If you are a frequent reader of our blogs, you likely know that eagles around the world face many challenges and human-caused threats. We’ve similarly shared concerning news about the status of Golden Eagles in the western U.S., as well as some of the tools we have been researching to benefit this species. In this blog, we’ll dive a bit deeper into one such tool, namely, the management of roadkill to reduce eagle-vehicle strike (EVS) risks for scavenging eagles.
Golden Eagles drawn to a roadkill deer in western Wyoming “captured” flushing from a passing vehicle with a previously installed motion-sensitive camera.
First, you might be wondering how Golden Eagles get into trouble with vehicles. After all, they are huge birds that mostly inhabit remote landscapes and shy away from people, right? True, but they also require lots of food to survive the winter, which can be hard to come by when many prey species are hibernating, hidden by or under the snow, or simply occur at lower abundances. Eagles wintering in cold climates rely on the increased mortality of large mammals like deer to get them through this tough time. Unfortunately, human-caused habitat change has shifted where many big game animals die in the winter, with many more now dying along our roadways. Eagles that take advantage of the abundance of roadkill in “hot spots” can then be struck when flushing away from approaching vehicles.
HawkWatch International’s interest in the EVS issue coalesced in late 2014, shortly after we began placing transmitters on nestling Golden Eagles (2013) and we found our first monitored eagle struck along a road in central Utah. Investigating this bird’s demise led to the discovery of a previously unknown eagle and roadkill winter hot spot. At about the same time, we were in the thick of attending meetings where the U.S. Fish and Wildlife Service (USFWS) and wind companies were discussing how best to offset eagle mortalities that occurred at wind farms. The USFWS had developed a means to estimate how many power poles needed to be made “safe” to equal an eagle saved from electrocution. This was the only tool available to wind companies trying to do the right thing (i.e., offset their wind turbine eagle deaths), but there was concern that the calculations were based on a single study from a small area, in addition to various implementation hurdles. This sparked the realization that we could and should research the eagle-vehicle strike issue in greater depth as a possible solution.
A Golden Eagle caught on camera flushing from a roadkill deer during our pilot field season.
After conducting a small pilot study in central Utah in the winter of 2015-16, we were convinced that this issue was bigger than widely believed and ripe for in-depth study. We crafted a research proposal and shared it widely with energy companies, USFWS, and other possible partners. To make a long story short, we were fortunate enough to gain the support of multiple companies and carried out a 3-year research project in Oregon, Utah, and Wyoming, in what was to become our “Phase I” work. Our goal was to quantify the issue over large landscapes in distinct areas to make the results as applicable as possible.
As is often the case with new research, we learned an incredible amount in those first years, adapting as we went, and ending with a whole new set of questions. Most importantly, we found that eagle-vehicle strikes occurred most commonly where densities of live eagles and big game roadkill overlapped, making such areas relatively easy to identify. This is important because we quickly learned that dead eagles disappear very quickly, through both legal and illegal collection for feathers, so identifying problem areas by searching for dead eagles alone was not the way to go. We also published our first paper on this topic, showing that moving roadkill 12 m from the road had the dual benefits of increasing eagle feeding, and decreasing flushing from vehicles (Slater et al. 2022; see graph at left).
The likelihood of Golden Eagles flushing off roadkill in response to vehicles decreases with each meter farther from the road edge.
Taking what we learned from Phase I and our new set of questions, we were able to obtain funding from the National Fish and Wildlife Foundation and a few wind companies to move into Phase II.
The next two years of research in western Wyoming focused on more intensive driving surveys, detailed tracking of each eagle carcass to determine “persistence rates”, and weekly relocation of roadkill to “eagle safe” distances from the road. This research not only generated additional data to quantify the EVS issue, it also allowed us to demonstrate the feasibility of roadkill management with 2-person teams. Additionally, we learned that eagles may still put themselves at collision risk, even when we move lots and lots of roadkill, due to high competition between eagles in roadkill hot spots and past learned behavior. This suggests the frequency of roadkill relocation or removal needs to be on pace with the local accumulation of roadkill.
A roadkill deer being moved from the side of the road by our EVS field crew.
Throughout the two phases of this research, we have collected a wealth of data, including 6.15 million photos from over 400 camera deployments, 7,249 photographed interactions between eagles and vehicles, and 4,570 observations of roadkill. We found 65 dead Golden Eagles (and 14 Bald Eagles), despite how quickly they get picked up. What we’ve learned from our EVS data and complementary eagle tracking studies is that vehicle collisions are a leading anthropogenic (human-caused) source of eagle mortality, likely resulting in hundreds of deaths per year. The good news is that our research has already led to a publication on how far to move roadkill to make it eagle safe (see link and graph above). Our data is also being used by partners in an updated model that quantifies the relationship between roadkill removals or relocations and eagles saved in Wyoming. Our next crucial step will be to create a West-wide map overlaying hot spots of big game roadkill and eagle winter distributions to reveal where to prioritize this work. Finally, we are working with the USFWS and wind industry in various other ways to move roadkill management towards acceptance as a quantifiable mitigation tool.
In the meantime, we aren’t letting the necessarily slow process of model development, peer review, and changing the status quo get in the way of saving eagles! We are currently in the second year of a roadkill relocation demonstration project in central Utah (where it all began for us), covering 120 miles of roadway with weekly visits. Thanks to the small army of field technicians that have participated in this work in the past, and a special thanks to our current crew members, Frankie Vierela and Ricky Robbins. And many thanks to the numerous funders and partners that made this work possible!
This blog was written by Dr. Steve Slater, HWI’s Conservation Science Director. You can learn more about Steve here.