Pronghorn Passages: Will Large-Scale Solar Keep Animals From Moving?

Photo by Collin Sanchez

*All observations are preliminary and subject to change 

Background

Among the great evolutionary adaptations of nearly all animals is their ability to move. Movement freed animals from patiently waiting in one spot for food or chances at reproduction, and the ability to move is critical for populations or individuals to secure important resources, avoid deep snow, locate seasonal water sources, or seek mating opportunities.  

For more than 30 years, understanding and maintaining the ability for animals to move and connect has been the cornerstone of Wildlands Network’s mission.   

The term “corridor” has, to some degree, become synonymous with animals’ movements and connectivity. In particular, corridors are often associated with seasonal migration, and indeed the conservation value of corridors for migration has been well described in the example of the Path of the Pronghorn, the nation’s first federally protected wildlife corridor. Movement ecologists identify and classify different types of movements with concomitant consequences and benefits.

Such classifications include commuting or daily movements that allow animals to connect to water or food, dispersal which is generally seen as movements of young animals moving to new areas away from where they are born, and seasonal migration where individuals make relatively large movements from one area to another.  

The term corridor can generally be thought of as “any space that facilitates connectivity over time among habitat patches” (1). Yet, referring to a space as such or creating a location that animals might move through does not make it a corridor.   

Among the potential effects that solar construction may have on wildlife, especially pronghorn, is to alter or even block their daily or seasonal movements. All large-scale solar installations must, by law, be fenced. The kinds of fencing can vary but are generally chain-link or woven wire and are at least six feet tall (Figure 1). In addition to keeping humans out, these fences are also impermeable for most large wildlife like pronghorn, deer, and elk. 

Figure 1. (Left) Woven-wire fence surrounding solar panels in northern New Mexico and (Right) A pronghorn standing in front of fencing and panels. Photos by Wildlands Network

Although we expect that large mammals will be excluded from the interior of solar facilities, there has been little research on determining if the effects of solar development extend beyond the perimeter of the fencing. In addition to impermeable fencing, the photovoltaic panels themselves are large and can obstruct views through the facility.  

Because pronghorn rely on their vision to identify predators and conspecifics, we hypothesized that the interactions of fencing and panels might cause pronghorn to avoid facilities altogether or refuse to come within some unknown distance of them.  

If this were true, then solar facilities could negatively affect animals at several times the size of the fenced facility. Moreover, it could negate the usefulness of passages within or near solar facilities designed to accommodate animal movements.  

In 2022, when we began to think about how wildlife might interact with utility-scale solar energy (USSE) (also known as large-scale solar) restrictions or alterations to all types of animals’ movements and connectivity were chief among our thoughts.  

Within industry and agencies, we often hear the term ‘corridors’ used when discussing the possibility of creating passages between fenced arrays that would facilitate connectivity. To try and create a distinction between true corridors, that animal use, and spaces that we hope they will use, we have taken to calling spaces between fenced arrays passages or wildlife movement pathways.  

Semantics aside, the creation of these passages for animals has raised as many questions as it answers. Will animals use these passages? How large must a passage be or how should they be constructed? Will all species respond the same way to similar types of passage? How many passages are needed for any given solar array? The complexity can seem overwhelming; particularly when there is no guarantee that wildlife will use them.  

Current observations 

As we have detailed in previous updates, we have affixed global positioning system (GPS) collars to 75 female pronghorns across two study areas, and since March 2024 have been collecting locations once every hour. During this same period, construction of the 1,100-acre San Juan solar facility was already underway and was completed in the fall of 2024. The San Juan solar facility was designed to accommodate existing public roads, a multitude of private landowners, and landscape features such as dry washes (arroyos), which led to the construction of many individually fenced solar arrays (Figure 2).  

The passages between panel arrays vary dramatically in their lengths, widths, and in proximity to varied terrain (washes, hills and cliffs, and roads), and has given us a unique opportunity to begin answering some of the many questions about how pronghorn will avoid or use these areas.  

