Honolulu (Hawaii): Four out of six great ape species are now "Critically Endangered" - only one step away from going extinct -- with the remaining two also under considerable threat of extinction. Of the great ape species - the Eastern gorilla, Western gorilla, Bornean orangutan, Sumatran orangutan, Chimpanzee and Bonobo - only the Chimpanzee and Bonobo are not in critically endangered list but are listed as endangered. The Eastern Gorilla - the largest living primate - has now been listed as critically endangered owing to illegal hunting, said the latest update of the International Union for Conservation of Nature and Natural Resources' (IUCN) "Red List of Threatened Speciesa. The IUCN Red List now includes 82,954 species of which 23,928 are threatened with extinction. The Eastern Gorilla -- which is made up of two subspecies - has moved from Endangered to Critically Endangered due to a devastating population decline of more than 70 per cent in 20 years. Its population is now estimated to be fewer than 5,000. "To see the Eastern gorilla - one of our closest cousins - slide towards extinction is truly distressing," said Inger Andersen, IUCN Director General. "We live in a time of tremendous change and each IUCN Red List update makes us realise just how quickly the global extinction crisis is escalating," he added. The once widespread and abundant Plains Zebra has moved from Least Concern to Near Threatened. The population has reduced by 24 per cent in the past 14 years from around 660,000 to a current estimate of just over 500,000 animals. In many countries, Plains Zebra are only found in protected areas, yet population reductions have been recorded in 10 out of the 17 range states since 1992. The Plains Zebra is threatened by hunting for bushmeat and skins, especially when they move out of protected areas. Three species of antelope found in Africa - Bay Duiker, White-bellied Duiker and Yellow-backed Duiker - have moved from Least Concern to Near Threatened. "Illegal hunting and habitat loss are still major threats driving many mammal species towards extinction," noted Carlo Rondinini, coordinator of the mammal assessment at Sapienza University of Rome. This update of the IUCN Red List also brings some good news and shows that conservation action is delivering positive results. Previously listed as Endangered, the Giant Panda is now listed as Vulnerable, as its population has grown due to effective forest protection and reforestation. The improved status confirms that the Chinese government's efforts to conserve this species are effective. "However, climate change is predicted to eliminate more than 35 per cent of the Panda's bamboo habitat in the next 80 years and thus Panda population is projected to decline, reversing the gains made during the last two decades," the authors noted. To protect this iconic species, it is critical that the effective forest protection measures are continued and that emerging threats are addressed, they added. Due to successful conservation actions, the Tibetan Antelope has moved from Endangered to Near Threatened. The population underwent a severe decline from around one million to an estimated 65,000-72,500 in the 1980s and early 1990s. This was the result of commercial poaching for the valuable underfur - shahtoosh - which is used to make shawls. "Conservation action does work and we have increasing evidence of it. It is our responsibility to enhance our efforts to turn the tide and protect the future of our planet," the authors said during the release of the list at the IUCN World Conservation Congress in Hawaii.