Inferring extinction from biological records:: Were we too quick to write off Miss Waldron's Red Colobus Monkey (Piliocolobus badius waldronae)?

We are now entering a time of immense environmental upheaval where experts are increasingly required to provide conservation assessments. Quantitative assessment of trends in species' range and abundance is costly, requiring extensive field studies over a long period of time. For many species in dense habitats, it may be very difficult to establish reliable and sensitive survey and monitoring techniques, which are able to warn of potentially catastrophic population declines. Unfortunately many other species are only known through a few 'chance' sightings or a handful of museum specimens and therefore extinction may be even harder to ascertain. In 2000 Miss Waldron's Red Colobus, Piliocolobus badius waldronae, was reported as extinct, but since then (in 2001) a single specimen has been collected. Four probabilistic methods were used to infer extinction based on a record of sightings of the subspecies. Based on the date when the extinction statement of Miss Waldron's Red Colobus was made, all four methods returned probability values > 0.05, suggesting that the subspecies is extant, but is extremely rare. If we cannot successfully monitor populations of critically endangered taxa, it becomes almost impossible to predict their extinction with any certainty and we can expect increasing numbers of false alarms in future years, which may undermine the potential for conservation action and, more worryingly, public support for conservation. (c) 2005 Elsevier Ltd. All rights reserved.