Data Organization



Before 2000 the IUCN Red List was produced in book format. However, since 2000 the Red List has only been available electronically. The reasons for this departure are simple:

  • The decision to incorporate plants and animals into a single Red List, rather than treating them separately, meant that the total species coverage more than doubled in 2000, and continues to increase with each update of the Red List.
  • The 2000 Red List marked the start of a process to document all species listed. This documentation greatly increases the size but also the utility of the Red List.
  • The IUCN Red List now makes better use of the electronic medium as it provides a wider audience with easy access to the information.
  • The Red List is updated at least every two years and increasingly is updated annually, and so the production of a book for each update would be too prohibitive both in terms of time and cost.

The IUCN Red List of Threatened Species is available only as an electronic version on the World Wide Web. A CD-ROM version of the Red List was produced in 2000 and funds permitting, a new version will be produced in the future. The information presented is based on data extracted from the Species Information Service (SIS) database maintained by the Red List Unit of the IUCN Species Programme. The information provided here covers all taxa that have been assigned an IUCN Red List Category with the exception of those designated as Not Evaluated (NE). All the assessments presented, except those for geographically isolated subpopulations or stocks, are for the taxon (species, subspecies or variety) as a whole (i.e. they indicate the global risk of extinction). No national or regional Red List assessments are included, except for national extinctions (where known) and an occasional note about national or sub-national status in one of the documentation fields.

Documentation of Species

A set of minimum documentation requirements have been adopted to support all listings on the Red List. Anyone making submissions for inclusion on the Red List is requested to provide (in addition to the usual details about the taxon's name, status, criteria and distribution) a justification to support the listing; a map of the extent of occurrence; a list of the major habitats the species is found in; what the major threats are; an indication as to whether the species' population trend is increasing, decreasing, stable or unknown; what conservation actions are in place or are needed; and information on the utilization of the species. Non-mandatory information is also collected on life history attributes, the value of species for human livelihoods and the importance of species to ecosystem processes. If the taxon assessed falls within the jurisdiction of an appointed Red List Authority then it will be referred to them for evaluation (for further details about Red List Authorities and how to submit assessments see the Red List Overview ).

The degree of documentation achieved is extremely variable across the list, but an increasing number of species are meeting the minimum requirements. In a growing number of cases the amount of documentation is substantial, hence to allow users easier navigation through the documentation, the information described above has been grouped under five major headings:

  • Summary (all of the fields below excluding the list of habitats, major threats, conservation actions, external links, and bibliography),
  • Classification Schemes (includes only the lists of habitats, major threats and conservation actions),
  • Images & External Links (retrieves images from the Arkive web site if available, links to image search engines and links to other sites which may contain additional information),
  • Bibliography,
  • Full Account (provides the full documentation for the taxon described below except for the items on the Images & External Links tab) presented as tabs across the top of each Fact Sheet (previously called the Detailed Results page).

For anyone wishing to submit a Red List assessment for inclusion on the Red List please see the details given under The Red List Assessment Process.

The documentation on the Fact Sheet (formerly called the Detailed Results page) for each taxon may include some or all of the following information under the headings indicated:


  • Higher taxonomy details are shown for Kingdom, Phylum, Class, Order and Family.
  • Scientific name (genus and species) including authority details wherever possible. Infra-specific details may also be provided if relevant. (Note: for animals the date of description is usually shown, but for plants this is not the case).
  • Taxonomic notes are included when there are particular problems or issues. These notes may also indicate taxonomic changes that will be made in future updates. A number of taxonomic notes also include generic and species synonyms.
  • Synonyms include names that appeared in past Red Lists that are no longer accepted as being correct, names that were incorrectly spelt in previous Red Lists (orthographic errors), or alternative names that are still in common use. The synonymy provided is not complete because the Red List is not intended to be used as a comprehensive taxonomic reference.
  • Common names only in English, French and Spanish are provided if available (on the Search Results pages the languages are indicated by means of the abbreviations Eng., Fre. and Spa. respectively. Preferred common names are not indicated at present.
  • Under the species assessments, links are provided to any infra-specific assessments that may exist (i.e., subspecies, variety or subpopulation assessments)
  • The Taxonomy section under the subspecies and varieties provides extra details on the scientific names for the taxa and their authority details.

