Research looks at relocation as a management strategy for mitigating bird depredation
Kristen Amicarelle, a graduate research assistant at Colorado State University (CSU)-Pueblo, spent a year and a half working with producers across Wyoming to study the effectiveness of relocating golden eagles as a management strategy for mitigating sheep depredation.
On Dec. 4, 2023, during the Wyoming Stock Growers Association Winter Roundup Convention and Trade Show, Amicarelle presented her research to those in attendance.
Finding a solution for rising depredation
To begin, Amicarelle noted sheep depredation by golden eagles has been increasingly reported by Wyoming producers over the last decade and has only continued to rise in recent years.
According to the U.S. Department of Agriculture (USDA) National Agricultural Statistics Service, over $700,000 in herd damages were caused by eagles in 2022, and Amicarelle explained many experts suspect depredation has increased because of modern challenges eagles face, including lack of prey due to habitat fragmentation and human development.
“We also know there is a substantial nonmigratory breeding population of golden eagles in Wyoming, so that could be a contributing factor as well,” she stated.
“Golden eagles are not only federally protected under the Migratory Bird Treaty Act, they also have their own policy – the Golden Eagle Protection Act of 1940,” she continued. “Relocation management strategies have recently been brought back into the spotlight because they may be the only means to offset sheep depredation in the state.”
Amicarelle explained her project set out to modernize research conducted by Robert Phillips of the U.S. Fish and Wildlife Service (FWS) in the late 1980s, in which 14 adult golden eagles were relocated, 12 of which returned to their former territories in a short 11 to 14 days.
Through their own research, the CSU team hoped to understand golden eagle movement, particularly after relocation, predicting age and how distance of relocation would impact return rates.
“Golden eagles reach breeding maturity around four to five years of age, and they return to the same place they breed every year,” Amicarelle said. “Adults are likely to return in a short amount of time, whereas younger birds haven’t established their breeding territories yet so they are not likely to return to the ranch. Instead, they will exhibit more exploratory behavior.”
Studying the effectiveness of relocation
Before Amicarelle could put her boots on the ground to test these theories, she wanted to understand golden eagle habitat to ensure relocation sites provided ample resources and opportunities for the birds to thrive.
She began by using the Wyoming National Diversity Database and U.S. FWS data to find areas with concentrated densities of jack rabbits, cottontails, prairie dogs and Wyoming ground squirrels – common prey species of golden eagles – as well as eagle nesting sites.
“I wanted to consider bird-to-bird conflict, human conflict and the available opportunities for a bird to adjust to their relocation – would they be able to hunt, perch and rest?” she asked. “I also wanted to consider distance from other sheep operations, oil and gas fields and wind energy farms.”
After combing through online data, the researchers came up with several permissible sites through the Wyoming Game and Fish Department on wildlife management areas, national wildlife refuges and state land scattered throughout Wyoming and one in Montana.
Amicarelle then laced up her boots and set out to these sites to conduct preliminary habitat surveys, ensuring the sites were indeed suitable for golden eagles, through protocol she developed using vegetation sampling and pellet count density sampling.
Once the relocation sites were secured, the team began trapping and relocating golden eagles from 13 sheep producers around the state. After each bird was caught, Amicarelle fashioned a small GPS transmitter to its back and moved it 400 miles away from its original habitat.
“Over a year and a half, we trapped 12 golden eagles and relocated 10. The two other birds were not relocated as our study control so we could make comparisons,” she explained. “We had nine adults in our sample size, one subadult and two hatch years.”
Amicarelle also noted the research team was able to obtain additional research from other eagle biologists, bumping their sample size to 42 birds.
“With the transmitters, we were able to get fine-scale data on everything from flight speed and altitude to daily movements and seasonal migrations,” she added.
Analyzing
research results
Amicarelle admitted, as of Dec. 4, 2023, her research results weren’t fully finalized.
However, from what she has been able to evaluate, younger birds showed far more exploratory behavior – in line with her early predictions – with one eagle flying all the way to the edge of the Northwest Territories and returning to Colorado to spend its winter on the Eastern Plains.
