Information Sources and Quality


Data Quality and Peer Review

The information about each taxon listed on the IUCN Red List often represents an accumulation of knowledge derived from previously published Red Lists, including the 1996 IUCN Red List of Threatened Animals and The World List of Threatened Trees which were the last Red Lists to be published as hardcopy books. Users are therefore referred to these previous publications when checking on information sources and data quality. A number of the assessments done for the 1996 Animals Red List are still in the present Red List unchanged (i.e., those assessments have simply been rolled over with each subsequent update of the IUCN Red List) and the original people who provided either the information or the assessments are still recognized. Assessments done ten or more years ago are annotated as 'needs updating', and users are requested to use these with caution (the assessments may no longer be an accurate reflection of the species' extinction risk and/or the supporting documentation presented may no longer be correct).

The assessments, including all the supporting documentation for every taxon on the Red List is credited to one or more assessors or to the members of a specific SSC Specialist Group or to specific organizations. In some cases assessments are the product of group discussion, but often they represent the judgement of individual Specialist Group members or individual experts. In order to ensure greater accuracy, consistency and transparency in the listing process, a peer review system of Red List Evaluators has been initiated (see Red List Overview for further details). The intention of the system is that the assessments of all taxa on the Red List should be scrutinized and evaluated by at least two people from a designated Red List Authority. The Red List Authorities will be responsible for ensuring that all taxa they are responsible for are documented and re-assessed at regular intervals.


BirdLife International is the Red List Authority for birds and as such they have provided all the bird assessments that appear on the IUCN Red List. These assessments and their accompanying documentation reflect the information that appears on the World Bird Database developed and maintained by BirdLife International. Users are referred to the species accounts on the World Bird Database to see additional supporting data for all the bird listings and to see the details of the references used (these references are cited on the Fact Sheet for each bird species on the Red List mostly as a superscripted number in the text or occasionally the authors and dates of the publications are cited). In addition, the individual species accounts on the World Bird Database provide additional information on the data contributors and evaluation process for each species. The link to BirdLife International on the External Links tab on the Fact Sheet for each bird species on the Red List should take users directly to the relevant species on the World Bird Database web site.

BirdLife's Global Species Programme continually collates up-to-date information on Globally Threatened Birds from the published literature and from a worldwide network of experts. This is used to evaluate the status of each species using the IUCN Red List Categories and Criteria.

New information on the population or range size and trends of a species, or the threats impacting it, may indicate that a species warrants uplisting or downlisting to higher or lower categories of threat. In such cases, BirdLife's web-based Globally Threatened Bird Forums are used to advertise the proposed change and to solicit relevant information or comment from a wide network of experts and organisations.

In these discussion forums, topics describe the current status of particular species, new information that has become available, the proposed new Red List category that this information suggest is appropriate, and a request for comments or further input. See the Globally Threatened Bird Forums site for further information.


Global Amphibian Assessment team have evaluated the status of all of the world's amphibian species, and they provided the assessments and all the supporting documentation used on the IUCN Red List. A process is being developed to keep these assessments up-to-date.


All mammal species (as listed in Wilson and Reeder 1993) were supposedly assessed for the 1996 Red List. Since 1996 a large number of new mammalian species have been described and in addition there have been substantial taxonomic changes as a result of the increasing use of molecular techniques. As a result of these new descriptions and taxonomic changes all mammal species have not yet been assessed. The quality of the mammal assessments is highly variable, with many of the older assessments being based on relatively poor or sparse information, particularly in the case of the rodents, shrews and insectivorous bats, although the status of many of the latter group of species was re-evaluated during the preparation of the microbat action plan (Hutson et al. 2001). The Global Mammal Assessment (GMA) team together with the IUCN SSC Mammal Specialist Groups, have re-evaluated the status of all the world's mammal species, which includes the collation of all the supporting documentation for each listing.

Freshwater Taxa (fishes, crabs, molluscs and odonata)

The IUCN Freshwater Unit is involved in a number of projects to assess selected freshwater species (primarily fishes, crabs, molluscs and odonata) in specific geographic areas, e.g. Africa, Madagascar and the Mediterranean; for further details see: About the Freshwater Biodiversity Unit on the IUCN site. Assessments conducted through these projects are fully documented and peer reviewed before they are included on the Red List.

Marine Taxa

Nearly 40,200 species were assessed under the IUCN Red List Criteria by the year 2006, of which only around 1,380 are marine species. The bulk of marine species assessed include seabirds, marine mammals, sharks and rays. There is a growing realization that a much broader range of marine species are under threat of extinction and marine biodiversity is experiencing potentially irreversible degradation. Furthermore, the information needed to guide marine conservation plans and policy is seriously deficient.

