Geothermal energy is a hot topic in Nevada these days. That’s true in a literal sense--geothermal energy is a type of renewable energy that draws on heat deep within the earth’s core—but it’s also true in a figurative sense. As the United States looks to renewable energy sources as part of a strategy to adapt to climate change, geothermal energy is getting more attention.  

Assessments by the USGS have found that the western states hold huge potential for geothermal power production, especially in Nevada, California, and Idaho. This region happens to be the same area where many remaining greater sage-grouse live. Greater sage-grouse populations have declined more than 80% range-wide over the past 55 years, a result of loss and degradation of their sagebrush habitat from fire, invasive species, development, and other threats. USGS scientists have spent decades studying the greater sage-grouse and developing tools that can help sage-grouse persist in this rapidly changing landscape. Now, their focus has turned to geothermal energy. 

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Until recently, the potential impacts of geothermal energy on greater sage-grouse were relatively unknown, though other studies have explored different types of energy development on sage-grouse or how geothermal impacts other wildlife species. USGS scientists published the results of a 13-year study of greater sage-grouse populations that lived within 50 kilometers (about 30 miles) of two new geothermal energy plants, analyzing data from six years prior to development through six years afterwards. 

They found that greater sage-grouse population numbers declined substantially in years following the development of the geothermal energy plants. Sage-grouse abundance decreased within 5 kilometers, or about 3 miles, of a geothermal facility while leks (traditional breeding grounds) were abandoned or extirpated if they were within 2 kilometers (1.2 miles).  

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“Geothermal infrastructure such as roads, well pads, transmission lines and buildings and the bright lights and noise that they produce can disrupt breeding and nesting behaviors,” explained Peter Coates, the lead biologist of the study. “Those disruptions may leave individual grouse less likely to breed and more susceptible to predation while nesting.”  

Many of these impacts are similar to those found for other kinds of energy development, but some features are specific to geothermal. The cooling towers, for example, produce a consistent, loud hum. Noise pollution has been linked to increased levels of stress hormones and decreased lek attendance in sage-grouse. The researchers found that sage-grouse in hilly areas surrounding the geothermal sites seemed to do better than those in flatter areas, possibly because the topography blocked some of that light and noise.  

Then there are the ravens. 

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Ravens are a native species across western and northern North America, but their populations have skyrocketed in recent decades as humans expand deeper into sagebrush. Humans and our structures provide food, water, and shelter for ravens, whether we intend to or not. And when ravens aren’t busy eating from our garbage, they like to eat greater sage-grouse eggs and chicks. 

The geothermal energy plants in the study attract ravens much like other types of human developments. In the largely treeless landscapes of the Great Basin, ravens don’t have many high places to perch and nest. Transmission lines and vertical piping are therefore attractive places for ravens to build nests that keep their own young safe from predators on the ground. The ravens also feed on roadkill on the newly established roads and on garbage from the plant. While the new study found that topography and distance could likely mitigate some impacts of geothermal infrastructure, like light and noise, sage-grouse declines were substantial where raven densities were high, regardless of distance or topography. 

These findings indicate that geothermal energy can pose many risks to vulnerable grouse. However, the goal of the USGS research is not to simply outline the threats to the sage-grouse: it’s to help managers and other stakeholders, like energy developers, figure out how to develop renewable energy while mitigating the effects of development on sensitive species like the greater sage-grouse. That’s why Coates and his team are building maps. 

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Coates has spent decades observing and counting sage-grouse in their breeding and nesting areas. He and his team have built an enormous dataset they use to answer questions about where sage-grouse are found, how they select sites for breeding and nesting, how their populations have grown or declined over time, and what factors are affecting population growth and losses.  

Using their field observations and sophisticated computer modeling techniques, Coates and his collaborators create large-scale maps that show where sage-grouse breeding areas and nests are located and where populations are growing or shrinking. The latest mapping tool they’ve developed draws on the geothermal study findings. The tool considers local information about sage-grouse abundance and behavior, the distance and topography between the proposed site and sage-grouse populations, and information about ravens. They tested the tool on 135 potential sites possessing geothermal energy potential within the Great Basin, finding that more than two-thirds of sites had little-to-no impact on sage-grouse populations, because current sage-grouse populations did not overlap the site where they would be impacted. 

“Our geothermal application tool was developed to provide energy developers and land managers with options when planning geothermal energy projects,” says Coates. 

The maps are built on models that can incorporate new information over time. As the Great Basin undergoes rapid change, so too can the findings and maps change. For example, even though the study identified a buffer of 5 km (the distance within which impacts to sage-grouse were strongest), Coates cautioned that this value might shift over time. In preliminary studies, they found a smaller buffer distance, but by the end of the 10-year study, as the energy infrastructure continued its development, the area within which they observed negative impacts had grown. 

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The geothermal tool is just the latest in the toolbox of mapping applications developed by Coates’s team. In 2021, the team introduced a framework for monitoring greater sage-grouse populations across the Great Basin, known as the Targeted Annual Warning System. It helps disentangle whether changes in grouse populations are the result of human-driven threats or simply experiencing normal fluctuations in response to climate conditions. The system uses “watches” and “warnings” to help managers determine where sage-grouse populations are most at risk. It’s a little like the system meteorologists use for tornadoes—under a watch, it’s time for intensive monitoring. A warning indicates more persistent declines. (Applying this warning system to the sage-grouse populations near the geothermal sites in the new analysis, Coates and his team found that since construction of the geothermal plant, sage-grouse leks have experienced 11 watches and 12 warnings within 5 km distance of the plant.) The team has also a developed tool to map predicted raven densities across the Great Basin, which can guide help managers identify where raven-deterrents or other interventions could be most useful. 

The Great Basin and the habitat of the greater sage-grouse will continue to change in the years to come, especially as humans and wildlife contend with climate change. Science-based, adaptable tools like those developed by Coates and other USGS scientists can help managers navigate tricky decisions in that changing world. 

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