Conflicts, Consortships and Copulations: A Promising Start to my Research Year

By Amy Scott, PhD Candidate, Boston University, and GPOCP Graduate Student Researcher
As a PhD candidate in the Anthropology Department at Boston University, the next phase in my degree is conducting my dissertation research on the orangutans at Cabang Panti Research Station in Gunung Palung National Park (GPNP). This is the second time that I have been to Cabang Panti. My first was in the summer of 2015 when I collected pilot data (Code Red Vol 34) and attended the GP 30 conference. The GP 30 conference celebrated 30 years of research in Gunung Palung National Park, and was attended by many researchers who have studied the rich biodiversity of GPNP. It was fascinating to learn more about this research and the history of the research station, and it is a privilege to be able to work at this field site. My research project is only possible due to the long-term field study of orangutans at Cabang Panti.
Amy Scott following Walimah at Cabang Panti Research Station.
My dissertation research focuses on the reproductive strategies of male and female orangutans. Reproductive strategies are a fundamental aspect of animal behavior because they impact the reproductive success (number of surviving offspring) of an individual, which is the currency of natural selection. The term ‘reproductive strategy’ is used to describe a suite of adaptive behaviors that are employed by individuals to increase mating and reproductive success. The reproductive strategies of male and female orangutans are often at odds with each other because the costs and benefits of social associations and mating differ for male and female orangutans. This is largely due to differences in parental care. Females invest a minimum of 7 years of time and energy (pregnancy, lactation, and parental care) in one offspring while males, on the other hand, do not provide any parental care. Because females invest so heavily in one offspring, they are selective about when and with whom they mate. Male orangutans, on the other hand, are often less selective, which is another source of conflict.
Bibi forages for ants, while her 3.5 year old son, Bayas, watches.
In order to better understand the conflict between male and female reproductive strategies in orangutans I will examine male-female social interactions, including matings. While following a male-female pair, I record the following measures of the social interaction: which individual leads and stops travel, which individual enters and leaves a fruit tree first, and which individual is responsible for lengthening and shorting the distance between the pair. These measures indicate whether the male or female controls an interaction or if the interaction is mutual. Combining these measures with feeding data and mating data will give us a better understanding of the costs and benefits of associations and reproductive strategies for male and female orangutans.

I also plan to perform genetic paternity analysis of infant orangutans born in the Cabang Panti Research Station. DNA for genetic paternity analysis is obtained non-invasively from fecal samples collected off of leaves and the forest floor after an orangutan defecates. Because orangutans are very slow reproducers (females don’t have their first baby until age 15 and only have one baby every 6-8 years), it requires many years of fecal collection to have a large enough sample of offspring, mothers, and candidate fathers to conduct this analysis. Laboratory analysis will be carried out at The Eijkman Institute for Molecular Biology in Jakarta, Indonesia. My laboratory analysis in only possible because researchers at Cabang Panti have been collecting and preserving orangutan feces for a decade. Paternity data will show whether flanged or unflanged males have higher reproductive success and will help us to better understand ‘flanging’ as a male reproductive strategy and female preference for certain males.

Berani, an adolescent female, and Bosman, an unflanged male, feeding in the same tree during a 5-day consort, or when a male and female travel together for several days.
Since orangutans are semi-solitary animals, I was not sure how much social data on male and female behavior I would be able to collect, but I have been very lucky. At Cabang Panti, adult female orangutans only spend about 10% of their time in social interactions with other adult orangutans. However, in the first three months of my field research, I have collected data on nine different male-female pairs and nine different matings. While this may not sound like a lot, it often takes a year of data collection to observe this many matings! I also recorded a rare behavior called ‘tolerated food theft’. Tolerated food theft is when one orangutan takes a food item from another orangutan, and the victim does not protest.
Orangutan Stealing Fruit
In this video you see Berani (left) attempt to take a Nessia fruit from Bosman (right) before successfully stealing the fruit. Photos and video credit Amy Scott.
One of the reasons that I have seen so many male-female interactions is that there are currently two females whose home ranges include the research station area. Berani, an adolescent, and Walimah, a young adult, do not currently have babies and are old enough to get pregnant. This age group of female orangutans is especially social and often has many mating sessions before conceiving, so it is an exciting time to be studying these male-female interactions. I am eager to see how many more interesting social interactions I will have the opportunity to see over the course of the next nine months!