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The World Wildlife Fund has declared that global warming, a phenomenon that most scientists agree is caused by human beings' burning of fossil fuels, will create havoc among migratory birds by altering the environment in ways harmful to their habitats.

The World Wildlife Fund has declared that global warming, a phenomenon most scientists agree that is caused by fossil fuels burned by human beings, will create havoc among migratory birds by altering the environment in ways harmful to their habitats.