1. The IUCN Red List Categories and Criteria are intended to be an easily and
widely understood system for classifying species at high risk of global extinction.
The general aim of the system is to provide an explicit, objective framework for
the classification of the broadest range of species according to their extinction
risk. However, while the Red List may focus attention on those taxa at the highest
risk, it is not the sole means of setting priorities for conservation measures for
their protection.
Extensive consultation and testing in the development of the system strongly
suggest that it is robust across most organisms. However, it should be noted that
although the system places species into the threatened categories with a high
degree of consistency, the criteria do not take into account the life histories of
every species. Hence, in certain individual cases, the risk of extinction may be
under- or over-estimated.
2. Before 1994 the more subjective threatened species categories used in IUCN
Red Data Books and Red Lists had been in place, with some modification, for
almost 30 years. Although the need to revise the categories had long been
recognized (Fitter and Fitter 1987), the current phase of development only began
in 1989 following a request from the IUCN Species Survival Commission (SSC)
Steering Committee to develop a more objective approach. The IUCN Council
adopted the new Red List system in 1994.
The IUCN Red List Categories and Criteria have several specific aims:
• to provide a system that can be applied consistently by different people;
• to improve objectivity by providing users with clear guidance on how to
evaluate different factors which affect the risk of extinction;
• to provide a system which will facilitate comparisons across widely different
taxa;
• to give people using threatened species lists a better understanding of how
individual species were classified.
3. Since their adoption by IUCN Council in 1994, the IUCN Red List Categories
have become widely recognized internationally, and they are now used in a range
of publications and listings produced by IUCN, as well as by numerous
governmental and non-governmental organizations. Such broad and extensive
use revealed the need for a number of improvements, and SSC was mandated by
the 1996 World Conservation Congress (WCC Res. 1.4) to conduct a review of
the system (IUCN 1996). This document presents the revisions accepted by the
IUCN Council.
The proposals presented in this document result from a continuing process of
drafting, consultation and validation. The production of a large number of draft
proposals has led to some confusion, especially as each draft has been used for
classifying some set of species for conservation purposes. To clarify matters, and
to open the way for modifications as and when they become necessary, a system
for version numbering has been adopted as follows:
Version 1.0: Mace and Lande (1991)
The first paper discussing a new basis for the categories, and presenting
numerical criteria especially relevant for large vertebrates.
Version 2.0: Mace et al . (1992)
A major revision of Version 1.0, including numerical criteria appropriate to
all organisms and introducing the non-threatened categories.
Version 2.1: IUCN (1993)
Following an extensive consultation process within SSC, a number of changes
were made to the details of the criteria, and fuller explanation of basic
principles was included. A more explicit structure clarified the significance of
the non-threatened categories.
Version 2.2: Mace and Stuart (1994)
Following further comments received and additional validation exercises,
some minor changes to the criteria were made. In addition, the Susceptible
category present in Versions 2.0 and 2.1 was subsumed into the Vulnerable
category. A precautionary application of the system was emphasised.
Version 2.3: IUCN (1994)
IUCN Council adopted this version, which incorporated changes as a result
of comments from IUCN members, in December 1994. The initial version of
this document was published without the necessary bibliographic details,
such as date of publication and ISBN number, but these were included in the
subsequent reprints in 1998 and 1999. This version was used for the 1996
IUCN Red List of Threatened Animals (Baillie and Groombridge 1996), The
World List of Threatened Trees (Oldfield et al. 1998) and the 2000 IUCN Red
List of Threatened Species (Hilton-Taylor 2000) .
Version 3.0: IUCN/SSC Criteria Review Working Group (1999)
Following comments received, a series of workshops were convened to look
at the IUCN Red List Criteria following which, changes were proposed
affecting the criteria, the definitions of some key terms and the handling of
uncertainty.
Version 3.1: IUCN (2001)
The IUCN Council adopted this latest version, which incorporated changes
as a result of comments from the IUCN and SSC memberships and from a
final meeting of the Criteria Review Working Group, in February 2000.
All new assessments from January 2001 should use the latest adopted version and
cite the year of publication and version number.
4. In the rest of this document, the proposed system is outlined in several
sections. Section II, the Preamble, presents basic information about the context
and structure of the system, and the procedures that are to be followed in
applying the criteria to species. Section III provides definitions of key terms used.
Section IV presents the categories, while Section V details the quantitative
criteria used for classification within the threatened categories. Annex I provides
guidance on how to deal with uncertainty when applying the criteria; Annex II
suggests a standard format for citing the Red List Categories and Criteria; and
Annex III outlines the documentation requirements for taxa to be included on
IUCN’s global Red Lists. It is important for the effective functioning of the
system that all sections are read and understood to ensure that the definitions and
rules are followed. ( Note: Annexes I, II and III will be updated on a regular basis.)