Earth's preeminent list of endangered species marks its 50th anniversary this year, but there isn't much time to celebrate. With nearly a third of all surveyed species at risk of disappearing, and potentially millions more still unsurveyed, the International Union for Conservation of Nature (IUCN) Red List is scratching at the surface of what increasingly looks like a worldwide wildlife extinction crisis.

The IUCN Red List has so far surveyed 76,199 species, nearly halfway to its goal of surveying at least 160,000 species by 2020. This week the group announced that 22,413 of those are threatened with extinction, an increase of 310 species since its last update five months ago. This is part of a long-simmering crisis many scientists now describe as a mass extinction event. Earth has endured five such events before, but this would be the first one in human history — and the first with human help.

"Each update of the IUCN Red List makes us realize that our planet is constantly losing its incredible diversity of life, largely due to our destructive actions to satisfy our growing appetite for resources," says IUCN Director Julia Marton-Lefèvre. "Our responsibility is to increase the number of protected areas and ensure that they are effectively managed so that they can contribute to saving our planet's biodiversity."

The IUCN has already assessed most mammals and birds, but it still has a long way to go with less visible, relatable or charismatic creatures such as fish, insects, plants and fungi. Its latest update includes several species with less star power than tigers or pandas, including many that suffer from some of the most salient ecological threats: overhunting, habitat loss and climate change.

These animals are still key parts of their ecosystems, even if they're not all household names. Here's a look at seven of the most recent additions to the Red List — plus one whose outlook is improving.

Giant East Usambara blade-horned chameleon (Endangered)

Giant East Usambara Blade-horned Chameleon

Photo: IUCN

At least 66 chameleon species on the Red List are threatened by habitat loss, and this one is no exception. Found in Tanzania's Amani Nature Reserve, it's at risk from the clearing of old-growth forests for agriculture, charcoal production and timber extraction. It uses color for communication and also darkens its skin when stressed, wrapping its tail around tree branches for security.

Pacific bluefin tuna (Vulnerable)

Pacific bluefin tuna

Photo: IUCN

Fished heavily for sushi and sashimi in Asia, the Pacific bluefin tuna has moved from the IUCN's "Least Concern" category to "Vulnerable," which means it's now threatened with extinction. Most of the fish caught are juveniles that haven't had a chance to reproduce yet, helping the species decline by up to 33 percent since 1992. Existing conservation areas can't provide enough protection, but the IUCN says expanded offshore coverage — especially in breeding areas — could still save the species.

Bombus fraternus (Endangered)

Bombus fraternus

Photo: Wikimedia Commons

This North American bumblebee is endangered by the loss of its grassland habitat across the Eastern U.S., much of which has been converted to cornfields in recent decades. The bee's modern range and abundance have shrunk 29 percent and 86 percent, respectively, compared with historical records dating back to 1805. "Corn seed in North America is now almost ubiquitously treated with neonicotinoids," the IUCN explains, "a pesticide group known to negatively impact bees."

American eel (Endangered)

American eel

Photo: IUCN

The American eel is a wonder of nature. Born from eggs laid in the middle of the Atlantic Ocean, its larvae drift for years until they reach U.S. estuaries and streams. Once there, they transform again while maturing through several more life stages, finally returning to the Atlantic to lay eggs. Dams have wiped them out from some traditional freshwater habitats, and they're threatened at various points in their life cycle by fishing, pollution, parasites, habitat loss and climate change. The decline of the endangered Japanese eel has also reportedly led to more international poaching of American eels.

Kaputar pink slug (Endangered)

Kaputar pink slug

Photo: IUCN

The existence of these bright pink, 8-inch slugs was only recently confirmed, but scientists think they're survivors from an ancient period when rain forests covered eastern Australia. A volcanic eruption millions of years ago created a high-altitude oasis for them, helping them endure as Australia dried out and its rain forests receded. They're now restricted to the upper reaches of Mount Kaputar in New South Wales, where the warming and drying effects of climate change now threaten their final stronghold.

Chinese cobra (Vulnerable)

Chinese cobra

Photo: Wikimedia Commons

The Chinese cobra is still common across a swath of China, Vietnam and Laos, but its population has plummeted by 30 to 50 percent in the past 20 years. The main causes of this decline — habitat loss and hunting — have not ceased, so the IUCN now considers it an endangered species. The use of agricultural pesticides poses a major threat, as does overexploitation of the snakes for sale as food.

Black grass-dart butterfly (Endangered)

Black Grass-Dart Butterfly

Photo: IUCN

Similar to the pink slugs of Mount Kaputar, the black grass-dart butterfly occupies a tiny, embattled habitat in Australia. Its coastal home faces a "clear threat" from rising sea levels, according to the IUCN, as well as from drier weather, more frequent wildfires and the spread of invasive weeds, which outcompete the native grasses these butterflies have evolved to eat.


Andinobates tolimensis (Vulnerable)

Ranitomeya tolimensis

Photo: IUCN

The IUCN didn't only add or downgrade species in this Red List revision. It also upgraded a few whose prospects have improved due to conservation. One example is the tiny frog above, which is limited to a single Colombian forest fragment that measures less than a quarter square mile (0.5 square km). It was listed as endangered in 2010, but because that patch of forest became part of the Ranita Dorado Reserve in 2008 — which has ongoing restoration efforts and an environmental education program — the IUCN has grown more optimistic. It notes, however, that "there exists a plausible future threat associated with habitat loss and land use change if the reserve is not well enforced into the future."

As evidence of what the Red List is meant to prevent, the IUCN has also added two species to its list of extinctions. One is a Malaysian snail whose entire habitat was destroyed when a company turned it into a limestone quarry, a threat that still faces several more species in the region. The other is the St. Helena giant earwig, which inhabited the small Atlantic island of St. Helena until it was killed off by humans' removal of surface stones and the introduction of mice, rats and other invasive species.

"These recent extinctions could have been avoided through better habitat protection," says Simon Stuart, chairman of the IUCN Species Survival Commission. "Today's update also highlights two amphibian species which have improved in status thanks to successful management of Colombia's Ranita Dorada Reserve, where they occur. We need to take more responsibility for our actions to see many more successes like this one, and to have a positive impact on the health of our planet."

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Russell McLendon ( @russmclendon ) writes about humans and other wildlife.