Fruitful Orangutan Seed Dispersal

By Andrea Blackburn, PhD Candidate, Department of Anthropology, Boston University

Orangutans have powerful jaws and teeth adapted for crushing hard food objects. This selection of traits would suggest orangutans are crushing and eating seeds as a main component of their diet. Based on these observations orangutans have been labelled as ‘seed predators’. However, my research this year in Gunung Palung National Park tested an alternate hypothesis. I predicted that in addition to chewing up and destroying seeds, orangutans are also swallowing seeds intact and dispersing these seeds throughout the forest. Many species of primates that consume a large quantity of fruit are important seed dispersers, so I hypothesized that orangutans may similarly be dispersing viable fruit seeds.

Andrea Blackburn following an orangutan on a hillslope while collecting behavioral data.

I followed orangutans, analyzed their feeding behavior, and counted seeds defecated by orangutans for my dissertation research at Boston University. In addition to following orangutans, I also conducted germination experiments to test if seeds dispersed by orangutans would germinate better than seeds collected from fruits. Camera traps were valuable in helping me understand what other animals interact with seeds dispersed by orangutans. Sometimes rodents stash the seeds elsewhere in an act called ‘caching’ and sometimes other animals eat the dispersed seeds. Excitingly, I was able to do my research alongside Ahmad Rizal, an undergraduate student from Jakarta, who is also interested in understanding the ecological role of orangutans as seed dispersers.

Pregnant Walimah searching for fruit during an early morning in March.

My research showed that orangutans are frequently dispersing a wide diversity of seeds throughout the forest. I will analyze the data back at Boston University to figure out which of these genera orangutans are dispersing most effectively. Orangutan dispersed seeds do germinate and often times a higher percentage of orangutan dispersed seeds germinated compared to the seeds collected directly from fruit. It appears that the act of an orangutan consuming and defecting a seed does actually help the seed germinate. Although orangutans do predate a portion of fruit seeds, for a different group of fruits orangutans are important seed dispersers.  

Andrea Blackburn with her germination experiment at Cabang Panti Research Station.

Throughout my year at Cabang Panti Research Station I made many friends and had many great experiences. The help of the Cabang Panti’s research staff was invaluable to me. The field assistants assisted me with collecting behavioral data while following orangutans and the lab assistants helped with processing samples brought back from the forest. The many students, interns, volunteers, and managers were incredible to work with as well. I would not have had a successful research year without all of their help. I will miss my time and friends at Cabang Panti.