People often confuse the identities of the golden eagle and the immature bald eagle, but sharp-eyed observers can learn to tell the two apart. Top row: Undersides of an immature bald eagle's wings have mottled white patterns that extend to the "wing pits." The immature golden has distinct white patches in mid-wing, and the adult has dark wing undersides. Middle row: The bald eagle has a large head and beak. Its head and tail extend similar distances from the body. The golden's head and beak are notably smaller than the bald's. The golden's head protrudes only about one-third as much from the body as the tail does. Its tail has a dark terminal band. Bottom row: Up close, the mottled white-and-brown wing underside of the immature bald looks markedly different from the dark brown and gray wing of the adult golden.

A couple of hours into our designated 90-mile route southeast of Red Wing, we've spotted a flock of wild turkeys, one bald eagle, and four red-tailed hawks. But we're in search of golden eagles, and our tally so far this day is a big old goose egg.

"You have to be kind of lucky," says Mark Martell, director of bird conservation for Audubon Minnesota, acknowledging the challenge of our task. The other surveyors, Tim Schlagenhaft, an Audubon community conservation coordinator, and Suzanne Blue, who has started a Red Wing chapter of Audubon, are intimately familiar with the region's rugged landscape. They know that among the limestone bluffs, farmland, and forestland, wintering golden eagles have found ample roosts in the hardwood trees and abundant prey, such as fox squirrels and wild turkeys.

If we do turn up a golden eagle (Aquila chrysaetos), we know it will be one of the more than 100 golden eagles that winter in the bluff country of southeastern Minnesota, western Wisconsin, northern Illinois, and northeastern Iowa—50 to 60 of them in Minnesota. After nine years of surveys along more than 50 routes, researchers with the Golden Eagle Project have concluded that this region has a resident population of golden eagles from November through March. With the addition of tracking technology in the past five years, they have also learned where these birds breed and nest in Canada. Because these birds are endangered in parts of Canada, the research findings could provide critical information to help protect them.

Observation Routes.

We are among 160 volunteers who are counting the birds today for the survey, which is conducted each year on the third Saturday in January. Each team of surveyors, typically several people per vehicle, spends at least three hours driving slowly through a designated area between midmorning and midafternoon, when the eagles are most active. They choose when to stop for a closer look, paying special attention to likely golden eagle habitat such as native blufftop goat prairies and to places where eagles have previously been spotted. Each team's leader has attended an information session on survey protocols and the finer points of golden eagle identification.

One of the largest birds of prey, coffee-brown with a handsome orange-yellow nape that inspires its name, the golden eagle would seem to be easy to spot. It can stand nearly 3 feet tall with a wingspan of 7 feet.

But out on the road, it's becoming clear to me why these magnificent birds have flown under our radar: The wintering golden is a master of camouflage. Sitting in the middle of a roosting tree, it can appear as nothing more than a brownish lump, easily mistaken for a squirrel's nest or a tree burl. Soaring in the sky, it can be nearly indistinguishable from other raptors. Even on closer viewing, a golden eagle might be mistaken for an immature bald eagle with similar mottled-brown markings.

Finally, a couple of hours and dozens of non-eagles later, our persistence is rewarded: Martell spots a golden eagle on the wing. He notes several subtle distinguishing features, including a relatively small head and a dark terminal band on its tail, as it soars among two bald eagles and three redtails. It turns out to be our only golden eagle of the day, which is right in line with expectations: In nine years of surveys, the daily count on this route has ranged from zero to two.

The overall 2013 survey results are impressive: Observers in four states covered 51 similar-sized routes and found 132 golden eagles, the most ever tallied for the survey. The ever-rising count doesn't necessarily mean the population is increasing: It might reflect that surveyors are more numerous and experienced than they were in the early days of the survey, which began in 2005. It will take more time, perhaps another 10 years according to researchers, to establish a baseline from which to draw conclusions.

Bluffland Mystery.

The survey is a key component of the Golden Eagle Project, a collaboration of Audubon Minnesota, the National Eagle Center in Wabasha, and the Minnesota Department of Natural Resources' Nongame Wildlife Program. In addition to the annual count, the research includes radio telemetry—think high-tech mini-backpacks—to track the eagles' movements.

The Golden Eagle Project, which is also supported by the Wisconsin DNR and the U.S. Fish and Wildlife Service, never would have gotten off the ground if not for one particularly observant birder. More than 20 years ago, Scott Mehus began making annual pilgrimages from his home in the Mississippi River valley to Duluth's Hawk Ridge to watch thousands of raptors on their fall migration. If you sought to add the golden eagle to your list, he says, "you went to Hawk Ridge or you went to Whitewater State Park and the Whitewater Wildlife Management Area."

