The future of our closest living relatives is much more fragile than previously thought. According to a report published online today by the journal Nature, the number of great apes in the wilds of western Africa has been more than halved over the past two decades. If the current trend continues, scientists say, these primates could suffer population declines of another 80 percent over the next 30 years, endangering their survival.

Peter Walsh of Princeton University and the Wildlife Conservation Society led an international team of researchers who studied wild populations of great apes in Gabon, which is located in central Africa. The small equatorial nation still retains 80 percent of its forest cover and is a stronghold for wild chimpanzees and gorillas. The team traipsed through 4,800 kilometers of dense jungle on several surveys to count ape nests and determined that the ape population declined by 56 percent between the early 1980s and 2002. "This is a catastrophic decline of great apes in an area that contains the bulk of the world's remaining populations," Walsh says. "If chimps and gorillas continue to disappear at the current rate, our closest relatives will be confined to a few small pockets in a matter of years."

Previous estimates of the plight of Africa's great apes had relied heavily on the assumption that the amount of undisturbed forest cover was a good indicator of ape abundance in a region. But the new study highlights the impact of factors other than deforestation that can kill wild chimps and gorillas, namely illegal hunting and the Ebola virus. The authors conclude that "without aggressive investments in law enforcement, protected areas management and Ebola prevention, the next decade will see our closest relatives pushed to the brink of extinction."