Nov 14

A new study in Indonesian Borneo has revealed that orang-utans in unprotected areas are being killed at rates which pose a serious threat to their existence.

Oran-utan image

Bornean orang-utan adult and infant interacting

Heading towards extinction

The Bornean orang-utan, a primate whose name means ‘person of the forest’, is classified as Endangered on the IUCN Red List, and has long been a cause for concern for conservationists. A comprehensive new study, published last week in the scientific journal PLoS One, has revealed that populations of this species are currently being diminished at higher rates than previously thought as a result of conflict with humans.

This latest study, which was carried out over a period of 18 months, focussed on unprotected areas within Indonesian Borneo, and involved interviews with over 7,000 people across 687 villages in areas of East, Central and West Kalimantan where orang-utans can be found.

Orang-utan image

Orang-utans come into conflict with humans as a result of raiding crops

Conflict with humans

Areas of forest that have been fragmented and converted for timber, wood-pulp and palm oil production were found to harbour the highest levels of conflict between orang-utans and humans, although hunting still occurs even in relatively intact forest zones far from industrial development.

In agricultural areas, crop-raiding by orang-utans was commonly given as the motivation for conflict, while in more isolated, intact forest areas, hunting for food was the prime reason. The results showed that conflict and killing for crop-raiding was most prevalent in villages where palm oil, rice, and industrial pulp and paper were being produced, and that those involved with logging, hunting or mining were most likely to kill an orang-utan.

Throughout the study, villagers were asked about their knowledge of wildlife laws and orang-utan conflict and killing. Although the researchers found that only a small number of people have killed an orang-utan themselves, the study revealed that a quarter of villages had killed at least one orang-utan. Nearly a sixth of villages reported agricultural conflicts with the species, with East Kalimantan having the highest rate of conflict at 18 percent.

Deforestation image

Illegal gold mine inside Tanjung Puting National Park, Borneo

Population viability

Population viability analysis is a way of evaluating and predicting the likelihood that a species will persist into the future. Using such analyses, this latest study has concluded that orang-utans in unprotected areas of Indonesian Borneo are being killed at faster rates than the population can sustain, meaning that the species is quickly heading towards extinction in those areas.

Population viability studies of orang-utans suggest that if annual mortality of females is higher than 1% then populations will go extinct,” say the authors, who explain that current kill rates in Indonesian Borneo were found to be higher than this. “These mortality rates caused by hunting alone are higher than the theoretical maximum mortality for population viability, suggesting that unless they can be reduced most Kalimantan populations will go extinct.

The results of the study also highlighted a difference in the level of knowledge between ethnic groups in the area, with traditional forest people being better able to correctly identify an orang-utan, but less likely to know that killing an orang-utan was illegal.

Infant orang-utan image

Bornean orang-utan infant hanging from a tree

Cause for concern

From their data, the authors of the study concluded that the conversion of forests to other land uses could result in orang-utans entering gardens in villages and raiding crops, which could in turn lead to direct conflict and killing of orang-utans.

The study had some startling results, indicating that the scale of orang-utan killing was higher than previously thought, with between 750 and 1,790 orang-utans killed in the last year, and between 1,970 and 3,100 killed during the lifetimes of the respondents. Such levels are unsustainable, and could pose a threat to the continued existence of orang-utans in Kalimantan.

The data suggest no orang-utans outside Kalimantan’s protected areas are safe. They are either threatened by habitat degradation and deforestation, or they are threatened by ongoing hunting within their forest habitats,” say the authors. The killing of female orang-utans is a particular cause for concern, as they have low reproductive rates as a result of the lengthy period of parental care they provide for their young.

The authors concluded their paper with a call for better anti-killing schemes, targeting specific groups within Kalimantan.

Read more on this story at – Orang-utans in Indonesian Borneo doomed to extinction?

Read the original paper in PLoS One.

View photos and videos of orang-utans on ARKive.

Kathryn Pintus, ARKive Species Text Author