Metadata Factsheet

3. Goals And Targets Addressed

3a. Goal

Headline Indicator for Goal A: The integrity, connectivity and resilience of all ecosystems are maintained, enhanced, or restored, substantially increasing the area of natural ecosystems by 2050; Human induced extinction of known threatened species is halted, and, by 2050, the extinction rate and risk of all species are reduced tenfold and the abundance of native wild species is increased to healthy and resilient levels; The genetic diversity within populations of wild and domesticated species, is maintained, safeguarding their adaptive potential.

3b. Target

Headline indicator for Target 4: Ensure urgent management actions to halt human induced extinction of known threatened species and for the recovery and conservation of species, in particular threatened species, to significantly reduce extinction risk, as well as to maintain and restore the genetic diversity within and between populations of native, wild and domesticated species to maintain their adaptive potential, including through in situ and ex situ conservation and sustainable management practices, and effectively manage human-wildlife interactions to minimize human-wildlife conflict for coexistence.

As noted in CBD/ID/OM/2022/1/2 “Report of the Expert Workshop on the Monitoring Framework for the Post-2020 Global Biodiversity Framework”, Annex III, specific disaggregations of the Red List Index are relevant to a number of other targets described in section 9.

5. Definitions Concepts And Classifications

5a. Definition

Indicator definition:

The indicator “Red List Index” measures change in aggregate extinction risk across groups of species. It is based on genuine changes in the number of species in each category of extinction risk on The IUCN Red List of Threatened Species (www.iucnredlist.org) and is expressed as changes in an index ranging from 0 to 1.

Other key concepts and definitions:

Threatened species are those listed on The IUCN Red List of Threatened Species in the categories Vulnerable, Endangered, or Critically Endangered (i.e., species that are facing a high, very high, or extremely high risk of extinction in the wild in the medium-term future). Changes over time in the proportion of species threatened with extinction are largely driven by improvements in knowledge and changing taxonomy. The indicator excludes such changes to yield a more informative indicator than the simple proportion of threatened species. It therefore measures change in aggregate extinction risk across groups of species over time, resulting from genuine improvements or deteriorations in the status of individual species. It can be calculated for any representative set of species that have been assessed for The IUCN Red List of Threatened Species at least twice (Butchart et al. 2004, 2005, 2007). To calculate the Red List Index for individual countries and regions, each species contributing to the index is weighted by the proportion of its global range within the particular country or region. The resulting index therefore shows the aggregate extinction risk for species within the country or region relative to its potential contribution to global species extinction risk (within the taxonomic groups included) (Butchart et al. 2024). Complementing such national disaggregations of the global index, national RLIs can be generated from repeated assessments of national extinction risk (e.g., national Red Lists). Guidance for assessing national extinction risk of species has been developed by IUCN (IUCN 2012b), and most countries have developed national red lists for at least one taxonomic group. National RLIs may be more sensitive than disaggregated global RLIs to factors influencing biodiversity loss within each country (including national policies), but require repeated assessments of national extinction risk for multiple groups in each country (with associated costs), and cannot be directly compared between countries (Raimondo et al 2022, Butchart et al. 2024).

Unit of measure:

The disaggregated global Red List Index for a particular country or region is an index of the aggregate extinction risk for species within the country or region relative to its potential contribution to global species extinction risk (within the taxonomic groups included), measured on a scale of 0 to 1, where 1 is the maximum contribution that the country or region can make to global species survival, equating to all species being classified as Least Concern on the IUCN Red List, and 0 is the minimum contribution that the country or region can make to global species survival, equating to all species in the country or region having gone extinct.

5b. Method Of Computation

The Red List Index is calculated at a point in time by first multiplying the number of species in each Red List Category by a weight (ranging from 1 for ‘Near Threatened’ to 5 for ‘Extinct’ and ‘Extinct in the Wild’) and summing these values. This is then divided by a maximum threat score which is the total number of species multiplied by the weight assigned to the ‘Extinct’ category. This final value is subtracted from 1 to give the Red List Index value.

