Orphaned orangutan survives in the wild – with thanks to her older sister

Researchers have observed a remarkable case of sibling adoption among wild Bornean orangutans in Gunung Palung National Park, Indonesia. After losing their mother, the older sister began providing “alloparental care” to her younger sister. And, thanks to the care she received, the younger sister survived!

The sisters generally kept a greater distance from each other than a typical mother-baby pair. However, they were just as willing to share food and were tolerant towards each other. The younger sister reached her developmental milestones faster than the average young orangutan.

However, she spent less time playing compared to others, which suggests that losing her mother may have accelerated her independence. As for the older sister, the adoption didn’t delay her own reproductive timeline (meaning she was still able to have her own offspring at the expected age).

Orangutans are known for the longest and most intensive mother-infant bond of any non-human mammal. The fact that an older sister stepped in and successfully raised the orphan provides valuable insight into the behavioural flexibility of these amazing apes.