A Grauer’s gorilla. A.J.Plumptre/WCS)

HONOLULU, Hawaii — An update to the International Union for the Conservation of Nature’s Red List of Threatened Species, which assesses the extinction risk of the world’s plants, animals and fungi, was released here Sunday — and it moves a key gorilla subspecies, Congo’s Grauer’s gorilla, to “critically endangered” status.

Just 3,800 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. More than 8,000 delegates from 184 countries are in attendance.

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 assessed, more than a quarter are threatened with extinction.

Arguably the biggest update to the Red List on Sunday was its report on the decline of the Grauer’s gorilla, one of two subspecies of the Eastern gorilla and the world’s largest living primate. The subspecies was moved from “endangered” to “critically endangered” after 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 eastern Congo, other people in the region were displaced. “Big populations ended up in some of the protected areas, which were relatively uninhabited,” Robinson said. This opened up the protected areas to artisanal mining, charcoal extraction and bushmeat hunting.

Over the past 20 years, 77 percent of Grauer’s gorillas have been lost; a 2015 assessment finds that just 3,800 Grauer’s gorilla remain, compared with 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, on Sunday.

The Plains zebra has moved from “least concern” to “near threatened” after a 24 percent population decline over the past 14 years — down from about 660,000 to 500,000 animals. They are found only 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 — also have 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 “least concern” to “near threatened,” as well. Habitat destruction and fragmentation, brushfires, disease and drought have all taken a toll on Australia’s favorite 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.

The latest IUCN assessment also shows that of the 415 endemic Hawaiian plants assessed, 87 percent are threatened with extinction. Thirty-eight plants have been listed as extinct, and four are listed as extinct in the wild. Invasive species, such as pigs, goats, rats and slugs, as well as non-native plants, have imperiled Hawaii’s flora, and the IUCN Species Survival Commission Hawaiian Plant Specialist Group anticipates that the remaining species to be assessed also will be highly threatened.

“[The IUCN Red List] has to drive imperative and important conservation action or we will lose these species forever,” said IUCN Director General Inger Anderson. “Once they are gone, they really are gone.”

Amid this bad news, there are signs of hope, as well. Two endemic Hawaiian plants thought to be extinct — Mark’s Cyanea and Hairy Wikstroemia — were rediscovered during the most recent assessment. And several other species have been down-listed, 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.

Bamboos are quite sensitive to climate change, and models show that 35 percent of the bamboo that pandas rely could be wiped out over the next 80 years. “All the good work done by Chinese authorities on the ground could be easily be undone by a threat which is caused by the global community, not just the Chinese,” Hilton-Taylor said.

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 down from 1 million 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.”

On Saturday night, the IUCN, its Species Survival Commission and nine Red List partner institutions committed to supporting the IUCN Red List, pledging more than $10 million over the next five years toward achieving a goal of assessing 160,000 species by 2020.

“Our goal is to make that IUCN Red List an even more complete barometer for life and, therefore, being a real driver for action,” Anderson said.

Allie Wilkinson is an independent multimedia journalist specializing in science, technology and the environment.