We know that great apes can communicate with gestures, sounds and facial expressions, but to date, research has been largely limited to African great apes, with research into orang-utans restricted to a handful of studies of the apes in captivity.
But for the first time, new research describes both gesture-based and vocal communication among wild orang-utans: specifically Southwest Bornean orang-utan mothers and their young.
The researches studied 16 orang-utans in the peat swamp forests of Sabangau National Park on the Indonesian island of Borneo, in a 500 square-kilometer protected area managed by the University of Palangkaraya for the purposes of scientific research.
Working in small teams for more than two years, they captured a total of 681 hours of video as well as recording communication by hand. The researchers were careful. When their presence seemed to affect the orang-utans, they would stop gathering data and withdraw to a greater distance.
In total, they identified 858 vocal signals and 441 gestures. Of these, they identified 11 vocal signals and 21 gestures that could be said to form a recognizable repertoire. Facial expressions were excluded because, it turns out, these are quite hard to gauge and record in a forest setting.
It’s clear that orang-utans use gestures to get another orang-utan to do something, but the data was too limited to link any one gesture and any one goal. However, some definitive and fascinating conclusions could be drawn. For instance, that gestures can be used in different contexts, i.e. to request more than one goal; and similarly that any one goal can be requested with more than one gesture.
In an email reply to New Atlas, University of St Andrews researcher and study author Cat Hobaiter explains further. “We showed that gestures have specific meanings no matter who uses them, and that many of the meanings were shared between chimpanzees and bonobos.” Prior research into chimpanzee and bonobo communication has demonstrated a link between specific gestures and goals. (Hobaiter apologizes for the delay in her response which she attributes to a spate of storms in the forest.)
By gauging when gestures stopped, the researchers could identify various goals being requested, including giving an object, climbing on the signaler, moving away, resuming play, and stopping an activity. Interestingly, a greater range of gestures (22) was used by immature offspring than by adult females (14).
Observed gestures, meanwhile, were not exclusively visual in nature. Though all had a visual component, some were also audible, or involved direct contact. Gestures included beckons, bites, dangles and flings as well as grabs, pokes and pushes.
All of the 21 gestures in the repertoire have been previously observed, but the researchers did see five one-off gestures that didn’t qualify for inclusion. But they were interesting. Of the five, two were new to orang-utans, though they have been observed in the repertoires of other apes.
Why would different ape species on different continents share physical gestures? “We think the gestures are biologically inherited – the way many animal signals are,” Hobaiter tells New Atlas. “One interesting pattern that gives us a clue about this is that the more closely related two ape species are the more gestures they have in common – and that includes us! Young children tend to use many of these same gestures before they use language.”
The orang-utans were seen to adapt their communication to the circumstances, using gestures more frequently when the orang-utan they were communicating with was looking at them.
Orang-utans gesture with hands and arms as well as legs and feet. Though they favor hands and arms, they seem to use their legs and feet more often than chimpanzees making similar gestures. “That makes real sense,” Hobaiter adds. “Chimps are great climbers but they’re fundamentally terrestrial, orangs are arboreal: their feet even look more like hands, shaped for grasping rather than balancing on top of.”
She explains that, even in the best zoos, adult orang-utans are often kept together, and in an environmental totally different to their natural habitat. “That’s going to impact who they have to communicate to, how they can communicate, and what they have to communicate about.”
Of the vocal signals observed, all had been recorded in prior research. The researchers describe a so-called “kiss squeak” made by inhaling through “trumpet-lips.” The sound is sometimes modified with cupped hands, or a leaf or leaves around the mouth. They also document grumphs, grumbles, gorkums (a kiss squeak followed by a number of grumphs, naturally), lorks and throatscrapes.
Unlike other great apes, orang-utan social groups tend to be limited to mothers and offspring. Even sibling communication is rare thanks to the typical six- to eight-year interval between a mother having another infant. Because of the makeup of these social groups, the range of gestures lacked those associated with sexual behavior that are seen both in wild African apes and captive orang-utans.
Of the 16 orang-utans studied, seven were mothers, five were young dependent offspring, and two were older siblings able to do some things for themselves. The researchers believe one of the mothers was new to the protected area having been displaced by nearby forest fire in 2015.
The researchers found that the orang-utans are very responsive to gestures. In 90 percent of cases, recipients responded to requests either before the gesture had finished, or in under a second afterwards. In 80 percent the outcome seemed satisfactory to the signaler.
The range of gestures observed supports the findings of studies based based on captive orang-utans, but those relating to responsiveness and limb use do differ, which could be to do with the fact that captive orang-utans spend more time on the ground and have longer lines of sight because there’s less foliage in the way.
The researchers say this highlights the need to study orang-utans in their natural habitat. “To have gesture data from wild orang-utans is incredibly important,” Hobaiter says, “both because they fill an important gap in our scientific understanding but also because they’re endangered, so anything we can find out about them that might help us protect them is really valuable.”
Serge Wich is a Professor in Primate Biology at Liverpool John Moores University, and not involved with this research. In an email reply, he tells New Atlas that this research is important because wild orang-utans are understudied, both compared to other wild great apes and captive orang-utans.
“The results indicating that there are 21 gesture types that are more used when the other orangutan is paying visual intention indicates that even within these complex arboreal environments visual contact is important,” he adds. “I hope researchers at other sites will conduct similar studies so that repertoires for gestures between sites can be compared.”
According to the research, the data suggests that further types of gestures are likely to be identified in future. This is because the rate new types were discovered didn’t slow as data was gathered. The team hopes to go on collecting data, one goal being to work out whether different communities of ape communicate in different ways, akin to an accent or dialect.
The research team included researchers from University of Exeter, University of St Andrews, University of Palangkaraya and the Bornean Nature Foundation. The research is titled Gesture Use in Communication between Mothers and Offspring in Wild Orang-Utans (Pongo pygmaeus wurmbii) from the Sabangau Peat-Swamp Forest, Borneo. It has been published in the peer-reviewed International Journal of Primatology and is free to read online.
Sources: International Journal of Primatology, University of Exeter