Arfah Nasution, Dyah Perwitasari-Farajallah, and Sri Suci Utami-Atmoko. “Declining Orangutans Population in the Unprotected Forest of Batang Toru”. Tropical Life Sciences Research 29, no. 2 (July 6, 2018): 77–87. Accessed March 22, 2026. https://ejournal.usm.my/tlsr/article/view/tlsr_vol29-no-2-2018_6.