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Preserving orangutan culture an ingredient for successful conservation

  • Scientists once thought that all animal behavior was instinctual, but now know that many animals — particularly social animals — are able to think and to learn, and to display culturally learned behaviors.
  • Orangutans are one animal in which occurrences of culture have been fairly well proven, with orangutan groups at different study sites displaying variant behaviors that have neither environmental nor genetic origins, meaning they can only be cultural in nature.
  • Among these cultural behaviors are basic tool making and use for food harvesting, purposeful vocalizations, and variations in nest building materials and methods. Scientists fear habitat loss and crashing populations could cause this cultural heritage to vanish.
  • The loss of varied cultural behaviors could potentially make orangutans less adaptable to changes in their environment at a time when, under extreme pressure from human development, these great apes need all the resources they can muster.
An adult female orangutan performs a kiss-squeak call using leaves that she is holding. Researchers are finding that orangutan calls vary from population to population, and can represent an example of culturally learned behavior. Photo © by Tim Laman

Subtle variations seen in a species across its range often turn out to be important to successful conservation. That’s because, on closer examination, populations are found to be genetically different subspecies. But what of geographic differences in behavior? Think about our own species, with its varied foods, clothing and customs. We call these differences culture.

Not so long ago scientists dismissed the possibility of culture in animals, assuming that all their behaviors arose from instinct alone. But now it is recognized that some species — especially social animals — can think and learn new behaviors, and that they do possess culture. A lot of recent research offers good evidence that orangutans are among them.

But what is the evidence for culture in these great apes? And once cultural variations in orangutan groups are recognized, what do those differences mean for successful conservation?

Could the preservation of subtle cultural variations be a key to aiding orangutans in their survival as they suffer extreme pressures from habitat loss and degradation in Borneo and Sumatra?

Behaviors differ orangutan group to group

Orangutans have been observed to possess complex behaviors that are common at one study site while being absent (or very rarely seen) at similar sites. One example: Cheryl Knott of Boston University and her colleagues have watched orangutans feeding on neesia fruit at two different study sites in two different ways. At one location, the animals extract the nutritious seeds without the help of utensils, at the other they use a stick.

“They modify [the stick], which is part of the definition of tool. They take the stick, and they bite the end to make [it] a certain length,” Knott says. “If they can’t get into [the fruit] with a certain stick, they’ll modify it or try a different one. They also have tools for [harvesting] insects that are different.”

Orangutan researcher Cheryl Knott and field assistants check data on orangutans they are following in the rainforest of Gunung Palung National Park, Borneo. Photo courtesy of Cheryl Knott

Researchers have observed a variety of other behaviors where orangutans employ tools. Some populations use a “leaf glove” to handle spiny fruits or branches; others employ a clump of moss, much as we would use a washcloth, to clean their hands. Notably, both of these behaviors appear to be cultural: common in some groups of orangutans but rare or absent in others.

There are also activities that all orangutans do, but that different groups do differently, just as all human cultures cook, but different countries have very different cuisines. All orangutans build a new nest in the forest canopy each night, for example, but there are variations in how orangutan groups “decorate” their nests.

“Some places they make pillows, other places they put roofs over nests, other places they line them — there are different subtleties,” Knott explains.

These variations, however, aren’t absolute proof of culture. There could be simple environmental reasons for some of the differences. If, for example, one population eats bananas and another doesn’t, maybe it’s because the range of the latter group doesn’t include any banana trees – that’s an environmentally perpetuated variant, not a cultural one.

An adult female, and her 11-month-old daughter eating fruit of Ardisea sp. The youngster is learning how to eat this fruit from her mother. There is little specific orangutan behavior that is instinctual, and young orangutans must learn how and what to eat from their mothers. Photo © by Tim Laman

Sussing out cultural differences

Researchers trying to scientifically identify culture in an animal species need to rule out two alternatives: first, that the difference in behavior is due to a difference in habitat; and second, that the populations have evolved genetic differences that correlate with the behavioral differences.

“Ideally, if it weren’t morally incorrect, you would take an orangutan from one population and put it in the other population,” explains Meredith Bastian, curator of primates at the Smithsonian’s National Zoo in Washington D.C. That’s been done in the lab with fish, for instance, but with orangutans, it’s more difficult — instead, you need to set up a natural experiment.

“You find a situation in the wild that’s already set up to give you the information that you need,” says Bastian, who did exactly that in her dissertation work.

