Endangered Species

Extinction risk and different levels of threat

Have you ever noticed the expressions “vulnerable”, “endangered” or “extinct in the wild” which are associated with some species? The loss of biodiversity has made it more common to hear these classifications. Learn about the categorisation created by the International Union for Conservation of Nature, its meaning and importance in determining a species’ extinction risk.

When we hear about the extinction risk of a species, this risk has been determined by teams of experts—from biologists to ecologists and conservation specialists—who, after prior work on the history of occurrence and years of field observation, have assigned to that species a level of threat that is applicable in a certain region and at a given point in time, determined by internationally accepted criteria.

The criteria that allow us to determine extinction risk and the level of threat were established by the International Union for Conservation of Nature (IUCN), an organisation founded in 1948 that brings together official and non-governmental entities from over a hundred countries around a common objective: the global conservation of natural resources and biodiversity.

The criteria in question, followed by all red lists or books, assess elements such as the size and fragmentation of the populations, the number of mature specimens (reproducers), the geographical distribution of the species, and the area it occupies (and how this changes over time), threats and pressures, among other variables, based on which a probability of extinction risk is estimated, allowing the species to be assigned to one of three threat categories:

  • Critically Endangered (CR): species whose risk of extinction in the wild is extremely high.

Some species included in this category:
The Algerian oak (Quercus canariensis), which has less than 300 specimens in Portugal, is an example; the Iberian Lynx (Lynx pardinus) is one of the animals included in this category, according to data from the Book of Mammals of Mainland Portugal.

  • Endangered (EN): species that are at very high risk of extinction in the wild.

Some species included in this category:
The Scots pine (Pinus sylvestris) and the yew tree (Taxus baccata) are considered “Endangered” species in the North and Centre of Portugal, according to the Red List of Vascular Flora in Mainland Portugal, as is the grey wolf (Canis lupus), according to the Book of Mammals of Mainland Portugal.

  • Vulnerable (VU): species at high risk of extinction in the wild.

Some species included in this category:
In Portugal, the wildcat is one of the animals included in this category, according to data from the Book of Mammals of Mainland Portugal. As for plants, Rhaponticum exaltatum (formerly known as Leuzea rhaponticoides) is a “Vulnerable” (VU) species according to the Red List of Vascular Flora in Mainland Portugal.

risco de extinção

When the species observed have sizeable populations and are present over large areas of their native territory, they do not fit into any of the previous categories. Depending on the evidence, the species can be considered as:

  • Near Threatened (NT): during the period in which it was observed, the species is not threatened, but there is information and evidence that it may, in the near future, deteriorate and become part of one of the threat categories.
  • Least Concern (LC): is assigned to species whose populations and range are large and stable or growing, so the species does not raise any concerns about the risk of extinction. Examples in the animal world include: the European hedgehog (Erinaceus europaeus) or the common mole (Talpa europaea), listed both in the (previous) Red Book and by the IUCN.

Designations are also given to species considered extinct:

  • Extinct (EX): a species is considered extinct when there is no reasonable doubt about the death of its last remaining specimen. The category is assigned after all exhaustive attempts to find a specimen of a species in its known and potential habitats (throughout its historical range) have failed. This means that the surveys were carried out over a period of time appropriate to the life cycle and biological form of the species in question.

Similarly, the category “Regionally Extinct” (RE) can be attributed when there is no doubt that in a given region the final remaining specimen of the species has died, although there are populations in other regions where it is native. One example is the brown bear (Ursus arctos) which, despite being considered “Regionally Extinct” in more than 20 countries where it naturally existed, has stable populations in vast expanses of the planet, so it has been globally classified on the IUCN Red List as a “Low Concern” (LC) species that is not at risk of extinction.

  • Extinct in the Wild (EW): This is the category assigned to species that only exist in captivity, as a result of cultivation or with one or more naturalised populations outside their natural range. This category is also assigned after exhaustive studies have been conducted without identifying at least one specimen in the wild.

It should be noted that species lacking adequate and/or sufficient information to be directly or indirectly evaluated as to their risk of extinction are also identified with the classification “Data Deficient” (DD), and that additional relevant information is required for further evaluation. Examples of animals for which insufficient information is available are the stoat (Mustela erminea), the pine marten (Martes martes), and the common polecat (Mustela putorius). Similarly, species that have not yet been subject to the assessment criteria may be identified as “Not Evaluated” (NE).

risco de extinção

Did you know that…

  • The IUCN Red List has nearly 143,000 species listed on it? Of these, more than 40,000 are endangered. They include 41% of amphibians, 37% of sharks and rays, 34% of conifer species (plants/trees), 33% of corals, 26% of mammals, and 13% of birds. The aim is to catalogue 160,000 species, enabling a broad view of world biodiversity and the creation of an appropriate conservation plan. This list is updated a few times a year.
  • Under the Habitats Directive, a similar process to that of the IUCN is used to determine the Conservation Status of habitats and their species. The three classes assigned – “Favourable” (FV), “Unfavourable” or “Inadequate” (UI) and “Unfavourable or Poor” (U2) – provide clues as to the long-term status of the species. There is also a fourth rating for instances where the information does not enable an assessment to be carried out: “Unknown” (XX).

There can be no effective protection of biodiversity if we do not have adequate information


The assessment carried out through these methods is an indicator of biodiversity at a global level. The information it provides supports the creation of conservation policies and actions consistent with the threat levels of species and habitats.

If the information collected on a local scale contributes to drawing up this global scenario, it is also essential to define regional, national and cross-border strategies that favour the preservation of species at greater risk of extinction and habitats in a more unfavourable state of conservation.

In the forests managed by The Navigator Company, this tool supports the assessment of impacts and their mitigation. It also helps classify areas of conservation interest, where active management measures are implemented to maintain and improve valuable natural habitats, as well as defining strategies to protect and, in some cases, support the proliferation of species that are under threat.