Data Deficient birds on the IUCN Red List: What don’t we know and why does it matter?
Introduction
The IUCN Red List is generally regarded as the most objective and authoritative system available for classifying species in terms of their risk of extinction (Lamoreux et al., 2003, Hambler, 2004, Rodrigues et al., 2006, Regan et al., 2005). Quantitative criteria based on population size, rate of decline, and area of distribution are used to assign species to categories of relative extinction risk (IUCN, 2001). The criteria are clear and comprehensive but are sufficiently flexible to deal with uncertainty (Akçakaya et al., 2000). Assessments have to be supported with detailed documentation of the best available data, with justifications, sources, and estimates of uncertainty and data quality (IUCN, 2008a). Red List Authorities are appointed to organize independent scientific review and to ensure consistent categorization between species, groups, and assessments. BirdLife International takes this role for birds, and has assessed the status of all c.10,000 bird species five times since 1988 (Collar and Andrew, 1988, Collar et al., 1994, BirdLife International, 2000, BirdLife International, 2004, BirdLife International, 2008). For all taxa, an independent Red List Standards and Petitions Subcommittee monitors the process and resolves any challenges and disputes to listings. The IUCN Red List is advanced in partnership among the three pillars of IUCN (commissions, secretariat, and members), specifically the Species Survival Commission, the Species Programme, and a number of Red List Partner organizations.
The Red List categories range from Least Concern through Near Threatened, Vulnerable, Endangered and Critically Endangered to Extinct in the Wild and Extinct (IUCN, 2001). An additional category, Data Deficient, can be assigned to a taxon “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” (IUCN, 2001). However, IUCN provides guidance that positive use should be made of whatever data are available, and cautions that if the range of a taxon is suspected to be relatively circumscribed and a considerable period of time has elapsed since the last record, threatened status may well be justified. Furthermore, “the liberal use of Data Deficient is discouraged” because “taxa that are poorly known can often be assigned a threat category on the basis of background information concerning the deterioration of the habitat and/or other causal factors” (IUCN, 2001, IUCN, 2008a). As an example of the application of such guidance, Good et al. (2005) assessed the 67 Coleeae (Bignoniaceae) endemic to Madagascar and were able to reassign nine initially ‘Data Deficient’ species to categories of threat using contextual information.
Data Deficient is probably the most controversial and misunderstood Red List category, with some scientists arguing for its more widespread application even in cases where IUCN guidance would indicate that an alternative category is appropriate (e.g. Mrosovsky, 1997, Rodríguez et al., 2000, Pimenta et al., 2005, Wienecke, 2009; but see Meylan, 1998, Hilton-Taylor et al., 2000, Stuart et al., 2005), or questioning the appropriateness of that guidance (e.g. Tobias and Brightsmith, 2007). In some cases the discrepancies are because of different attitudes between assessors regarding evidentiary versus precautionary approaches. IUCN’s guidelines on dealing with uncertainty (IUCN, 2001, IUCN, 2008a) state that assessors should adopt a “precautionary but realistic” attitude; a more evidentiary attitude results in a higher percentage of species being listed as Data Deficient, and greater risk that species in urgent need of conservation attention are not flagged as such before it is too late (Stuart et al., 2005). Application of Data Deficient is also probably the least consistent between assessments of different taxonomic groups (e.g. between birds, amphibians, mammals, corals and cycads).
Here, we review bird species listed as Data Deficient on the IUCN Red List, examining why they are listed in this category, what data are lacking, what actions are required for them, how threatened they are likely to be, and how this category can be used in setting priorities for conservation funding and action. Our aim is to clarify: (a) when it is (and is not) appropriate to use this category for poorly known birds and other taxa; (b) how assessments of Data Deficient species may influence estimates of how threatened are different groups of species; and (c) how Data Deficient species should be incorporated into priority setting.
Section snippets
Methods
A total of 65 bird species are listed as Data Deficient on the 2009 IUCN Red List (BirdLife International, 2009). Two of these will be probably be recategorised in the 2010 Red List (see http://www.birdlifeforums.org): Scottish Crossbill Loxia scotica as Not Recognised (it is probably not distinct at the species level) and Sinaloa Martin Progne sinaloae as Endangered. These two are excluded from the analyses relating to Data Deficient species here, but are included in the analysis of the fate
Results
The total of 63 Data Deficient bird species represents 0.6% of extant bird species (see Table 1 in Supplementary Online Materials). Data Deficient species are found in 44 countries and territories, with Indonesia (16) and Papua New Guinea (15) supporting the highest numbers (and the island of New Guinea and its satellites, shared by these two nations, supporting 17), and significant concentrations also occurring in D.R. Congo (8), Cameroon (6), Colombia, Philippines and Somalia (5 each; Fig. 1
Application of the Data Deficient category for birds and other taxa
Many of the world’s birds are poorly known, with no information on their population sizes or trends, incomplete information on their distribution and a poor understanding of their status and possible threats. Nevertheless, just 0.6% of bird species are categorised on the IUCN Red List as Data Deficient. This is because BirdLife has attempted to follow IUCN guidance in using this category sparingly, through making plausible inferences from contextual information where available. Such information
Conclusions
Relatively few bird species are considered Data Deficient because birds are relatively well known, and because inferences are made about extinction risk from contextual information, where available, during the Red List assessment process, in accordance with IUCN guidelines. We hope that the explanations and discussion presented here will help to clarify the purpose and application of the Data Deficient category within birds, and will contribute to greater consistency in its application for
Acknowledgements
For providing useful information and helpful comments we thank Nigel Collar, Ben Collen, Will Darwall, René Dekker, Guy Dutson, Lincoln Fishpool, Craig Hilton-Taylor, Mike Hoffmann, Beth Polidoro, Jorn Scharlemann, Alison Stattersfield, Simon Stuart and Joe Tobias. BirdLife’s Red List assessments for the world’s birds, including Data Deficient species, are based on many different sources of information, but we are particularly grateful for input from thousands of species experts, birdwatchers,
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