A male sage-grouse performs a display at a breeding site in Bodie Hills, California. Greater sage-grouse were the focus of a study on the relationship between geothermal plants and the sagebrush environment. Photo courtesy of Megan Milligan, USGS.
A new study published in the journal Biological Conservation found that the presence of geothermal plants “adversely affected” greater sage-grouse populations within sagebrush ecosystems. The study analyzed over twenty years of greater sage-grouse population data, both ten years before and after the implementation of two geothermal plants in Nevada.
By exploring the relationship between sage-grouse, whose nesting and breeding habitats often coincide with land suitable for geothermal development, researchers developed a tool that will better inform strategic planning for geothermal energy opportunities in the state.
The Sierra Nevada Ally’s Scott King recently spoke with Dr. Peter Coates, a research wildlife biologist with the U.S. Geological Survey, Western Ecological Research Center, who served as a project lead on the study.
King: Let’s start off with the basics. What was the purpose of this study?
Coates: The study came about largely because of a gap in scientific information regarding environmental effects of geothermal activity. But the broader picture was to just try to understand the relationship between geothermal activity and sage-grouse population performance, and draw comparisons with studies that focus on other forms of energy-related infrastructure. We went into this to collect information to develop a quantitative decision support tool for developers, as well as wildlife and land managers and planners, for coming up with the best design and location for energy infrastructure that would minimize impacts to wildlife populations.
It appears the study focused on greater sage-grouse populations as an indicator species. Can you explain why greater sage-grouse is an appropriate indicator species for the broader sagebrush environment?
Sage-grouse represent many components of sagebrush ecosystems because they use many different parts of these ecosystems to meet their life history needs. When one of those components is stressed, sage-grouse will often respond in a predictable manner. Because sage-grouse occupy broad areas that encompass many other sagebrush species, their response to stressors can serve as an early warning for the broader biological community. This is why we did an in-depth study on sage-grouse, not just evaluating changes in their population numbers, but also marking birds and following them throughout the year to understand impacts of geothermal infrastructure on different life history phases of the bird.
So now that you’ve talked a little bit about the relationship between sage-grouse and the sagebrush environment, what did the study find in terms of how that relationship was affected by the presence of a geothermal plant?
Our results indicated that sage-grouse population numbers declined substantially in years following the development of a geothermal energy plant. Specifically, following development of the geothermal plants, sage-grouse abundance at leks [breeding sites] decreased within five kilometers of the infrastructure and leks were completely abandoned at significantly higher rates within about two kilometers. So, we looked at the mechanisms responsible for declines in numbers and lek abandonment, and we found adverse impacts to survival of female sage-grouse and their nests.
Sage-grouse may be negatively affected by geothermal energy because of the anthropogenic [human-related] features associated with the energy plant, such as light and noise that’s emitted from the facilities. The geothermal infrastructure can disrupt breeding and nesting behaviors, possibly leaving individuals less likely to breed and more susceptible to predation. Individual sage-grouse might also choose to move away from the disturbance and breed elsewhere, which would imply a loss in available habitat that extends beyond the physical footprint of the development.
The study also found an increase in ravens adversely affects nest survival. Quite a body of literature exists that indicates that ravens and other avian predators are attracted to anthropogenic features, many of which are associated with geothermal power production such as transmission lines, roads and so forth. The presence of those anthropogenic features poses indirect and direct risk to sage-grouse populations.
Those are some pretty comprehensive findings. But first, I’d like to hone in on how light and sound from a geothermal plant influenced these populations. Can you tell me more about that?
We investigated light and sound effects because they have been shown to increase stress hormones in sage-grouse and decrease the rate at which sage-grouse attend leks. We developed a topographic impedance index, which served as a proxy for the abatement of light and sound emanating from the plant. This index had a very strong influence on both nest survival and adult survival, such that higher values resulted in higher survival probabilities.
We also found that nests located farther from the plant tended to experience higher rates of survival. Interestingly, where hills were located between sage-grouse nests and infrastructure [high topographic impedance], we found the distance effect to be less important. Under those circumstances topography was compensating for the lack of distance and likely serving to reduce effects of light and sound. When high levels of topographic impedance were not possible, such as a valley floor, large distances were likely providing a similar set of ambient conditions, since both light and sound lose intensity with increasing distance. Our study identified these complex mechanisms of how the infrastructure from the plant influenced population vital rates, like nest survival, which helped explain the overall finding that population numbers declined in association with plant infrastructure.
You also mentioned that the presence of ravens was registered as a result of the study. Can you elaborate on what you found and why that’s important?
Recent studies show that ravens are an effective predator of sage-grouse nests. Specifically, ravens prey on sage-grouse eggs. Raven presence has been shown in many studies to potentially limit sage-grouse population growth, but definitely adversely affect sage-grouse nest survival. Estimating the attraction of ravens to geothermal energy infrastructure was beyond the scope of this study, but a body of literature supports ravens using tall structures for perching and nesting. For example, in undisturbed habitats, ravens typically nest within trees and rocky cliffs, both of which are relatively sparse and often dispersed throughout sagebrush ecosystems. Geothermal infrastructure provides vertical nesting and perching structures such as transmission lines, facilities, vertical piping, etc., for ravens that may otherwise be absent from these local environments.
