. Bulletin of the British Ornithologists' Club. 5. H. M. Buichart el al. 10 Bull. 2006 126A continued record (see Fig. 1). For example, for species with recently confirmed records to be placed at the Extinct end of the spectrum, there had to be greater confidence in the extinction, greater confidence in the adequacy of surveys, the absence or inadequacy of local/unconfirmed records, greater severity of threatening processes, and better documentation of, and confidence in, observed population declines. In contrast, species that had not been recorded for many decades ( more than
. Bulletin of the British Ornithologists' Club. 5. H. M. Buichart el al. 10 Bull. 2006 126A continued record (see Fig. 1). For example, for species with recently confirmed records to be placed at the Extinct end of the spectrum, there had to be greater confidence in the extinction, greater confidence in the adequacy of surveys, the absence or inadequacy of local/unconfirmed records, greater severity of threatening processes, and better documentation of, and confidence in, observed population declines. In contrast, species that had not been recorded for many decades ( more than 100 years) were judged to be more likely to have become extinct for a given balance of evidence for and against extinction, owing to the sheer length of time without records. Deciding the strength of evidence for and against extinction is necessarily subjective. However, this framework helped to make these judgements as objective as possible, by setting out the evidence, and weighing this against the time since the last confirmed record. We tested this framework on 40 Critically Endangered bird species that we considered candidates for Possibly Extinct status. This included all species for which there was any reasonable possibility that they might be extinct, including any that had not been seen for >10 years (despite reasonable searches and/or for which there was a plausible threatening process), and any that had been last seen <10 years High Low Low High Atitlan Grebe Aldabra Warbler Night Parrot. Critically Endangered White-chested White-eye Pohnpei Mountain Starling Magdalena Tinamou Himalayan Quail Samoan Moorhen .50 >100 No. of years since last record Figure 1. Schematic showing, with selected examples, how time since last record interacts with confidence of extinction to determine how species are classified as Critically Endangered, Possibly Extinct or Extinct. For species last recorded quite recently there needs to be greater confidence that the hist indiv
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