“We had to have two populations that were currently separated, where we had reason to think that their genetics weren’t that dissimilar,” she says. But other features of the local geography needed to suggest that the two groups could have mixed in the past.

The two populations chosen by Bastian and her team were divided by a wide river; an impassable barrier because orangutans don’t swim. Fecal and hair samples were analyzed to confirm that the genetics of the apes on both sides of the stream matched. The ecology of the sites also needed to match, so plants at both sites were carefully surveyed and found to be alike.

“You need to rule out that there’s just not a geographic or habitat difference,” says Bastian.

When environmental and genetic variables hold constant, but differences in behavior are seen, those differences can be reliably attributed to culture.

This young female in Gunung Palung National Park is making her night nest. All orangutans build a new nest each night, but there are variations in how different populations “decorate” their nests. Photo © by Tim Laman

One example of orangutan culture involves the varied materials used to build nests, a behavior Bastian calls leaf carrying. “They’re carrying leaves from one place to another place, where they want to build a nest,” she explains. What’s particularly interesting is that the leaves they use have anti-mosquito properties.

At one study site this behavior was common among all orangutans. At other sites, the behavior was either quite rare — maybe one individual was observed doing it — or completely absent.

In another study, Serge Wich and his colleagues found variations in orangutan calls that didn’t correlate with either genetic or environmental differences. When building nests, orangutans at one site made sounds humans might equate with “raspberries,” while at another, they sounded with “nest smacks,” while at two other sites the great apes didn’t have a special vocalization at all to accompany the task.

The researchers also found that orangutan mothers at some study sites had a special vocalization made before retrieving an infant from which they’d become separated. “The mother would call, which would make the infant move closer to her,” Wich explains. “This can be in situations where the mother might be aware of a threat, or when the mother would like to leave the tree and have the infant with her.” Two populations were found in which mothers from each group used different calls, while three more populations were discovered in which mothers made no call at all when retrieving their infant.

Deforestation for an oil palm plantation. Habitat loss due to agribusiness expansion is devastating orangutan populations. No one knows how much damage it is doing to orangutan culture. Photo by Rhett A. Butler

What orangutans learn

These very carefully structured “natural experiments” have helped prove that orangutans show cultural variations in behavior, says Knott, though she cautions that such rigorous experimental perimeters must surely exclude many cases of orangutan culture that cannot be so meticulously confirmed.

“Scientifically we consider something cultural if it’s a behavior that differs between two populations, and we can’t explain [the difference] using genetics or environmental differences,” she says. “That’s a pretty strict definition though, that excludes some things that really are cultural as well, [behaviors] that are passed on by social learning.

Knott notes that there is really very little specific great ape behavior that is instinctual — that’s because orangutans basically learn to be orangutans from their mothers. This fact is confirmed by orphans, who, when they arrive in rehabilitation centers need to be taught everything.

Orangutan young “don’t know how to find food instinctively, they don’t know how to make a nest, they don’t even really know how to climb and move around,” Knott explains. “A lot of animals are much more instinct driven: if you dumped [their young] someplace, they’d figure out how to get food. With orangutans they have to learn what’s edible and what’s not.”

Unfortunately, scientists can’t set up “natural experiments” in most cases in order to gain absolute proof that a given orangutan group behavior, such as tool making, is cultural. But “Obviously any kind of tool use is cultural,” Knott asserts, even without experimental confirmation that controls for the other variables.

But since we humans are so good at anthropomorphizing — seeing our emotions and motivations in animals, even when the meaning of their behavior may be very different — it’s important that some examples of orangutan culture have met the most rigorous standard of proof.

This adult male orangutan in Gunung Palung National Park in West Kalimantan is performing a kiss-squeak, a threat vocalization. Researchers have found variations in orangutan calls that do not correlate with either genetic or environmental differences, providing evidence of culture. Photo © by Tim Laman

Applying cultural differences to conservation

While the discovery of cultural differences in orangutans is fascinating, do the findings have implications for conservation? Should conservationists, for example, strive to preserve the wide range of known orangutan cultures, or is it sufficient to simply preserve enough animals, and in so doing, protect the species’ potential for future cultural innovation?

A human-centric answer to this difficult question: if we lose these orangutan cultural variations, we lose evidence that might be valuable to the science of our own origins.