Mathematically this calculation is expressed as:

RLIt = 1 – [(Ss Wc(t,s) / (WEX * N)]

Where Wc(t,s) is the weight for category (c) at time (t) for species (s) (the weight for ‘Critically Endangered’ = 4, ‘Endangered’ = 3, ‘Vulnerable’ = 2, ‘Near Threatened’ = 1, ‘Least Concern’ = 0. ‘Critically Endangered’ species tagged as ‘Possibly Extinct’ or ‘Possibly Extinct in the Wild’ are assigned a weight of 5); WEX = 5, the weight assigned to ‘Extinct’ or ‘Extinct in the Wild’ species; and N is the total number of assessed species, excluding those assessed as Data Deficient in the current time period, and those considered to be ‘Extinct’ in the year the set of species was first assessed.

The formula requires that:

• Exactly the same set of species is included in all time periods, and
• The only Red List Category changes are those resulting from genuine improvement or deterioration in status (i.e., excluding changes resulting from improved knowledge or taxonomic revisions), and
• Data Deficient species are excluded (or treated according to the procedure described above).

In many cases, species lists will change slightly from one assessment to the next (e.g., owing to taxonomic revisions). The conditions can therefore be met by retrospectively adjusting earlier Red List categorizations using current information and taxonomy. This is achieved by assuming that the current Red List Categories for the taxa have applied since the set of species was first assessed for the Red List, unless there is information to the contrary that genuine status changes have occurred. Such information is often contextual (e.g., relating to the known history of habitat loss within the range of the species).

To avoid spurious results from a biased selection of species, Red List Indices are typically calculated only for taxonomic groups in which all species worldwide have been assessed for the Red List, or for samples of species that have been systematically or randomly selected. National RLIs based on national extinction risk should similarly be compiled only for taxonomic groups in which all species in the country (or a systematic or random sample) have been assessed. The methods and scientific basis for the Red List Index were described by Butchart et al. (2004, 2005, 2007, 2010, 2024).

Butchart et al. (2010) also described the methods by which Red List Indices for different taxonomic groups are aggregated to produce a single multi-taxon Red List Index. Specifically, aggregated Red List Indices are calculated as the arithmetic mean of modelled Red List Indices. Red List Indices for each taxonomic group are interpolated linearly for years between data points and extrapolated linearly (with a slope equal to that between the two closest assessed points) to align them with years for which Red List Indices for other taxa are available. The Red List Indices for each taxonomic group for each year are modelled to take into account various sources of uncertainty:

1. Data Deficiency: Red List categories (from Least Concern to Extinct) are assigned to all Data Deficient species, with a probability proportional to the number of species in non-Data Deficient categories for that taxonomic group;

1. Extrapolation uncertainty: although RLIs were extrapolated linearly based on the slope of the closest two assessed point, there is uncertainty about how accurate this slope may be. To incorporate this uncertainty, rather than extrapolating deterministically, the slope used for extrapolation is selected from a normal distribution with a probability equal to the slope of the closest two assessed points, and standard deviation equal to 60% of this slope (i.e., the CV is 60%);

1. Temporal variability: the ‘true’ Red List Index likely changes from year to year, but because assessments are repeated only at multi-year intervals, the precise value for any particular year is uncertain.

To make this uncertainty explicit, the Red List Index value for a given taxonomic group in a given year is assigned from a moving window of five years, centred on the focal year (with the window set as 3-4 years for the first two and last two years in the series). Note that assessment uncertainty cannot yet be incorporated into the index. Practically, these uncertainties are incorporated into the aggregated Red List Indices as follows: Data Deficient species are allotted a category as described above, and a Red List Index for each taxonomic group is calculated interpolating and extrapolating as described above. A final Red List Index value is assigned to each taxonomic group for each year from a window of years as described above. Each such ‘run’ produces a Red List Index for the complete time period for each taxonomic group, incorporating the various sources of uncertainty. Ten thousand such runs are generated for each taxonomic group, and the mean is calculated.

5c. Data Collection Method

A detailed description of the Red List Assessment process is provided at https://www.iucnredlist.org/assessment/process.

5d. Accessibility Of Methodology

See references in section 11, and https://www.iucnredlist.org

5e. Data Sources

The Red List Index is based on data from The IUCN Red List of Threatened Species (www.iucnredlist.org), in particular the numbers of species in each Red List category of extinction risk, and changes in these numbers over time resulting from genuine improvements or deteriorations in the status of species. Data on species’ distribution, population size, trends and other parameters that underpin Red List assessments are gathered from published and unpublished sources, species experts, scientists, and conservationists through correspondence, workshops, and electronic fora.

