The Red List

Extinction threatens over 38,500 species. The possibility of disappearing impacts 41% of amphibians, 37% of sharks and rays, 26% of mammals, and 14% of birds. But how do scientists determine if an animal is threatened with extinction or not?

IUCN’s RED LIST

The International Union for Conservation of Nature (IUCN) — the first global environmental organization — publishes a Red List of Threatened Species. This list provides the best information about the conservation status of more than 138,000 of Earth’s species.

The Red List categorizes species based on how threatened they are. The categories include least concern, near threatened, vulnerable, endangered, critically endangered, extinct in the wild, and extinct.

LEAST CONCERN

Species named as least concern have widespread and healthy populations. Since wild populations of these species are abundant, the IUCN does not need to worry about protecting them.

The honey badger falls in the category of least concern. Honey badgers get their name from their favorite food: honey. However they really are not after honey; instead, they hunt bee larvae hidden in the sticky sweetness. They inhabit sub-Saharan Africa, the Middle East, and India, living in both in humid rainforests and cold mountains. Honey badgers are fierce for their size. They can take down and eat scorpions and venomous snakes, and will fight predators more than twice their size.

NEAR THREATENED

Species categorized as near threatened currently have healthy populations. Although not at risk right now, these species may become at risk in the future.

Weighing up to 2,000 pounds and running in thunderous herds, the IUCN lists thick-coated plains bison as near threatened. According to the World Wildlife Fund (WWF), up to 60 million bison once grazed North America’s grasslands. Unfortunately, westward expansion — starting in the 1800s and continuing today — has taken over land once roamed by North America’s largest animal. With land loss and population declines, plains bison could become vulnerable in the future.

WHAT ABOUT THREATENED SPECIES?

When determining if a species is threatened with extinction — either vulnerable, endangered, or critically endangered — the IUCN looks at the following factors:

Population size: how many members of the species exist in the wild

Population reduction: how much the population has decreased over time

Geographic range: the amount of land the species inhabits

Probability of extinction: how soon scientists predict a species will become extinct

VULNERABLE

Vulnerable is the first category on the IUCN’s Red List where an animal is considered threatened with extinction. A species is vulnerable if the population has less than 10,000 mature individuals — or individuals that can reproduce babies. A species also may be vulnerable if the population declines 30 to 50% over ten years or within three generations (whichever is longer). A generation starts at an animal’s birth and ends when it can reproduce. For example, giant pandas reproduce between the ages of four and six. For a giant panda, three generations would take roughly twelve years, so these black and white bears could be vulnerable if their population declined 30 to 50% over twelve years.

Third, a species is vulnerable if the total land that all species inhabit is less than 7,722 square miles. Think about adding the land that one group of pandas inhabits plus the land that another group of pandas lives on, plus the land of a third group. If the land for all the groups in one species is less than 7,722 square miles, IUCN may list the species as vulnerable. Furthermore, species may be vulnerable if one group lives on less than 772 square miles. For example, if a group of pandas loses their habitat due to deforestation and squeezes on a small plot of land smaller than 772 square miles, they also could be labeled vulnerable.

Finally, scientists use complex formulas and technology to figure out the likelihood that a species will go extinct without protection and help from humans. Vulnerable species face a high risk of extinction in the wild.

The IUCN classifies giant pandas as vulnerable. About 1,800 wild pandas live hidden in China’s mountain forests. These hefty bears mostly eat bamboo and lots of it — between 26 and 84 pounds each day. In 2016, pandas’ conservation status improved from endangered to threatened due to decreased poaching and more protected habitats. According to National Geographic, giant panda populations rose by 17% from 2003 to 2014. Yet,​​ growing cities and development continue to destroy panda habitats and bamboo. In addition, giant pandas reproduce slowly, only giving birth to a cub about every two years, keeping them vulnerable to extinction.

ENDANGERED

The IUCN classifies a species as endangered if the population has fewer than 2,500 mature individuals. Additionally, endangered species show population declines between 50 to 70% over ten years or within three generations. Third, a species may be endangered if its geographic range — or the amount of land that all species inhabit — is less than 1,930 square miles. According to scientific predictions, endangered species face a very high risk of extinction.

Blue whales are the largest animals on the planet, equaling the weight of 33 elephants. Interestingly, they are also the loudest. Their bellows can reach up to 188 decibels, even louder than a jet engine. The IUCN lists blue whales as endangered. From the 1860s until the 1960s, whalers hunted blue whales for their fat and body parts, killing up to 99% of the blue whale population.

Today, an estimated 10,000 to 25,000 blue whales inhabit Earth’s oceans. Ship crashes, entanglement in fishing nets, and climate change threaten these marine mammals. Another threat is noise pollution caused by ships, oil rigs, and coastal industry. Man-made noises in a normally quiet ocean interrupt blue whales’ communication, confusing them as they swim, feed, and breed with other blue whales.

CRITICALLY ENDANGERED

The IUCN classifies a species as critically endangered if the species has fewer than 250 mature individuals or if the population declines by 80 to 90% over ten years or three generations. In addition, a species may be critically endangered if its geographic range is less than 39 square miles or if a group is forced to live on less than four square miles of land. Critically endangered species have a 50% chance of extinction within ten years. Thus, critically endangered species face a very, very high risk of extinction in the wild.

The eastern lowland gorilla lives in the tropical rainforests of the Democratic Republic of Congo (DRC) in Africa. Years of human war and violence in the DRC led to these gorillas being critically endangered.  On top of the conflict, their habitat has been destroyed to make room for farms, ranches, and mines. According to WWF, the eastern lowland gorilla occupies only 13% of its native habitat. Scientists estimate that the gorilla population has declined by more than 50% since 1990.

EXTINCT IN THE WILD

After years and years of not finding a species in their native habitat, the species is declared extinct in the wild. Species classified as extinct in the wild only live in zoos and conservation centers. One example is Spix’s macaws. You may recognize this fluffy-headed, blue bird from the movie Rio.

Considered one of the world’s rarest birds, only 177 live in captivity. However, conservationists hatched a plan to release 52 macaws into their natural habitat. They hope that reintroducing Spix’s macaws to Brazil can grow a wild population of these birds.

EXTINCT

When the last individual of a species dies, the species is considered extinct. Scientists thought that the Pinta tortoise, found in the Galapagos Islands, went extinct in the 1900s after fishermen overtook the tortoises’ natural habitat. But in 1971, a scientist found one last Pinta tortoise. The scientist named him Lonesome George.

Lonesome George died in 2012, officially making the Pinta tortoise extinct. However, Yale University scientists have studied the genes of other Galapagos tortoises and found some that are half Pinta. Researchers hope to breed these tortoises and restore a half-sibling of the Pinta tortoises on Pinta Island.