Eagle watchers still learning from Decorah hatchlings
Tiny transmitter following female's travels since leaving area in mid-August
The three Decorah eaglets hatched this spring before the wondering eyes of millions have split the scene, but Bob Anderson, their godfather, still has a celestial eye on one of them.
D-1, which signifies Decorah first satellite, was fitted with a satellite transmitter on July 12, and she stayed close to the nest, atop a cottonwood tree at the Decorah Fish Hatchery, until Aug. 14.
“Then, boom, like a light switch went on, she was gone,” said Anderson, director of the Raptor Research Project, whose nest-cam website was visited more than 206 million times this year as viewers worldwide watched the eaglets mature and finally leave the nest on June 16.
Anderson said he has been repeatedly queried about the fate of the hatchlings, which until now has remained a mystery even to raptor experts like Anderson and colleague Brett Mandernack, who fitted D-1 with her solar-powered transmitter.
“It was so exciting to see her pack up and leave. But where is she going to stop? Now we’ll find out,” Anderson said.
Anderson said it was “stunning” to discover that D-1 traveled 32 miles northwest on her first day of independence and 52 miles north on the second day.
After overflying the National Eagle Center in Wabasha, Minn., and tarrying two days along the Chippewa River, the 4 1/2-month-old eagle has since moved farther north into Wisconsin to a spot just east of the St. Croix River.
"For sure, we are plowing new ground with research into where immature eagles go when they leave the nest,” Anderson said.
Mandernack, who has studied raptors for 30 years and manages an eagle preserve in southwest Wisconsin, said tracking studies have been conducted on southern immature eagles, but the wanderings of northern hatchlings is uncharted territory.
If D-1 survives the hazards of youth and if the transmitter operates as expected, “we will be able to follow her into adulthood and the establishment of her own nest site,” Anderson said.
Mandernack said he and Anderson had not specifically targeted the only female in the brood.
It was first come, first served, and she was the first one into their trap, he said. After Anderson had chummed the trap site with trout, they attempted to spring a bow net on an unwary eagle, but the siblings kept their distance. They succeeded on the second day with a pandam trap, a metal hoop with monofilament nooses that snare the bird’s leg.
Anderson said he has been stung by criticism that the transmitter, which with its harness is about the size of a matchbook, will hurt the eagle or impair its flight.
“She weighs between 12 and 14 pounds, and the transmitter weighs less than 2 ounces. I have been putting bands and transmitters on birds for 40 years, and I would never do anything to hurt a bird,” he said.
Mandernack, who has fitted 19 eagles with transmitters, agrees.
“You have to know what you are doing to get federal approval to put a transmitter on an eagle,” he said. “The bird’s welfare is our top priority. We don’t want to damage a feather.”Both of D-1’s brothers had left the nest at least a week before the more slowly developing female departed.