To address the need for intensive and coordinated marine conservation planning and action, IUCN and Conservation International are collaborating to complete Red List assessments of approximately 20,000 marine species by the year 2010 under the Global Marine Species Assessment(GMSA). A strategy meeting in support of the GMSA was held in November 2005. The outcomes concluded that priority taxa to complete should include all marine vertebrates (primarily fishes); habitat forming primary producers such as selected macro-algae, sea grasses, mangroves and corals; and selected molluscs and echinoderms.

To complete Red List assessments of this large number of species, the GMSA will follow the successful methodology pioneered by IUCN's Biodiversity Assessment Unit, which is responsible for the Global Amphibian and Global Mammal Assessments described above. All assessments produced for the GMSA will be incorporated on the IUCN Red List once they have undergone the necessary peer review.

Taxonomic Standards Followed

Taxa Included on the IUCN Red List

The IUCN Red List includes global assessments for:

  • Species.
  • Subspecies.
  • Varieties (only for plants).
  • Geographically separate subpopulations.

Geographically separate subpopulations of a species are defined as those populations that are so isolated from others of the same species that it is considered extremely unlikely that there is any genetic interchange. In general, listings of such subpopulations should be restricted to those that have been isolated for a long period of time.

Assessments of subspecies, varieties and geographically separate subpopulations must adhere to the same standards as for species assessments. However, these assessments will only be accepted provided there is a global assessment of the species as a whole.

Newly Described Species

The inclusion of newly described species will be addressed on a case-by-case basis. The Red List Authority and/or Species Programme staff should consult with relevant experts to ascertain how widely accepted these are. An exception will be made for highly distinct species that are clearly new.

Undescribed Species

The listing of undescribed taxa is discouraged, but in exceptional circumstances these may be included under the following conditions:

  • There is general agreement that the undescribed taxon is in fact a good species.
  • Clear distribution information can be provided.
  • Listing the undescribed species will potentially aid in its conservation.
  • Specimen reference numbers (voucher collection details) are provided which will enable the species to be traced without confusion.
  • The museum, herbarium or other institution holding the collection and the individual responsible for the proposal can be identified.
  • Whenever possible a common name can be added.

Undescribed species are represented in the Red List by the generic name and the abbreviation sp. or sp. nov. sometimes followed by a 'provisional name'. Details of specimen numbers and institution should ideally be included in parentheses after the sp. nov. There are some instances where this has been done, but in many cases there have been requests for this information to be withheld because of fears that someone else will describe the species concerned.

Taxa Not Included on the IUCN Red List

  • Taxa assessed locally, nationally or regionally are not considered for inclusion on the IUCN Red List unless they are global assessments.
  • Hybrids (except for apomictic plant hybrids which are treated as 'species').
  • Infraspecific ranks such as formas, subvarieties, cultivars, etc.
  • Taxa known to have gone Extinct before 1500 AD.
  • Undescribed taxa assessed as Data Deficient or Least Concern.
  • Assessments of higher taxa (i.e., above the species level).
  • Taxa that do not adhere to the general taxonomic standards outlined below.

General Taxonomic Standards

  1. All taxa assessed (with the exception of the undescribed taxa described above) must be validly published in accordance with the appropriate international nomenclatural codes and should be currently accepted names. Standard taxonomic checklists should be used wherever possible for names. The standard lists adopted by IUCN are listed below under the respective taxonomic groups. These lists are periodically reviewed. For many groups no standards are available, or there may be a valid reason for adopting another treatment. In such cases, the taxonomic treatment followed is usually indicated and if not one of the standards followed by IUCN, the reference is cited in full and a reason for the deviation may be provided.
  2. The following higher level taxonomic information is provided for each taxon assessed: Kingdom, Phylum, Class, Order and Family.
  3. The authorities for all specific and infra-specific names used in the Red List are provided wherever possible following the appropriate nomenclatural rules. This includes the date of publication, except in the case of plant names. For a number of earlier assessments, particularly for invertebrates, the authority details are currently missing. The abbreviations used for author names of plants generally follow Brummitt and Powell (1992) and subsequent updates on the International Plant Names Index web site (
  4. Any taxonomic problems or issues are generally documented under the 'Taxonomic Notes' for each species and appropriate synonyms are listed.


Where possible, standard world checklists have been used in order to promote nomenclatural stability. In a few instances Specialist Groups have used alternative systematic opinion and provided justification for doing so. All names of taxa on the Red List are checked and verified as far as is possible. In doing this, the correct authority name is included in an attempt to clarify what species concept is being followed. The names of the phyla and classes used in general follow Margulis and Schwartz (1988), but there are a number of deviations based on new evidence and thinking, particularly with regards to the plant groups. The following paragraphs note the main taxonomic sources used.


