Arxiu d'etiquetes: endangered species

What is IUCN and its Red List?

A lot it is talked about endangered, critically endangered and vulnerable species. In fact, in this blog we have given some examples: Mediterranean monk seal is an example of a critically endangered species and Iberian lynx of an endangered species. But, which is the meaning of these names? Who is responsible of categorising them and how do they do it? Here, there are the answers. 


Have you ever seen this logo in some report or in Internet?

logo iucn uicn
International Union for Conservation of Nature logo (Pictrure: IUCN).

The International Union for Conservation of Nature (IUCN) is a union with more than 1,000 government and NGO member organizations, and about 11,000 scientists from 160 countries.

Its purpose is to preserve nature and, for this reason, it seeks to solve the most urgent environmental problems.

The IUCN is composed by 6 commissions, among which there is the Species Survival Commission (SSC), which have more than 10,000 volunteer experts from all over the world, distributed in different working groups.

The IUCN and the Species Survival Commission are the responsibles of elaborating the Red List. What is a Red List?


The red list of threatened species is an inventory of the the conservation state of plant, animal and fungi species. So, it evaluates the risk of extinction of a species in case no conservation actions are taken.

Lista Roja de la Flora Vascular Española 2008. (Imagen: Jolube).
Red List of Spanish Vascular Flora 2008. (Picture: Jolube).

This list is produced following objective criteria that permit to classify species in 8 threat categories, so that it is easier to compare different taxa. Let’s see them!



To use these criteria, some requirements have to be followed:

  • They can be applied to species and lower taxonomic levels.
  • They can only be applied to wild populations in their natural distribution and to populations resulting from benign introductions.
  • Criteria have to be applied to taxon whatever the level of conservation action affecting it.
  • The conservation status of a species doesn’t have to be necessarily the same in a global scale or a regional or national scale.


From less to more extinction risk, evaluated taxa can be classified in one of the following categories:

  • Least concern (LC): when a taxon cannot be classified in any of the following categories, it is said that there is a least concern for its conservation.
  • Near Threatened (NT): when a taxon cannot be classified in any of the following categories, but is close, it is said that is near threatened because in the near future it will possibly classified in some of them. The dwarf cassowary (Casuarius bennetti), a bird that could be the current velociraptor, has this category.
quandong, cassowary, eating, fruit
Cassowary eating quandongs, one of its favourite fruits (Picture: Christian Ziegler).
  • Vulnerable (VU): when a taxon is considered to be facing a high risk of extinction in the wild, it is classified as vulnerable. Two examples are whale shark and the basking shark, the two biggest fishes in the world and feed on plankton.
  • Endangered (EN): a taxon is endangered when faces a very high risk of extinction in the wild. An example is the Iberian lynx (Lynx pardinus).
  • Critically Endangered (CR): a taxon is critically endangered when faces an extremely high risk of extinction in the wild. An example, it is the Mediterranean monk seal (Monachus monachus).
  • Extinct in the Wild (EW): it means that only survives in cultivation, in captivity or as a naturalized population well outside the past range.
  • Extinct (EX): a taxon is extinct when there is no doubt that the last individual has died. An example is the thylacine.
Un dels pocs llops marsupials que es conserven taxidermitzats en el món. Museo nacional de Ciencias Naturales, Madrid. Foto: Mireia Querol
Thylacine was extinct by humans. Museo nacional de Ciencias Naturales, Madrid (Picture: Mireia Querol).

Vulnerable, Endangered and Critically endangered categories are those that show a threatened condition of the species. So, an endangered and a threatened species are not exactly the same.

Moreover, there are two other categories for those species not evaluated:

  • Data deficient (DD): when there is inadequate information to make an assessment of its risk of extinction.
  • Not evaluated (NE): when it has not yet been evaluated.


