There are almost 3 billion fewer birds in North America today than there were fifty years ago.
If this is correct it's deeply disturbing. I don't doubt that habitat loss, both in the birds' breeding grounds and in their wintering grounds in Central and South America have taken a toll.
It's interesting that among the species hardest hit were grassland species in the midwest (717 million fewer birds) where vast tracts of grassland acreage have been sacrificed to development and agricultural production.
I do have a concern about the methodology of the study, however. It relies heavily on estimates of numbers by amateur observers, and among the species showing severe declines are blackbirds (440 million fewer since 1970) which are so numerous and which in the non-breeding season throng together in flocks numbering in the thousands, that accurate counts are very difficult to obtain.
Much more distressing than the drop in numbers of abundant species like blackbirds, though, is the decline in woodland species like warblers which breed in the boreal north. The warbler population has shrunk, according to the study, by some 617 million birds since 1970.
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| Cape May Warbler |
Whatever the explanation, it seems obvious that habitat loss, and perhaps diseases like West Nile virus, wind turbines, collisions with skyscrapers and even feral house cats are taking a toll. Every new shopping center and housing development eliminates acres of habitat, and every new highway is a killing field for birds and other wildlife.
But if these stressors really are what's causing the collapse it's very hard to imagine a solution.