The estimation of demographic parameters and a growth model for Tapanuli orangutan in the Batang Toru Landscape, South Tapanuli Regency, Indonesia

Biological and ecological information on the Tapanuli orangutan (Pongo tapanuliensis) remains limited. This study was designed to analyze the demographic parameters and build a growth model of the Tapanuli orangutans to help guide policy in developing a conservation program for them. Data were collected from tapanuli orangutans that were directly observed over four years in the Batang Toru Landscape, South Tapanuli Regency, North Sumatra. There were 32 distinct individual orangutans, 27 of which were adults or sub-adults. Only five were children or infants. The adult sex ratio, male to female, was 1: 0.83, the birthrate was 0.13, and the highest mortality rate was among sub-adults and adults. The population growth rate (r) was estimated to be 0.051 per year and predicted to reach the potential carrying capacity of the habitat they now occupy in about 60–80 years from 2020. Conservation activities that might help to increase the tapanuli orangutan population include increasing the number of food plants in production forests around nature reserves and increasing patrols to monitor the population and minimize potential damage to the animal and their habitat due to human activities.