February 20, 2014
Golden eagles winter range larger than thought, WVU-led study finds
By Rick Steelhammer
A study led by a WVU professor on the over-wintering habits of eastern golden eagles shows that the solitude-loving raptors spend the cold months over a much wider range than previously thought, stretching as far south as Alabama and as far west as Indiana and Michigan.
The study uses both tracking data supplied by golden eagles outfitted with miniature GPS units and cell phones, and motion-activated cameras at 250 sites baited with road-kill deer. The tracking component of the study began eight years ago, while the camera-equipped bait sites began capturing images of golden eagles and other wildlife species three years ago.
All eastern golden eagles are believed to nest in Canada starting in late winter or early spring, and remain north of the border until fall. But until now, little has been known about how and where the birds of prey spend their winters.
In West Virginia, the relatively few golden eagles spotted in winter were initially believed to be migrants passing through the state, possibly to more temperate climes. That theory was quickly dispelled during the first year the study made use of camera-equipped bait sites.
Golden eagles were photographed in such abundance in the eastern highlands of West Virginia and the bordering counties of Virginia that it soon became evident the area was the birds’ primary over-wintering zone.
“That’s still the area where the densest populations of eastern golden eagles are found in winter,” said Todd Katzner, a research assistant professor at WVU and the coordinator of the study through Appalachian Eagles and the Eastern Golden Eagle Working Group..
But as the number of bait sites grew and expanded over the following years, “We started to see that the winter distribution is a lot bigger than we had thought,” Katzner said. “It’s amazing! They’re on the bait from Maine to Alabama and most of the states in between. They’re in Michigan, Indiana, Ohio and Tennessee. They’re everywhere!”
With wingspans that can exceed seven feet, golden eagles are North America’s largest bird of prey, yet not much is known about the species’ range and population in the east. The eastern population of golden eagles is thought to be about one-tenth that of golden eagles found the western U.S. and Canada, where 20,000 to 30,000 members of the species make their home.
“There are some birding records in the east where golden eagle sightings have been recorded, but this is the first systematic look at their distribution and population,” Katzner said. “They’re showing up in greater numbers, and over a much larger range than expected.”
The reason the mountains of West Virginia and Virginia seem to be a winter mecca for the birds is probably due to the area’s large population of whitetail deer, which has been in a growth pattern for the past 40 years, creating an abundance of road-killed and winter-killed deer. Deer that are no longer moving are much easier for the carrion-eating golden eagles to dine on.
This winter, 30 bait sites were established in West Virginia, from Morgan County in the Eastern Panhandle to Wayne County on the Kentucky border.
“Golden eagles were seen at a majority of our sites,” said Kieran O’Malley, a state Division of Natural Resources biologist stationed in Romney who is a participant in the study.
“I had one in my back yard,” said Katzner, who lives in a rural section of Marion County. “We photographed a golden eagle there this year.”
“We’re looking at wintering populations and population density,” O’Malley said. “We have really good numbers of golden eagles wintering in West Virginia. The highest density anywhere is in the highlands of West Virginia and western Virginia, since they prefer forested uplands away from a lot of human activity.
Golden eagles tend to live solitary lives, with pairs maintaining hunting territories that can be as large as 60 square miles. Golden eagle mates stay together for several years, and in some cases, for life.
“Unlike bald eagles, goldens don’t get together in big groups,” O’Malley said. “They prefer to live in areas that are more remote than the places bald eagles live.”
Katzner said preliminary results of genetic studies comparing DNA from eastern golden eagles to those in the west indicate there are few differences between the two populations.
“Other than the fact that one group lives in the east and the other lives in the west, there doesn’t seem to be much difference between them,” he said.
Because golden eagles spend the first four or five years of their lives “in a pre-breeding phase, traveling around and trying to figure out where to stay,” there’s likely to be some crossover breeding between the two populations, Katzner said.
Current estimates of the eastern golden eagle population range between 2,000 and 5,000 individuals.
“We’ll be doing some computer modeling, but right now, I’m starting to think the population is on the high side of those estimates,” Katzner said.
One side benefit of operating the remote camera sites is being able to get an idea about how other wildlife species fare during the winter.
Last winter, cameras at bait sites in West Virginia photographed 17 bird species and 15 mammal species, according to O’Malley.
Bird species photographed dining on the deer carcasses included owls, crows, ravens, blue jays and titmice, while mammals included coyotes, foxes, bobcats, fishers, skunks, raccoons and wood rats.
O’Malley is involved with a spin-off study that evolved from the remote photos. “We started seeing spotted skunks, which have become very uncommon in the state, turning up in the photographs,” he said. By taking note of the camera site locations that recorded spotted the seldom-seen skunks, “We’ve been able to add to their range,” O’Malley said. “They’re a lot more widespread than we thought, but still not very abundant.”