Golden eagles have ridden the winds that whip across Pennsylvania’s Appalachian ridgetops for centuries, soaring northward to breeding grounds each spring and southward to hunting grounds each fall.
Up until now, the eagles have encountered relatively few obstructions during their migrations across the state. But with energy companies scrambling to erect 400-foot windmills that convert those ridgetop winds into electricity, conservationists fear hundreds of eagles could be killed by a technology widely regarded as environmentally friendly.
‘Pennsylvania’s ridge and valley province plays an important role in the development of wind power and as a migratory corridor for eastern golden eagles,” said Dan Brauning, supervisor of the Pennsylvania Game Commission’s wildlife diversity section. ”That could mean the future of this small population of eagles hinges on our ability to make responsible and informed decisions concerning the development of wind farms.”
Wind power is the world’s fastest-growing source of electricity. And with 153 megawatts of wind generation already in place – enough to power about 70,000 homes – Pennsylvania is the top wind power state east of the Mississippi. By 2020, state projections say Pennsylvania could be home to 3,000 megawatts of wind generation, which would require about 2,000 windmills statewide.
The expected onslaught of wind farm development has state wildlife and environmental officials scrambling to develop regulations that ensure damage to birds and other wildlife is kept to a minimum. Currently, wind power developers are not required to conduct any wildlife-related studies, leaving regulation of the fast-growing industry largely to local zoning officials.
”There have been no scientific studies of the impacts of turbines on migrating raptors in the Appalachians,” said David Brandes, acting head of civil and environmental engineering at Lafayette College. ”The wind power industry is understandably reluctant to fund such studies, which are not cheap.”
As part of its ongoing effort to assess the risks wind power poses to wildlife, the Game Commission, Lafayette and several other partners are conducting a multi-year, $225,000 research project that will track the migratory habits of golden eagles and use that data to develop a computer model capable of gauging the relative risks of proposed wind farm sites.
”The Game Commission does not oppose harnessing wind power as an alternative energy source. It offers substantial environmental benefits over burning fossil fuels,” said Bill Capouillez, director of the commission’s Bureau of Wildlife Habitat Management.
”Nonetheless, the agency must ascertain what risks”¦to wildlife instate wind turbines pose. Turbine locations should ultimately be the product of a thorough wildlife impact analysis, of which migrations of golden eagles is only one part that needs to be taken into consideration.”
Other organizations involved in the project include: the National Aviary and Carnegie Museum of Natural History, both of Pittsburgh; Penn State University; and Hawk Mountain Sanctuary in Berks County, which is providing raptor observation data and other support through the sanctuary’s Acopian Center for Conservation Learning. In addition, ornithologist Keith Bildstein, Hawk Mountain’s director of conservation science, is serving as a project consultant who will help evaluate field data and incorporate it into the computer model.
Why golden eagles?
Golden eagles are found in mountainous areas throughout the world and are commonly seen in Pennsylvania during spring and fall migrations. About the same size as the bald eagle, golden eagles can weigh up to 14 pounds and have a wingspan that can exceed seven feet. Their plumage is predominantly dark brown, with the exception of their trademark golden feathers on the head and neck. They prey mainly on medium-sized mammals.
No one knows for sure, but scientists believe fewer than 1,000 golden eagles exist in the Eastern United States, said Todd Katzner, the National Aviary’s director of conservation and field research. Virtually all of those birds are believed to migrate across Pennsylvania, Katzner said, which is one reason the commission categorized the species as ”vulnerable” in its state Wildlife Action Plan approved by the U.S. Fish and Wildlife Service last year.
Katzner and Brandes said an analysis of field observations indicate the majority of golden eagles migrate through a 30-60-mile-wide corridor between the Allegheny Front and the Kittatinny Ridge, also known as the Blue Mountain. For example, Hawk Mountain Sanctuary in Berks County counted 171 migrating golden eagles during its 2006 Autumn Hawkwatch, while observers at Bake Oven Knob tallied 130.
According to the U.S. Fish and Wildlife Service, the ridges in that corridor are also the ones with the highest potential for wind-power development – creating the potential for eagles to come into contact with spinning windmill blades that can rotate at speeds of several hundred miles per hour.
”Their biannual passage through this”¦corridor provides Pennsylvania a chance to play a leading role ensuring the future eastern golden eagles,” Katzner said. ”We must determine if threats to their preferred habitat in this corridor will impact the population’s stability in any way.”
