Estimating Orangutans Population Size in Sabah Rainforest in Malaysia Using Spatial Modelling

The distribution of Orangutans has not been accurately mapped, as forest habitat is extensive and there is limited access to remote forests such as upland and swamp forest. The main objective of this study is to map the distribution density of Orangutans in seven key habitats using spatial modeling, which includes (i) investigating the relative abundance of Orangutans in different habitat types and terrain altitude, and (ii) investigating the factors that could influence an estimation of the Orangutans population. Based on these findings, potential conservation strategies are determined and discussed in this paper. In this study, distribution and density patterns for forest areas were determined, along with abundance of different forest types and altitude. Observations of nest production rates and nest decay rates were carried out. A series of aerial surveys, covering seven key Orangutans forest habitats, were conducted between 2007 and 2010 to map the spatial distribution. A ground survey followed in each forest habitat. Based on the aerial survey, it was demonstrated that the Orangutans distribution is not evenly spread. A line-transect nest-count methodology was also used to calculate the Orangutans population based on each spatial digital distribution zone. In short, this study provides an estimation of the conservative population size of Orangutans in each forest habitat.