Another bird, she shared, flies to Mexico every winter, then returns to the Shirley Basin during summer months.
“In Wyoming, our relocated golden eagles are keying into certain areas like the Shirley Basin, the Big Horn National Forest, the edges and foothills of the Medicine Bow and around Flaming Gorge in southwest Wyoming,” Amicarelle explained.
She continued, “Per my early prediction, we found age was significant to return rate, with all of the adults returning to the same ranch at some point, whereas none of the younger birds have. And, to my knowledge, they still haven’t returned at all.”
Additionally, Amicarelle noted they found an 80 percent success rate for relocation, as eight out of 10 birds did not return within three weeks of relocation.
“If relocation was to be used during lambing season, eagles might stay away for a long enough time for a lamb to grow and not be as susceptible to the elements, including avian depredation,” she remarked.
However, Amicarelle also admitted relocation isn’t a very cost-friendly management strategy, estimating it could cost producers hundreds of thousands of dollars to implement.
Brainstorming
alternative management strategies
With little expertise in sheep ranching, Amicarelle confessed her suggested alternative strategies may be naive, but she presented them to those in attendance anyway.
“I want to throw out some other methods to consider, one being the depredation probability model,” she shared.
“I also used to work for Hawk Watch International, a nonprofit located in Utah where they are doing research on an avian supplemental feeding program, which helps boost their nest productivity and populations,” she added. “But, on the flip side, if we used this method on a sheep operation, it might give the eagles more opportunities to feed on the landscape, and they might not be as driven to go for live prey.”
Amicarelle also suggested agencies like USDA could hire seasonal staff to monitor sheep herds, deter eagle activity and document depredation in real time or provide funding to ranchers to construct lambing barns, take advantage of more livestock guardian dogs or install camera technology to track sheep on the ground.
“I don’t think any of these are a one-all,” she concluded. “I think a combination of them could really go a long way in alleviating concerns ranchers have with avian depredation.”
Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
Kristen Amicarelle, a graduate research assistant at Colorado State University (CSU)-Pueblo, spent a year and a half working with producers across Wyoming to study the effectiveness of relocating golden eagles as a management strategy for mitigating sheep depredation.
On Dec. 4, 2023, during the Wyoming Stock Growers Association Winter Roundup Convention and Trade Show, Amicarelle presented her research to those in attendance.
Finding a solution for rising depredation
To begin, Amicarelle noted sheep depredation by golden eagles has been increasingly reported by Wyoming producers over the last decade and has only continued to rise in recent years.
According to the U.S. Department of Agriculture (USDA) National Agricultural Statistics Service, over $700,000 in herd damages were caused by eagles in 2022, and Amicarelle explained many experts suspect depredation has increased because of modern challenges eagles face, including lack of prey due to habitat fragmentation and human development.
“We also know there is a substantial nonmigratory breeding population of golden eagles in Wyoming, so that could be a contributing factor as well,” she stated.
“Golden eagles are not only federally protected under the Migratory Bird Treaty Act, they also have their own policy – the Golden Eagle Protection Act of 1940,” she continued. “Relocation management strategies have recently been brought back into the spotlight because they may be the only means to offset sheep depredation in the state.”
Amicarelle explained her project set out to modernize research conducted by Robert Phillips of the U.S. Fish and Wildlife Service (FWS) in the late 1980s, in which 14 adult golden eagles were relocated, 12 of which returned to their former territories in a short 11 to 14 days.
Through their own research, the CSU team hoped to understand golden eagle movement, particularly after relocation, predicting age and how distance of relocation would impact return rates.
“Golden eagles reach breeding maturity around four to five years of age, and they return to the same place they breed every year,” Amicarelle said. “Adults are likely to return in a short amount of time, whereas younger birds haven’t established their breeding territories yet so they are not likely to return to the ranch. Instead, they will exhibit more exploratory behavior.”
Studying the effectiveness of relocation
Before Amicarelle could put her boots on the ground to test these theories, she wanted to understand golden eagle habitat to ensure relocation sites provided ample resources and opportunities for the birds to thrive.
