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The World Wildlife Fund has declared that global warming, which most scientists agree on as a phenomenon caused by human beings who burn 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 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.