New research proves wind turbines aren't just a risk to local birds. Birds from as far as 100 miles away are getting caught in their blades.

Large birds like golden eagles are especially prone to collisions with wind turbines. Recently, scientists with Purdue University and the U.S. Geological Survey monitored the effects of turbines at Altamont Pass Wind Resource Area in northern California on nearby golden eagle populations.

With 5,000 turbines, APWRA is one of the largest wind farms in the world. It's also one of the oldest. The reason the turbines were placed along Altamont Pass is the same reason why eagles congregate there.

"Eagles tend to use that habitat around the turbines. It's windy there, so they can save energy and soar, and their preferred prey, California ground squirrels, is abundant there," J. Andrew DeWoody, a Purdue professor of genetics, explained in a news release. "As they soar, these eagles are often looking straight down, and they fail to see the rapidly moving turbine blades. They get hit by the blades, and carcasses are found on the ground under the turbines."

DeWoody and his fellow researchers collected and analyzed bird remains found beneath the turbines. DNA and isotopic analysis suggest roughly 75 percent of the deceased belonged to local golden eagle populations. But the remaining 25 percent had only recently migrated to the area, some from as far as 100 miles away.

"When a bird drinks water or eats animals in a particular place, the hydrogen isotope ratios of precipitation in that area get recorded in its tissues," said David Nelson, a stable isotope ecologist with the University of Maryland Center for Environmental Science. "You can use these hydrogen ratios in the feathers to determine the approximate place that the bird grew its feathers."

Using the isotopic data and DNA analysis, researchers built a migration model to reveal the wider effects of a wind farm on regional bird populations.

The findings -- detailed in the journal Conservation Biology -- suggest the environmental risks of turbines extend beyond local bird populations. The study might affect how environmental assessments of alternative energy projects are conducted.

"If you only consider local birds in an environmental assessment, you're not really evaluating the effect that facility may have on the entire population," said Todd Katzner, USGS wildlife biologist.

"The golden eagle fatalities at this one site have demonstrated consequences that extend across much of the range of the species across North America," DeWoody concluded.