Orangutans are one of the most solitary species of great apes – but a long-term study has discovered that orangutan mothers will interrupt their solitude to make sure their offspring have ‘playdates’.
The findings, published in the journal PNAS, reveal that mothers look for opportunities for their young to play with similarly-aged playmates – travelling further away from their ‘core’ area and towards another mother’s core area to do so.
Maria van Noordwijk and her team from the Max Planck Institute of Animal Behavior (MPI-AB) have followed habituated mother-infant pairs in Borneo since 2003. Encounters between mothers are rare. “Adults usually don’t get very close to each other,” explains van Noordwijk, who led the fieldwork while at the University of Zurich.
But infants don’t seem to show the same level of caution. “They zoom towards each other, roughhousing, biting, grappling,” she says. “Orangutan kids have a ‘play button’ that only mum can switch off when she decides it’s time to move on.”
The researchers noticed that these sessions came at a cost to the mothers. “It just looked like a really long, hard day for them,” says van Noordwijk. “I knew there was something going on with these playdays, but we needed the right statistical technique to verify this.”
Over 15 years, van Noordwijk’s team had collated 32,000 hours of observations from 31 mother-infant pairs. Odd Jacobson, a researcher at MPIA-AB, helped to test whether mothers were actively seeking playmates for their young using statistical analysis – and came back with surprising results.
“Mothers appear to match their kids with play partners that are physically and developmentally suitable,” says Jacobson. And that wasn’t all – mothers travelled throughout the forest to forge these meetings.
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“To find a suitable playmate, it seems that the mothers position themselves spatially to increase the likelihood of encountering mothers with similarly-aged offspring,” continues Jacobson. This movement might suggest that orangutan mothers are aware of what van Noordwijk calls the ‘forest gossip’.
“Orangutans might spend most of their day alone but they’re still embedded in a social network,” she explains. “They know exactly who their mostly lifelong neighbours are, and they know who had a baby when. From their treetop positions they can probably get a rough sense of where these neighbours are, at least on occasion.”
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Navigating this social landscape may draw upon the complex cognitive skills that orangutans possess. “We have accepted for a long time that they apply spatial navigation and route planning to locate and access food resources,” says van Noordwijk. “Now we show that they are combining a cognitive map of not only feeding, but also social resources, in order to provide for their young.”
However, the researchers acknowledge that the playdates were rare, occurring roughly once every 20 days a mother-infant pair was followed. And they’re currently unsure whether the orangutan mothers’ effort is rewarded.
“We still don’t know if the time and energy mothers spend arranging playdates give their young an advantage later in life,” says Sri Suci Utami Atmoko, one of the study’s co-authors, from Universitas Nasional in Indonesia. “What is certain is that only long-term studies like these can possibly unlock the answer.”
Read the full findings here.
Top image: a four-year-old infant is carried by its mother during travel. Credit: Tuanan Orangutan Research Project/UZH
