[Editor’s note: Nearly three years after settling a $1 million avian mortality suit with the U.S. Department of Justice for violating the Migratory Bird Treaty Act, Duke Energy Renewables continues to research and refine its avian mitigation techniques. Here’s the story.]


On a blustery day in early October of last year, a technician at the Top of the World Windpower Project, just outside Casper, Wyo., spotted a golden eagle on the ground near turbine 70. It appeared to be sick or injured. He and several other Duke Energy employees rounded up the bird, made the appropriate calls to the U.S. Fish and Wildlife Service (FWS), and then quickly transported the eagle to a bird rescue center in Cody, Wyo.

Clinicians at the Ironside Bird Rescue could find no signs of injury consistent with any kind of blade collision. They thought the bird may have had West Nile Virus or have gotten into some kind of poison. The eagle was too small for its six-month age. It weighed only five pounds, which indicated it had likely been sick for a while. The eagle, subsequently named Devon, survived the stress of capture, transport and early treatment, and the rehab center began hydrating and feeding him. Hopes were high that Devon would make it, and Duke Energy Renewables’ employees closely followed his progress.

The ending was not as happy as expected. Little Devon had a bacterial infection that ultimately robbed him of his sight and his quality of life, so the caregivers at the center made the difficult decision to humanely euthanize him.

“Despite the bird being too ill to save, it makes me proud that our folks in the field truly care about wildlife conservation and are willing to go above and beyond to save a sick eagle,” says Tim Hayes, Duke Energy biologist.

Undeterred, the next week, Duke Energy Renewables’ employees at Top of the World discovered a ferruginous hawk that had been hit by a car and sent it to the rescue center.


Wildlife and renewables

Duke Energy Renewables has taken a leading role in leveraging its resources and experience to address wind’s impacts to wildlife creatures and their habitats. Nowhere is this more evident than at its Wyoming Top of the World Windpower Project. At that site, the company has experienced several golden eagle fatalities.

“Wind energy is clean, with no emissions, and it doesn’t use any water,” says Hayes. “However, there is no free lunch, and every form of generation has an impact on the environment. Wind energy projects can, and sometimes do, have impacts to wildlife and their habitat. We’ve got to figure out how to deal with the issues we have.”

When Duke Energy entered the commercial renewable energy business in 2007, the company brought with it more than 100 years of experience generating and delivering electricity to its customers. Over this span of time, Duke Energy has addressed a wide variety of environmental issues and challenges. These challenges have included air emissions from steam electric plants, fish impacts from a large hydroelectric fleet, water quality from power plant cooling water discharges, and managing various waste products from scrubbers and other pollution-control technologies, to name a few. Duke Energy Renewables has experimented with and implemented a variety of measures to reduce its wind farms’ impacts to eagles.


“Specifically, we promptly remove wildlife and livestock carrion from the site so eagles won’t be attracted by food; we tested radar technology to assist in the detection of eagles on the site – the same technology used by our military to detect incoming mortars and missiles; and we’ve tested both visual and sound deterrent devices to deter eagles away from wind turbines.” These technologies and practices have shown mixed results.

Today, Duke Energy Renewables is implementing one of the most robust informed curtailment programs in the world. The business constructed an eagle observation control tower at Top of the World with full capabilities to observe eagles and immediately curtail the site’s wind turbines when the birds are flying in the vicinity.

“We have hired an on-site wildlife supervisor and six wildlife specialists, who are on the site during daylight hours 365 days a year. These observers scan the sky from the tower and from other points on the site and immediately curtail individual turbines or groups of turbines when eagles are spotted and are at risk of collision. This program is showing favorable results.”


Working together matters

The business is also gaining valuable insight into the seasonal movements and migration habits of golden eagles. It is working closely with the FWS on an eagle trapping and tracking project. Technicians at Top of the World and the FWS trap golden eagles on the wind site, fit them with GPS transmitter backpacks and release them back into the wild. This transmitter enables the FWS to track the eagles’ migration movements.


“A female eagle was trapped on the site in the winter of 2014, and what we have seen to date is simply amazing,” explains Hayes. “In early spring, this eagle migrated north from Wyoming, up the Rocky Mountain front range to Alaska’s northern coast, where she spent the summer. Then, later that fall, she migrated right back to the area to spend the winter. It’s remarkable that this eagle travels about 2,500 miles in just a few days.”

Another eagle was trapped and fitted with a GPS unit until recently. This study is providing valuable knowledge about eagle movements, migration and how the birds use the landscape.

Currently, Duke Energy Renewables is working closely with Renewable Energy Systems Americas, along with its technology collaborator Boulder Imaging, to bring IdentiFlight to market. This is a technology developed on a camera system that uses machine vision to detect eagles. One prototype camera system has been fully tested at Top of the World, and four additional commercial-ready units were installed in early March.

“This technology is showing very promising results,” Hayes says, “and we hope it will prove to effectively detect eagles and automatically curtail turbines when eagles meet certain pre-defined risk criteria.”

The American Wind Wildlife Institute (AWWI) will coordinate an independent and transparent assessment of the camera detection technology, which will benefit the entire industry. Duke Energy is an active member in AWWI and is engaged in all of its research initiatives.


Bats, too

Duke Energy Renewables is also active on the bat conservation front, notes Hayes. “We were an active participant on the American Wind Energy Association committee appointed to reduce bat collision fatalities.”

This committee worked to develop an operational best management practice to reduce wind energy’s impacts to bats. Under this new operating practice, known as feathering, the turbine control software is changed so that the pitch of the blades is feathered to slow down the turbine rotor rotation speed to one or two revolutions per minute during low-wind conditions in late summer and early fall.

Research has shown bats are most at risk of collision during these times. Slowing down rotor speeds during low-wind conditions reduces the risk of injury and death. The new protocols are based on more than 10 years of research by the Bats and Wind Energy Cooperative, of which Duke Energy is also a member. The group proposed new voluntary operating procedures that went into effect in fall 2015 and are expected to reduce bat deaths by as much as 40%.

“Duke Energy is engaged with a variety of groups and stakeholders to address wildlife concerns, and we recognize that no one can do it alone,” says Hayes. “It’s vital that the industry works together in a transparent and collaborative manner. If the true environmental impacts aren’t clearly identified and addressed in a rapid manner, using the best science and technology available, it will be difficult to reach wind’s full potential.”


Tammie McGee is a spokesperson at Duke Energy Renewables. She can be reached at tammie.mcgee@duke-energy.com.

Environmental Compliance

Duke’s Avian Mitigation Techniques Take Flight: What’s Working And Why

By Tammie McGee

The developer has implemented one of the most robust informed curtailment programs in the world.






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