Figure 2. The San Juan solar facility (red polygon) in northern New Mexico. The black lettering and arrows represent the width of passages between arrays, while the blue arrows show total length of one corridor. Map by Wildlands Network 

Although still early in our study, our current results suggest a relatively optimistic outlook for pronghorn movements near solar. Thus far, we do not see any strong evidence that pronghorn refuse to come near solar facilities or that there is a threshold distance from which pronghorn use decreased compared to other areas.  

Of the 30 females we originally collared near the San Juan Solar facility, 18 (60%) have come within 100 meters (328 feet) of the solar fencing. 

In sum, we have yet to see evidence that fencing or solar developments are keeping pronghorn from using areas right up to solar fencing or moving near at least one solar installation.  

Figure 3. Pronghorn locations (colored symbols) around San Juan solar (red polygon). The blue area shows a 300-meter buffer around the facility and green colored polygons show passages between fenced arrays. Map by Wildlands Network

The way pronghorn use space near solar appears to be related to the resources they need. When we began our research, we thought that the narrowest corridors would be universally avoided. Our research shows that the largest areas or passages near solar have indeed been used at the highest rates, while the longest and narrowest passages have had very limited use.  

To our surprise though, we have seen pronghorn using the narrowest, but also the shortest, passage to access critical resources over relatively short periods of time. In short, an animal’s willingness to use a passage must be placed in the context of what individuals and populations need from the landscape and how solar developments alter or impedes access to those needs. Pronghorns’ willingness to use passages of all sizes and shapes led us to take a closer look at how other resource values might be dictating that usage. 

Even within well-used passages, pronghorns are not using them equally. Within the largest passage of the solar facility, we have observed that pronghorns prefer to use only portions of the available space (Figure 4).  

At first, the data might suggest an affinity for solar fencing, but a closer inspection is instructive to our thinking. A large arroyo or dry wash runs through the passage and is among the reasons the area was not fenced. The arroyo has steep cliffs that prevent animals from crossing it in most areas, and, on the western edge, solar panels and fencing were constructed within 30 meters.  

Pronghorn appear to seldom use the space between the arroyo and fencing. Additionally, some land immediately adjacent to the arroyo itself is carved with small waterways, shrubs, and loose sand, and collared pronghorns use this area infrequently. 

Figure 4. Wildlife movement pathway (blue arrows show the width in meters) with locations of pronghorn (red dots). The thin dark line running through the pathway is a deeply incised arroyo. Map by Wildlands Network

Figure 5. Colored lines show estimated movements (dots represent true locations) around the San Juan solar facility by pronghorn females over 48 hours. Map by Wildlands Network 

Current Ideas 

What lessons might we take from our present observations? Among them is that the proximity of fencing to natural terrain can be important. Leaving additional space, when possible, between existing features (like rivers, arroyos, or roads) and solar fencing might increase the likelihood that animals will utilize those areas.  

More importantly, if there are locations that are important for animals, like those containing food or water, then creating additional space or larger passage is justified. Collecting such data can be difficult, but using GPS trackers, cameras, or other methods, we can begin to understand on a fine scale how animals use or avoid particular areas of landscapes and/or what passages they might prefer and possibly where we might build additional passage (Figure 5).  

At present, we can’t offer anything conclusive, but there is plenty to consider and continue to study. Despite all the data we have collected, it represents just one year in one landscape at a single solar facility. Consequently, we urge caution when considering our initial results. What occurs here may not occur elsewhere, and it’s important to consider the underlying ecology of the landscapes where solar is being developed and how it’s constructed.  

Additionally, movements and use around solar facilities do not mean that there are no long-term effects from solar development as the result of habitat loss or degradation. We think the area occupied by the San Juan solar facility was, and remains, among the best habitat our animals have available – they just have less of it now.  

Identifying good habitat and access to that habitat is a critical consideration for solar development. Our observations are encouraging for the potential to better create solar facilities that allow animals to retain their ancient movement patterns and have enough habitat to sustain them for generations to come.  

(1) Hilty, J.A., Keeley, A.T., Lidicker Jr, W.Z. and Merenlender, A.M., 2019. Corridor ecology: linking landscapes for biodiversity conservation and climate adaptation. Island Press 

Cover image: Wildlands Network