5 are the criteria to evaluate the state of conservation of taxa:

  • Criterion A: Reduction in population size. It has to accomplish some of the following subcriteria (A1-A4), evaluating the reduction in the largest period, 10 years or 3 generations.
  Critically endangered Endangered Vulnerable

Reduction in the past where the causes are reversible, understood and have ceased

90% or more 70% or more 50% or more

Reduction in the past where the causes may no have ceased, may no be understood or may not be reversible

80% or more 50% or more 30% or more

Reduction in the future (up to 100 years)


80% or more 50% or more 30% or more

Reduction where the time period mus include both the past and the future (up to 100 years in the future) and where the causes may not have ceased, may not be understood or may not be reversible

80% or more 50% or more 30% or more
  • Criterion B: Geographic range either extent of occurrence or area of occupancy. Let’s see these concepts:
    • Extent of occurrence: when you draw a line that joints all the most external places where there is a taxon (and all the places are included), you find the extent of occurrence.
    • Area of occupancy: it refers to the area inside the extent of occurrence having into account that there is not present in all its extent of occurrence.
Dos ejemplos de la diferencia entre extensión de presencia y área de ocupación. (A) es la distribución espacial de dos especies, (B) es la delimitación de la extensión de presencia y (C) muestra una medida del área de ocupación (Foto: IUCN).
Two examples of the difference between extent of occurrence and area of occupancy. (A) is the spatial distribution of a species, (B) show  the extent of occurrence and (C) shows the area of occupancy (Picture: IUCN).
  Critically endangered Endangered Vulnerable

Extent of occurrence

Less than 100 km2 Less than 5.000 km2 Less than 20.000 km2

Area of occupancy

Less than 10 km2 Less than 500 km2 Les than 2.000 km2
  • Criterion C: Small size of the population and decline.
  Critically endangered Endangered Vulnerable
Number of mature individuals Less than 250

(and C1 and/or C2)

Less than 2.500

(and C1 and/or C2)

Less than 10.000

(and C1 and/or C2)


Continuing decline

At least 25% in 3 years or 1 generation (up to 100 years) At least 20% in 5 years or 2 generations (up to 100 years) At least 10% in 10 years or 3 generations (up to 100 years)

Continuing decline and at least one of the 3 conditions (2a.i, 2a.ii, 2b)


Number of mature individuals in each subpopulation

At least 50 At least 250 At least 1.000

% of individuals in one subpopulation

90-100% 95-100% 100%

Extreme fluctuations in the number of mature individuals

  • Criterion D: Very small population or restricted
  Critically endangered Endangered Vulnerable
Number of mature individuals Less than 250 Less than 2.500 Less than 10.000
  • Criterion E: Quantitative analysis 
  Critically endangered Endangered Vulnerable

Probability of extinction in the wild

At least 50% in 10 years or 3 generations (up to 100 years) At least 20% in 30 years or 5 generations (up to 100 years) At least 10% up to 100 years.

Despite there have to be evaluated all the criteria, with just one of them is enough to classify the species in the category.

The previous criteria are simplified because there are complementary conditions that have to be accomplished. For further details, read the document IUCN Red List Categories and Criteria.



Nocturnal birds of prey: the barn owl, legends and myths

Nocturnal birds of prey have suffered since a long time ago an unfair bad reputation that has led them in some cases to be persecuted and hated. What are these superstitions? Which is their conservation state? What can you do for them? In this article you will discover owls and the barn owl, Tyto albaand the legends associated with them.


As its name suggests, most nocturnal birds of prey (owls, owls, tawny owls) have nocturnal or crepuscular habits. They are carnivorous, with beaks and claws (two toes forward and two backward) adapted to tear flesh from their prey (small mammals, birds, reptiles, large insects ).


Owls usually have a rounded shape and apparent large head, with the face feathers forming the so-called facial disk. The facial disc serves as a dish heading sounds towards the ears. The opening of the ear is large, with a fold of skin (preaural halda), which functions as a pinna and is movable as in some mammals.

Oído de lechuza norteña (Aegolius acadicus). (Foto tomada de Jim McCormac).
Norther saw whet owl ear (Aegolius acadicus). (Photo by Jim McCormac).

The position of each ear is asymmetric in some species (one is higher than the other), so some of them -like the barn owl- can locate prey in complete darkness: an ear perceives sound before the other, so their  brain can calculate the exact place where prey is (directional hearing).

Boreal owl skull, cráneo de mochuelo boreal
Boreal owl skull (Aegolius funereus) where can be seen the asymmetric hearing openings and sclerotic eye rings. (Photo taken of Jim Williams)


Owl’s vision is highly developed. Eyes, unlike most birds, are in front position, which allows a perfect estimation of depth and three-dimensional vision. On the other hand, eyes are tubular (not spherical like ours) due to the large size of the cornea and lens, which prevents owls from moving them within their sockets. Also they have a protective bone plate around the eyes (sclerotic rings) that also impede movement. To solve this problem, they are able to turn his head 270 degrees. It can be considered that they see in black and white (they best perceive changes in light rather than colors), the pupil dilates a lot in bad light conditions (iris is hidden by dilated pupil) and they are the only birds in which the eyelid closes up to below. They also have a transparent lid” that moistens and protects the eye, called the nictitating membrane.

