We welcome the recent announcement by the conservation partnership BirdLife International that they have launched a "global bid to try to confirm the continued existence of 47 species of bird that have not been seen for up to 184 years" (see http://go.nature.com/6Hc2Cn). But there are pitfalls, as the recent history of 'rediscoveries' has shown.
One of the species on BirdLife's target list is the ivory-billed woodpecker (Campephilus principalis), a bird that was prematurely alleged to have been rediscovered in 2005. This seemingly improbable reappearance provoked intense debate within the scientific community about the veracity of claimed sightings and, more generally, about what represents sufficient proof of continued existence (or extinction). Accusations of 'faith-based' ornithology resulted, increasing scepticism among politicians and policy-makers that conservation organizations are often too willing to put public relations before scientific rigour. [...]
Some people really know how to get my attention.
I've been kicking around this idea for a while, too, though not as eloquently. The authors of the opinion piece make their case that even if we re-discover species living in the wild, the discovery means very little unless there's a minimum viable population. I would have taken a different tact, saying the quest to re-discover these species burns through vast sums of critical conservation money; money that would be better spent on species who are a little more accessible.
I do see a small amount of scientific utility in this, though - extinction rate is sensitive to what we a) declare a species and b) an and can't find. It's hard to talk about, say, Giant Squid demographics without being able to look at them (or otherwise detect them). So how hard we try to look for relictant populations influences our measure of current extinction rate. To get an accurate measure of the current extinction rate, it makes sense to apply copious effort.
That said, these expeditions are expensive. They're multi-person, multi-year affairs frequently requiring access to remote areas by specialist personnel. If you can't hear the dollar signs ring up as you read that last sentence, you should get your hearing checked! The price on the knowledge that a species isn't totally extinct, but instead a hairs-breadth away from extinction, is very massive, and surely that money could be used to keep other species from getting that far-gone to begin with.
Ladie et al. Caution with claims that a species has been rediscovered. (2009) Nature 461, 723