a. But not every environmentalist is happy about that development. Critics charge that wind-energy development can cause habitat fragmentation-a displacement of a species that can eventually reduce its numbers-as well as the deaths of birds and bats (a species that is especially vulnerable due to its low reproductive rates) that collide with the wind turbines’ massive blades. A 2007 study by the National Academy of Sciences puts the number of birds killed each year at about 20,000 to 30,000. That’s a low estimate, says Michael Fry of the American Bird Conservancy. According to his group, turbines kill three to 11 birds per megawatt of wind energy they produce. According to critics, wind-energy development may cause the deaths of 20,000 to 30,000 birds. distinction of many species in the area. habitat fragmentation and deaths of birds. environment recovery from destruction.