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.

An endangered mountain gorilla from the Bitukura family, rests among vegetation inside a forest in Bwindi Impenetrable National Park in the Ruhija sector of the park, about 550 km (341 miles) west of Uganda's capital Kampala, May 24, 2013. -- File photo

Four of six species of great apes are now rated "critically endangered", or one step away from extinction, by threats such as hunting and a loss of forests to farmland from West Africa to Indonesia, according to the annual list by wildlife experts.

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 towards extinction is truly distressing," said Inger Andersen, director general of the IUCN (International Union for Conservation of Nature) which compiles the Red List.

Millions of people died in fighting in the mineral-rich east of Democratic Republic of Congo from 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 kg (440 lb), 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 eastern Democratic Republic of Congo.

Chimpanzees were most able to adapt to a loss of forest habitats 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," Elizabeth Williamson, of the IUCN species survival commission for primates, told Reuters. "They can raid crops and steal fruit from farms - gorillas and orangutans don't."

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" after being of least concern.

Source: Reuters