This post at Watts Up With That? makes it pretty clear:
Why do I think that their conclusion [about extinction rates] is so badly flawed?Ecochondriacs have a lot of evidence to produce or it's time for them to talk a lot less and a lot less stridently.
Like many modern scientists, rather than trying to find the most probable, they simply assume the worst. So they give their calculations assuming a 1% decadal extinction rate. Here’s the problem. That’s no more believable than Wilson’s 2.7% per decade rate. There are about 3,300 mammal species living on the continents (excluding Australia). If we assume that one percent of them go extinct per decade, that would mean that we should be seeing about 33 continental mammal extinctions per decade. It’s worse for birds, a 1% extinction rate for birds would be about 80 continental birds per decade. We have seen absolutely nothing even vaguely resembling that. That’s only slightly below Wilson’s estimate of a 2.7% extinction rate, and is still ridiculously high.
Instead of 33 mammals and 80 birds going extinct on the continents per decade, in the last 500 years on the great continental landmasses of the world, we’ve only seen three mammals and six birds go extinct. Only nine continental mammal and bird species are known to have gone extinct in 500 years. Three mammals and six birds in 500 years, that’s less than one continental mammal extinction per century, and these highly scientific folks are claiming that 30 mammals and 80 birds are going extinct per decade? … once again I’m forced to ask, where are the corpses?
This kind of world-blindness astounds me. I’ve heard of living in an ivory tower, but if you were making the claim that it’s raining, wouldn’t you at least look out the ivory windows to see if water were actually falling from the sky? How can you seriously claim that we’re losing dozens and dozens of species per year when there is absolutely no sign of that in the records?
Because the reality is that despite humans cutting down the forests of the world at a rate of knots for hundreds and hundreds of years, despite clearcutting for lumber, despite slash-and-burn, despite conversions to cropland, despite building hundreds of thousands of miles of roads and fences, despite everything … only nine continental mammal and bird species have gone extinct.