Visión lechuza, binocular, vista, búho, razces nocturnas
Binocular vison of a nocturnal bird of prey. Humans have a field vision of 180 degrees, 140 of them binocular). (Image by The Owl Pages)


Owls, unlike diurnal birds of prey, have a special flight feathers structure, fringed at the top surface and contours. The friction between them and the air is damped, achieving a spectacular silent flight undetectable by preys.

Pluma de lechuza común y autillo, donde se observan las barbicelas. (Foto tomada de Pedro Montoya).
Barn owl feather (Tyto alba) and european scops owl (Otus scops), (Image taken of Pedro Montoya).


The barn owl (Tyto alba), is unmistakable: it has a very well defined and heart-shaped facial disk. The back is gray with golden spots and fine black and white dots.


The barn owl lives all over the world (except Antarctica, north Europe and most Asia) and don’t build a nest, but lays eggs in tree holes, holes in the rock or human buildings (barns, attics, farmhouses, castles, churches ).

Why the barn owl has this negative reputation that caused their persecution in many parts of the world and in Spain? Causes are diverse, all fed by human fear:

  • They can nest in abandoned or sacred locations as churches (some with their own cemetery).
  • Nocturnal habits
  • They are sendentary, they can stay in the same hunting ground for years until food is scarce.
  • Ghostly appearance due to their colors and smooth and silent flight.
  • By their vocalizations (they have 17 different ones) like human screams and peculiar snorts. Listen to some owls making a defense vocalization in the following video:


In the Iberian Peninsula was believed that owls drank the oil of the lamps in churches, leaving the Saints in the dark (when the real thieves were sacristans). By landing on lamps or touching them and pouring the oil, it was believed that owls hated light, like evil spirits. In spanish and catalan there are sayings that refer to this myth. They were hunted, killed and hanged above the doors of churches and barns to ward off fire and lightning.

The vocalizations of barn owls are also interpreted as announcements of death, and there is a belief (without basis) that if someone hear an owl for several nights (something not difficult given their sedentary habits) a person suddenly will lose life.

Tyto alba, lechuza común, lechuza de campanario
Barn owl (Tyto Alba). (Photo by Kerkuil André).

In other cultures there are also negative legends about owls: in Africa that are sent by sorcerers to kill people or evil demons announcing disasters, in the Argentine pampas that they are sisters of the devil; in Sicily, death or illness for all these reasons they have been killed and tortured.

However, they can also be a good sign (such as guardians of women who die in Australia), but the best known case is the representation of Athena, Greek goddess of wisdom. Currently still appears as a symbol of many institutions and in Greek euro coins.

Euro grecia, euro griego
Greek euro. (Resource: RTVE)


Nowadays the barn owl is in a state of decline and with an uncertain future due to changes introduced by humans in rural areas, such as changes in cultivation or use of pesticides and rodenticides, which kill their prey (mice) or indirectly birds themselves. The works and renovations of buildings where they used to nest also interfere with reproduction. They also suffer accidents due to the towers and power lines and are often hit by cars. Canary subspecies (Tyto alba gracilirostris) is disappearing due its habitat fragmentation and the low number of individuals in their populations.

Lechuza muerta
Barn owl in a barbed wire. (Photo by PacoT).

It is listed as Endangered in the Red Book of Birds of Spain and included in the National Catalogue of Endangered Species in the category “Special interest“.


Try to find out about these magnificent birds and make them known to your immediate surrounding, banishing misconceptions, especially if you live near their nesting and feeding areas. If you own crops, try to minimize the use of pesticides: a pair of barn owls hunt in average about 2,000 mice a year, being therefore even beneficial to humans.

If you find an owl or wounded bird, you have to pick it carefully (using a towel or a jacket) to avoid hurt it or being hurt, and leave it in a dark, quiet place inside a box pierced so it can breathe. Do not feed it. Then contact a wildlife recovery centre.


If you enjoyed this article, please share it on social networks to spread it. The aim of the blog, after all, is to spread science and reach as many people as possible. Feel free to share your experience with birds of prey in the comments below. ¿Do you know someone who still believe in this owl legends?

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