In a process that went largely unnoticed, years of illegal hunting and an epidemic of Ebola virus have slashed the population of wild chimpanzees and gorillas by more than 50 percent in the last part of the world to have widespread ape habitats, according to the study, which was published in an online edition of Nature April 6. The findings contradict estimates, from as recently as 1995, that the number of wild apes has been relatively stable.
"The species that are most similar to humans are just disappearing before our eyes," said Peter Walsh, a Princeton University scientist who led an international group of 23 researchers from the Wildlife Conservation Society and other institutions.
The study authors called for immediate improvements in anti-hunting law enforcement and in Ebola research and intervention. "The stark truth is that if we do not act decisively our children may live in a world without wild apes," the researchers concluded.
Previous estimates were deeply flawed, said Walsh, because they assumed that the best indicator of ape populations is the amount of intact forestland, which is relatively abundant in Western Equatorial Africa. They did not account for the possibility that hunting and disease could deplete the population even in densely forested areas, he said.
The new study is based on several surveys conducted between 1998 and 2002 in which teams of trained observers traveled through 4,800 kilometers of dense jungle and counted ape nests. In their paper, the researchers compared their results with those of the last comprehensive ape survey, which was done between 1981 and 1983, as well as with results from smaller surveys completed in the intervening years.