DECORAH, Iowa — The three Decorah eaglets that hatched this spring as millions watched online have left the nest.

But one of them was fitted with a satellite transmitter that’s allowed researchers to track its growth. The eaglet, dubbed D-1 as Decorah’s first satellite eagle, was fitted with a transmitter on July 12.

She stayed close to the nest, atop a tree at the Decorah Fish Hatchery, until Aug. 14. Then suddenly the young eagle took off, according to Bob Anderson, director of the Raptor Research Project.

The project’s nest-cam website was visited more than 206 million times this year as viewers worldwide watched the eaglets mature and 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 experts like Anderson and colleague Brett Mandernack, who fitted D-1 with her solar-powered transmitter.

Both of D-1’s brothers had left the nest at least a week before the more slowly developing female departed.

“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 he was stunned to discover that D-1 traveled 32 miles northwest on her first day and 52 miles north on the second day.

After flying past the National Eagle Center in Wabasha, and spending two days along the Chippewa River, the 4 1/2-month-old eagle has since moved farther north into Wisconsin.

“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 are uncharted territory.

If D-1 survives the hazards of youth and if the transmitter operates as expected, Anderson said researchers will be able to follow her into adulthood and the establishment of her own nest site.