Click on any of the following for some background and an explanation of the technical terms used in the species factsheets and additional data tables:

• IUCN Red List Categories
• IUCN Red List Criteria
• Range and country distribution
• Habitats, altitude and migratory status
• Threats and impact
• Data quality and derivation
• Extinct species 
• Red List Index
• Generation length

IUCN Red List Categories

The IUCN Red List Categories and Criteria are an objective and widely accepted system for classifying species at high risk of extinction. BirdLife coordinates the assessment of the status of the world's birds using these categories and criteria and, as the official Red Listing Authority for birds for the IUCN Red List, submits this information to be included on the IUCN Red List along with that of other animals and plants. The IUCN Red List Categories and Criteria (in English, French or Spanish) can be viewed and downloaded at: http://www.iucnredlist.org/technical-documents/categories-and-criteria/2001-categories-criteria. Detailed guidelines on their use can also be seen at: http://www.iucnredlist.org/documents/RedListGuidelines.pdf. An overview of the categories is given below. See also IUCN Red List Criteria.

The categories, including the three globally threatened categories (Critically Endangered, Endangered and Vulnerable) are outlined below. For the total number of species in each category, see What's new.

EXTINCT (EX) - A species is Extinct when there is no reasonable doubt that the last individual has died. A species 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 species's life history.

EXTINCT IN THE WILD (EW) - A species is Extinct in the Wild when it is known only to survive in captivity or as a naturalized population (or populations) well outside the past range. A species 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 species's life history.

CRITICALLY ENDANGERED (POSSIBLY EXTINCT) CR (PE) - This is not an official category of the IUCN Red List, but a tag applied by BirdLife (and under review by the IUCN Red List) to identify those Critically Endangered species (see definition below) 'that are likely to be extinct, but for which there is a small chance that they may still be extant, and hence they should not be listed as Extinct until local or unconfirmed reports have been discounted, and adequate surveys have failed to find any individuals' (see below for further details).

CRITICALLY ENDANGERED (CR) - A species is Critically Endangered when the best available evidence indicates that it meets any of the criteria A to E for Critically Endangered (see IUCN Red List Criteria) and it is therefore considered to be facing an extremely high risk of extinction in the wild.

ENDANGERED (EN) - A species is Endangered when the best available evidence indicates that it meets any of the criteria A to E for Endangered (see IUCN Red List Criteria), and it is therefore considered to be facing a very high risk of extinction in the wild.

VULNERABLE (VU) - A species is Vulnerable when the best available evidence indicates that it meets any of the criteria A to E for Vulnerable (see IUCN Red List Criteria), and it is therefore considered to be facing a high risk of extinction in the wild.

NEAR THREATENED (NT) - A species 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 species 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 species are included in this category.

DATA DEFICIENT (DD) - A species 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 species 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 species 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 species is suspected to be relatively circumscribed, and a considerable period of time has elapsed since the last record of the species, threatened status may well be justified.

NOT EVALUATED (NE) - A species is Not Evaluated when it is has not yet been evaluated against the criteria. Note that all bird species have been evaluated in 2008, so this category has not been applied for any species.

NOT RECOGNISED (NR) - This is not an official IUCN Red List Category, but is used by BirdLife in order to document Red List history using taxonomically different lists.

Possibly Extinct species - BirdLife applies a 'Possibly Extinct' tag to certain Critically Endangered species. The definition for this, and guidelines for its application, have been developed by examining information on c.50 species that have not been recorded for a long time or with dwindling populations that may have finally disappeared. The framework is currently being tested on other classes of taxa, but has not yet been officially incorporated into the IUCN Red List.

Species classified as Critically Endangered (Possibly Extinct) are defined by BirdLife as:

Species that are likely to be extinct, but for which there is a small chance that they may still be extant, hence they should not be listed as EX until local or unconfirmed reports have been discounted, and adequate surveys have failed to find any individuals.

For each species, the following information is considered: (1) evidence pertaining to the timing of the last confirmed records; (2) any subsequent unconfirmed records or local reports; (3) knowledge about the strength of threatening processes currently and historically operating; (4) the adequacy of fieldwork relative to the (presumed) ease of detection of the species; and (5) the extent and quality of remaining suitable habitat (where 'suitable' incorporates the absence of introduced predators, pathogens etc).

Species are tagged as Possibly Extinct if, on balance, the evidence that they may be extinct outweighs any evidence that they may still be extant (although the latter remains a slim possibility, so they are not yet classified as Extinct).

Such evidence for extinction may include a combination of the following factors:

1. There have been no confirmed records for a long time (it is difficult to be more prescriptive: the duration will depend on the intensity of fieldwork and the ease of detection)
2. For species with recent last records, the decline has been well documented
3. There are severe threatening processes operating (e.g. extensive habitat loss, introduction of alien predators, intensive hunting)
4. The species has attributes known to predispose it to extinction, e.g. it was probably naturally rare and/or had a tiny range (as evidenced by paucity of specimens relative to collecting effort), or flightless etc. In some cases, allospecies or congeners may have gone extinct through similar threatening processes.
5. Surveys would have detected it (good/recent surveys have been adequate; species is unlikely to be overlooked).

Evidence that the species may remain extant may include a combination of the following factors:

6. The lack of records is best explained by inadequate fieldwork (any surveys have been insufficiently intensive/extensive, or inappropriately timed; or the species's range is inaccessible, remote, unsafe or inadequately known)
7. The lack of records is best explained by the fact that the species is difficult to detect (low density, cryptic, inconspicuous, nocturnal, nomadic, silent or call unknown, identification difficult)
8. There have been reasonably convincing local reports or unconfirmed sightings
9. Suitable habitat (free of introduced predators and pathogens if relevant) remains within the species's known range. In some cases, allospecies or congeners may survive despite similar threatening processes.

The IUCN Red List category of Data Deficient is usually only applied to species where there is no information that, either directly or by inference, implies they may be threatened. A few Data Deficient bird species have not been recorded for a significant period of time. However, in each case the evidence suggests that they are unlikely to be threatened (and hence unlikely to be near extinction or possibly extinct), because no threatening factor is known or plausibly inferred, and there are convincing practical reasons why there have been no recent records (e.g. because surveys have been inadequate and/or the species is difficult to detect). In some cases it is likely that the lack of records is because the taxon is invalid (e.g. the type represents an aberrant individual of a commoner species).

A more detailed description of the use of Possibly Extinct is currently in preparation and will be published in due course.