Two of man's closest relatives in the animal kingdom will be on the edge of extinction within a decade, unless drastic conservation measures are put in place immediately.
By Tim Hirsch
BBC environment correspondent
That is the alarming conclusion of a major international study of gorillas and chimpanzees in the forests of Western Equatorial Africa, published in the scientific journal Nature.
The dense jungles of the Republic of Congo and Gabon were previously thought to be the last stronghold of the two species, since deforestation in this region has been much less intense than in other parts of Africa.
But a comprehensive survey of ape numbers in Gabon between 1998 and 2002 has revealed a dramatic decline in the population in recent years, caused by a combination of commercial hunting for bush meat, and the deadly Ebola virus which has also attacked local people.
By comparing the figures with a survey carried out in the early 1980s, the researchers conclude that on a conservative estimate, gorillas and chimpanzees have declined by more than half within 20 years.
Gabon and Congo account for around 80% of the world's gorillas and most of the common chimpanzees, so this is described by the study as a major conservation crisis.
"Without aggressive investments in law enforcement, protected area management and Ebola prevention, the next decade will see our closest relatives pushed to the brink of extinction," the Nature paper says.
Gorilla and chimp numbers have dropped more than 50% since 1983
"The stark truth is that if we do not act decisively our children may live in a world without wild apes."
One of the major problems facing the apes is that they are now being killed for their meat on a commercial scale, where hunting used to be confined to local villagers providing food for themselves.
The real thing
The timber trade has driven roads deep into the forest, providing easier access for hunters to areas previously out of reach. Bush meat finds a ready market in the towns and cities of the region - this has long ceased to be a subsistence activity.
And rivalling hunting as a threat to the apes is Ebola haemorrhagic fever, steadily spreading through Gabon and Congo. The epidemic is now approaching Odzala National Park, which boasts the world's highest recorded gorilla and chimpanzee densities.
The lead author of the study, Peter Walsh of Princeton University, US, says he recognises that people have become accustomed to dire warnings about endangered species.
He told BBC News Online: "Environmentalists are always saying the sky is falling in, but in this case it is.
"The reason we published this in Nature is because we realised people would have those objections. We did a careful scientific study with a lot of data - they sent it out to the best experts in the world, and they all said yes this is valid.
"The populations are crashing really quickly. In the course of about 10 years we're going to be in the situation where gorillas and chimpanzees are going to go from being widely distributed and abundant to being just in a few small pockets.
"That's bad because in the long term those small pockets just won't be sustainable, we won't be able to protect 10 here and 50 there - it will be impossible.
"The idea that our closest relatives would go extinct is shattering to us. We don't want to have people looking back in 20 years and say they didn't do enough - they knew what to do but they didn't do it.
"This is a problem for the global community - everybody in the world has to get together and do something about this."