Nearly half of the monkeys, apes and lemurs in the world are in imminent danger of disappearing from the planet, according to a new survey. The news comes even as a separate new census has uncovered far more gorillas than expected.

The International Union for Conservation conducted its first survey of the 634 known primates in five years and found that 48 percent face extinction. Particularly at risk are the great apes like orangutans.

"The situation is far more severe than we imagined," said Russell Mittermeier, president of Conservation International and chairman of the IUCN's primate group, at the release of the analysis in Edinburgh. Although tropical forest destruction remains the main cause, "in many places, primates are quite literally being eaten to extinction."

Asian primates are at particular risk, with nearly all of the monkeys of Vietnam and Cambodia dying out, including gibbons, langurs and leaf monkeys. And in Africa, relatively obscure species of red colobus monkeys may already be extinct: Bouvier's red colobus and Miss Waldron's red colobus have not been seen in at least 25 years.

But the news out of Africa isn't all bad. A survey by the Wildlife Conservation Society and the government of the Republic of Congo turned up more than 125,000 western lowland gorillas—a formerly critically endangered species. That more than doubles the entire known population of the human relative.

The key to their survival -- and the reason so many gorillas had been hidden for so long --was the remoteness and inaccessibility of the jungle fastnesses and swamps where they make their home. "We knew from our own observations that there were a lot of gorillas out there, but we had no idea there were so many," said Emma Stokes, who led the survey efforts, at the announcement in Edinburgh.

Unfortunately, the hopes for a similar find of African red colobuses or Asian gibbons are not as good, according to the IUCN.