An update to the International Union for the Conservation of Nature Red List of Threatened Species, which assesses the extinction risk of the world's plants, animals, and fungi, moves a key gorilla subspecies, the Democratic Republic of Congo's Grauer's gorilla, to "critically endangered" status.

Just 3800 Grauer's gorilla remain - a sharp decline in numbers for the world's largest gorilla, and one largely driven by geopolitical upheaval as the Rwandan genocide drove large numbers of refugees into the gorilla's habitat.

The sharp decline of Grauer's gorilla meant that the larger species to which it belongs, the Eastern gorilla - which also includes the Mountain gorilla - was listed as "critically endangered".

The international meeting, which convenes every four years, is the world's largest environmental decision-making forum, bringing together heads of state and other government officials, civilians, indigenous peoples, business leaders, and academics to address the world's biggest conservation challenges. Over 8000 delegates from 184 countries are in attendance.

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The IUCN uses the Red List to classify organisms according to the severity of their extinction risk; in descending order of threat, the categories are "critically endangered," "endangered," "vulnerable," "near threatened" and "least concern," The list also includes categories for extinct and data-deficient species. Of the 82,954 species currently assessed, more than a quarter are threatened with extinction.

Arguably the biggest update to the Red List is its report on the decline of the Grauer's gorilla, one of two subspecies of Eastern gorilla and the world's largest living primate. The subspecies was moved from "endangered" to "critically endangered" following a report by the Wildlife Conservation Society and Flora & Fauna International released earlier this year, which found devastating population declines due to illegal hunting and civil unrest.

John Robinson, a primatologist and chief conservation officer at the Wildlife Conservation Society, cites the Rwandan genocide as a major driver of the decline in Grauer's gorillas.

The exodus of Rwandan refugees had ripple effects: as people moved into the eastern Democratic Republic of Congo, other people in the region were displaced. "Big populations ended up in some of the protected areas, which were relatively uninhabited," said Robinson. This opened up the protected areas to artisanal mining, charcoal extraction, and bushmeat hunting.

Over the last 20 years, 77 per cent of Grauer's gorillas have been lost; a 2015 assessment finds that just 3800 Grauer's gorilla remain, down from 16,900 in 1994.

Four of the six great ape species - the Eastern Gorilla, Western Gorilla, Bornean Orangutan and Sumatran Orangutan - are now listed as "critically endangered," while the Chimpanzee and Bonobo are listed as "endangered".

And there were other dismaying updates as well.

The Plains Zebra has moved from "least concern" to "near threatened" following a 24 per cent population decline over the past 14 years-down from around 660,000 to 500,000 animals. They are only found in protected areas in many of their range countries, yet many range states still report population declines. They are threatened by hunting for their meat and skins.

Three species of African antelope - Bay Duiker, White-bellied Duiker, and Yellow-backed Duiker - have also moved from "least concern" to "near threatened." Populations within protected areas are relatively stable, but elsewhere they are threatened with illegal hunting and habitat loss.

Koalas have moved from from "least concern" to "near threatened" as well. Habitat destruction and fragmentation, brushfires, disease, and drought have all taken a toll on Australia's favourite marsupial. While management plans are in place, they require improvements; a recent parliamentary inquiry concluded that Australia's conservation and management strategy was largely ineffective.

A park ranger escorts visitors through the Virunga National Park, near the Uganda border in eastern Congo. Photo / AP
A park ranger escorts visitors through the Virunga National Park, near the Uganda border in eastern Congo. Photo / AP

The latest IUCN assessment also shows that of the 415 endemic Hawaiian plants currently assessed, 87 per cent are threatened with extinction. Thirty eight plants have been listed as extinct, and another four are listed as extinct in the wild.

Invasive species, such as pigs, goats, rats, slugs, and non-native plants have imperiled Hawaii's flora, and the IUCN Species Survival Commission Hawaiian Plant Specialist Group anticipates the remaining species to be assessed will also be highly threatened.

Amid this bad news, there are signs of hope as well. Two endemic Hawaiian plants believed to be extinct - Mark's Cyanea and Hairy Wikstroemia - were rediscovered during the most recent assessment. And several other species have been downlisted, indicating that conservation actions are working.

The Giant Panda was moved from "endangered" to "vulnerable," as its population has grown as a result of effective forest protection and reforestation efforts by China. "We've kept it in the vulnerable category because there are concerns about climate change," said Craig Hilton-Taylor, head of the Red List Unit.

Another success story due to conservation action is the Tibetan Antelope, which has moved from "endangered" to "near threatened." After a severe population decline due to poaching in the 1980s and early 1990s which brought the animals from one million down to an estimated 65,000 to 72,500, rigorous protection measures have been enacted and enforced, bringing the population back up to between 100,000 and 150,000.

Two Australian species have seen an upswing as well: the Greater Stick-nest Rat, which moved from "vulnerable" to "near threatened" and the Bridled Nailtail Wallaby, which moved from "endangered" to "vulnerable."