by Sophie Kirklin (BNF Orangutan Scientist)
In 2015 I spent four months in the Sabangau Forest, collecting data for my Masters dissertation with Borneo Nature Foundation. My project was on the development of orangutan infants, and how they eventually become independent from their mothers.
My fascination with orangutans developed into a bit of an obsession in the year leading up to my research and I hungrily absorbed as much information as I could about their behaviour. When I secured a position doing research on wild orangutans…on wild BABY orangutans…I was almost deliriously happy! I read up on what to expect, and what I learnt got me hooked.
Orangutans remain dependent on their mothers for about 7 to 8 years, and in this time the mother will not have other offspring. It’s not completely clear why this period is so long, in fact it’s the longest of all the great apes, including humans, but there are two leading theories that might explain why.
The solitary lifestyle hypothesis utilises our knowledge that orangutans are semi-solitary, meaning they live alone rather than in social groups because of the distribution and density of food available in the forest. There is not enough resources to support a group of orangutans in the same area. The solitary lifestyle hypothesis is that the habitat of an orangutan can only support a mother and one developing offspring. If another offspring was born, there would not be enough food. So, as long as an infant is unable to feed themselves and needs to share resources with their mother, their mother cannot afford to have a second offspring at the same time.
Another theory is the learning of skills hypothesis. This suggests that the skills needed to navigate through life and survival in the forest are so numerous that the period of 8 years is the necessary time period for young orangutans to acquire these skills, through social transmission, learning and imitation.
After the data collection period of my research project, I got down to analysing the data collected not only from the four months that I was in the field, but spanning the entire dataset since the mother-infant project began in Sabangau; this included 4,575 hours of behavioural data.
I focused on two behaviours indicative of a transition from dependence to independence; feeding and travelling. I found independent feeding by a young orangutan increased with age, as the orangutan becomes more able to forage and process food without the help of his/her mother. The distance maintained between a mother and her offspring increased as the offspring becomes independent. As a result of being more competent feeding and travelling independently the offspring will not be dependent on the physical proximity of the mother.
Next, I started thinking about the effect that the two behaviours have on one another and their relationship. I also considered the relationship between the manifestation of emerging independence in an offspring and the manifestation in a mother, of having a young offspring transitioning to independence.
But, I found that more data is needed to be certain of any relationship. As with many ecological studies, sample size is a problem and having a lower than ideal number of subjects to collect data on is an inherent problem in collecting data of wild and long-lived primates. However, we can start to see patterns emerge and I believe that seeing the beginnings of these patterns inspires and motivates further research with larger sample sizes. For example, it appeared that the difference between the development of the distance maintained between mother and her male offspring, and a mother and her female offspring, is different.
Differences in male and female development surely must exist, but the magnitude of these differences is unclear with this dataset and what exactly they are. I will keep looking at this data and will try to discover more about offspring development.
Now, as BNF’s Orangutan Scientist, I am continuing this research. The field team are following young individuals, either newly independent or approaching independence, to learn more about this stage of a Bornean orangutan’s life. These results, and the resounding conclusion that we need more data to get definitive results about these Critically Endangered primates, reminds me of the importance of the long-term research we do at Borneo Nature Foundation. 20 plus years might feel like a long time to study one species, but we have only scratched the surface and our continued research will help us to dig a little deeper!
