PORT AUSTIN, Mich. (AP) -- The sky above a tabletop-flat expanse of eastern Michigan farmland near Lake Huron is a well-traveled pathway for migratory birds journeying between summer nesting areas in Canada's boreal forests and wintering grounds to the south. Thanks to reliably brisk winds, the ground below is dotted with hundreds of electricity-generating turbines.
Federal guidelines from the U.S. Fish and Wildlife Service urge wind energy developers to locate turbines with special care in places such as the 'Thumb' region of Michigan's mitten-shaped Lower Peninsula - or avoid them altogether, to prevent fatal collisions between birds and the towers' whirring blades. But an advocacy group says the government's voluntary approach is allowing too many wind farms to be built or planned for construction in important nesting areas and flight paths across large sections of the nation.
A new analysis by the American Bird Conservancy said more than 30,000 of the existing 48,000 turbines are in places that government agencies or nonprofit organizations such as the National Audubon Society describe as having special significance to birds. More than 50,000 others are planned for construction in such locations - about half of all turbines on the drawing board nationwide, according to the study, which the conservancy provided to The Associated Press.
Locations that the group considers sensitive range from the Prairie Pothole region of the Great Plains, home to the threatened piping plover, to the entire state of Hawaii, where 32 bird species that exist only there are listed as endangered or threatened. Another is Huron County, at the tip of Michigan's Thumb, where 328 turbines already generate power and local officials have approved 50 more.
'Wind turbines are among the fastest-growing threats to our nation's birds,' said Michael Hutchins, coordinator of a conservancy program that encourages 'bird smart' wind energy production.
The AP produced similar results after independently calculating data on which the conservancy based its report. The group used data from the U.S. Geological Survey, which keeps records of existing turbines, and the Federal Aviation Administration, which developers are required to notify before building new ones.
The conservancy said more than 96,000 planned turbines nationwide were listed in the FAA database, even after eliminating those it considered likely to be canceled because the agency designated them as posing a high-risk to air traffic. But the American Wind Energy Association, which represents the industry, said even that adjusted total is overstated.
A spokesman for the wind association, Tom Vinson, said the FAA figures aren't meaningful because many will be scrapped because of wildlife concerns, inability to find a purchaser for the power or secure land agreements, high transmission costs or other reasons. 'It won't be anywhere near 96,000, and certainly not over the next several years,' Vinson said.
Spokesman Paul Takemoto said the FAA doesn't track which projects on its list eventually are completed, although developers are required to remove ones from the list that are abandoned.
The record year for new wind energy was 2012, when about 6,750 turbines were installed, Vinson said, so companies would have to continue putting up turbines at that rate for more than 14 years to match the number in the FAA database - a highly optimistic scenario for an industry dependent on federal tax credits with shaky prospects in Congress.
The wind industry also said some of the high-risk areas are too broadly defined, and said some migrating birds fly high enough not to be endangered by turbines. The flyway of the endangered whooping crane is a swath of the nation's midsection up to 200 miles wide extending from the Texas Gulf coast to the North Dakota-Canada border.
Mike Parr, the conservancy's chief conservation officer, said birds fly at different altitudes depending on circumstances such as weather, often dipping low enough to encounter turbines.
Location is important - but how much is an unsettled question, said Andrew Farnsworth, a bird migration expert with the Cornell University ornithology laboratory. There is little peer-reviewed scientific research about the relative risk posed by the density of turbines in an area, their siting and height, nocturnal lighting and the habitat needs of particular bird species, he said.
What's certain is that lots of birds have fatal encounters with turbines, Farnsworth said. Studies have produced varying numbers, he said, but the most recent and comprehensive analysis estimated the annual death toll between 140,000 and 328,000. The wind energy association says that's a small number compared to the millions that collide with buildings and telecommunications towers or are killed by cats. Parr said the conservancy is concerned about all those threats but is focusing on wind power because it's a 'large-scale, newly developing threat to birds,' especially during migration.
More than 6,000 existing turbines and more than 20,000 planned ones are in areas with federal designations such as national wildlife refuges, critical habitat for endangered and threatened species and core areas for the greater sage grouse, the analysis says. Of those, about 90 percent are within the whooping crane corridor.
The Fish and Wildlife Service's voluntary guidelines, issued in 2012, urge companies to consider risk to birds and other species when choosing turbine locations and say some areas 'may be inappropriate for development because they have been recognized as having high wildlife value based on their ecological rarity and intactness.'
The government said it can regulate wind development only on lands it administers, such as national wildlife refuges. Elsewhere, it can threaten legal action against companies whose turbines kill species protected under federal law, such as bald and golden eagles. The government has charged and reached settlements with only two wind energy companies for such kills. Spokesman Gavin Shire said the Fish and Wildlife Service is investigating 16 other cases of bird deaths at wind facilities, five of which have been referred to the Department of Justice for possible prosecution.