One local raptor expert, however, believes that the area used by migrating golden eagles is much larger than Katzner says.
”We have data demonstrating that”¦in the autumn at least, we have a broad front migration,” said Donald S. Heintzelman, an Upper Milford ornithologist who founded the annual Bake Oven Knob autumn hawkwatch in 1961. ”It’s a series of zig-zagging down [from ridge to ridge] as they progress southward, and as a result, golden eagles can and do appear on all of these ridges.”
Although Heintzelman acknowledges there isn’t a lot of existing raptor observation data available for many ridges – particularly those in the state’s northern tier – he is concerned the research project could downplay the potential danger posed to eagles by wind farm development anywhere in the Appalachian range.
”My main criticism,” Heintzelman said, ”is this statement that they are going to draw migration maps of eagles as if they are carved in stone, and that’s the only place they are going to occur – not only because the sample is appallingly inadequate, but also because it’s only going to go over a period of a few years.”
But Katzner said the main purpose of the research project is to learn more about how and why golden eagles use Appalachian ridges. He said migration maps created during the project will include not just data from tagged research birds but also historical observations from established hawkwatches conducted at places such as Hawk Mountain and Bake Oven Knob.
Brandes, the Lafayette professor, added that he authored a research paper 10 years ago that shows golden eagles do pass through a bottleneck during the Pennsylvania portion of their migration.
”We feel pretty strongly it’s not a broad migration across the state,” Brandes said. ”Particularly in spring, it’s absolutely true these birds are moving through Pennsylvania in a narrow corridor.”
Brandes also said golden eagles are a good species to study because their migration – which peaks in November – is highly dependent upon wind-driven updrafts created by the Appalachian ridges. Species that migrate earlier in the fall, such as broadwing hawks, rely mainly on thermal currents created by the sun.
Raptor species that migrate on thermal currents typically soar at higher altitudes than those that ride updrafts created by ridges. Because of that, the danger poses by windmills is not as great. Brandes also noted that broadwing hawks are among the most numerous of all raptors, which makes it unlikely they would be decimated by a proliferation of wind farms.
”If we lose a few broadwing hawks, that’s not a good thing,” Brandes said. ”But it’s not going to have as big an impact as if we lose a few golden eagles. That’s much more significant to the population size.”
Gathering data on the fly
Field work on the eagle study began in November, when Katzner and other researchers captured two golden eagles near Central City, Somerset County, and fitted them with 70-gram GPS transmitters, which send information about the birds’ location 10-15 times per day.
One of the birds has been wintering in West Virginia, while the other has spent most of its time in Kentucky. The eagles’ movements can be monitored through the National Aviary’s Web site at http://www.aviary.org/csrv/eaglePA.php .
Trapping efforts will resume this spring, and funding is already in place for four more GPS transmitters. Eventually, Katzner hopes to track 10-20 eagles, which will be monitored for the life of their transmitter – a period of about three years.
Unlike field observations gathered in annual raptor counts, which merely document the presence of a bird, data from GPS transmitters tell researchers the bird’s exact location, altitude and flight speed. That data can then be combined with topographical information and weather data such as temperature and wind speed to help scientists better understand exactly how the eagles make use of Appalachian ridges to aid in migration.
”We’re trying to get a better handle on how flight elevations and routes used by migrating eagles are influenced by topography and meteorology,” Katzner said. ”The information is crucial to understanding the correlation of eagle movements, landscape features and weather, and should help us determine if differently constructed wind turbines expose eagles to greater risk or provide increased protection.”
Analyzing that data and incorporating it into a computer model that can be used as a screening tool for proposed wind farm locations will be the responsibility of Brandes, an avid birder who helped found the annual Tussey Mountain Spring Hawkwatch near State College while earning his doctorate in civil engineering at Penn State. Tussey Mountain is a prime viewing point for the spring eagle migration.
”If we get these [satellite] trackers on 10 or a dozen birds, it’s going to be a wealth of information,” said Brandes, who is taking a year-long sabbatical to work on the project.
Brandes plans to have an initial version of his computer model ready for use by the Game Commission, state Department of Conservation and Natural Resources and others by summer 2008. However, he said he will continue to refine the software as additional GPS data is gathered.
”Like any model, it can’t do everything,” Brandes said. ”It’s really how those birds are using the topography that we’re interested in.”
By Christian Berg Of The Morning Call
13 February 2007
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