Some white-faced capuchin monkeys stick their fingers deep into the eye sockets of their friends, and others will use an ally’s body parts to whack a common enemy.
A new study found that older, sociable capuchins are prone to inventing more new types of social behaviors, many of which seem to function as tests of friendship or displays against enemies.
However, younger monkeys are more innovative with their behavior in different categories – for example, ways to interact with the physical environment, such a flipping over cow pies to use as see-saws.
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Some white-faced capuchin monkeys stick their fingers deep into the eye sockets of their friends. In this instance, one capuchin slips its finger deep between the eyelid and the bottom of the eyeball, up to the first knuckle
The researchers say that studying behavioral innovation is important because cultural change mostly occurs when new activities are introduced and picked up by more members of the community.
The study, led by UCLA professor of anthropology Dr Susan Perry, observed behaviors involving games, new ways to interact with infants, and novel forms of sexual interaction.
‘Capuchins have intricate societal structures, long-term, kin-based relations in both sexes and a rich behavioral repertoire, making them an intriguing subject of scientific observation,’ Dr Perry said.
‘Learning about the minutiae of other, nonhuman primate societies reminds us that we are not the only species on this planet that has emotions, personalities, friends, enemies, politics, culture and social drama.’
The findings about these behavioral innovations wouldn’t have been possible without Dr Perry’s 27-year practice studying primates at the Lomas Barbudal Monkey Project near Liberia, Costa Rica.
Dr Perry’s research team has been collecting data year-round in the tropical dry forest, tracking 234 capuchins in 10 social groups by recording 250 different types of species-typical behaviors.
The researcher then turned each new behaviors into a data point for statistical modeling, and their data for this study was based on 10 years of research.
‘In 2001, I added to the core data collection protocol the practice of recording detailed descriptions of any behavior that had not previously been seen,’ said Dr Perry.
By using this protocol, Dr Perry was able to figure out what behaviors were new, when or if they spread throughout the group, and which capuchins were responsible for sharing them.
Although the study found that older monkeys are better at inventing social-interaction behaviors, it also found that younger monkeys innovate behaviors in different categories – ways of interacting with the environment (such as flipping over cow-pies to use as see-saws), obtaining food (wrapping caterpillars in leaves to rub off the stinging hairs) or interacting with their own bodies (for example using twigs and vines as dental floss).
Because true innovations are rare, Dr Perry’s protocol helped standardize note-taking across her teams and mitigate some natural observed bias.
‘This is possibly the best data set on innovation rates in a primate in a natural context,’ Dr Perry said.
‘It shows the different behavioral domains in which these animals innovate because we are not just doing experiments based on a particular experimenter-defined task; we are writing down every crazy thing these animals do and then also watching whether those things stay in the repertoire.’
The researchers then sorted the behaviors into four categories: Social, foraging, self-directed and investigative.
They team tracked 187 innovations, 127 of which were unique behaviors, and 80 per cent were one-off actions that were never repeated by the monkey or transmitted to others.
Most of the innovations were investigative (42.5 per cent), followed by social (37 per cent), foraging (13.4 per cent) and self-directed (7.1 per cent).
For eyeball-poking, the pair can remain in this posture for several minutes, and the one being poked in the eye will often inserts fingers in the partner’s nose or mouth
Dr Perry says that some ‘really kooky things’s turned up – for example, one monkey launched an infant into the air by the tail and juggled it, and another performed similar behaviors with a squirrel carcass – throwing it between it’s hands and feet repeatedly.
However, neither of these caught on with other monkeys.
In another case, one monkey took another monkey’s hand and used it to scratch its own head, and some monkeys even groomed animals from other species, including porcupines, anteaters and howling monkeys.
Several devised ways of playing with sand, like burying body parts of tossing sand between their legs.
In a different study, led by Dr Brendan Barrett, a UC Davis graduate student who Dr Perry advised for several years, a team documented how a group of capuchins figured out how to open the fruit of the Panama tree.
A mix of learning techniques spread throughout the group as they gained experience.
Although the study found that older monkeys are better at inventing social-interaction behaviors, younger monkeys innovate behaviors in different categories – for example, ways of interacting with the environment such as flipping over cow-pies to use as see-saws (pictured)
Some of the older animals were familiar with the fruit—which contains seeds protected by a hard shell lined on the inside with prickly hairs—and some weren’t.
Dr Barrett introduced the fruits to the new area two at a time, so that the researchers could document each instance of interaction.
The researchers found that most monkeys adopted the most efficient technique for opening the fruit, even though Napoleon, the monkey that developed the technique, was not a high-ranking member of the group.
‘It will be interesting to do similar studies in similar societies and see if this is fairly standard,’ Dr Perry said.
‘It does make more sense for monkeys to have a payoff bias rather than a prestige bias in a foraging task for which there is a clear efficiency advantage.
‘But there might be other behavioral domains where you would expect different types of social learning biases.’
The study provides an important link to the natural world for an increasingly technology-obsessed human culture, Dr Perry said.
‘This is really eye-opening to people who naturally assume that we are the only species capable of such things, and it makes people empathize more with other species,’ said Dr Perry.