Not a golden year for eagles

With fewer young, golden eagles struggling in area

Posted 10/3/19

2019 has been a bad year for golden eagles in northwest Wyoming, according to researchers with the Draper Museum of Natural History.

Chuck Preston, Draper Museum curator emeritus, said there were …

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Not a golden year for eagles

With fewer young, golden eagles struggling in area

Posted

2019 has been a bad year for golden eagles in northwest Wyoming, according to researchers with the Draper Museum of Natural History.

Chuck Preston, Draper Museum curator emeritus, said there were only 0.29 fledglings per occupied nest in the region this year — about one fledgling for every three nests. It’s the lowest reproduction rate the team has ever seen.

In 2016, at the height of reproduction in the past 10 years, the team recorded 1.37 fledglings per nest. “We had some nests that had three fledglings that year,” Preston said.

For the past decade, scientists and assistants at the museum have been painstakingly studying the reproductive rate of the species, watching known nests around the area. Their primary area of study is in the Oregon Basin, southwest of Cody. Many factors play into reproduction rates, Preston said, as well as the overall health of the entire ecosystem.

“The West is changing so rapidly, from increased development and invasive plant species such as cheatgrass, to climate change and increased recreational use of the habitat,” Preston said. “All potentially have an impact on golden eagles, the apex predator.”

In recent years, extensive data relating to the key topics have been collected in two study areas near Yellowstone National Park: one in Livingston, Montana, to the north and the Draper’s study to the east. Complimentary research within the park has been ongoing since 2011. Preston said while other studies involving similar habitat and elevation have also seen a decline in birth rates for the past two years, Yellowstone has had a good year.

In general, golden eagle reproduction rates are lower in the park than in the Big Horn Basin, said Doug Smith, senior wildlife biologist with Yellowstone National Park.

“Park reproduction is more stable but low and we rarely have ‘good years,’” Smith said. “This is likely due to no solid single prey food source and higher elevation leading to more bad weather during the nesting season.”

Weather plays a part in reproduction rates.

The past two years have brought wet, cold winters. It’s too short of a time period to even consider the trend as being part of climate change, said assistant curator Corey Anco. It’s important to consider future trends in continuing the research. Eagle birth rates run on a six- to eight-year cycle.

“We’re in the trough of the cycle right now. We have hope next year populations will rebound,” Anco said.

While the studies are centered on golden eagles, what researchers are really watching is the entire sagebrush steppe ecosystem. “Golden eagles are the lens we are using to look at the ecology of the sagebrush steppe on the whole,” Anco said.

In 2016, the Draper team recorded a high population of cottontail rabbits, the primary prey species of golden eagles in the area. In the past two years, cottontail populations have plummeted, coinciding with eagle reproduction rates. Yet cottontail population isn’t the only factor affecting golden eagle reproduction rates, Anco said.

“The longer we’re out there monitoring, the more [all-terrain vehicles] we’ve seen. The question is, how is recreational use affecting populations,” he said.

In continuing their study, the Draper team plans to band fledglings in the summer, adults in the winter and watch intently for changes that not only affect eagles, but the environment as a whole.

Golden eagles live in the Northern Hemisphere around the world. Researchers are watching the species carefully in many places, Preston said, including Scotland, Sweden, Norway and Japan.

In response to broad concerns about golden eagle populations, Wyoming initiated a golden eagle working group and the U.S. Fish and Wildlife Service instituted a western U.S. study to model eagle habitat suitability, human development risks, lead exposure and large-scale movements.

The team at the Draper — which unveiled a permanent collection on golden eagles last year —happily share their information not only with regional study teams, but internationally as well.

“The real value of our work is the ability to collaborate with other studies, networking across the globe to get a robust portrait of golden eagles,” Preston said.

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