The ecology and behaviour of proboscis monkey (Nasalis larvatus) in mangrove habitat of Labuk Bay, Sabah

A study on the ecology and behaviour of proboscis monkey (Nasalis larvatus) was carried out at Labuk Bay Proboscis Monkey Sanctuary (LBPMS) in Sandakan, Sabah. The study was aimed at determining the social organization, social behaviour, feeding ecology and ranging behaviour of proboscis monkeys under semi-wild conditions in a small (263 ha) isolated patch of mangrove forest within a large matrix habitat of mature oil palm plantations. Intensive field data collection was carried out over a period of 12 months commencing from August 2008 to July 2009. Data collection involved following monkey groups and observing their behaviour by using instantaneous scan sampling method with a scanning period of 5 minutes at every 10 minutes scan intervals. Observations were conducted from dawn (06:00 hrs) to dusk (18:00 hrs). Eight proboscis monkey groups, i.e., five one-male-unit and three all-male-unit, and consisting of a combined total of 148 individuals within the LBPMS area, were followed for a total of 1,440 hours. The number of Individuals observed In a scan ranged from 5 to 35, comprising 34 adult males (ADM), 60 adult females (FAD), 33 juveniles (JV) and 21 infants (INF). The total individual behavioural activity recorded was 35,878. The most frequent activity was resting (32.62%) followed by moving (18.71%), feeding (16.41%) and grooming (13.11%). These results indicated that the activity patterns for semi-Wild proboscis monkeys are similar with those In the wild. The number of food plant species eaten by proboscis monkeys In LBPMS was generally low with only 8 to 10 species taken with a monthly average of 7.75 ±0.45 species. Rhizophora apiculata and Bruguiera paflliflora made up about 60% of the plant species eaten by the proboscis monkeys, and these two species were the most dominant tree species in the study area. Young leaves were the major plant parts eaten (62.5%) followed by flowers (5.11%) and young fruits (4.38%). The proboscis monkeys also spent 27.14% of their time feeding on supplemented pancakes, making this food item as among the major food sources. The average amount of pancakes consumed by an individual proboscis monkey per day ranged from 130 grams to 300 grams. The significant positive correlations between monthly feeding frequencies to monthly pancakes and young leaves feeding frequencies suggest that pancakes and mangroves plants are equally important food sources for proboscis monkeys in LBPMS. The significantly higher percentage of pancake feeding observations as compared to other food items when pancakes were given indicated that pancake is an important food source for proboscis monkeys in LBPMS. The mean daily ranging distance for the proboscis monkey population in LBPMS was 850 m. The shortest daily path length recorded was 335 m. The core ranging areas of the proboscis monkey groups in this study concentrated only within the immediate areas around the feeding platforms in the mangrove forest. The estimated home range of proboscis monkeys at these isolated patches of mangrove forest was approximately 1.5 - 5.75 hectares. This indicated that while the small patches of mangrove forest may be able to sustain the proboscis monkey population in LBPMS, the continued existence of the monkey may also depend on the availability of supplemented food