A new study puts Sumatra's orangutan population at two times the previous figure, but that bright spot could be washed out if the dark clouds of deforestation continue to wash over the Indonesian island.
A survey of the orangutans' nests on the island place the population of the apes at around 14,600, more than twice the previous estimate of 6,600.
The reason the last estimate may have been so far off the mark is because many of the orangutans have been nesting at elevations previously thought to be out of their range, concluded a study that was published in the journal Science Advances.
On top of that, there were some orangutans found to be nesting in logged areas, while others were found in areas to the west of Toba Lake that were not surveyed in previous studies.
Despite finding that Sumatra is home to more orangutans than previously thought, models of several plausible scenarios for the island's future predict a marked decline in the apes' population. Serge Wich, one of the study's authors, says that while it was a thrill to discover that the Sumatran orangutan population is actually larger than documented before, it doesn't mean it should be left at that.
"Numerous development projects are planned in the area that - if they are not stopped - could sharply reduce the number of orangutans over the coming years," says Wich from Liverpool John Moores University.
By 2030, the number of orangutans on the island is projected to fall by 4,500. The researchers have urged that all future development on the island be preceded by environmental impact studies.
Wich adds that they will need to continue working with the Indonesian government and other concerned groups for the conservation of the species and prevent population decline from happening. Wich believes it's a difficult task but they are hopeful that they can "turn the tide for the Sumatran orangutan."
Sumatra's orangutan population is the first taxon of apes to see its population estimates corrected so dramatically, says Hjalmar Kuehl, of the German Centre for Integrative Biodiversity Research and the Max Planck Institute for Evolutionary Anthropology.
In years to come, researchers will make more upwards and downwards corrections of some of the other 12 taxa of apes, notes Kuehl, who led the research.
"This will help us to better inform conservation policy and management and provide guidance for the improved protection of great apes," Kuehl says.