HOPE Report No.39, 11th, April 2005.

Program No.39 (Joint 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.

Place of visit: Danum Valley Conservation Area, Sabah, Malaysia

Period of visit: 21 February,2005-30 March,2005

I continued the field research on wild orangutan in a research area of about 2km2 which we newly settled in 2004 around a tourist lodge in Danum Valley Conservation Area, Sabah, Malaysia. This time, I conducted field research on orangutans during rainy season (February- March) to compare the results with those of dry season (July- September) that we got last time. In this field research, I tried to track an orangutan as far as possible and record its behavior. In addition, I conducted a census on fallen fruits two times and a census on the nest once during the research period.

I could observe wild orangutans for 22 hours 21 minute (in 4 days) in total during the total observation trial of 102 hours 30 minutes (in 20 days). The discovery rate of orangutan was 21.8 % (one time per 5 days). It largely decreased from that in the dry season of the last year (53.8 %, one time per 2 days). During the research period, I observed seven individuals in total. I could track 2 individuals: a flanged male of over thirty years old and an adolescent female of under ten years old. Besides these individuals, I found 2 pairs of a mother and an infant and a pregnant female. In the census on nest and fruits along the trail of 21 km long, I counted 23 nests and collected 29 types of fallen fruits (11 family 25 genus). In the census of last field research during dry season, I counted 97 nests and collected 94 types of fallen fruits (24 family 37 genus). The result suggested that density of orangutan and variation of fallen fruit in this area decrease during rainy season.

Activities budget of individuals observed in this time was as follows; feeding (39%), resting (34%), moving (25%), other (1%) and lost (1%). Those of last time was as follows; resting (38%), feeding (36%), moving (14%), aggressive behaviors against observer (4%), and lost (7%). The result suggested that orangutans of this area tended to move more frequently in rainy season than in dry season. Rate of each food type observed in this time was as follows; fruit (68%), young leaves (12%), cambium (11%), and flower (9%). Those observed in last field research in dry season were as follows; fruit (48%), leaves (38%), bark (7%), flower (2%) and others (4%). The result suggests that of the rate of fruit use increased in rainy season. In rainy season, orangutans tended to eat the same fruits species for a longer time than in dry season.


An adolescent female eating fruits.


A flanged male in a rest.


The canopy walkway near the Borneo Rain forest Lodge.