As gusts of wind blasted over the Great Bear Wilderness late last month, a golden eagle hitched a ride. Wearing a transmitter no bigger than a tiny matchbox, he surfed high above Great Northern Mountain, catching updrafts that rocketed him north over the Polebridge Mercantile.
The eagle is the first golden to carry a satellite transmitter on long-distance fall and spring migrations on the Rocky Mountain Flyway. Biologist Rob Domenech, founder of Raptor View Research Institute in Missoula, outfitted two goldens last fall. His goal was to snoop at the nation’s biggest migratory raptor highway stretching from Alaska to northern Mexico.
The raptors head south to winter, but fewer survive to fly north for breeding and despite the recovery of balds, golden numbers are dropping. That concerns Domenech. “There’s lots of activity in wintering areas like proposed gas and oil development and wind farms,” Domenech said.
In autumn, Domenech and his crew hang out atop blustery ridgelines near Rogers Pass outside Helena to trap and band golden eagles. This past October, he strapped a male and female with satellite transmitters, tracking them on nearly identical southbound routes 10 days apart. “We suspected they would take similar routes,” Domenech said. “But we had no idea how identical the flight lines would be.”
The tiny transmitters, weighing only 2.8 ounces, look like backpacks, attaching to the eagle with crisscrossing breakaway Teflon ribbon. “If they really want to get it off, they can,” Domenech said. “You hope they accept it and get used to it.”
Melanie Smith, a Geographic Information Systems analyst from Missoula volunteering with Domenech, followed the birds, providing him with maps of their movements. “I look for how they are moving through the landscape – eyeing what they are flying through, what they are avoiding, and what they are doing,” Smith said. Each day she plotted the route southward as the female covered 1,600 miles in two weeks.
Via GPS coordinates sent through satellites, Smith and Domenech studied the route, stopovers and final wintering habitats. The male opted for New Mexico, the female for West Texas. “It was surprising just how small their wintering territory is,” Domenech said.
When the spring northward migration started in February, Domenech waited for his satellite eagles to depart. And waited. “I was sweating it and biting my nails,” he said. Late in the migratory season, the male finally launched on March 15, retracing parts of his southbound mountain range route along big windy ridges.
He moved in short spurts through Colorado and Wyoming, most likely stopping to feed on grouse. After fueling up, the golden surprised Domenech. North of Wyoming’s Wind River Range, the eagle shot across Yellowstone in a beeline for Rogers Pass – a shocking distance of 260 miles in one day.
Then the eagle surprised Domenech again. Instead of flying up the Rocky Mountain Front, the suspected route most goldens take, the eagle jumped across the Bob Marshall Wilderness in a second long flight the following day. It cruised right over Great Northern Mountain, Huckleberry Lookout and Polebridge en route to the Canadian North Fork. “Apparently there’s some nice interior ridges,” he says. “It’s an adult bird that knows how to move through the land, and presumably he’s done this path several times before. He may be showing us an important migratory corridor.”
“Getting the flight to the breeding grounds is a bonus,” Domenech added. This past week, the bird reached its eastern British Columbia summering range just west of Banff National Park.
Meanwhile, the female’s transmitter still sends Texas coordinates – a sign she may have lost her transmitter or is dead. Using her blood taken at trapping, Heiko Langner, a University of Missoula geochemist, discovered that she had the highest lead levels of any of Domenech’s birds tested – 185 micrograms per deciliter. “We don’t know where they are getting the lead, but we’re thinking rifle bullet fragments from eating gut piles,” explains Domenech.
Domenech has one more satellite transmitter he hopes to deploy this fall on another adult golden. “This is using technology in such a great way,” Domenech said. “These birds are going to tell us so much.”