An effort to track eagle movements in Southwest Colorado, spearheaded by Colorado Parks and Wildlife, has given new insight into just how far the iconic birds migrate across the continent.

“We would have never guessed they are going 1,200 to 1,700 miles,” said Brian Magee, a land-use coordinator with CPW.

But the tracking project is also offering information to the contrary: Two bald eagles in the Animas Valley, for instance, choose instead to stay around Durango pretty much year-round, and have since at least 2012.

In recent days, the two eagles have been drawing the attention of passersby as the birds perform the annual ritual of courting. Assumed to be lifetime mates, the two eagles have been together for at least nine years.

“Those two have been together all these years,” Magee said. “They’re very successful in the Animas Valley at their nests.”

In 2011, BP America Production Co. signed a sort of good faith agreement with CPW, pledging to minimize its impacts to wildlife and habitat loss from oil and gas extraction in La Plata County, as well as in Archuleta County.

As part of the agreement, BP donated money for wildlife study, some of which is now being used for the eagle-tracking project, which monitors both bald and golden eagles.

The first eagles in this part of Southwest Colorado were collared with tracking devices in 2014 – one of which was the female eagle in the pair in the Animas Valley, which more or less stays within a 5-mile radius around Durango.

From 2014 to 2018, CPW tried to tag more eagles, but the task proved too difficult.

In 2019, however, CPW changed its capturing tactics, using bait in winter, when other usually easily available food sources, such as prairie dogs, are under the frozen ground.

And it worked. CPW was then able to place transmitters on the eagles. Expected to last about five years, the transmitters send back a signal about every hour, allowing wildlife officials to see where eagles move year-round.

CPW had tagged eight birds in total, but as of this year, only four transmitters are functional.

Most of the eagles were caught in winter at a communal roosting site on the Pine River, where anywhere from 20 to 50 birds gather every year. Nearly all those birds, Magee said, went to Canada in the summer.

One eagle, for instance, flew 1,700 miles to the Great Slave Lake in the Northwest Territories. Two others went 1,300 miles to Saskatchewan. And another eagle flew 1,200 miles to British Columbia.

“That’s crazy,” Magee said. “We knew we had a bunch of eagles in the winter, but we didn’t know where they came from.”

As for the pair in the Animas Valley, only the female has a transmitter. For the most part, she stays around Durango, but every once in a while has taken sojourns at the end of summer up to the Grand Mesa, east of Grand Junction.

On two occasions in 2014 and 2015, the female went for a short trip to Idaho. But because the male is not tracked, it’s unclear if the pair flies together in the summer or separate.

“I wish we did (have a transmitter on the male),” Magee said. “Then we could see when they’re together or if they separate and do their own things.”

Eagles are highly territorial, Magee said, but it’s unclear what makes one bird want to stay in one area, like the female in the Animas Valley, rather than migrating to different pastures, like the birds in the communal roost.

It’s also unknown, but assumed, that mating eagles are life partners. In recent days, the pair in the Animas Valley has been going through the annual courting, which includes extravagant aerial displays and loud vocalization.

Geoff Hickcox, a Durango resident and former environmental attorney, said he was taking photos up and down the Animas River when he noticed the two eagles singing and flying around.

“I had never seen anything like that before,” he said. “It was such a privilege to witness it. To hear an eagle singing like that. It was really beautiful.”

Eagles typically begin courting in January, and then lay eggs around March or April, which hatch about a month later. Chicks will attempt their first flight at about the end of June, and by August, are off on their own.

While it is entertaining to watch the maps to see where the eagles are hanging out, there is a loftier goal to the eagle-tracking project.

Eagles were taken off the endangered species list in 2007, but the iconic bird is still under federal protection.

As a result, when any project or development is proposed that would alter the landscape, such as drilling new oil and gas wells, building a new road or putting in a subdivision, potential impacts to eagles have to be considered.

In Colorado, that task usually falls to CPW, which must provide recommendations to best protect eagles from new developments.

The tracking study is intended to provide insight for wildlife managers about how eagles use the landscape in an effort to better inform CPW’s recommendations about potential developments.

“I think we’re still in the monitoring phase,” Magee said of the project. “We’re going to keep collecting data as long as the transmitters keep working.”

Restoring eagle populations is seen as a national conservation success story.

By the 1970s, hunting and agricultural pesticides had driven the bird to the brink of extinction. But in recent years, eagle populations have rebounded and stabilized.

In Colorado, for instance, only one bald eagle nest was documented in a 1974 study. In 2017, however, CPW reported nearly 200 nests.

A 2016 U.S. Fish and Wildlife Service report estimated there are 40,000 golden eagles and 143,000 bald eagles throughout the United States. It also concluded bald eagle populations are increasing at about 5% every year while golden eagle populations appear to remain stable.

But Dana Bove, a retired federal geologist who founded Front Range Nesting Bald Eagle Studies, a nonprofit eagle advocacy group, said previously booming development and growth in Colorado still poses a risk to eagles.

“It’s an issue everywhere in Colorado,” he said. “And it’s something we’re certainly looking to address to see if there’s a way we can make some changes in state law that would give recommended buffers some real teeth.”

jromeo@durangoherald.com