Orangutan twins are a rare occurrence in nature! On October 15,2009 an orangutan female named Tut gave birth to twins at Camp Leakey in Tanjung Puting National Park, Central Indonesian Borneo.
She first appeared on the bridge in the morning carrying her two newborn infants . Since one of the twins seemed weak, the Camp Manager contacted OFI’s Orangutan Care Center and Quarantine in Pasir Panjang near Pangkalan Bun to request medical assistance. Unfortunately, the veterinary team was unable to save the male infant who died shortly afterwards. So far the surviving twin is doing well.
This is the first time that orangutan twins have been witnessed at Camp Leakey and/or Tanjung Puting National Park. Since orangutan females frequently come to Camp Leakey with their newborn infants after an absence of several days or more having given birth in forest solitude, it is possible that twins had been previously born but only one survived. In cases like this, when the female finally arrived in camp with the sole surviving twin, there is no way that the assistants or I would have known that the female had initially given birth to twins.
Among humans there are 32 twin live births per 1,000 live births. Living human twins constitute about 1.9% of the world’s human population. Of these, only 8% are identical.
We don’t know the equivalent figures for great ape twins. There have been twins born among the wild chimpanzees at Gombe. Melissa, one of the chimpanzees initially studied by Jane Goodall, had twins many years ago sometime in the 1970’s but only one survived. I remember Jane mentioning Melissa’s twins with excitement (at the birth) and sadness (for the death) in a letter she wrote to me at the time and which I received in Camp Leakey. Then in 1998 Melissa’s offspring Gremlin gave birth to a healthy pair of twins, Goldie and Glitta. So it must run in the family! This is also true of humans. That was the comment that actor (the term she perfers as she made clear when she filmed at Camp Leakey)) Julia Roberts made when she was congratulated on the birth of her twins, saying she wasn’t surprised as her family tended to twin.
An orangutan female carrying twins was sighted by observers in the Lower Kinabatangan region in Sabah (one of two Malaysian states on Borneo) during November 2007. This is the first observation of a wild orangutan with twins ever recorded. Unfortunately, it is not known if that particular orangutan female was ever seen again with her twins.
Orangutan twins were also seen in 1991 at the Sepilok Rehabilitation Center where the mother was most likely a rehabilitated ex-captive orangutan. There have also been at least three known births of twins in captivity, two in the United States and one in Indonesia.
Among most large mammals who normally give birth to singletons, twins tend to be smaller and have higher neonatal mortality rates. I have read that in deer populations which are hunted, that the does are more likely to give birth to twins rather than single fawns as compared to populations where hunting does not occur. Females also reproduce more quickly and at younger ages. I am speculating wildly here but I wonder if a similar phenomenon could occur in non-human primates due to excessive stress. Who knows?
All I can say is that it took me almost 40 years of observation to see the first twin births among the population of orangutans who are resident in the forests around Camp Leakey. Who knows what else we might see if we have the patience and robustness to observe for another 40 years?