Red List Assessments are checked before submission to IUCN by Assessors and Red List Authority Coordinators, to ensure that all of the required supporting information is provided in the appropriate format, distribution maps follow the required mapping standards (https://www.iucnredlist.org/resources/mappingstand..., and the IUCN Red List Criteria have been applied appropriately and consistently following IUCN Guidelines (IUCN SPSC 2019). For further details, see https://www.iucnredlist.org/assessment/process. All submitted assessments must be reviewed by at least one Reviewer designated by the Red List Authority. For more details on the review process, see the Rules of Procedure (https://nc.iucnredlist.org/redlist/content/attachm...).

When Red List Indices are updated each year, the updated index (and underlying numbers of species in each Red List Category) are made available for review by countries prior to submission to the SDG Indicators Database. This is achieved through updating the country profiles in the Integrated Biodiversity Assessment Tool (https://ibat-alliance.org/country_profiles and circulating these for consultation and review to CBD National Focal Points, SDG National Statistical Office Focal Points, and IUCN State Members.

In sum: all global Red List assessments are peer reviewed through the relevant Red List Authority for the species or species group in question; and all Red List assessments undergo consistency checks (to ensure consistency with assessments submitted for other taxonomic groups, regions, processes, etc.) by the Red List Unit before publication on the Red List website (http://www.iucnredlist.org/). Finally, the Chair of the IUCN Species Survival Commission (elected each four years by the government and non-governmental Members of IUCN) appoints a Chair for a Standards and Petitions Sub-Committee (https://www.iucn.org/theme/species/about/species-s...), which is responsible for ensuring the quality and standards of the IUCN Red List and for ruling on petitions against the listings of species on the IUCN Red List.

5f. Availability And Release Calendar

The Red List Index is updated annually in November-December using the latest data from reassessments on the IUCN Red List.

The IUCN Red List of Threatened Species is updated at least three times per year. Red List Indices for sets of species that have been comprehensively reassessed are usually released alongside the relevant update of the IUCN Red List. Data are stored and managed in the Species Information Service database, and are made freely available for non-commercial use through the IUCN Red List website and can be found under the Advanced Search functionality (www.iucnredlist.org). Re-assessments of extinction risk are required for every species assessed on The IUCN Red List of Threatened Species once every ten years, and ideally undertaken once every five years. A Red List Strategic Plan details a calendar of upcoming re-assessments for each taxonomic group.

5g. Time Series

Time series available: 1980 –2023. Updates are released annually

5h. Data Providers

National agencies producing relevant data include government, non-governmental organisations (NGOs), and academic institutions working jointly and separately. Data are gathered from published and unpublished sources, species experts, scientists, and conservationists through correspondence, workshops, and electronic fora. Data are submitted by national agencies to IUCN, or are gathered through initiatives of the Red List Partnership. The members of the Red List Partnership are listed at https://www.iucnredlist.org/about/partners, and currently include: ABQ BioPark; Arizona State University Centre for Biodiversity Outcomes; BirdLife International; Botanic Gardens Conservation International; Conservation International; Global Wildlife Conservation; Missouri Botanical Garden; NatureServe; Royal Botanic Gardens, Kew; Sapienza University of Rome; Texas A&M University; and Zoological Society of London.

5i. Data Compilers

Compilation and reporting of the Red List Index at the global level is conducted by the International Union for Conservation of Nature (IUCN) and BirdLife International, on behalf of the Red List Partnership.

Responsibility for overseeing Red List assessments, which underpin the Red List Index, is assigned to Red List Authorities according to the IUCN Red List Rules of Procedure (https://nc.iucnredlist.org/redlist/content/attachm...). The role of Red List Authorities is to ensure that all species within their remit are correctly assessed against the IUCN Red List Categories and Criteria at least once every ten years and, if possible, every five years. Further details of the roles and responsibilities of Red List Authorities are provided at https://www.iucnredlist.org/assessment/authorities, and the full list and contact details for all appointed Red List Authorities are available at https://www.iucn.org/commissions/ssc-groups.

