Extant Unless Proven Extinct? Or, Extinct Unless Proven Extant?

Whitten, Bishop, Nash, and Clayton (1987; see pp. 4248) report that recent ornithological surveys of Sangihe Island in Indonesia failed to encounter a previously described species of small bird endemic to that island, the Sangihe flycatcher. Recent surveys of the larger Indonesian island of Sulawesi (Celebes) similarly failed to encounter three endemic species of small fish. The authors conclude that these species may be extinct. At first, these findings may appear particularistic and unlikely to command headlines in Indonesia, let alone elsewhere. In fact, they are of potentially broad significance, for they illustrate a serious recurrent problem in assessments of the present extinction crisis. Lists of taxa judged extinct or endangered, as exemplified by the IUCN Red Data books, are assembled as follows. Authorities take a species list for a local fauna or flora (e.g., the birds of North America), initially identify particular taxa which they suspect might be extinct or endangered, and seek more information about those taxa. It will thus be learned that some of those putatively extinct or endangered taxa are really extant or secure, thereby shortening the preliminary "red list." The remaining taxa are assembled into a book of statements of the form that species X is presumed extinct because the last sighting was in 1973 despite particular searches for it, while species Y is presumed endangered because the sole known population numbered 124 individuals as of 1986. An example of such reasoning is the Red Data book Endangered Birds of the World (King 1981), which concludes that, out of the ca. 8000 bird species extant in 1600, 87 are now extinct and 283 are endangered. The implicit assumption behind this approach is that taxa are "extant unless proven extinct." Biologists concerned about an extinction crisis bear the burden of proof. The 8000 87 283 = 7630 bird species omitted in the Red Data book are presumed extant and secure and are not up for further discussion. Thus, the proportion of the world's bird species for which extinct or endangered status is even suggested is trivial (1% and 4o/, respectively). Because there is always some difficulty in establishing a population's true status, advocates of unrestrained economic growth proceed to dispute some of those 370 claims and suggest that the true proportion is even smaller. Biologists are left to defend the weak proposition that they think the proportion will be much higher in the future, despite the low proportion now. The assumption "extant unless proven extinct" seems appropriate for well-studied taxa in regions with many observers-e.g., birds in North America or Europe. The field marks, geographic ranges, and preferred habitats of all North American and European bird species are well described. Every North American and European bird species is specifically searched for every year, and almost all are observed. No species could escape observation for several consecutive years without becoming a subject of debate. Bird watchers make special efforts to find rare or supposedly extinct species. Hence there is no chance that a species could become extinct without first having been considered endangered for many years. Species not specifically mentioned as being possibly extinct or endangered are known to be extant in good numbers. The situation is quite different in regions with few observers-e.g., the tropics, where most of the world's species live. The situation is also different for taxa with less popular appeal than birds. Many tropical species described in the nineteenth century have never been observed in recent years, either because a) no observer has recently visited their habitat, b) it is uncertain where