Environment: Bye Bye Birdies

Populations of many migratory species have plummeted--and, in some cases, global warming seems to be at fault

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Other birds seem to be in trouble because of habitat loss. The decline of the rusty blackbird, for example—one of the most rapidly dwindling species in North America, says Butcher—may also be due to global warming, but the immediate cause seems to be a drying up of the Canadian wetlands where it breeds. The same may apply to the Canada warbler. The cerulean warbler, also in decline, is losing habitat not because of global warming but because of another human activity: the destruction of Appalachian mountaintop forests by coal-mining operations.

And some birds are actually doing fine, adjusting to change and even increasing their numbers--at least in the bird counts. Some hummingbirds, for example, that used to winter in Mexico don't bother to make the trip anymore because the U.S. is now warm enough all year long. A number of migratory species that nest in northeastern forests have rebounded because that part of the country is reforesting as agriculture declines. Bluebirds are thriving, says Butcher, because bluebird lovers have been setting up nesting boxes for them for the past half-century.

But even those success stories can be troubling. Natural ecosystems evolved at a glacial pace, over millenniums. And while human-induced change may help some species thrive, it can also throw off the balance that keeps an ecosystem healthy--as some hungry Dutch hatchlings have discovered.

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