Assessment Information

  • Red List Category and Criteria (only the criteria which are met for the highest category to which the species can be assigned are specified). The version of the Red List Category and Criteria used to make the assessment is indicated. Assessments made up until and including 2000 used the 1994 Red List Categories and Criteria (version 2.3) whereas all assessments made since 2001 use the 2001 Red List Categories and Criteria (version 3.1)
  • Date of assessment (used to show the year when the assessment was done). Any assessments older than ten years will have a '(needs updating)' annotation alongside the Red List assessment on both the Search Results pages and the Fact Sheets. The annotation is only present when there are assessments that need updating.
  • An indication if a petition about the status of the species has been lodged and is pending a decision from the Standards and Petitions Working Group (see PDF Document Procedure for Handling of Petitions against Current Listings on the IUCN Red List of Threatened Species™ ). This is indicated on the web site by '(petitioned)' as an annotation alongside the Red List assessment on the Search Results pages and the Fact Sheets. The annotation is only present when there is a petition.
  • The Assessor/s field indicates the names of the people or organizations responsible for making the assessment and compiling the supporting information.
  • The Reviewers field indicates the names of the people who have peer reviewed and accepted the assessment and the supporting documentation. The Reviewers check that the data used have been interpreted correctly and consistently, and that any uncertainty has been handled appropriately. The review process also checks that the Red List Categories and Criteria have been correctly applied and that the supporting data provided is consistent with the final assessment. There is always a minimum of two reviewers (these may overlap with the assessors in older assessments, but the requirement as from 2009 is that these should be independent people). In the older assessments the name of the Red List Authority or organization the reviewers worked for may also indicated.
  • The Contributor/s field provides the names of any other individuals that have provided data, information, comments or helped in some way with the assessment, but who are not responsible for the Red List assessment itself and/or were not involved in the overall compilation of the account.
  • A rationale for the listing (including inferences or uncertainty that relate to the interpretation of the data and information in relation to the Red List Criteria and their thresholds). The rationale should also summarise any numerical data and parameter estimates that underpin the assessment. This may include a link to a PDF file containing extra information.
  • Red List History (a history of global listings for the taxon concerned on the IUCN Red Lists and BirdLife lists – this is a work in progress).

Geographic Range

  • Detailed description of the distribution of the taxon; this might include a link to a PDF file with further supporting documentation.
  • A GIS map of species' distribution, preferably shown as polygons (but point occurrences may also be displayed). These maps are currently only available for recently assessed or reassessed taxa, but each year the number of maps on the Red List is increasing with the ultimate aim of having maps available for all taxa on the Red List.
  • Countries of occurrence and sub-country units for large countries and islands far from mainland countries (see below).
  • Occurrence in marine regions (see below).



  • Detailed description of the population (size and trends), this might include a link to a PDF file with further supporting documentation.
  • Current population trends (where Up = improving, Down = deteriorating, Stable = stable and Unknown = uncertain or don't know, while a blank indicates that this has not been looked at yet).

Habitat & Ecology

  • Detailed description of the habitat and ecology, this might include a link to a PDF file with further supporting documentation. Some utilization information may be included here if use is not a threat, but more detailed use information is being collected and will be included under a separate heading in a future update of the Red List.
  • The major systems the species occurs in (i.e., marine, freshwater, terrestrial).
  • List of habitat preferences .


  • Detailed description of the major threats to the taxon, this might include a link to a PDF file with further supporting documentation.
  • List of threats (past, present, future, ongoing, or timing unknown).

Conservation Actions

  • Detailed description of what conservation measures (or actions) are in place or are required to improve the status of the taxon. This might include a link to a PDF file with further supporting documentation.
  • List of conservation actions in place and needed.


Links to Images and Other Sources of Information

  • Links to other web sites that may contain further information and images of the taxon concerned.


  • The list of references (published and unpublished) used for the assessment and the supporting documentation.

Extinct, Extinct in the Wild and Possibly Extinct Species

For Extinct species (and infra-specific taxa), extra documentation is required indicating the effective date of extinction, the causes of the extinction and the details of surveys which have been conducted to search for the species. The starting date for the inclusion of extinctions is 1500 AD. An attempt has been made to collate whatever information is available on each Extinct and Extinct in the Wild species and this is presented in the various documentation fields. In general, a precautionary approach is adopted in listing taxa as Extinct or Extinct in the Wild.

Although a precautionary approach to classifying extinctions is appropriate, this approach biases analyses of recent extinctions when based only on those species classified as Extinct or Extinct in the Wild. For example, the number of recent extinctions documented on the IUCN Red List is likely to be a significant underestimate, even for well-known taxa such as birds. A tag of 'Possibly Extinct' has therefore been developed to identify those Critically Endangered species that are in all probability already Extinct, but for which confirmation is required. Note that this is a tag, and not a new Red List Category.

'Possibly Extinct' species are those that are, on the balance of evidence, likely to be extinct, but for which there is a small chance that they may be extant. Hence they should not be listed as Extinct until adequate surveys have failed to find the species and local or unconfirmed reports have been investigated and discounted. 'Possibly Extinct in the Wild' correspondingly applies to such species known to survive in captivity.

At present the search function on the Red List does not provide an option to find the Critically Endangered (Possibly Extinct) taxa. This functionality will be made available in a future update. For the present the Possibly Extinct tag is included within the text under the Red List justification field.

Subspecies, Varieties and Subpopulations

Although the name IUCN Red List of Threatened Species implies that the primary focus is at the species level, the IUCN Red List also includes assessments that are done at the infra-specific or subpopulation levels. Ideally, for such taxa to be included in the Red List, the global status of the species itself should be assessed. In most instances this is the case and generally these are assessed as Least Concern (LR/lc or LC). There are some cases, however, especially amongst the plants where this has not been done and it may well be that some of these species warrant a threatened status. For subpopulations (also called stocks), only geographically isolated subpopulations, between which there is little genetic exchange (typically one migrant individual or gamete per year), are included on the IUCN Red List.

