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Attention-Grabbing Apes: Studying Gorilla and Orangutan Gestures

  • Gorillas Calaya and Moke at the Great Ape House outdoor yard.
    Western lowland gorilla Moke was born to mom, Calaya, in April 2018.
  • Redd and Batang at the Zoo's Think Tank exhibit.
    Bornean orangutan infant, Redd, wrestles with his mom, Batang, at Think Tank.

How does western lowland gorilla mom Calaya get her son Moke’s attention? And how closely does Bornean orangutan Batang keep her son Redd when other adults are sharing their space? With two youngsters growing up at the Great Ape House, primate staff are taking the rare opportunity to study the gestures and spatial proximity between these mother-infant dyads. Get the scoop about this ongoing research from primate curator Dr. Meredith Bastian and primate keeper Alex Reddy.

What sparked your interest in studying great ape gestures?

We are experiencing a very unique moment in time at the Great Ape House. When our western lowland gorilla Moke was born in April 2018 to mother, Calaya, it marked the first birth of this species at the Zoo since January 2009, when Kibibi was born. On the orangutan side of the building, Redd’s birth in September 2016 was also a special occasion. Prior to his arrival, the last orangutan birth at the Zoo was 25 years ago.

It is rare to have a gorilla infant and an orangutan infant that are so close in age—Moke just turned 1 year old, and Redd will be turning 3 years old soon. We couldn’t pass up the opportunity to take a deep dive into the gestural development of these two species!

This study combines both of our expertise. Meredith studied wild Bornean orangutans, documenting the relationship between opportunities for social learning based on patterns of spatial proximity and cultural variation across populations. Alex wrote her master’s thesis on gestural communication in great apes.

With our combined knowledge and our current great ape collection, it seemed a rare chance to do something innovative while contributing to a gap in the literature regarding gestures and spatiality in great apes living under human care.

Which apes participate in this study?

For this study, we focused on our mother-infant dyads: Bornean orangutans Batang and Redd, and western lowland gorillas Calaya and Moke. Not only are we are interested in looking at gestures between mother-infant dyads, but also we are keen to learn how these relationships and communications are altered when other individuals are present.

What is a gesture, in great ape terms?

Non-human great apes communicate using gestures, just like us. Although their gestures may seem simplistic or unsophisticated to the untrained eye, their non-verbal interactions actually have quite a bit of nuance and variation. Two elements are key when defining the term gesture: they have a purpose and a goal. In other words, do the apes’ limb or head movements elicit a response from another individual?

A key point here is that gestures are used in dyad or group contexts. The complexity of these gestures highlights the social networks these animals live within and gives us a sense of how they navigate their day-to-day social interactions.

How do great apes use gestures to communicate?

Great apes use gestures to communicate with other individuals within a certain range of spatial proximity. Although we cannot derive exact meaning from each unique gesture, we do know that there are complex modes of communication occurring between and across non-human primate species, and that these interactions can be both nuanced and multifaceted.

One common gesture that is unmistakable in gorillas is a “clap.” This action is frequently employed by Calaya, our gorilla mother, to indicate a desired reaction from Moke and Kibibi during their play sessions.

Another common gesture that we see in both of our infants is a “reach.” Because Redd and Moke are still so young, they are heavily dependent on their mothers and constantly reach out to them.

What do the gestures mean?

We can learn a lot about ourselves—and the origins of our own gestures—by observing the way great apes use them. However, we must be careful and avoid attributing human characteristics to the actions of our gorillas and orangutans. Since we have no way of confirming the intentions behind each gesture, we are not attaching a subjective explanation to their actions.

Instead, we want to look at the apes’ movements through a lens of how these gestures “fit” into the context of gorilla and orangutan biology, behavior, socialization and so on—in other words, their species-specific natural histories.

Both apes are highly intelligent and adapted to the environment from which they evolved. Orangutans, the most solitary of the great apes, and the largest tree-dwelling animals, have different life histories from the large troops of primarily ground-dwelling gorillas.

How do you collect data?

We track how frequently interactions occur and what kind of gestures are used using an app called ZooMonitor. For example: do the apes raise their arms? Reach out with their palm or wrist? Move an enrichment item? Present a body part? In all, we look for more than 30 different gestures. We observe the apes for 30 minutes at a time, noting the kinds of gestures that are used.

Within that time frame, we record every instance the mother-infant dyad approaches or moves away from one another, noting their proximity—whether they are less than two meters apart; between two and 10 meters apart; or more than 10 meters apart. At the same time, we also record the location of other individuals in relation to the mother-infant dyad.

Bornean orangutans Redd and Batang wrestle at Think Tank. 

What patterns are you seeing?  

We have noticed that there is frequent gesturing between mother-infant dyads when mothers are in environments in which they appear to be more at ease. Based on the Zoo’s recent nest study and primate keeper observations, we know that our great apes prefer to socialize with certain individuals over others. This personal preference may influence their choice of gesture based on who they are sharing space with at the time the data is collected.

Whereas Calaya always spends time with her troop—Moke, Baraka (Moke’s father), Mandara and Kibibi—Batang and Redd’s social group changes frequently—Kyle (Redd’s father) and Bonnie; Iris and Kiko; and Lucy. Batang tends to be more at ease when she and Redd are with her preferred social group, and when they choose to spend time inside. In situations where Batang is not with her preferred group or is spending time in the outdoor yards, she tends to hold Redd closer to her. This leaves little room for gestures to occur between the dyad.  

One-year-old Moke at the Zoo's Great Ape House is helping scientists learn how infant gorillas communicate with their mothers. 

How can this study help gorillas and orangutans?

If we hope to better understand apes and their unique modes of communication, an increase in knowledge will allow those who care for (and about) them to better co-exist alongside them. The results of our study may help primate keepers better understand how mother and infant gorillas and orangutans communicate with one another and how they navigate their group lives. It will be interesting to learn which gestures are successfully communicated when mothers and infants are in close proximity to one another, and which are more effective from a distance.

In the wild, both orangutans and gorillas are critically endangered, which means they are teetering on the brink of extinction because of threats like deforestation, disease, poaching and bushmeat, as well as the illegal wildlife trade. Scientists estimate that only 100,000 Bornean orangutans remain in the wild, and their habitat is largely made up of unprotected, fragmented forests. Western lowland gorilla numbers in the wild are slightly higher—estimated at 360,000—but about 80 percent of those individuals live in unprotected habitat.  The Zoo participates in the Association of Zoos and Aquariums’ Species Survival Plan for both species, as well as the Ape Taxon Advisory Group (TAG), which contributes to protection of these species in the wild. To be successful in conserving apes and their habitats, the Ape TAG serves to coordinate efforts among AZA zoos to protect wild apes. They also contribute funds and expertise directly to field projects and offer grants to conservation organizations.  

In June, Meredith and Alex will travel to Tuanan, a wild orangutan research field station in Central Kalimantan, Indonesian Borneo. Stay tuned for details of their journey to come and more on how individuals can make difference in the lives of these amazing apes!

This story appears in the June 2019 issue of National Zoo News. Follow the latest Moke news using the hashtag #GorillaStory; and, don't miss the Zoo's #OrangutanStory updates!

Collaborators on this study include Alexandra J. Reddy, Meredith L. Bastian, Mariele Saunders-Shultz, Caroline Ratliff, Sonia Dahmer, Molly Burdine, Mimi Rebein and Courtney Berne.

Love gorillas and orangutans? Don’t miss the daily gorilla keeper talk at 1 p.m. at the Great Ape House. Check out all of the Zoo’s animal demonstrations here.