Program No.17-015 (Collaborative Research)

Study on Social Behaviors of Wild Orangutans in Danum Valley, Sabah, Malaysia

Tomoko Kanamori : Doctor Course Student, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology.

Period of visit: 13th June,2005-03th September,2005

Danum Valley Conservation Area, Sabah, Malaysia

I continued the field research on wild orangutan in a research area of about 2km2 which we newly settled around a tourist lodge in Danum Valley Conservation Area, Malaysia. About 1 year has passed since I set up this new research area. Here, I summarize the preliminary results of the research.

In this research area, I observed 23 individuals in total to date; 3 flanged males, 5 unflanged males, 10 mother-baby pairs, 1 adult female, 2 adolescent females, and 2 juveniles. Fifteen individuals of these orangutans are already identified. The total number of individuals will increase because we still encountered new orangutans in every previous research periods. In the research during the rainy seasons, I observed only 7 individuals in the research, while I observed 11 and 14 individuals during the dry season in the last year and this year, respectively. In nest census, we counted only 21 nests in rainy season, while we counted 76 and 83 nests during the dry season in the last year and this year, respectively. In addition, the discovery rate of orangutan was 21.8% during the rainy season, while 53.8% and 50.0% during the dry season of the last year and this year, respectively. These results suggested that the density of orangutan in this area increased in dry season and decreased in rainy season.

Census of the fallen fruit revealed that species number of fallen fruits in this area was small during rainy season (about 25~30 from February to March), but increased in dry season up to 120 (from July to August). The result suggests the relationship between the amount of fruits and the density of orangutan. In Danum valley, some Dipterocarpaceae trees were blossoming and setting seeds from July to August of this year. Over half of 120 types's fallen fruits that we collected were fruits of Dipterocarpaceae trees. Although activities budget, nest density and discovery rate of orangutans in this dry season were not so different from those of the last dry season without Dipterocarpaceae blossoming, rate of fruit in their food items largely increased (91%) compared with last year (68%). In this dry season, observation of social behavior also increased because orangutans were often feeding at the same fruit tree. I will examine the relationship between blossoming of Dipterocarpaceae and behavior of orangutans.

A Juvenile of 3-4 years old

A Unflanged male

Dipterocarpaceae of fruits

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