MORGANTOWN, W.Va.–In Mother Nature’s world, everything is related to everything else – some call it the butterfly effect.
So when researchers at West Virginia University were trying to figure out why so many golden eagles were being killed by wind turbines – and how to prevent it – they decided they needed to know how the birds figured out where to fly.
And that led them to try to understand whether birds opted to fly fast, and get to their feeding grounds early, but tired, or fly more slowly, and arrive well-rested. Why would that help with a solution to placement of wind turbines? If the answer was “fast, but tired,” then the birds would be choosing to fly in the same areas that were also the best places for wind turbines – locations with high winds.
The answer? Fast, but tired.
The early bird
“Our research shows that it is better to arrive on your breeding grounds early – and presumably tired – than late and well-rested,” said Adam Duerr, a research biologist with the WVU Research Corp. “If an eagle is early, it can reclaim its breeding territory from the previous year or lay claim to another territory. Such early arrival will help to ensure successful breeding. Late arrivals to breeding grounds run the risk of not acquiring a territory, not finding a high-quality and experienced mate, or not finding a mate at all.”
The impetus for the research is to understand risks that wind energy development poses to golden eagles. Placement of wind turbines is dependent upon adequate winds in terms of both speed and consistency.
“In the western United States., there are wind developments that kill multiple golden eagles each year, Altamont Pass of California being the most extreme with nearly 70 eagles killed per year,” Duerr explained. “In the eastern United States, wind development is accelerating with little understanding of the potential interaction between turbines and eagles.”
Additionally, the population of eastern golden eagles is small, about 2,000-5,000, and therefore vulnerable.
“The goals of our research are to fill these knowledge gaps and determine risk of colliding with turbines that eagles face during migration based on their flight choices,” Duerr added.
Birds of a feather
“To understand risk, it is critical to understand how birds fly,” said Todd Katzner, research assistant professor of wildlife and fisheries resources in WVU’s Davis College of Agriculture, Natural Resources and Design. “This research is our first step in the process of characterizing flight behavior so that we can understand how birds fly and then evaluate risk to birds from development of wind energy.”
Katzner, Duerr, and colleagues in the Mid-Atlantic United States and Canada used global positioning system-global system for mobile communications telemetry units that his company, Cellular Tracking Technologies, LLC created to study the eagles’ flight choices.
“Such a study as ours would not have been possible with other technology,” Duerr said. “The high-frequency data, one location every 30 seconds, allows us to distinguish the different flight types and compare speed of flight. Other competing technology does not provide great enough temporal resolution – the eagle locations are spaced too far apart in time with locations once every hour.”
The team placed GPS-GSM transmitters on many eagles to record the specific locations and altitudes of flight. For a subset of these eagles, WVU wildlife biologist Trish Miller categorized flight types, and the team then analyzed flight speed by flight type.
“Understanding flight speed helps us to understand the trade-offs between early arrival and energy demands on breeding grounds,” Duerr explained. “With better understanding of such trade-offs, we have a much better understanding of the age classes of eagles that are potentially at risk.”
Flight speed, amount of time spent using different flight types, and altitude of flight also play important roles in determining the amount of time that eagles may spend at the same altitudes above ground level as spinning turbine blades.
The research was funded by the U.S. Department of Energy. Partners in the research came from Penn State, Lafayette College in Easton, Pa., the Virginia Department of Game and Inland Fisheries, the West Virginia Division of Natural Resources, the Ministries des Resources naturelles et de la Faunes of Quebec, Canada, and the USDA Forest Service.
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