An Introduction to Red-Listing
The IUCN Red List of Threatened Species
The IUCN Red List is the world's most comprehensive inventory of the global
conservation status of plant and animal species. It uses a set of criteria to evaluate the
extinction risk of species, subspecies and varieties (but not micro-organisms). These
criteria are relevant to all species and all regions of the world. With its strong
scientific base, the IUCN Red List is recognised as the most authoritative guide to the
status of global biological diversity.
The overall aim of the Red List is to convey the urgency and scale of conservation
problems to the public and policy makers, and to motivate the global community to
try to reduce species extinctions. Information about species and ecosystems is
essential for moving towards more sustainable use of our natural resources.
How is the Red List compiled?
There are nine categories in the IUCN Red List system: Extinct, Extinct in the Wild,
Critically Endangered, Endangered, Vulnerable, Near Threatened, Least Concern,
Data Deficient, and Not Evaluated. Classification into the categories for species
threatened with extinction (Vulnerable, Endangered, and Critically Endangered) is
through a set of five quantitative criteria that form the heart of the system. These
criteria are based on biological factors related to extinction risk and include: rate of
decline, population size, area of geographic distribution, and degree of population and
distribution fragmentation.
The Categories and their application
EXTINCT (EX)
A taxon is Extinct when there is no reasonable doubt that the last individual has died.
A taxon is presumed Extinct when exhaustive surveys in known and/or expected
habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range
have failed to record an individual. Surveys should be over a time frame appropriate
to the taxon's life cycle and life form.
EXTINCT IN THE WILD (EW)
A taxon is Extinct in the Wild when it is known only to survive in cultivation, in
captivity or as a naturalized population (or populations) well outside the past range. A
taxon is presumed Extinct in the Wild when exhaustive surveys in known and/or
expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its
historic range have failed to record an individual. Surveys should be over a time
frame appropriate to the taxon's life cycle and life form.
CRITICALLY ENDANGERED (CR)
A taxon is Critically Endangered when the best available evidence indicates that it
meets any of the criteria A to E for Critically Endangered (see Red List Categories
and Criteria booklet for details) and it is therefore considered to be facing an
extremely high risk of extinction in the wild.
ENDANGERED (EN)
A taxon is Endangered when the best available evidence indicates that it meets any of
the criteria A to E for Endangered (see Red List Categories and Criteria booklet for
details), and it is therefore considered to be facing a very high risk of extinction in the
wild.
VULNERABLE (VU)
A taxon is Vulnerable when the best available evidence indicates that it meets any of
the criteria A to E for Vulnerable (see Red List Categories and Criteria booklet for
details), and it is therefore considered to be facing a high risk of extinction in the wild.
NEAR THREATENED (NT)
A taxon is Near Threatened when it has been evaluated against the criteria but does
not qualify for Critically Endangered, Endangered or Vulnerable now, but is close to
qualifying for, or is likely to qualify for, a threatened category in the near future.
LEAST CONCERN (LC)
A taxon is Least Concern when it has been evaluated against the criteria and does not
qualify for Critically Endangered, Endangered, Vulnerable or Near Threatened.
Widespread and abundant taxa are included in this category.
DATA DEFICIENT (DD)
A taxon is Data Deficient when there is inadequate information to make a direct, or
indirect, assessment of its risk of extinction based on its distribution and/or population
status. A taxon in this category may be well studied, and its biology well known, but
appropriate data on abundance and/or distribution are lacking. Data Deficient is
therefore not a category of threat. Listing of taxa in this category indicates that more
information is required and acknowledges the possibility that future research will
show that threatened classification is appropriate. It is important to make positive use
of whatever data are available. In many cases great care should be exercised in
choosing between DD and a threatened status. If the range of a taxon is suspected to
be relatively circumscribed, and a considerable period of time has elapsed since the
last record of the taxon, threatened status may well be justified.
NOT EVALUATED (NE)
A taxon is Not Evaluated when it is has not yet been evaluated against the criteria.
The Red List Process
The process of Red-Listing involves compiling data on a species (either globally or
within a defined region) and then assessing that species against a set of criteria to
predict the risk of that species going extinct. This process is described in detail in the
Red List Categories and Criteria booklet version 3.1, and a one-page summary of the
criteria used for the threatened categories is also available (included as an appendix to
this document).
Regional Assessments
In this project, we will be assessing the risk of extinction of species at the regional
level. At this level, certain changes are needed to the methods used for global
assessments, but the process is otherwise the same. Two additional categories are
included for regional assessments:
NOT APPLICABLE (NA)
Taxa that have not been assessed because they are unsuitable for inclusion in the
regional Red List (e.g. a taxon that occasionally breeds in the region under favourable
circumstances in the region but regularly becomes regionally extinct; see Guidelines
for Application of IUCN Red List Criteria at Regional Levels for other examples of
when this category might be used).
REGIONALLY EXTINCT (RE)
Taxa that are considered extinct within the region but populations still exist elsewhere
in the world.
The following diagram shows a conceptual scheme of the procedure for assigning an
IUCN Red List Category at the regional level. In step 1 all data used should be from
the regional population, not the global population. The exception is when evaluating a
projected reduction or continued decline of a non-breeding population, in such cases
conditions outside the region must be taken into account in step 1. Likewise, breeding
populations may be affected by events in, e.g., wintering areas, which must be
considered in step 1. See Table 1 in the “Guidelines for Application of IUCN Red List
Criteria at Regional Levels” for further details on the procedures to follow, especially
for the second step.
Upgrading and Downgrading Categories at the Regional Level
If the regional population is a demographic sink and the extra-regional source
population is expected to decline, the preliminary category from step one may be
upgraded: e.g. EN upgraded to CR; VU upgraded to EN; NT upgraded to VU. EX,
EW, RE, CR, DD, NA and NE categories cannot be upgraded.
If the regional population experiences a “rescue effect” through immigration from
outside the region, the preliminary category from step one may be downgraded: e.g.
CR downgraded to EN; EN downgraded to VU; VU downgraded to NT. EX, EW, RE,
DD, NA, NE and LC categories cannot be downgraded.
Applying the Red List Categories to Wetland Species
The Red List methodologies were designed for all species, but in practice certain
adaptations are necessary when assessing wetland species and creating distribution
maps of these species. For example, the area occupied by river species is, strictly
speaking, only the width of the rivers they are found in multiplied by the length of
those rivers; the area thus calculated is usually much smaller than that of most
terrestrial species, and could result in all river species being categorised as
Threatened. In order to take account of such issues, a “Red Listing Freshwater Issues
Protocol” document has been prepared.
Further Literature on the Red List Process
For more detail on how to apply the Red List process, see the Red List Categories and
Criteria booklet version 3.1 and Guidelines for Application of IUCN Red List Criteria
at Regional Levels.
The Red List, IUCN Species Survival Commission, and Species Information Service
The Red List is produced by the IUCN Species Survival Commission (SSC) - a
network of some 8,000 species experts working in almost every country in the world,
and data from a number of partner organizations. Collectively, this network holds
what is probably the most complete scientific knowledge base on the biology and
current conservation status of species.
All data underlying the Red List will eventually be maintained in a series of databases
that make up the SSC's emerging Species Information Service. This is a major
initiative that aims to make the vast amount of information held by the SSC network
easily and quickly accessible to users around the world.