“If we had only one [orangutan] population, we wouldn’t know how flexible they are,” Knott says. “We wouldn’t understand this behavioral flexibility and that they share that with humans. We can understand the origins of human culture by studying orangutans and how these behaviors are passed on.”

We might also lose potentially valuable insight into the evolution of human language. “If we continue to lose [orangutan] populations, we will never be able to map the call variation that is out there and compare that with the variation we find in humans and other species,” says Wich. “That would be a huge loss to studies that try to understand our own evolution.”

Peat forest in Borneo, Indonesia, home to orangutans. Orangutan populations found on the opposite sides of wide rivers often possess differing behavioral traits, which upon careful study in some cases have been proven to be culturally caused. Photo by Rhett A. Butler

The cultural toolbox

Some culturally learned survival techniques could be especially useful in hard times and difficult situations, like those being encountered by today’s beleaguered orangutans.

Knott has observed that the simple stick tools used to get at prickly and well-protected neesia fruits make it easier for orangutans to consume a very high-value food — the seeds are 70 percent fat. The fruit is “surrounded by really nasty, fiberglass-like hairs,” she says. “When we’re following orangutans eating them, we wear ponchos to avoid getting the stuff all over us. You can’t wash it out; it gets in your clothes; it can cut your fingers.”

Bastian notes that at her study site, where resources were limited, orangutans had to rely heavily on less desirable, hard-to-acquire foods like the inner bark of certain trees. And that was where she observed interesting cultural differences in populations. Realize, she says, that there may be hundreds of species of plants in these animals’ habitat. “How do you know which to try, which are palatable?”

In a given forest, orangutans might only eat five plant species out of hundreds. So there’s a lot of individual experimentation. But where the situation is challenging, shared experience becomes critical: it was with these hard-to-acquire fallback foods where evidence of cultural transmission was seen.

An orangutan in a forest nest. Scientists are in only the early stages of investigating orangutan culture and how its preservation might enhance their chances for conservation. Photo © by Tim Laman

Disappearing cultures

Wiping out orangutan cultural variations may be exactly what humans are doing as they destroy rainforest and force animals to cram together in smaller and smaller patches of habitat.

In orangutans, higher population density in a forest locale has generally been observed to correlate with more diverse interacting cultures — something like the way urban humans from many ethnic backgrounds are exposed to more opportunities to learn from each other.

But in her study site, Bastian found something unexpected and quite opposite.

“We thought going into this, since my site had such a high density of orangutans — the highest density every recorded in Borneo — that they’d be everywhere, being highly social with each other.”

Instead, where the habitat had suffered extreme compression from human influence, and there was high competition for resources, the scientists found that females avoided associating with each other — possibly in the same way that humans on a very crowded city street, or in a packed subway, will not make eye contact.

Thus, when orangutans live in a forest where population density and resources are optimal, cultures are shared. But when they’ve got no choice but to crowd together and compete for resources, cultural transmission diminishes.

“There were fewer opportunities for social learning [in the crowded forest site], so, we found, fewer of these innovations that reach the level of culture,” she explains.

This loss of cultural variability — whether due to local extinctions, or to multiple populations being unnaturally squeezed together — likely reduces orangutan resilience, the ability to adapt to change. That’s because cultural differences provide species with alternative life strategies.

“Ways for [orangutans] to survive and figure out their environment could be compromised if they don’t have enough opportunities to learn from each other,” says Bastian.

Sunset over tropical rainforest in Sabah, Malaysia on the island of Borneo. The future survival of orangutans could be aided by the preservation of orangutan culture. Photo by Jeremy Hance

Learning from the orangutans

Scientists continue to gather data, but it now appears likely that the varied cultural innovations orangutan groups have developed over time could be critical to the great apes, if they are to successfully withstand the intense pressures they are currently suffering.

Bastian experienced this particular proof in a dramatic personal way. Once, when she stayed out in the field longer than was wise, she became seriously dehydrated. “I had run out of water, and I was way too far away from camp. I was desperately needing water,” she remembers.

In her research, she’d seen orangutans break off the bottoms of climbing palms known as rotan plants, and then drink the water that flowed out. She took her machete and slashed at a plant.

“It has giant thorns coming out of it at every angle, it’s very painful stuff. I don’t think I would have thought there’d be running water at the base of that,” she says. “But I saw an orangutan do it, so I knew there [would be] pure water coming out of the bottom of the rotan. If you don’t learn from others, you may lose an ability to deal with difficult situations. It probably saved my life.”


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