Last updated February 16, 2018 at 8:30 am
Borneo is one of the last refuges for wild orangutans, but numbers have dropped by around half since 1999
Orangutans are a close relative of humans, but are endangered in the wild due to our own actions. Now limited to the rainforests of Borneo and Sumatra, their numbers continue to decrease every year, and a new analysis has revealed just how sharp that decline is.
Over a 16-year period, from 1999 to 2015, about half of the orangutans living on the island of Borneo were lost as a result of changes in land cover.
That equates to over 100,000 of the animals dying.
Researchers are more than alarmed at the drop.
Rapid loss of numbers
Much of the decrease in numbers was due to deforestation driven by the demand for logging, oil palm, mining and paper. However, many orangutans also disappeared from more intact forested areas, the researchers say. That suggests that hunting and other direct contact between orangutans and people is still a major threat to the species.
“The decline in population density was most severe in areas that were deforested or transformed for industrial agriculture, as orangutans struggle to live outside forest areas,” says Maria Voigt from the Max Planck Institute for Evolutionary Anthropology in Germany. “Worryingly, however, the largest number of orangutans were lost from areas that remained forested during the study period. This implies a large role of killing.”
To estimate changes in the size of the orangutan population over time, Voigt and a collaboration of researches from 38 international institutions, collated surveys conducted in Borneo from 1999 to 2015. They extrapolated the overall size of the island’s population from the number of orangutan nests observed throughout the species’ range in Borneo.
Over the 16 year period, they estimated a decline in numbers of Bornean orangutans by 148,500. The data also suggest that only 38 of the 64 separated groups of orangutans now include more than 100 individuals, which is the accepted lower limit to be considered viable.
By reviewing the change in forest coverage of the areas known to house orangutans they concluded that land clearance caused the most dramatic rates of decline. Selective logging of other forested areas was also responsible for a large number of deaths.
When comparing land use in 2015 and 1999, they found that about half of the orangutans estimated to live on Borneo in 1999 were in areas which had significantly changed due to resource use.
They estimated that based on predicted future losses of forest cover, over 45,000 more orangutans will be lost over the next 35 years.
Management and education are key to survival
Conservationists say that building effective partnerships with logging companies and other industries is now essential to the Bornean orangutan’s survival.
Building public education and awareness will also be vital to protect the species in the future.
“Orangutans are flexible and can survive to some extent in a mosaic of forests, plantations, and logged forest, but only when they are not killed,” Serge Wich, from Liverpool John Moores University in the UK, who was one of the collaborators, says. “In addition to protection of forests, we need to focus on addressing the underlying causes of orangutan killing. The latter requires public awareness and education, more effective law enforcement, and also more studies as to why people kill orangutans in the first place.”
Both the Indonesian and Malaysian governments have management plans in place to try to protect orangutans long-term. However, based on this research, efforts may need to be even more urgently instigated to ensure the survival of this wonderful species.
The study has been published in Current Biology