Golden Eagles in the West appear stable, but Nevada tells a different story

Golden Eagles (Aquila chrysaetos) have been protected in North America since 1962 and their populations in the West are considered stable. However, a new study published in the Journal of Raptor Research found that the Nevada population is declining and could be headed for something worse. This paper, titled “Estimating Survival and Population Trajectories of Golden Eagles in Nevada,” suggests that Nevada may be a population sink — an area with conditions unsuitable for maintaining a stable population of Golden Eagles. Most studies on the population health of this species have focused on adult eagles, however this paper underscores the importance of including nonbreeding individuals in such assessments to better understand who exactly is contributing to the population and how impacts to immature eagles may ultimately undercut the breeding adult population. In Nevada, too many local eagles are dying to support a stable population. How then, do eagles keep showing up on nesting territories?

Golden Eagles are apex predators that live throughout most of the northern hemisphere and yet, they are challenging to study. Co-author on the study Joe Barnes, from the U.S. Fish and Wildlife Service in Reno Nevada, has been studying this species for 15 years. “Golden Eagles are difficult to detect,” he says, “and they are sparsely spread across very remote and rugged areas.” His work aims at identifying important knowledge gaps for the species, to help address conservation threats and minimize impacts of human-development on eagles throughout the state. This study was conducted within the Great Basin and Mojave Desert portions of Nevada, which includes a substantial portion of the continent’s Golden Eagle population, and threatened sagebrush steppe habitat. The team also included a focal study on a breeding population of eagles near a proposed solar energy project. Nevada is in the top five states for potential solar and geothermal energy generation and therefore habitat loss is of high concern. Golden Eagles here also rely heavily on rabbits, which have declined since 2020 due to Rabbit Hemorrhagic Disease Virus 2 (RHDV2). 

Barnes and his team tagged 43 Golden Eagles, both subadult and adult, from 2014 to 2024 to assess survival rates across Nevada. They tracked individuals across the study period and confirmed which individuals held territories and bred, as well as which birds died, and then funneled their results into a model that predicted rates of future population change. The results were sobering.    

Although Barnes suspected Golden Eagles were declining in Nevada, he was surprised to learn just how unsustainable the population might be. At least 30 of the 43 tracked eagles died during this study, from causes including electrocution, collisions with structures and vehicles, and starvation. This is a relatively high death rate across all ages. However, territories were consistently occupied through the state during the study period. This could mean that birds from out-of-state are the ones filling nests, which is concerning because they may encounter the same fates as local eagles, yet all appears stable by typical monitoring methods. Additionally, Golden Eagle populations are well known to include nonbreeding adults, called “floaters,” which are exceedingly difficult to quantify and track. So, the declining populations that his team has identified is almost certainly drawing from elsewhere in addition to the floater population to sustain high territory occupancy rates statewide. Hence, a dangerous loop is born. “Population sinks can be particularly detrimental because they draw individuals in from an area far larger than the area of concern,” says Barnes, “and persistent local sink conditions can impact the greater regional population.”  It’s important to note that high death rates are not the only cause of sinks. Sometimes they are caused by issues in the breeding success of the species as well. 

Barnes and his colleagues declare habitat conservation as the number one management action that could benefit Golden Eagles in Nevada. Drought, wildfire, RHDV2, and development of hard rock mining and solar energy will challenge this goal. Barnes, however, remains optimistic. “I have had success working directly with large-scale landscape development projects to proceed in a way that maintains natural habitat structure and quality that minimizes impacts to eagles and other wildlife.” Fine scale population studies that include nonbreeding individuals could be the key in getting ahead of the storm. Golden Eagles are hearty, but they can only handle so much.