Volunteers monitor nesting golden and bald eagles in Colorado

For more than an hour, monitoring a golden eagle nest high on South Table Mountain from a roadside observation post more than 500 yards away had been uneventful, if not downright tedious, for veteran Jeffco Open Space volunteer Teresa Van. Peering through a telescope, she could catch occasional glimpses of one eagle, but it was well-camouflaged with its rocky surroundings.

With little happening above and time passing slowly, important questions hung in the air. Was the resident eagle pair incubating eggs in this nest perched 500 feet above in a rocky cliff band at the top of the mesa? Or, had an eaglet already hatched, as typically happens in early April? Answering such questions was the reason Van was at her volunteer post, observing a nest she has monitored for six nesting seasons.

“You kind of get invested with the couple,” Van said. “After all these years, you’re cheering them on.”

Suddenly there was activity. In what is known as a “nest exchange,” the other occupant of the nest — likely the male — returned from a hunting trip. For a few moments, male and female sat perched on the rim of the nest. Were they feeding an unseen eaglet? Maybe, but it was impossible to be sure.

“An hour and a half later,” Van said, her long wait over, “we have drama.”

Then the eagle that had been tending the nest, likely the female, took off in majestic flight toward North Table Mountain, carried by wings likely measuring six to seven feet across. Golden eagles are North America’s largest birds of prey, bigger even than bald eagles, although they don’t provoke as many headlines.

Teams like Jeffco’s volunteer raptor monitoring program are stationed across the Front Range during nesting season every spring. Michelle Desrosiers, a senior wildlife ecology specialist for Jeffco Open Space, oversees a volunteer crew of 35 monitors. Nests are observed weekly during nesting season and notes are taken. Boulder Open Space and Mountain Parks has a similar program, and the Bird Conservancy of the Rockies coordinates volunteer monitors who keep watch on bald eagle nests.

“It’s the equivalent of having two full-time employees, working full days devoted only to monitoring raptors during the nesting season,” Desrosiers said of her Jeffco crew. “By monitoring these nests, we’re making sure that our management actions are not adversely impacting the persistence of natural resources on the landscape.”

Jeffco issues a raptor monitoring report annually. Last year the volunteers monitored golden eagle nests in seven far-flung locations, five of which produced seven hatchlings. Six of the eaglets “fledged,” meaning they matured to a point where they were capable of flying from the nest. The Jeffco raptor program also monitors other nesting birds of prey, including peregrine falcons, great horned owls, prairie falcons, red-tailed hawks and American kestrels.

Bald eagles do tend to be the social media darlings of raptor nation, though. In a widely publicized 2020 affair, a female nesting at Standley Lake was attacked and driven away by another female. The interloper took up with the male of the nest, which at the time was covered 24/7 by an “Eagle Cam” maintained by the city of Westminster.

That couple produced two eggs the following year, but the cottonwood tree holding the nest collapsed and the nest crashed to the ground, killing an eaglet. Last year, two eaglets there died of unknown causes. This month, one eaglet died when wind brought the nest down yet again.

Barr Lake State Park also has had tree collapses that killed bald eaglets in recent years, but currently there is an active nest there with two eaglets that hatched this month. Another active nest at Xcel’s Fort St. Vrain generating plant currently has two eaglets and is covered by eagle cams.

According to Reesa Conrey, an avian researcher with Colorado Parks and Wildlife who is conducting a four-year study tracking bald eagles, there are 117 active bald eagle nests across the Front Range. As of this week, 81% either contained eggs or hatchlings. The 19% that “failed” were due to nests being destroyed by events such as tree collapses or deaths by other causes. Conrey says the Front Range bald eagle population appears to be “robust” despite the threat of Highly Pathogenic Avian Influenza (HPAI), commonly known as bird flu.

“We confirmed HPAI as the cause of death for three wild adult eagles in Colorado during 2022, including one female tagged for CPW’s research study,” Conrey said. “We think that HPAI was responsible for a 20% drop in nest success that we observed in 2022.

“It appears that eaglets were much more susceptible to HPAI than older birds. Fall and winter were very rough for many bird species affected by HPAI, but detections have been much lower so far this spring. We are crossing our fingers that 2023 will be a better year for bald eagles and other birds impacted by HPAI,” Conrey added.

While bald eagles typically nest in trees near bodies of water because their preferred diet is fish, golden eagles nest in rocky cliffs and prey on rabbits, snakes and prairie dogs.

They are very territorial. Desrosiers believes the golden eagle pair nesting at South Table Mountain considers that mesa and nearby North Table Mountain as their territory. There is an unused eagle nest on North Table.

“They basically own South Table Mountain, and North Table, based on the behavior that we’ve seen,” Desrosiers said. “It’s unclear from some of our old data whether these two territories were occupied (by separate eagle pairs) at the same time. It could have been a separate territory (on North Table) at one point, but all signs now point to this being one territory.”

Jeffco Open Space imposes partial closures on both mesas and at six other locations during breeding season, ranging from February to July, to prevent nesting raptors from being disturbed. That means some popular trails are off limits for now.

“We try to do wildlife closures where they make sense, and we try to do them so we’re not overstepping,” said Mary Ann Bonnell, Jeffco Open Space visitor services and natural resources director. “We strive to have that balance between, ‘This is a natural resource, we love the natural resource, that’s why we’re here. We love to see eagles and this is what we need to do to protect them during their most sensitive time of the year.’”

Violators are typically ticketed with violations that come with $100 fines.

“Compliance is actually very good,” Bonnell said. “I would like to think that people who enjoy the outdoors, when they understand that a closure is in place to protect the wildlife they love, they respect that. Violations of these protection closures are unusual.”

Based on what she saw at South Table last week, Desrosiers believes at least one of the eaglets there has hatched. Typically two eggs are laid.

Van has seen a lot of cool things in the years she’s been serving in the raptor monitoring program. She enjoys watching her golden eagles put on aerial displays, doing loopy-de-loops and dives. One time while bike-riding nearby with her husband, she saw a fight between one of the resident eagles and an intruder that evolved into a death spiral similar to the one that started the Standley Lake soap opera in 2020.

“The craziest thing we saw, one of the eagles had flown down and was sitting on a rock,” Van said. “I think this was after the chick had hatched but hadn’t fledged yet. It was just sitting on this rock and we watched this deer come in. The deer was really alert, and all of a sudden the deer charged the eagle. The eagle rises up and the deer charges. You would never think to see something like that. We think the deer might have had a fawn, because golden eagles could take a small fawn. You never know what you’re going to see here.”

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