She began by using the Wyoming National Diversity Database and U.S. FWS data to find areas with concentrated densities of jack rabbits, cottontails, prairie dogs and Wyoming ground squirrels – common prey species of golden eagles – as well as eagle nesting sites.
“I wanted to consider bird-to-bird conflict, human conflict and the available opportunities for a bird to adjust to their relocation – would they be able to hunt, perch and rest?” she asked. “I also wanted to consider distance from other sheep operations, oil and gas fields and wind energy farms.”
After combing through online data, the researchers came up with several permissible sites through the Wyoming Game and Fish Department on wildlife management areas, national wildlife refuges and state land scattered throughout Wyoming and one in Montana.
Amicarelle then laced up her boots and set out to these sites to conduct preliminary habitat surveys, ensuring the sites were indeed suitable for golden eagles, through protocol she developed using vegetation sampling and pellet count density sampling.
Once the relocation sites were secured, the team began trapping and relocating golden eagles from 13 sheep producers around the state. After each bird was caught, Amicarelle fashioned a small GPS transmitter to its back and moved it 400 miles away from its original habitat.
“Over a year and a half, we trapped 12 golden eagles and relocated 10. The two other birds were not relocated as our study control so we could make comparisons,” she explained. “We had nine adults in our sample size, one subadult and two hatch years.”
Amicarelle also noted the research team was able to obtain additional research from other eagle biologists, bumping their sample size to 42 birds.
“With the transmitters, we were able to get fine-scale data on everything from flight speed and altitude to daily movements and seasonal migrations,” she added.
Analyzing research results
Amicarelle admitted, as of Dec. 4, 2023, her research results weren’t fully finalized.
However, from what she has been able to evaluate, younger birds showed far more exploratory behavior – in line with her early predictions – with one eagle flying all the way to the edge of the Northwest Territories and returning to Colorado to spend its winter on the Eastern Plains.
Another bird, she shared, flies to Mexico every winter, then returns to the Shirley Basin during summer months.
“In Wyoming, our relocated golden eagles are keying into certain areas like the Shirley Basin, the Big Horn National Forest, the edges and foothills of the Medicine Bow and around Flaming Gorge in southwest Wyoming,” Amicarelle explained.
She continued, “Per my early prediction, we found age was significant to return rate, with all of the adults returning to the same ranch at some point, whereas none of the younger birds have. And, to my knowledge, they still haven’t returned at all.”
Additionally, Amicarelle noted they found an 80 percent success rate for relocation, as eight out of 10 birds did not return within three weeks of relocation.
“If relocation was to be used during lambing season, eagles might stay away for a long enough time for a lamb to grow and not be as susceptible to the elements, including avian depredation,” she remarked.
However, Amicarelle also admitted relocation isn’t a very cost-friendly management strategy, estimating it could cost producers hundreds of thousands of dollars to implement.
Brainstorming alternative management strategies
With little expertise in sheep ranching, Amicarelle confessed her suggested alternative strategies may be naive, but she presented them to those in attendance anyway.
“I want to throw out some other methods to consider, one being the depredation probability model,” she shared.
“I also used to work for Hawk Watch International, a nonprofit located in Utah where they are doing research on an avian supplemental feeding program, which helps boost their nest productivity and populations,” she added. “But, on the flip side, if we used this method on a sheep operation, it might give the eagles more opportunities to feed on the landscape, and they might not be as driven to go for live prey.”
Amicarelle also suggested agencies like USDA could hire seasonal staff to monitor sheep herds, deter eagle activity and document depredation in real time or provide funding to ranchers to construct lambing barns, take advantage of more livestock guardian dogs or install camera technology to track sheep on the ground.
“I don’t think any of these are a one-all,” she concluded. “I think a combination of them could really go a long way in alleviating concerns ranchers have with avian depredation.”
Hannah Bugas is the managing editor of the Wyoming Livestock Roundup. Send comments on this article to roundup@wylr.net.
