever they were doing and looked toward the noise to determine whether it was a threat.
“If wild gorillas are able to distinguish between people who behave differently, not only by sight but also by voice, it would be extremely helpful,” Salmi says. “It would help me sleep better to know that researchers aren’t making the gorillas more vulnerable to hunters.”
