ATLANTA - The effects of global warming appear to be causing Georgia's official songbird, the brown thrasher, and other species to shift their ranges farther north and migrate earlier in the spring, according to a new environmental study. <br>
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The thrasher seems to be returning to its nesting grounds, from Florida and points south, 21 days earlier on average in the spring than it did 20 years ago, according to the report issued Monday by the National Wildlife Federation and the American Bird Conservancy. <br>
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The study will be a major topic of discussion at the wildlife federation's annual meeting, which starts Friday in Atlanta. <br>
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Experts are not sure exactly what to make of the information. <br>
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The president of the wildlife federation, Mark Van Putten, said earlier spring migration can make it more difficult for the birds to find food insects, flowers and berries when they need it. <br>
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The result, Van Putten said, could be far fewer brown thrashers in Georgia by the middle of this century. <br>
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``Since songbirds play a critical role by eating insects, pollinating plants and dispersing seeds, such changes risk throwing ecosystems off balance,'' he told The Atlanta Journal-Constitution. <br>
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Georgann Schmalz, president of the Atlanta Audubon Society, agreed that many bird species appear to be altering their ranges and migratory patterns. But with current information, she said, it is difficult to know where birds might be decades from now. <br>
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Ornithologists and U.S. Fish and Wildlife Service officials have warned for decades that many common songbird species were steadily declining. An investigation by the Journal-Constitution last year found that 37 species in Georgia were becoming more scarce, mostly because of habitat loss. <br>
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The report released Monday said that global warming, thought to be a result of pollution from burning fossil fuels and other man-made sources, is an added threat. <br>
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The brown thrasher is one of nature's most versatile songsters. Its repertoire of songs has been estimated at 2,000 or more often taken for those of its more famed cousin, the mockingbird.
