Ape Conversations: Researchers Listen To, Analyze Gibbons At The Racine Zoo

Aug 8, 2019

Does the way apes communicate tell us something about how human language developed? That’s what researchers at the Racine Zoo are hoping to find out.

Some sounds the researchers have recorded include territorial calls from two white-handed gibbons protecting their turf. That's according to researcher Dr. Angela Dassow, biology professor at Carthage College. She's been studying the communication patterns of gibbons for years.

She says of the territorial call, "even though there’s no other gibbons at the zoo and no one to defend this against, that’s part of an innate behavior that will persist throughout their lives," she says.

Gibbons are an endangered species native to Southeast Asia.
Credit Alesandra Tejeda

The apes are small — under 15 pounds. They have black fur, with white feet and hands. And the pair are father and daughter, named Yule and Robyn.

Dassow is researching how gibbons communicate, and how their patterns form the fundamentals of a communication system. She hopes to compare how they communicate to about 20 other gibbon species, in addition to other apes and even humans.

Yule is a 53-year-old male who's lived in the zoo for most of his life.
Credit Alesandra Tejeda

"We were trying to figure out what exactly it is that the gibbons are really saying to one another. We wouldn’t refer to it as language, per se, because it doesn’t have the same types of properties that human languages have. But we do call it a communication system because there is some information that’s being transferred between individuals," she explains.

Yule and Robyn spend their days in an outdoor enclosure, surrounded by a tall chain link fence. There are ropes to swing on, a high platform to lounge on, and a dog house to hide in.

Dassow’s team includes Carthage College students Asniv Khaligian and Joy Layton. The team had one main focus this summer— the sounds Yule and Robyn make when they play. While the apes spend a lot of time lounging, things can suddenly switch into high gear.

"What’s happening here is they’re grabbing each other’s arms and their feet are going to lock together. There’s going to be a little bit of teeth-bearing, eventually, and then this bleat is going to come out," she says.

Here's what a bleat sounds like:

Dassow’s team has been recording the gibbons in Racine for the past few months.
Credit Alesandra Tejeda

Gibbons are an endangered species native to Southeast Asia. Researchers haven’t been able to catch the sound of the bleat in the wild because the gibbons are too high up in the tree canopy.

"And it’s a really noisy environment, noisier than in captivity. A lot of different species and it’s hard to record a low amplitude sound. Here we have the child species, yes, but that’s one versus the hundreds of species in the wild that we’re competing with," she says.

The noisy gibbons caught the attention of kids visiting the zoo, including nine-year-old Josh Oostman.

“They kind of squeak a little. Some looked at us, just stared at us blinking for a long time, I’m like, 'What are they wondering?’ ” he says.

Dassow and her crew are trying to figure out what the gibbons’ "squeaks" and bleats mean. They're doing that by examining the sounds themselves and the context in which the apes make them. The researchers measure how high and low the sounds are, how frequent, and note any gestures the apes are making at the time.

Inside the enclosure are ropes to swing on, a high platform to lounge on, and a dog house to hide in.
Credit Alesandra Tejeda

Through this type of analysis, Dassow has discovered that gibbons make predator warnings.

"They have a sequence of sounds that they produce when they see a clouded leopard, a complete different sequence when they see a tiger that’s been sitting versus a tiger that’s been running. Our captive ones here actually have a little warning for their veterinarian. The other captive group that I’m working with is at the Henry Vilas Zoo in Madison, and they have a warning for the Goodyear Blimp. They don’t like that one," she explains.

But she's uncovered more than just a fear of blimps. Dassow says she’s the first researcher to discover that when gibbons make one sound, they're already thinking about what their next sound will be.

"That’s a level of cognition that not all species possess. So, that tells us a little more about how closely related their system is to us," Dassow says.

So how does this tie into human language?

Dassow says by understanding how gibbons use sounds to interact, researchers can piece together their communication system – possibly an ancient predecessor to the complex language we use today.