Explanation of the different IUCN Red List categories

I very often refer to the different Red List categories when I write about endangered or threatened species, but what I’ve been forgetting is that most of you probably aren’t as familiar with the different categories as I am myself, so I’ve decided to write a short introduction to these different categories.

This topic is actually pretty complex, so think of this as a crash course to better understand what I mean when I write about which group the organisms belong to, and not a complete guide. I will most likely link to this post in the future, so if you think there are any details that I should include or edit, please let me know.

What does the Red List measure?

The Red List is based on several different criteria, including both population size, population decline rate, projected population decline, the health of the populations, habitat fragmentation and even some more. Each species gets compared against a certain set of requirements for each different category, and (this is important) only needs to fit 1 of these to be placed in that group!

This means that the species can be very healthy in certain aspects, but one major problem is putting them high up on the endangeredness scale. Often (and this is just a rule of thumb, not a fact) species are put in groups based on a projected population decline over the next 100 years, which mostly is because of habitat loss. This is what the Red List most often measures, but it also measures the criteria I wrote above, and gets placed based on the worst one. Just keep this in mind when you read about organisms on the Red List.

The different criteria used to measure and place them in a group is a pretty long list, but it is available at the IUCN website, so check it out for yourself.

A final thing to keep in mind is that the criteria are universal for all organisms, so some of them tend to more easily get placed in a worse category than others. For example, and species with less than 2,500 mature individuals is automatically considered Endangered; this is obviously a lot "easier to reach" for large mammals than it is for insects, plants, rodents or any other small organism.

The different categories

Not threatened categories

There are two not threatened subcategories:

Least Concern (LC): Least concern is the best group an organism can belong to. As the name implies, organisms in this group should not be of concern, and they do not qualify for any of the other categories. These organisms are likely to survive for a long time.

Near Threatened (NT): The organisms in this group is not threatened by extinction, but is suspected to becoming threatened in the near future, so they require a bit more monitoring than the LC group.

Threatened categories

Vulnerable (VU): Organisms in this group has a high chance of becoming endangered within the near future. This often includes lots of animals that experience habitat loss, but are somewhat healthy at the moment.

Endangered (EN): All endangered organisms have a high chance of going extinct in the near future. These are still possible to save, but requires human effort!

Critically Endangered (CR): The organisms in the CR category has an extremely high chance of going extinct in the near future. The ones on this list is mostly doomed for extinction, and has already suffered a huge population loss. Getting these species back to a healthy state is unlikely, but it can of course happen if we work hard to achieve it.

A lot of extinct species are also in this category. The reason for this is that it is actually pretty difficult to verify that a species is extinct, especially for species that are difficult to observe. For example, the baiji freshwater dolphin (Lipotes vexillifer) has not been confirmed seen since 2002, and the Ivory-billed woodpecker has not verified to be alive since since 1944(!), but both of these are still considered Critically Endangered.

Extinct categories

Regionally Extinct (RE): This category fits organisms that are no longer found in a certain location / region. This category is not used for the international Red List, but can be applied to animals in regional list. For example the Grey partridge (Perdix perdix) is considered LC by the international Red List, but considered Regionally Extinct by the Norwegian Red List.

Extinct in the Wild (EW): Organisms in this group has gone extinct in the wild, but there are still individuals alive in “captivity”. This can include animals that are only found in zoos or in private collections, but also other organisms. There are actually some plant species that are somewhat common to have in your garden or even inside your house that are extinct in the wild!

Many organisms in this group is part of a rewilding program where the owners try to breed the organisms and put them back in the wild. This might sound easy, but it takes extreme amounts of efforts to reintroduce a species that is extinct in the wild!

Extinct (EX): The organism is no longer found alive anywhere, either in the wild or in captivity.

Other categories

Data Deficient (DD): This category includes organisms that lack data. This is usually because they haven’t really been studied at all, so no one can really know if they are endangered or not.

Not Evaluated (NE): Any organism in this group has simply not been studied by the IUCN. This includes lots of different species in all taxa, and most will likely be added at one point or another. Evaluating species takes a lot of time, so just have patience if your favorite organism is not yet evaluated.

How to check the status of a species

The Red List has been moved entirely to being online, so you can check out any species at the IUCN Red List website. Just type in the common english name, or the scientific name to get a result. In addition to telling you about which category it belongs to, it will also explain why it is listed in that category, and link to the sources for the reasons. It’s a great tool to use if you are interested in learning more about a certain species!