Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Researcher Sean Strom looks up 70 feet monitoring climber Matt Stuber's progress as Stuber makes his way to a bald eagle's nest. © Dougal Walker

Researcher Sean Strom looks up 70 feet monitoring climber Matt Stuber's progress as Stuber makes his way to a bald eagle's nest.
© Dougal Walker

February 2014

A bird's eye view

What eagle research tells us about waterway cleanup and the comeback of an American icon.

Eric Verbeten

From the height of 70 feet, climber Matt Stuber checks his footing before continuing his ascent up a cottonwood tree. He pauses beneath a large bird nest and searches for a way around the obstacle. With 20 mph gusts causing the tree to sway, he continues his mission to climb above the nest and bag the bird inside. But not just any bird; the goal of this climb is to bag a bald eagle.

Stuber works for the U.S. Fish and Wildlife Service in the East Lansing (Michigan) Field Office and is part of a DNR research team studying eagle health and the health of the nearby waterways. Since 1990, the Department of Natural Resources has led a partnership with the U.S. Fish and Wildlife Service and National Park Service in Wisconsin to study eagles. Stuber has been professionally climbing trees for research for four years, peeking into more than 120 nests in his career, many of them in Wisconsin as part of this partnership.

"The U.S. Fish and Wildlife Service shares the same goals as the state of Wisconsin," Stuber says. "To maintain and protect a healthy population of bald eagles in the Midwest and to use what we know about bald eagles, through 40–plus years of incredible research, to tell us important things about contaminants in our environment today."

Stuber's role as the climber is to ascend these tall trees and safely retrieve the young eagles from their nests.

"Each climb presents its own challenges," Stuber explains, "but each time it's a rush because you get to see the world from the perspective of an eagle!"

The rest of the crew remains on the ground, craning their necks to watch his progress up the tree.

Once Stuber is able to peek over the top of the nest, he spots the young, brown–colored bald eagles anxiously squawking at him. The mother soars overhead in a holding pattern, but never intervenes.

Stuber secures himself to the tree using a rope around his waist and spikes on his boots in a counter–balanced configuration, allowing him to lean back with both hands free to do the delicate work with the birds. He extends a rod, known as the "chicken hook," to secure the eaglet's leg; this ensures the young bird does not escape in a dangerous premature flight.

"We specifically target our visits so the eaglets are between the ages of 4 to 8 weeks," says Stuber. "If they are too young, the eaglets aren't able to self–regulate body temperature. But if they are older than 8 weeks, the birds are more likely to try and evade us by flying away from the nest when their wings aren't fully developed."

Once the eagle's leg is secured, Stuber gently brings the bird toward him and places it in what resembles a neon–colored gym bag with a long rope tied to it. He slowly lowers the bird to the ground where DNR research scientist Mike Meyer detaches the bag and carries it to a workstation. The station consists of a tarp on the ground and various tools to measure the bird's growth. Talon length, beak size and weight inform the researchers about the bird's overall health. Additionally, they take small feathers from the bird's breast and also a blood sample to analyze for contaminants.

"This is what we refer to as a 'bio–sentinel''" explains Meyer. "By looking at the feather and blood samples, we are able to see evidence of pollutants, such as PCBs, that are in the eagle's body."

PCBs, or polychlorinated biphenyls, are pollutants found in some Wisconsin rivers due to past industry uses and waste discharges into waterways. An eagle's body acts as a kind of running tally for measuring PCBs in the environment because of the fish they eat.

The pollutants in the river get absorbed by plants and eventually make their way up the food chain where top predators like eagles consume the fish. PCB pollutants gradually accumulate in the eagle's body over time, and researchers are able to deduce the amount of PCBs in the bird through the blood samples. Young eaglets are important to sample because they feed only on prey brought by their parents from waterways near their nest.

"So in effect, the level of pollution we find in eagles reflects the overall cleanliness of the nearby river or lake system," says Meyer. "And since we have been doing this research from 1990, we've seen significant reductions in PCB levels in certain areas after the pollutant was banned in U.S. commerce."

Meyer's team has reported an 85 percent decrease in PCB levels since 1990 along areas of the Fox River from Appleton to Kaukauna. The number of eagles nesting on this stretch of the Fox River has also increased from one to five pairs over the same time period.

Returning home

After Meyer takes the feather and blood samples, he fastens a metal ID band onto the bird's leg. This lets researchers keep track of the eagle and can reveal information about the bird's age and life if they find it again.

During the bird's examination, Stuber remains tethered to the tree near the nest; he takes in the view and also searches for items in the nest such as prey or man–made objects.

A pair of young bald eagles in a nest in Outagamie County. © Matt Stubber / USFWS
A pair of young bald eagles in a nest in Outagamie County. Notice the leftovers from a recent meal — a fawn’s leg.
© Matt Stubber / USFWS

"Eagles are generalists when it comes to food," says Stuber. "I typically find a wide variety of prey items in the nest such as turtles, ducks, turkey legs and many kinds of fish."

Of the stranger finds, Stuber found fawn legs along with trash, like rope and fishing tackle. One time he found an eagle in its nest with a fishing lure hooked into its beak and leg. The tackle was later removed and the bird was okay.

With the measurements complete, the eagle goes back into the bag and is reattached to the rope which dangles from Stuber's location. The bag is securely fastened to the rope and Meyer shouts to Stuber to begin the eagle's return journey. Stuber places the bird back in the nest and then prepares for his own descent by rappelling down using the same rope he used to lower and raise the eagle. With faith in his rigging, Stuber transitions his weight from the security of the tree to the rappel line where he dangles and sways in the wind. He controls his descent using a device known as an "8," which applies friction to the rope to slow or speed up the descent. The rappel back to Earth lasts 20 seconds, with the entire process from climbing, retrieving the bird and rappelling taking roughly 1.5 hours.

"After you climb for a while, you learn some fundamental rules," says Stuber. "You learn to trust your equipment, and you learn to trust the tree."

With his feet firmly back on the ground, Stuber methodically removes his climbing gear, carefully packs it away and prepares to move to the next site to repeat the process.

On a typical day, the research team makes their way to about four nests, visiting more than 80 each year. Since beginning the research study in 1990, Meyer's team has banded and sampled 570 eaglets. The team has since shifted focus from a statewide effort to banding eagles that nest along the Fox River, Green Bay area and Lake Michigan.

"With the strong comeback that Great Lakes eagles are making, we are closing one chapter on environmental pollution — the lessons have been learned, which is great," says Meyer. "So far it has been a success story as we are able to see the results of the PCB cleanup efforts. Our recent sampling results have also detected new industrial contaminants in eaglet blood, however these chemicals have already been voluntarily replaced by industry. In the end, cleaner waters mean healthier eagles and everything else that depends on Wisconsin's waterways."

Eric Verbeten is a communications specialist for the DNR's Office of Communications. He writes about the department's scientists and their research.