Scientists long thought the ivory-billed woodpecker was extinct. It was last seen in 1944. Then, surprise, the bird was spotted in northern Arkansas. Details here.

This is great news for bird lovers -- and for the woodpecker. It's also hardly an isolated incident. The sad fact is that data on endangered species is quiet poor -- so poor that quite a few species have been erroneously listed as "endangered" that were doing just fine and were subsequently removed from the list. Conversely, given that only a fraction of extant species have been identified, it's possible for species to disappear before we ever know they exist.