5j. Gaps In Data Coverage

There are four main sources of uncertainty associated with Red List Index values and trends

1. Inadequate, incomplete or inaccurate knowledge of a species’ status. This uncertainty is minimized by assigning estimates of extinction risk to categories that are broad in magnitude and timing.

1. Delays in knowledge about a species becoming available for assessment. Such delays apply to a small (and diminishing) proportion of status changes, and can be overcome in the Red List Index through back-casting (Butchart et al. 2007).

1. Inconsistency between species assessments. These can be minimized by the requirement to provide supporting documentation detailing the best available data, with justifications, sources, and estimates of uncertainty and data quality, which are checked and standardized by IUCN through Red List Authorities, a Red List Technical Working Group and an independent Standards and Petitions Sub-committee. Further, detailed Guidelines on the Application of the Categories and Criteria are maintained (IUCN SPSC 2019), as is an online training course (in English, Spanish and French).

1. Species that are too poorly known for the Red List Criteria to be applied are assigned to the Data Deficient category. For birds, only 0.8% of extant species are evaluated as Data Deficient, compared with 24% of amphibians. If Data Deficient species differ in the rate at which their extinction risk is changing, the Red List Index may give a biased picture of the changing extinction risk of the overall set of species. The degree of uncertainty this introduces is estimated through a bootstrapping procedure that randomly assigns each Data Deficient species a category based on the numbers of non-Data Deficient species in each Red List category for the set of species under consideration, and repeats this for 1,000 iterations, plotting the 2.5 and 97.5 percentiles as lower and upper confidence intervals for the median.

The main limitation of the Red List Index is related to the fact that the Red List Categories are relatively broad measures of status, and thus the Red List Index for any individual taxonomic group can practically only be updated at intervals of at least four years. However, as the overall index is aggregated across multiple taxonomic groups, with groups reassessed asynchronously, it can be updated annually. A further limitation is that the Red List Index does not reflect particularly well the deteriorating status of more common species that remain abundant and widespread but are declining slowly in terms of their range and population. Hence the Red List Index is complemented by indicators of population abundance, such as the Wild Bird Index or Living Planet Index.

5k. Treatment Of Missing Values

At country level

Red List Indices for each taxonomic group are interpolated linearly for years between data points and extrapolated linearly (with a slope equal to that between the two closest assessed points, except for corals) back to the earliest time point and forwards to the present for years for which estimates are not available. The start year of the aggregated index is set as ten years before the first assessment year for the taxonomic group with the latest starting point. Corals are not extrapolated linearly because declines are known to have been much steeper subsequent to 1996 (owing to extreme bleaching events) than before. Therefore, the rate of decline prior to 1996 is set as the average of the rates for the other taxonomic groups.

At regional and global levels

The Red List Index is calculated globally based on assessments of extinction risk of each species included, because many species have distributions that span many countries. Thus, while there is certainly uncertainty around the Red List Index, there are no missing values as such, and so no imputation is necessary.

6. Scale

6a. Scale Of Use

Scale of application: Global, Regional, National

Scale of data disaggregation/aggregation

Global/ regional scale indicator can be disaggregated to national level: Yes

National data is collated to form global indicator: Yes

The indicator is available for use at the national, regional and global level. It should be noted that local and national data on each species are compiled to undertake global Red List assessments of each species, and it is these that are used to generate the global index, disaggregated to national indices.

6b. National Regional Indicator Production

Red List Indices for individual countries and regions can be calculated in two ways. Firstly, by disaggregating the global index to the national or regional scale, in which each species contributing to the national or regional index is weighted by the proportion of its global range within the particular country or region. The resulting index therefore shows the aggregate extinction risk for species within the country or region relative to its potential contribution to global species extinction risk (within the taxonomic groups included).

Secondly, complementing such national disaggregation’s of the global index, national RLIs can be generated from repeated assessments of national extinction risk (e.g. national Red Lists). Guidance for assessing national extinction risk of species has been developed by IUCN (IUCN 2012), and most countries have developed national red lists for at least one taxonomic group. National RLIs may be more sensitive than disaggregated global RLIs to factors influencing biodiversity loss within each country (including national policies), but require repeated assessments of national extinction risk for multiple groups in each country (with associated costs), and cannot be compared between countries.

