This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Playing with peers is a crucial part of growing up—so crucial that orangutan mothers will go out of their way to arrange playdates for their young, according to a 15-year study of wild Bornean orangutans. Orangutans are the most solitary of all great apes.
Mothers spend most of their time alone with their youngest offspring, who remain dependent for their first seven or more years of life. Infants have little opportunity to meet youngsters their own age, yet playing together helps build the strength and social skills that they need later in life. Now scientists have strong evidence that orangutan mothers look for opportunities for their young to play with similarly aged playmates, even traveling farther to do so.
"We reveal a hidden cost of solitary living," says Maria van Noordwijk, senior author of the study published in the Proceedings of the National Academy of Sciences. "On top of providing food and safety for their young, orangutan mothers are tasked with supplying social resources too." The study was led by scientists from the Max Planck Institute of Animal Behavior together with the University of Zurich, Universitas Nasional and Rutgers University. Since 2003, van Noordwijk and her team have followed mother-infant pairs at Tuanan Research Station on the island of Borneo in Indonesia, where they observed habituated orangutans from morning to night.
Encounters between mothers are rare, but when they do happen, they're a cautious affair. "Adults usually don't get very close to each other," says van Noordwijk, a fellow at the Max Planck Institute of Animal Behavior, who led the fieldwork while at the University of Zurich. Infants, though, are a different matter.
"They zoom toward each other, roughhousing, biting, grappling," she says. "Orangutan kids have a 'play button' that only mom can switch off when she decides it's time to move on." Van Noordwijk noticed that these infant encounters seemed to come at a cost to the mothers. "It just looked like a really long, hard day for them," she says.
"I knew there was something going on with these playdays, but we needed the right statistical technique to verify this." After 15 years, van Noordwijk's team had amassed 32,000 hours of observations from 31 mother–infant pairs. Working with Odd Jacobson, a postdoctoral researcher at the Max Planck Institute of Animal Behavior, she tested whether mothers were actively seeking out playmates for their young. "We applied a statistical technique that combined mothers' space use with social characteristics of neighboring mother-infant pairs," says Jacobson, the paper's first author.
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