Southwest Bornean Orangutan

Range countries
Indonesia

Population status
The Southwest Bornean orangutan subspecies has experienced a staggering decline of over 50% in the past four decades, which amounts to less than two generations (Meijaard et al. 2011), resulting in the disappearance of many small populations (Abram et al. 2015). The precise total population of Southwest Bornean orangutans remains uncertain, but the majority of their habitat exists beyond designated conservation areas (Ancrenaz et al. 2016). Historically, several populations within protected zones such as Sebangau National Park and its environs, boasting the largest orangutan population in Borneo (Wich et al. 2008), along with Tanjung Puting National Park and Gunung Palung National Park, were thought to be relatively stable. Overall, the subspecies is projected to decline by more than 86% in three generations (1950–2025), warranting its classification as Critically Endangered on the IUCN Red List of Threatened Species (Ancrenaz et al. 2016). The population trend for all subspecies of Bornean orangutans is decreasing (Voigt et al. 2018).

Threats
Despite their protected status, these populations face imminent threats from illegal logging, fires, and land conversion for agriculture, including the establishment of plantations and agroforests within these areas and their peripheries (Wich et al. 2012, Gaveau et al. 2013). Notably, fires pose a significant danger, with over 4,000 sq.km of Sebangau peatland forest being engulfed in flames during 1997–1998, resulting in an estimated loss of 8,000 orangutans from this population alone (Husson et al. 2015). Furthermore, despite being illegal, hunting is perceived as a genuine threat to the long-term viability of populations outside protected zones. As a consequence, all populations are anticipated to experience further decline over the next five decades (Abram et al. 2015). Forecasts indicate that ongoing development in Indonesia will lead to the destruction of more than half of the current orangutan habitat within the next five decades, primarily due to deforestation for agriculture and fires (Wich et al. 2012). Illegal hunting remains a significant threat across much of the Southwest Bornean orangutan's range, driven by demand for bushmeat, the pet trade, and conflicts (Davis et al. 2013, Abram et al. 2015).

Conservation activities
The Bornean Orangutan benefits from full legal protection in Malaysia and Indonesia, being designated under Appendix I of CITES. However, its forest habitat lacks comprehensive protection, with approximately 20% of the current orangutan range in Sabah and 80% in Kalimantan remaining vulnerable (Wich et al. 2012). Innovative strategies are urgently required to ensure the long-term survival of Bornean orangutans beyond formally protected forest areas (Ancrenaz et al. 2016).

References
Ancrenaz, M., Gumal, M., Marshall, A.J., Meijaard, E., Wich , S.A. & Husson, S. (2016). Pongo pygmaeus ssp. wurmbii. The IUCN Red List of Threatened Species 2016: e.T39782A17990568. https://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T39782A17990568.en. Accessed on 30 January 2024.

Abram, N.K., Meijaard, E., Wells, J.A., Ancrenaz, M., Pellier, A.S., Runting, R.K., Gaveau, D.L.A., Wich, S., Nardiyono, Tiju, A., Nurcahyo, A., & Menkersen, K. (2015). Mapping perception of species’ threats and population trends to inform conservation efforts: The Bornean orangutan case study. Diversity and Distributions, 21, 487–499.

Davis, J.T., Mengersen, K., Abram, N., Ancrenaz, M., Wells, J., & Meijaard, E. (2013). It’s not just conflict that motivates killing of orangutans. PLoS One, 8, e75373.

Gaveau, D.L.A., Kshatriya, M., Sheil, D., Sloan, S., Molidena, E., Wijaya, A., Wich, S., Ancrenaz, M., Hansen, M., Broich, M., Guariguata, M.R., Pacheco, P., Potapov, P., Turubanova, S., & Meijaard, E. (2013). Reconciling forest conservation and logging in Indonesian Borneo. PLoS One, 8, e69887.

Husson, S.J., Morrogh-Bernard, H., Santiano, Purwanto, A., Harsanto, F., McLardy, C., & D’Arcy, L. (2015). Long-term temporal trends in ape populations in four case studies: Bornean orangutans in the Sabangau peat-swamp forest. In Arcus Foundation (Ed.), State of the Apes 2015: Industrial Agriculture and Ape Conservation (pp. 200–207). Cambridge University Press.

Meijaard, E., Buchori, D., Hadiprakarsa, Y., Utami-Atmoko, S. S., Nurcahyo, A., Tjiu, A., ... & Mengersen, K. (2011). Quantifying killing of orangutans and human-orangutan conflict in Kalimantan, Indonesia. PloS one, 6(11), e27491.
Voigt, M., Wich, S. A., Ancrenaz, M., Meijaard, E., Abram, N., Banes, G. L., ... & Kühl, H. S. (2018). Global demand for natural resources eliminated more than 100,000 Bornean orangutans. Current Biology, 28(5), 761-769.

Last updated January 2024