Orangutans have long lives, often reaching 40 years old in the wild. Now, a new study has revealed that these great apes have one of the longest breastfeeding periods among mammals.
The research, published in the journal Communications Biology, shows that wild orangutan juveniles consume their mother’s milk continuously until they are at least six and a half years old.
Scientists already knew that orangutan offspring breastfeed for a long time. But previous studies have been unable to clearly quantifying milk intake, leading to contradictory estimates for their weaning age.
In the new study, the team spent almost three years collecting and examining faecal samples from wild Bornean orangutans in the Danum Valley Conservation Area in Sabah, Malaysian Borneo.
They used a technique known as faecal proteomics, which identifies specific proteins in faeces. Orangutan milk contains several proteins that other food sources do not, so discovering them in a juvenile’s faeces provides evidence that they are still consuming breast milk.
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Further studies comparing the milk‑specific proteins with biological defence proteins suggest the more milk a young orangutan consumes, the stronger its biological defences.
The researchers believe that breastfeeding for such a long period could explain why orangutans have one of the lowest infant mortality rates among primates. On the flipside, it also means they are slow to recover after population declines.
The study notes that “faecal proteomics can be applied to a wide range of wild animal populations, with the potential to uncover novel aspects of behaviour and physiology.”
Top image: View of Danum Valley Conservation Area in Sabah, Malaysian Borneo. Credit: Nora Carol Photography/Getty Images
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