Between 100 and 200 golden eagles pass by Hawk Ridge annually on their way south, but until recently no one knew where they wintered. A few were spotted at Whitewater each winter. Though considered an isolated mini-population, the Whitewater eagles stoked Mehus's curiosity.

"I thought, 'There's habitat up and down this river valley that looks just like this. Why aren't there golden eagles there?'" he says. "So I started looking, and sure enough, I was finding them."

Mehus's discovery was so out of step with conventional birding wisdom that he at times doubted his own figures, thinking he was perhaps double-counting some eagles. So he decided to enlist the eyes of other birders.

"I thought, if I can get people out on the same day, looking for golden eagles, and just get an idea of the numbers, that would be great," he says. The survey began in 2005 as a lark and a labor of love, with 24 volunteers and Mehus as its sole sponsor.

Word of Mehus's survey spread, eventually catching the ear of Mark Martell at Audubon Minnesota and Carrol Henderson at the DNR. Martell and Henderson, along with the late ornithologist Harrison "Bud" Tordoff and the DNR's Rich Baker and Lori Naumann, set out one day in January 2008 to visit Mehus, see some golden eagles, and discuss collaborating on research. By the end of the outing, over lunch in Wabasha, the group hatched the plan to create the Golden Eagle Project.

Mehus would bring his deep local knowledge of golden eagle wintering locations and his background in organizing the survey. Martell would contribute his raptor savvy and expertise in satellite telemetry. And the DNR would provide funding through the Nongame Wildlife Checkoff on state income-tax forms to help pay for the technology.

Eagles on the Air.

Since the first bird was tagged in 2009, two or three golden eagles have typically been "on the air" for the Golden Eagle Project at any one time, relaying location, altitude, and flight-speed data from their travels via those little satellite-transmitter backpacks. Five eagles have flown for the project; two of them have either died or dropped their transmitters.

The research team has succeeded in capturing two golden eagles in bluff country, and it got another golden that was netted at Hawk Ridge. The project's other two eagles came from the Raptor Center at the University of Minnesota, where they had been treated for injuries.

The first tagged eagle, number 42, surprised researchers by showing that Minnesota's golden eagles belong to a breeding population in eastern Canada. For years Henderson and other observers had spotted small numbers of golden eagles in far western and northwestern Minnesota. Most experts considered these birds to be odd strays from the western United States, where golden eagles live year-round. But golden eagle 42 headed not west but far north to Nunavut for the summer. It returned to the Mississippi River valley the next winter, then went north again in the spring that followed—this time bearing farther east to northern Quebec near Hudson Bay. When fall came, the eagle migrated to upstate New York and Pennsylvania for the winter.

"That really surprised a lot of folks," says Mehus, who is now education director of the National Eagle Center. "A lot of people thought these were mountain birds, desert birds, that had gotten off course and ended up here for the winter, and just went back out west again. A good chunk of people expected the bird to just go back west. And he didn't. So it was fun to watch that."

Subsequent birds have yielded other valuable information. Golden eagle 45 summered in the Northwest Territories, while eagle 46 summered near the Labrador Sea. Number 46 has returned to the same wintering territory two years in a row—a part of Whitewater WMA designated an Audubon Important Bird Area—showing that the birds will stick to a territory in the winter months, not just during breeding season.

"This is like a wonderful, long-evolving detective story," says Henderson, "first about what we thought were rumors, and then validating that, yes, these are golden eagles. And now we've got the technology where there's no place they can hide once we get those satellite transmitters on them."

Cooperative Protection.

Golden eagles that winter in the Midwest are listed as threatened or vulnerable in several Canadian provinces where they nest. The Golden Eagle Project shares data and findings with Canadian wildlife managers to help them protect the eagles on their breeding and nesting grounds.

The United States, through the Migratory Bird Treaty Act, has affirmed an international responsibility for studying and protecting migratory birds, including birds of prey. Moreover, says Martell, doing what's best for the wintering golden eagles is only fair and right. After all, he says, U.S. conservationists often push our partners in Latin America to ensure good wintering habitat for birds that breed in Minnesota.

"And in this rare case," he says, "the tables are flipped on us: These birds are breeding up in Canada, but they're wintering here. So the same obligation we want to put on Costa Rica or Panama, we need to assume for ourselves."

The DNR aims to do its part by continuing to fund research and using findings from the Golden Eagle Project to help develop habitat management guidelines, Henderson says. Mehus expects the project will continue for many years, and intends to head up the survey as long as he's able. In the meantime, the eagles fly on.

"These Midwestern golden eagles," says Henderson, "are like a whole new chapter in the eagle book."