The data underlying the global Red List Index are compiled under the authority of the IUCN Red List Committee, through application of the IUCN Red List Categories & Criteria (https://portals.iucn.org/library/node/10315). This includes submissions of endemics from national red list processes, where these have been conducted following the “Guidelines for application of IUCN Red List Criteria at Regional and National Levels” (https://portals.iucn.org/library/node/10336) and following the “Required and Recommended Supporting Information for IUCN Red List Assessments” (http://goo.gl/O52euG). Assessments may be submitted in all three IUCN languages (English, French and Spanish) and Portuguese. All assessments are peer reviewed through the relevant Red List Authority for the species or species group in question, as documented in the Red List Rules of Procedure (https://cmsdocs.s3.amazonaws.com/keydocuments/Rule...); see in particular Annex 3, the “Details of the Steps Involved in the IUCN Red List Process” (https://cmsdocs.s3.amazonaws.com/keydocuments/Deta...).

The key document providing international recommendations and guidelines to countries and all involved in application of the IUCN Red List Categories & Criteria (https://portals.iucn.org/library/node/10315) is the “Guidelines for Using the IUCN Red List Categories and Criteria” (in English - http://cmsdocs.s3.amazonaws.com/RedListGuidelines.... and in French - http://cmsdocs.s3.amazonaws.com/keydocuments/RedLi...) accompanied by the “Required and Recommended Supporting Information for IUCN Red List Assessments”. For countries (and regions), this is supplemented by the “Guidelines for application of IUCN Red List Criteria at Regional and National Levels” (https://portals.iucn.org/library/node/10336). To support the calculation of Red List Indices for any given country (or region), “Code (and documentation) for calculating and plotting national RLIs weighted by the proportion of each species’ distribution within a country or region” is posted online (Dias et al. 2020; https://github.com/BirdLifeInternational/rli-codes).

6c. Sources Of Differences Between Global And National Figures

The national Red List Index for a country may differ from the relevant national disaggregation of the global Red List index because: (a) it considers national rather than global extinction risk, (b) because it takes no account of the national responsibility for the conservation of each species, treating as equal both those species that occur nowhere outside the country (i.e. national endemics) and those with large ranges that occur in many other countries, and (c) the taxonomic groups considered may differ. Any such differences will be smaller for countries within which a high proportion of species are endemic (i.e., only found in that country), as in many island nations and mountainous countries, especially in the tropics. The differences will be larger for countries within which a high proportion of species have widespread distributions across many nations.

6d. Regional And Global Estimates And Data Collection For Global Monitoring

6d.1 Description Of The Methodology

The Red List Index can be downscaled to generate national and regional Red List Indices, weighted by the fraction of each species’ distribution occurring within the country or region, building on the method published by Rodrigues et al. (2014). These show an index of how well species are conserved in a country or region to its potential contribution to global species conservation (for the taxonomic groups of species included). The index is calculated as:

RLI(t,u) = 1 – [(Ss(W(t,s) * (rsu/Rs)) / (WEX * Ss (rsu/Rs))

where t is the year of comprehensive reassessment, u is the spatial unit (i.e. country), W_((t,s)) is the weight of the global Red List category for species s at time t (Least Concern =0, Near Threatened =1,

Vulnerable =2, Endangered =3, Critically Endangered =4, Critically Endangered (Possibly Extinct) =5, Critically Endangered (Possibly Extinct in the Wild) =5, Extinct in the Wild =5 and Extinct =5), WEX = 5 is the weight for Extinct species, r_su is the fraction of the total range of species s in unit u, and R_s is the total range size of species s.

The index varies from 1 if the country has contributed the minimum it can to the global RLI (i.e., if the numerator is 0 because all species in the country are Least Concern) to 0 if the country has contributed the maximum it can to the global RLI (i.e., if the numerator equals the denominator because all species in the country are Extinct or Possibly Extinct).

The taxonomic groups included are those in which all species have been assessed for the IUCN Red List more than once. Red List categories for years in which comprehensive assessments (i.e. those in which all species in the taxonomic group have been assessed) were carried out are determined following the approach of Butchart et al. 2007, i.e. they match the current categories except for those taxa that have undergone genuine improvement or deterioration in extinction risk of sufficient magnitude to qualify for a higher or lower Red List category.