Also, food subsidies can be provided for ravens in the form of roadkill, occurring on newly established roads associated with a geothermal infrastructure or pre-existing roads that are not directly associated with the geothermal infrastructure, but used quite a bit more as access by employees or plant operators. Food subsidies may also exist from human trash…that are associated with the operation of the plant.
Now, we included ravens in this study because of its potential to confound other effects associated with the geothermal infrastructure. For example, we found evidence of reduced sage-grouse survival probabilities at relatively high distances from the plant as a result of increased raven numbers, which was driven by other factors unrelated to the geothermal activity. So, we were able to account for raven density while estimating the influences of the plant itself. Although it’s important to point out that infrastructure associated with geothermal power likely has positive influences on ravens and may, in fact, be one of the major mechanisms that reduced sage-grouse nest survival near the plant.
This study particularly focused on geothermal plants, but could its findings be applied to other renewables such as wind or solar farms that also come with anthropogenic structures?
Although our study focused on the impact of only geothermal energy production, other research has found similar adverse effects of other types of renewable and non-renewable energy infrastructure, with a few exceptions. It is more commonly known that anthropogenic features in general impact sage-grouse populations. These are human-related features that are not natural to the environment, like a roadway, facility, or a transmission line, as opposed to those structures in the environment that are natural, like, for example, trees and rock outcrops. Sage-grouse face numerous other threats beyond energy infrastructure, and we didn’t really compare, if you will, all threats to sage-grouse populations to determine where geothermal energy fits in contrast to those other threats. It is also important to recognize that disturbances from geothermal energy occupy relatively less area than many other forms of anthropogenic disturbances, like urban development and non-renewable energy development across the range.
That said, the typical location within sagebrush ecosystems where geothermal energy is productive can align with critical habitats for sage-grouse populations. That is, similar conditions that benefit sage-grouse and other wildlife are often found along with geothermal activity, such as mesic conditions and water sources. Although geothermal might have less overall footprint compared to other forms of disturbances across sage-grouse range, we now know it has profound effects in some areas where it occurs, impacting multiple population vital rates like nest survival and adult survival, which can have profound impacts to nearby populations.
Tell me about this quantitative support tool. How might it be a solution for mitigating the adverse effects of geothermal plants in a sagebrush environment?
Our geothermal application tool was developed to provide energy developers and land managers with options when planning geothermal energy projects. The tool considers local habitat conditions, topography and information about space use and abundance of sage-grouse, based on a very large dataset of surveyed sage-grouse administered by the Nevada Department of Wildlife. The tool calculates topographic impedance given proposed infrastructure and implements the models we developed to predict impacts to other local sage-grouse populations where infrastructure is proposed. Because it is spatially explicit, it allows users to modify the plant location and infrastructure to minimize adverse effects.
Now, we investigated over 135 potential sites and processed that information within the Great Basin. Of those sites, just over 67% would have little to no impact on sage-grouse populations because current sage-grouse populations do not overlap at the site. The tool can also be used to evaluate planned expansions or modifications to an existing geothermal energy plant. So it can be used directly by the developer or producer in planning the design of the plant so that it helps to mitigate those effects at smaller spatial scales.
Providing resources like the geothermal application tool developed from this study can aid the decision-making process for new and distinct geothermal energy projects. We plan to expand this tool to account for other types of energy and non-energy related anthropogenic infrastructure in the environment. This will likely include investigations of mining, for example, and other mineral extraction activities.
So what’s the big takeaway that the average Nevadan should know about as it relates to this study?
I’m pretty certain the average Nevadan at some point in time has heard of sage-grouse. It’s a species that makes the media headlines quite often, and it has the interest of numerous groups. For example, it is still a game bird and has the interest of the hunting community. It has the interest of the birder community because of its elaborate courtship displays, which are spectacular to witness. It also is a species of high conservation concern as the species has experienced declines of about three percent annually over the last six decades amounting to ~80% losses since the 1960s, so it has earned interest of numerous conservation groups.
I discussed earlier that sage-grouse provide an indicator for the health of the sagebrush ecosystem based on using different habitats to meet their life history needs. For these reasons, sage-grouse are sometimes referred to as an emblem or icon of the West. In Nevada, sage-grouse populations are quite abundant; representing ~20% of the populations across 11 western states.
That said, Nevada offers some of the most ecologically rich and diverse ecosystems in the nation, as well as an abundance of resources that contribute to its economy, such as renewable energy production, like geothermal, solar and wind, but also mineral extraction from mining activities. So the importance of developing innovative decision support tools that rely on empirical data that inform how to minimize environmental impacts while meeting Nevada’s economic goals cannot be understated.
This study helps us understand mechanisms driving adverse impacts associated with geothermal energy production and offers an innovative tool for planning the design and placement of infrastructure to reduce adverse effects on sage-grouse populations, and perhaps other wildlife, leaving viable populations for future generations to enjoy.
This interview was edited slightly for clarity.