The default search option provides results at the species level only. Searches for subspecies, varieties and subpopulations have to be specified separately. If assessments for subspecies, varieties or subpopulations are available, these are clearly indicated from the Fact Sheets of the species concerned.

Taxa Removed from the Red List (Synonyms)

The Red List is highly dynamic with species moving on and off for a variety of reasons. The main reasons for removals from the list are changes in taxonomy. All changes are tracked, so that a complete audit trail is kept for each taxon name that ever appears on the Red List. Taxa removed from the Red List for taxonomic reasons (i.e., they are considered synonyms of other taxa) are searchable (searches will indicate the synonyms found under their accepted/correct names); and the synonym/s are listed on the Fact Sheet for the accepted taxon. The list of synonyms also includes misspellings (orthographic errors). It is not intended that the IUCN Red List will maintain an exhaustive synonymy for all taxa on the list, however, commonly used synonyms are often included. Any synonyms listed under the taxonomic notes are generally not searchable.

Distribution Information:

From 2007, country, sub-country and marine area distributions are recorded in separate lists, according to the nature of the distribution record (Native, Native (reintroduced), Native (uncertain presence), Vagrant, etc.). For example:


Native: Angola; Botswana; Namibia; South Africa (Eastern Cape (introduced), Northern Cape, Western Cape)

Native (reintroduced): Botswana

Native (extinct): Congo

Introduced: Cameroon

Countries and Sub-countries

Distribution is recorded in terms of country names following the 5th edition (and subsequent web updates) of the ISO-3166-1 standard (ISO 1997). Unless geographically very remote from each other, islands and other territories are included with the parent country. In the case of species that inhabit islands significantly distant from the mainland, the island name is given in parentheses (e.g., Spain (Canary Islands)). The naming of such islands follows the second edition of the World Geographical Scheme for Recording Plant Distributions (Brummitt et al. 2001) prepared for the Biodiversity Information Standards (TDWG), also known as the Taxonomic Databases Working Group. The TDWG geographic system also provides a standard set of Basic Recording Units (BRU) that are sub-country units based on provinces or states. The BRU's are used to subdivide very large countries like Australia, Brazil, China, South Africa, the Russian Federation and the United States of America, etc. into smaller more conveniently sized units for recording distributions. This system has been adopted for the IUCN Red List wherever possible. Most plant taxa on the Red List have had their distributions recorded down to BRU level where appropriate, but unfortunately sub-country information is still lacking for most of the animal species. Hence this feature is not currently searchable. Each country or territory has also been assigned to a single geographic region to enable users to search by larger geographic areas. View the list of Countries by Regions.

Geopolitical events during recent years may have led to some inconsistency or errors in the distribution information provided. For example, within reasonable limits every effort has been made to determine which of the new nations that were part of the former Czechoslovakia, Yugoslavia and USSR support species previously attributed to the larger unit. There may be some species in the Red List that have still not been fully resolved. Adherence to the ISO system also creates some problems, as there is often a time lag between a political change and a new ISO code being allocated for the new country. The version of the ISO codes used for example, maintains Hong Kong and Macao as separate units.

Native Distributions, Reintroductions and Extinctions

The default search function and the summary statistics tables exclude questionable distribution records, records of vagrants, and introduced ranges. The results of default searches on the Red List web site should therefore reflect only the certain native ranges, extinctions, and areas where reintroductions have taken place, and should match the figures presented in the summary tables.

For a number of very widespread Least Concern taxa, the list of country occurrences may be incomplete or in some instances not even recorded (e.g., Mus musculus) because such taxa are virtually cosmopolitan, so care should be taken when using the distribution information for subsequent analyses. Please note that the results presented in the published analyses of the Red List data (Baillie et al. 2004, Hilton-Taylor 2000), do not include questionable distribution records, introduced distributions, and vagrant distributions.

Doubtful Distributions, Introductions and Vagrants

The distributions of some species in certain countries have not been confirmed. These instances are usually distinct from vagrant distributions, but combinations of doubtful country occurrences and vagrants plus doubtful countries and dubious vagrants are also possible. Note that the default search on taxa in a specific country or group of countries excludes doubtful occurrences, introduced species and vagrants from the results (and also from the summary statistics tables). However, search options have been added to allow users to include uncertain distributions and/or introduced species and/or vagrant species in their search results if this information is needed.

Marine Distributions

For marine species, country records have been provided wherever possible. This information has been derived from a number of sources, e.g. FishBase and the many FAO publications For some marine species, especially those that are strictly marine, their distributions are also shown as generalized ranges in terms of the FAO Fishing Areas , indicated as follows (e.g., Native: Atlantic-eastern central). In past Red Lists, inland water ranges were also given for many inland water species. However, as from 2007 these inland water ranges are no longer listed, but instead are mentioned under the detailed description of the range.


The Red List contains assessments for some stocks or geographically isolated subpopulations. The geographic name of the subpopulation is indicated directly after the name of the species e.g., Balaena mysticetus (Spitsbergen stock).