Northeast Bornean Orangutan

Northeast Bornean orangutans (Pongo pygmaeus morio) are native to the island of Borneo, inhabiting the Malaysian states of Sabah and Sarawak, as well as two of the Indonesian Provinces of Kalimantan: North and East Kalimantan. Most of the remaining population of Northeast Bornean orangutans is concentrated in Sabah and East Kalimantan, with small scattered groups also present in North Kalimantan.

It has been estimated that fewer than 20,000 Northeast Bornean orangutans remain (Ancrenaz et al. 2016). In Kalimantan, the majority of P. p. morio populations are situated outside protected areas, in forests that have been set aside for conversion to other land uses (Wich et al. 2012). In Sabah, although approximately 80% of orangutans reside in protected forests, numerous populations continue to decline due to ongoing land conversion, hunting, and forest fragmentation. Recent research suggests a 25% decline in the orangutan population within Sabah over the past decade alone (Santika et al. 2017). Overall, more than 86% of this subspecies is anticipated to vanish within three generations (1950–2025), leading to its classification as Critically Endangered on the IUCN Red List of Threatened Species. Bornean orangutans hold the distinction of being the largest arboreal mammals globally, although they can also walk long distances on the ground (Ancrenaz et al. 2014).

Bornean orangutans lead a predominantly solitary existence, seldom congregating in groups. Males, as the dispersing sex, depart from their birthplaces upon attaining sexual maturity (typically at 10–12 years old) to establish expansive territories spanning several hundred hectares. Female territories are comparatively smaller, their actual size influenced by forest composition and food resource availability. These orangutans reproduce at a slow pace, typically giving birth to one offspring every 6–8 years, a factor contributing to their heightened vulnerability to hunting pressures. Female sexual maturity is attained at 10–15 years old (Kingsley 1981).

Threats
The main threats to Northeast Bornean orangutans are habitat loss, illegal hunting, fires, habitat fragmentation, and increasingly, climate change (Ancrenaz et al. 2016). In Sabah, genetic studies indicate that over the past two centuries, human activities have led to the loss of more than 90% of the original orangutan population (Goossens et al. 2006). The state of Sabah has witnessed the highest rate of forest loss in Borneo, with a 39.5% decrease in forest cover from 1973 to 2010, primarily affecting the eastern lowland forests, a favored orangutan habitat (Gaveau et al. 2014).

In Kalimantan, orangutan populations face similar threats, including hunting pressure, forest fires, and conversion of forests to agricultural land. Areas in East Kalimantan inhabited by orangutans exhibit a high risk of conflict, largely driven by rapid conversion of natural land cover to plantations. The subspecies is rapidly decreasing, with climate change and land-use alterations expected to exacerbate habitat loss (Struebig et al. 2015). Fires have also significantly contributed to declines; for instance, Kutai National Park lost 90% of its area to extensive fires in 1983 and 1998, resulting in a drastic reduction of the orangutan population from around 4,000 individuals in the 1970s to a mere 600 (Rijksen and Meijaard 1999, Wich et al. 2009).

The illegal killing of Northeast Bornean orangutans is also a main contributor to their population decline. Interview surveys conducted in Kalimantan have unveiled that several thousand individuals are slaughtered annually for purposes such as meat consumption, conflict mitigation, or other motives (Davis et al. 2013). Overall mortality rates for Bornean Orangutans in Kalimantan appear to far surpass the maximum sustainable rates for this species, known for its slow reproductive rate (Marshall et al. 2009, Meijaard et al. 2011).

Conservation Activities
While the Northeast Bornean Orangutan enjoys full protection in Malaysia and Indonesia and is listed on Appendix I of CITES, its forest habitat often lacks adequate protection: approximately 20% of the current orangutan range in Sabah and 80% in Kalimantan remain unprotected (Wich et al. 2012). Urgent innovative measures are required to ensure the long-term survival of Bornean Orangutans beyond protected forests.

The future of Bornean Orangutans will very much depend on the long-term security of large, strictly-protected forests where illegal logging and hunting will be efficiently controlled and the orangutan populations large enough to cope with catastrophic events such as fires and disease outbreaks (Meijaard et al. 2011). These forests need to contain the ecological gradients that will provide the key resources to sustain orangutans through climate and other gradual environmental changes (Gregory et al. 2012). In the larger landscape, scientifically-based, regional land-use planning is needed to delineate zones of interaction around protected forests and their surroundings, encompassing hydrological, ecological and socio-economic interactions. Ideally, the core protected areas will remain connected to other areas of forest that could be used sustainably for (commercial) timber extraction. (Ancrenaz et al. 2016).