6d.2 Additional Methodological Details

The Red List Categories and Criteria are applied for each species on The IUCN Red List of Threatened Species and are determined globally and provided principally by the Specialist Groups and stand-alone Red List Authorities of the IUCN Species Survival Commission, IUCN Secretariat-led initiatives, and Red List partner organizations. The staff of the IUCN Global Species Programme compile, validate, and curate these data, and are responsible for publishing and communicating the results. Each individual species assessment is supported by the application of metadata and documentation standards (IUCN 2013), including classifications of, for example, threats and conservation actions (Salafsky et al. 2008).

Red List assessments are undertaken through either open workshops or through open-access web-based discussion fora. Assessments are reviewed by the appropriate Red List Authority (an individual or organization appointed by the IUCN Species Survival Commission to review assessments for specific species or groups of species) to ensure standardisation and consistency in the interpretation of information and application of the criteria. A Red List Technical Working Group and the IUCN Red List Unit work to ensure consistent categorization between species, groups and assessments. Finally, a Standards and Petitions Sub-committee monitors the process and resolves challenges and disputes over Red List assessments.

While global Red List Indices can be disaggregated to show trends for species at smaller spatial scales, the reverse is not true. National or regional Red List Indices cannot be aggregated to produce Red List Indices showing global trends. This is because a taxon’s global extinction risk has to be evaluated at the global scale and cannot be directly determined from multiple national scale assessments across its range (although the data from such assessments can be aggregated for inclusion in the global assessment).

6d.3 Description Of The Mechanism For Collecting Data From Countries

7. Other MEA And Processes And Organisations

7a. Other MEA And Processes

Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES): global assessment, regional assessments, thematic assessments on sustainable use, IAS etc

Sustainable Development Goal (SDG) indicator 15.5.1. The Red List Index has been classified by the IAEG-SDGs as Tier 1. Current data are available for all countries in the world, and these are updated annually. Index values for each country are available in the UN SDG Indicators Database https://unstats.un.org/sdgs/indicators/database/.

Strategic Plan for Migratory Species (SPMS) indicator: 5.1, 6.2 & 8.1

Used by:

• Convention on the Conservation of Migratory Species of Wild Animals (CMS)
• African-Eurasian Migratory Waterbird Agreement (AEWA),
• Agreement on the Conservation of Albatrosses and Petrels (ACAP)
• Raptors MOU
• Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES)
• United Nations Convention to Combat Desertification (UNCCD)

Disaggregations of the Red List Index are also of particular relevance as indicators towards the following SDG targets (Brooks et al. 2015): SDG 2.4 Red List Index (species used for food and medicine); SDG 2.5 Red List Index (wild relatives and local breeds); SDG 12.2 Red List Index (impacts of utilisation) (Butchart 2008); SDG 12.4 Red List Index (impacts of pollution); SDG 13.1 Red List Index (impacts of climate change); SDG 14.1 Red List Index (impacts of pollution on marine species); SDG 14.2 Red List Index (marine species); SDG 14.3 Red List Index (reef-building coral species) (Carpenter et al. 2008); SDG 14.4 Red List Index (impacts of utilisation on marine species); SDG 15.1 Red List Index (terrestrial & freshwater species); SDG 15.2 Red List Index (forest-specialist species); SDG 15.4 Red List Index (mountain species); SDG 15.7 Red List Index (impacts of utilisation) (Butchart 2008); and SDG 15.8 Red List Index (impacts of invasive alien species) (Butchart 2008, McGeoch et al. 2010).

Red List Index graphs and underlying index data are available for each country, SDG regions, IPBES region, CMS region and various thematic disaggregations at https://www.iucnredlist.org/search. Red List Index graphs are also available for each country in the BIP Indicators Dashboard (https://bipdashboard.natureserve.org/bip/SelectCou...), the Integrated Biodiversity Assessment Tool Country Profiles (https://ibat-alliance.org/country_profiles), and (for birds) on the BirdLife International Data Zone (http://datazone.birdlife.org/species/dashboard).

7b. Biodiversity Indicator Partnership

Yes

10. Data Reporter

10a. Organisation

International Union for Conservation of Nature (IUCN)

BirdLife International (BLI)

10b. Contact Person

Dr Thomas Brooks (thomas.brooks@iucn.org)

Dr Stuart Butchart (stuart.butchart@birdlife.org)