- The Loom
Reports of My Extinction Are Greatly Exaggerated
From time to time, scientists discover that a species that was once thought to have become extinct is actually surviving in some remote place. If the species is a salamander or a lemur, it gets a quick headline and then promptly goes back to its obscure, tenuous existence. But here’s one rediscovered creature that I suspect will get some major press: the Ivory-billed woodpecker is back. Science is publishing a paper in which scientists report several sightings and a video of the magnificent bird, which hadn’t been seen since in the United States since 1944. Here is a report from the AP.
The challenge of studying extinctions is that it can be hard to know when a species is finally gone for good. If a species of flower lives only on a single bare island the size of a hot-dog stand, you can be pretty sure that if you don’t see any of the flowers for a few years, it’s gone. But if, as is the case for the Ivory billed woodpecker, a species exists in remote forests and at low density, the failure to see it may just mean scientists haven’t looked everywhere. Eventually, most scientists will just give up and presume the animal extinct. As a result, ornithologists and amateur birders have been wondering for decades whether the woodpecker is actually still alive. Incredibly, it is–in some remote woods in Arkansas.
So what does it mean that today the Ivory billed woodpecker seems to be alive? Is it proof that environmentalists have been crying wolf about the dangers of extinction? Do we not need to worry? Is wildlife taking care of itself?
A couple maps can help put the discovery into perspective. This first map shows the original range of the ivory-billed woodpecker. It thrived in mature forests in the southeastern United States, particulary along the coasts and up the Mississippi. The second map shows its range in between 1900 and 1930. The striped regions are habitat that the woodpecker lost between 1900 and 1930. The orange spots were all that was left of its range in 1930.
The reports today do not mean that the woodpeckers are actually living in their former range. They don’t even show that the bird exists in its 1930 range. The sightings were all made in the Arkansas patch–a tiny portion of the area in which the woodpecker once lived. The researchers say in their paper that the sightings were made in some 200,000 hectares of Arkansas forest that all might be well-suited to the woodpeckers. Is that cause for optimism? It depends on the biology and ecology of the birds. Will they be able to sustain a healthy population in a relatively small remnant of their original range? That’s an open question. It is possible that the woodpecker may also be lurking in other parts of its former range, but that doesn’t necessarily boost the species’s odds of survival. Such a hypothetical population might well be isolated from the Arkansas population, like two islands separated by hundreds of miles of ocean. If one population disappears due to inbreeding, disease outreaks, or some other disaster, its numbers won’t be boosted by immigrants from the other population.
This gets to the heart of the extinction process. Conservation biologists have argued for a long time that as habitats get fragmented, the chances of the species they are home to becoming extinct go up. Given the rate at which forests have been cleared, wetlands drained, and so on, they’ve warned that we face a massive pulse of extinctions. (Of course, pollution, hunting, invasive species, and other assaults don’t help, either.)
Some skeptics such as Bjorn Lomborg have claimed that this is just fear-mongering. They pointed out that of the 200-some species of birds in eastern North America when Europeans arrived with their axes, only 4 were considered extinct–including, at the time, the Ivory-billed woodpecker. Given that the European settlers cleared vast swaths of forests, some simple calculations would suggest that 26 species should have become extinct.
Ten years ago Stuart Pimm, now at Duke, demonstrated that this argument was meritless. In a paper in the Proceedings of the National Academy of Sciences, he pointed out that predictions of extinction based on habitat loss have to take into consideration the range of the species and the extent of the habitat loss. Most of the birds of eastern North America lived across vast expanses. When farmers were cutting down trees in New England, those birds might be living happily in Pennsylvania and Ohio. When the settlers moved to Pennsylvania and Ohio, the birds could still live in Kentucky or Arkansas–and might even start recolonizing the forests that returned to the farmed-out regions of New England. In fact, many species of birds that live in the eastern United States can be found far north in Canada. If you consider only the birds that live in the forests of the eastern United States (between 11 and 28, depending on how strict you make the rules for membership in this club), the rate of extinction has actually been a bit higher than conservation biologists would predict.
I won’t be at all surprised if various bloggers and pundits try to turn the rediscovery of the Ivory billed woodpecker into a refutation of the idea that fragmentation leads to extinction. (I’ll post links to them if I come across them this week.) But I will be surprised if these pseudoskeptics actually address Pimm’s paper. The paper also makes an important point that Pimm has followed up on with more recent research: a lot of the world’s biodiversity is very different from the robins and crows and other birds that I see out my window here in Connecticut. A lot of biodiversity is made up of species with relatively small ranges, living in the tropics where forests are currently being wiped out at a rapid rate. These species may be able to hang on for a few decades in relatively large fragments, Pimm argues, but they’re waiting out a death sentence. While extinction rates among birds in North America may be relatively low, the same process appears to be causing a catastrophe in the tropics.
It is wonderful that so many people–scientists, government officials, environmental groups, private land owners, and obsessed birders–have helped rediscover the Ivory-billed woodpecker and may be able to help it thrive in one corner of its former range. But this good news shouldn’t be misused to distort the big picture.