References
Ancrenaz, M., Sollmann, R., Meijaard, E., Hearn, A. J., Ross, J., Samejima, H., ... & Wilting, A. (2014). Coming down from the trees: Is terrestrial activity in Bornean orangutans natural or disturbance driven?. Scientific reports, 4(1), 4024.
Ancrenaz, M., Gumal, M., Marshall, A.J., Meijaard, E., Wich , S.A. & Husson, S. (2016). Pongo pygmaeus ssp. morio. The IUCN Red List of Threatened Species 2016: e.T63544A17990681. https://dx.doi.org/10.2305/IUCN.UK.2016-1.RLTS.T63544A17990681.en. Accessed on 26 January 2024.
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(10), e75373.
Gaveau D.L.A., Sloan S., Molidena E., Yaen H., Sheil D., Abram N.K., Ancrenaz M., Nasi R., Quinones M., Wielaard N., & Meijaard E. (2014). Four decades of forest persistence, loss and logging on Borneo. PLoS One, 9(7), e101654.
Goossens, B., Chikhi, L., Ancrenaz, M., Lackman-Ancrenaz, I., Andau, P., & Bruford, M.W. (2006). Genetic signature of anthropogenic population collapse in orang-utans. PLoS Biology, 4, e285–e291.
Gregory, S.D., Brook, B.W., Goossens, B., Ancrenaz, M., Alfred, R., Ambu, L.N., & Fordham, D.A. (2012). Long-term field data and climate-habitat models show that orangutan persistence depends on effective forest management and greenhouse gas mitigation. PLoS One, 7(9), e43846.
Kingsley, S. (1981). The reproductive physiology and behavior of captive orangutans (Pongo pygmaeus). University of London.
Marshall, A.J., Lacy, R., Ancrenaz, M., Byers, O., Husson S.J., Leighton, M., Meijaard, E., Rosen, N., Singleton, I., Stephens, S., Traylor-Holzer, K., Utami Atmoko, S.S., van Schaik, C.P., & Wich, S.A. (2009). Orangutan population biology, life history, and conservation. In: S.A. Wich, S.S. Utami Atmoko, T. Mitra Setia and C.P. van Schaik (eds), Orangutans: Geographic Variation in Behavioral Ecology and Conservation, pp. 311–326. Oxford University Press, Oxford, UK.
Meijaard, E., Buchori, D., Hadiprakarsa, Y., Ancrenaz, M., et al. (2011). Quantifying killing of orangutans and human-orangutan conflict in Kalimantan, Indonesia. PLoS One, 6(11), e27491.
Rijksen, H.D. and Meijaard, E. (1999). Our Vanishing Relative: The Status of Wild Orangutans at the Close of the Twentieth Century. Kluwer, Dordrecht, The Netherlands.
Santika, T., Ancrenaz, M., Wilson, K. A., Spehar, S., Abram, N., Banes, G. L., ... & Meijaard, E. (2017). First integrative trend analysis for a great ape species in Borneo. Scientific Reports, 7(1), 4839.
Struebig, M.J., Fischer, M., Gaveau, D.L.A., Meijaard, E., Wich, S.A., Gonner, C., Sykes, R., Wilting, A., & Kramer-Schadt, S. (2015). Anticipated climate and land-cover changes reveal refuge areas for Borneo's orang‐utans. Global Change Biology, 21, 2891–2904.
Wich, S. A., Gaveau, D., Abram, N., Ancrenaz, M., Baccini, A., Brend, S., ... & Meijaard, E. (2012). Understanding the impacts of land-use policies on a threatened species: is there a future for the Bornean orang-utan?. PloS one, 7(11), e49142.
Wich, S.A., de Vries, H., Ancrenaz, M., Perkins, L., Shumaker, R.W., Suzuki A., & van Schaik, C.P. (2009). Orangutan life history variation. In: S.A. Wich, S.S. Utami Atmoko, T. Mitra Setia and C.P. van Schaik (eds), Orangutans: Geographic Variation in Behavioral Ecology and Conservation, pp. 65–75. Oxford University Press, Oxford, UK.