Illegal hunting in Democratic Republic of Congo has wiped out 70 percent of Eastern gorillas in the past two decades and pushed the world's biggest primate close to extinction, a Red List of endangered species showed on Sunday.

Four of six species of great apes are now rated "critically endangered," or one step away from extinction. Threats include hunting, a loss of forests, and farming, from West Africa to Indonesia, according to the annual list by wildlife experts, the world's most comprehensive inventory of plant and animal species.

Eastern gorillas, revised from a lesser category of "endangered", join their sister species, the Western gorilla, and both species of orangutan which were already on the list as critically endangered.

The other two species of great apes, chimpanzees and bonobos, are rated endangered.

"To see the Eastern gorilla - one of our closest cousins - slide toward extinction is truly distressing," said Inger Andersen, director-general of the International Union for Conservation of Nature, which compiles the Red List.

Millions of people died in fighting in the mineral-rich eastern area of the Democratic Republic of Congo between 1996 and 2003 and militias and miners often hunted gorillas for food.

The main population of Eastern gorillas, the biggest primates weighing up to about 200 kilograms, tumbled to an estimated 3,800 animals in 2015 from 16,900 in 1994, according to the report issued at an IUCN congress in Hawaii.

A smaller branch of the Eastern gorilla family - the mountain gorilla - has fared better with the population rising to 880 from perhaps 500 in Rwanda, Uganda and Democratic Republic of Congo.

Chimpanzees were most able to adapt to a loss of forest habitat to oil palm plantations or other farms, while gorillas and orangutans were less flexible.

"Chimps get by even if there is only a remnant of a forest," said Elizabeth Williamson, of the IUCN species survival commission for primates. "They can raid crops and steal fruit from farms - gorillas and orangutans don't."

'Wrong direction'

Among other changes, the IUCN said the population of plains zebra in Africa had fallen to about 500,000 animals from 660,000, also because of hunting for their meat and stripy skins. That put the species on a watchlist as "near threatened", deemed of lesser concern.

The IUCN Red List includes 82,954 species - both plants and animals - and undergoes a major update every four years.

Almost one third - 23,928 - are threatened with extinction, it said.

Compared with previous years, even more species are under threat.

Carlo Rondinini, mammal assessment coordinator at Sapienza University of Rome, said almost 28 percent of mammals are threatened with extinction, 3 percentage points more than in the previous mammal assessment in 2008.

"A takeaway point we would like to emphasize is we are not journeying in the right direction with respect to species conservation," Andersen said.

"We are losing species at a faster pace than we have ever done."

Reuters-Afp