The names of mammal orders, families and contents of families generally follows Wilson and Reeder (1993), but in many cases the taxonomy has been updated to be in line with the new accounts prepared for Wilson and Reeder (2005) (see also Species nomenclature generally also follows these sources, except when a Specialist Group has expressed a very strong preference for another system, or has used nomenclature that is different to what appears in Wilson and Reeder (1993 and/or 2005) and we have been unable to resolve subsequent ambiguities about the population content of the species concerned and their distribution. The Global Mammal Assessment process described above is using the species names published in Wilson and Reeder (2005) as their primary starting point. Principal departures from Wilson and Reeder are relatively few in number, and are currently found mainly in the primates, mustelids, viverrids and the bovids. A new treatment of primate taxonomy was published by Groves (2001) and further refined by Groves in the account that appears in Wilson and Reeder (2005). Parts of the revised primate taxonomy have been adopted by the SSC Primate Specialist Group and used in the Red List, but there are some significant differences.


The nomenclature used for birds follows that provided by BirdLife International. BirdLife International maintains its own taxonomic list of all the world's bird species because there are so many different global, regional, national, site and family taxonomic checklists, and thus many differences of opinion over the taxonomic rank of certain taxa. For details about the BirdLife system see:


Turtles and tortoises generally follow Iverson (1992) (see; crocodilians follow King and Burke (1989) (see; and tuatara systematics are after Daugherty et al. (1990). Names in common use, including those used by Specialist Groups or in national sources, have been employed for other groups of reptiles. Increasing use is being made of the TIGR Reptile Database compiled by Peter Uetz and made available on the World Wide Web at:


Nomenclature generally follows Frost (1985) as updated by Duellman (1993). The Amphibian Species of the World Database is now available on the World Wide Web and is updated regularly, so this has become the source for any recent changes: Another important web site for documentation on amphibian species, especially those in decline is the Amphibia Web Database. The Fact Sheets for all amphibian species on the Red List include deep links to the relevant species pages on both the sites described above.


The names of orders, families, and the species content of families currently follows Eschmeyer (1990), but a number have been updated to be in line with the new thinking presented in Eschmeyer (1998). Some of the fish names used are derived from national sources, from Specialist Groups or are the result of consensus achieved at regional workshops conducted under the auspices of the IUCN SSC Freshwater Biodiversity Assessment (see above). Extensive recent taxonomic changes mean that the status of many fish species on the Red List needs to be re-assessed. This was not possible for the current Red List, and the names and assessments are left as they appeared in the 1996 Red List. However, under the expanding Freshwater Biodiversity Assessment and a new Global Marine Assessment initiative, many of these fishes will be reviewed in the next few years. An updated version of Eschmeyer's publication is maintained as an on-line Catalog of Fishes at the California Academy of Sciences. This catalogue is generally followed by FishBase developed and maintained by the WorldFish Center. FishBase along with a number of other taxonomic datasets is also available through Species 2000.


Parker (1982) has generally been followed for nomenclature at class, order and family level. There is a lack of widely accepted class-level checklists for invertebrates, although there are a growing number of global checklists being made available via the Internet (e.g., Arachnida Catalog, The World Spider Catalog, Coleoptera, Global Lepidoptera Names Index, World List of Odonata and Orthoptera Species File Online). Attempts are being made to follow these standards, but for the remaining invertebrates for which global lists are not yet available no attempt has been made to standardize names for inclusion. The Integrated Taxonomic Information Service (ITIS) web site developed jointly by the US Departments of Agriculture and US Geological Survey is a useful source for a number of global and North American checklists covering a wide range of taxonomic groups including many invertebrates.


For plant families and genera, Brummitt (1992) is generally followed, but for the content of genera reference is made to a wide range of taxonomic treatments including papers on individual species, monographic treatments, standard floras, global checklists (e.g., Farjon 2001) and even site-specific checklists (e.g., Cable and Cheek 1998). The taxonomy of plant families and orders is undergoing major revision at present (see for example, the Angiosperm Phylogeny Site). Until such time that some level of stability is achieved, the orders of Cronquist (1981, 1988) are followed. There are a growing number of on-line resources that can be used for checking plant names. These include:

  • The International Plant Names Index (incorporates Index Kewensis, the Gray Index and the Australian Plant Names Index).
  • Provisional Global Plant Checklist compiled under the auspices of the International Organization for Plant Information (IOPI).
  • The World Checklist of Selected Plant Families hosted by the Royal Botanic Gardens Kew. This Checklist provides information on the accepted scientific names and synonyms of selected plant families (150 seed plant families in September 2007). It allows users to search for all the scientific names of a particular plant, or the areas of the world in which it grows.
  • TROPICOS - the Missouri Botanical Garden database. This is a key source for checking names of bryophytes and vascular plants found in particular parts of the world, especially species in China, Madagascar, Ecuador, Peru, Panama, etc. The Species Fact Sheets for all plant taxa on the IUCN Red List include a link to the TROPICOS database.

The author citations for all plant taxa follow Brummitt and Powell (1992) and as updated on the IPNI web site (see above).