Major threats include:
- Habitat loss. Between 2000 and 2010, the mean annual rate of deforestation for Borneo was 3,234 km2 per year (Gaveau et al. 2014). Assuming a similar deforestation rate in the future, 32,000 km2 of forest could be lost by 2020; 129,000 km2 by 2050 and 226,000 km2 by 2080 (Wich et al. 2015). In the early 2010s, only 22% of the current Bornean Orangutan distribution was located in protected areas (Wich et al. 2012). Approximately a third of the entire Bornean orangutan range was in commercial forest reserves exploited for timber, and about 45% was in forest areas earmarked for conversion to agriculture or other land uses. A business-as-usual scenario, whereby non-protected forests would be converted along the lines of current development plans, will result in the loss of more than half of the current orangutan range on the island of Borneo in the next 50 years or so.
- Illegal hunting. Illegal killing of Northeast Bornean Orangutans is a major cause of their decline. Recent interview surveys conducted in Kalimantan revealed that several thousand individuals are killed every year for meat consumption, as a way to mitigate conflict, or for other reasons (Davis et al. 2013). Overall Bornean Orangutan mortality rates in Kalimantan seem to significantly exceed the maximum rates that populations of this slow-breeding species can sustain (Marshall et al. 2009, Meijaard et al. 2011). If hunting does not stop, all populations that are hunted will decline, irrespective of what happens to their habitat. These findings confirm that habitat protection alone will not ensure the survival of orangutans in Indonesian Borneo, and that effective reduction of orangutan killings is urgently needed.
- Fires. Fires occur in Borneo on a yearly basis and are responsible for significant forest loss with dramatic results for certain orangutan populations. For example, 90% of Kutai National Park was lost to massive fires in 1983 and 1998 and its Bornean Orangutan population was reduced from an estimated 4,000 individuals in the 1970s to a mere 600 (Rijksen and Meijaard 1999); over 4,000 km2 of peatland forest in southern Kalimantan was burnt to ashes in six months of 1997–1998, resulting in an estimated loss of 8,000 orangutans. In 2015, more than 20,000 km2 of forest were lost to fires, which resulted in hundreds (or more) of additional orangutan deaths.
- Habitat fragmentation. With the current scale of habitat exploitation and forest conversion to other types of land uses in Borneo, only a small percentage of current orangutan habitat will remain undisturbed by infrastructure development by 2030 (Gaveau et al. 2013). Several orangutan PHVAs have shown that Bornean Orangutan populations of fewer than 50 individuals are not viable in the long term (Marshall et al. 2009), and that many small populations will go extinct unless they are actively managed (Bruford et al. 2010).
- Lack of awareness. A recent study suggested that 27% of the people in Kalimantan did not know that orangutans are protected by law (Meijaard et al. 2011). Campaigns to effectively inform the public and encourage rural people to support the principles of environmental conservation and be actively responsible for the management of their resources are therefore a crucial requirement for successful orangutan conservation.
- Climate change. Spatial models point to the possibility that a large amount of current orangutan habitat will become unsuitable because of changes in climate (Struebig et al. 2015). Across all climate and land-cover change projections assessed in a recent analysis, models predicted that 49,000–83,000 km2 of orangutan habitat will remain by 2080, reflecting a loss of 69–81% since 2010. This projection represents a three to five-fold greater decline in habitat than that predicted by deforestation projections alone. A major reduction in the extent of suitable orangutan habitat can be expected. However, core strongholds of suitable orangutan habitat are predicted to remain to the west, east and northeast of the island where populations of P. p. wurmbii and P. p. morio are found.