Using field observations and high-tech tracking technology to identify golden eagle migration flyways

Author

Carol McIntyre, wildlife biologist for Denali National Park and Preserve and the Central Alaska Inventory & Monitoring Network

Golden eagles are just one of the many migratory birds that benefits from the protection of Wrangell-St. Elias National Park and Preserve.

NPS/Jared Hughey

If you study a map of Alaska, it probably isn’t too surprising to learn that a substantial number of golden eagles migrate through the interior portions of Wrangell-St. Elias National Park and Preserve. The park is located at the northwestern curve of the North American continent, where multiple mountain systems bend together in a sweeping westerly turn (Brown and Elder 1982). Migration corridors for many species of birds follow these contours—from sea ducks that migrate along the coastline to blackpoll warblers that migrate inland. The people who proposed the park boundaries knew the importance of the area to nesting trumpeter swans and other waterfowl, but I often wonder if they knew about how important the area was to myriad species of other migratory birds. I thought about this when I was finishing this essay during the week when we are honoring the legacy of U.S. President Jimmy Carter. Forty-five years ago, Carter signed the Alaska National Interest Lands Conservation Act that brought Wrangell-St. Elias National Park and Preserve into the U.S. National Park System. With the stroke of a pen, Carter protected some of Alaska’s most important golden eagle migration corridors ensuring that they had places to rest and refuel as they returned to their northern breeding areas. I am not sure if he knew this, but he clearly understood the importance of protecting the resources within this park and all of Alaska’s national parklands. In the forward to William Brown and Carolyn Elder’s 1982 book, Alaska National Parklands, This Last Treasure, Carter wrote: “This book describes how these lands were protected in the past. They must continue to be protected now and in the future.” For golden eagles, and all the other migratory birds that migrate through our parks, Carter’s words ring clear.

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Documenting Where and When

The list of documented places where raptors concentrate during migration in Alaska is relatively short. Using data from multiple telemetry-based projects focused on quantifying movements of Alaska golden eagles and field observations of migrating golden eagles, we’ve put portions of Wrangell-St. Elias National Park and Preserve firmly on that list. This essay highlights some of our recent findings and builds upon information reported in McIntyre and Lewis (2016).

Telemetry data were key for revealing the spring migration corridors through the park (Figure 1). Telemetry data from breeding-age golden eagles telemetered by Alaska Department of Fish and Game biologists near Gunsight Mountain during spring migration in 2014 to 2016 were particularly important for showing how migrating golden eagles avoid flying over the higher elevations of the Wrangell Mountains (Eisaguirre et al. 2018). They also revealed the two primary migration corridors in the area: one to the south and one to the north of the higher elevations regions of the Wrangell Mountains (Figure 1). Telemetry data revealed that golden eagles that are members of breeding populations migrate through the area from mid-March to early April, while those that are not generally migrate through the area from mid-April through late May. We also learned from the telemetry data that golden eagles from territories ranging from southcentral to northwest Alaska migrate through the northern corridor, but only eagles from territories in southcentral and southwest Alaska migrate through the southern corridor (Eisaguirre et al. 2018, USFWS, ADF&G, and NPS unpublished data).

Figure 1. Compiled relocations of golden eagles from multiple studies ranging from 1997 to 2024 during spring migration in and adjacent to the park. A black star notes the location of the Mentasta Mountains study sites and black circle notes the general location of Gunsight Mountain Hawk Watch.

Counting How Many

We conducted field work in study sites along the southern flanks of the Mentasta Mountains (Figure 1) from mid-March through early April from 2020 to 2024 focused on capturing breeding-age eagles for a telemetry-based study. During those years, we made annual counts of migrating golden eagles incidentally when we were engaged in other field activities or through dedicated searches when we had time to learn more about how many golden eagles were migrating through the area. Despite the limitations of our counts, due to incomplete coverage across the season, they clearly indicated that a substantial number of golden eagles migrated through the area in some years. We were curious about how these numbers compared to those compiled at the Gunsight Mountain Hawk Watch (Gunsight), which is about 130 miles (210 km) southwest of our study area and is the only other area in Alaska where people counted migrating golden eagles during spring migration during the same time periods. The Gunsight area is the most well-known raptor migration concentration area in Alaska. People have been watching spring raptor migration in that area for decades and earlier observers suggested that more golden eagles migrate by the Gunsight area each spring than anywhere else in North America, save for a few sites in the Rocky Mountains (Fritz and Fritz 2011). What these observers didn’t consider at the time, but what the telemetry data clearly show, is that all of the golden eagles that migrate by Gunsight during spring migration first migrate through the park. And, thanks to the telemetry data, we now know that, in many years, some of them migrated north of the Wrangell Mountains before veering southwest and passing by the Gunsight area. Thus, it wasn’t too surprising to learn that the numbers of golden eagles we detected per observation hour was often higher than those detected by the counters at Gunsight during the same time period (Figure 2). And since our counts provide a conservative minimum estimate of the number of golden eagles migrating during our study period, it is highly likely that far more migrated through our study area than indicated by our counts.

Figure 2. Number of golden eagles detected per observation hour at the Mentasta Mountains and Gunsight Mountain study sites from mid-March to early April 2021-2024.

Significant Migration Paths

In both 2022 and 2023, we counted more than 1,300 golden eagles migrating through our study area during our three-week study period. Our count data clearly show that a substantial number of golden eagles migrate through the northern corridor, but we still don’t know how many eagles migrate through the southern corridor in spring, or how many more eagles migrate through both corridors after early April. However, the telemetry data, our spring count data, and information presented in McIntyre and Lewis (2016) show that substantial numbers of golden eagles migrate through portions of the park in autumn and spring migration, clearly suggesting that these areas are important golden eagle migration flyways in Alaska.

References

Brown, W. E. and C. Elder. 1982. Alaska National Parklands, This Last Treasure. Alaska Natural History Association, Anchorage, Alaska. 191 pages.

Eisaguirre, J. M., T. L. Booms, C. P. Barger, C. L. McIntyre, S. B. Lewis, and G. A. Breed. 2018. Local meteorological conditions reroute a migration. Proceedings Royal Society B 285:20181779.

Fritz, P. and C. Fritz. 2011. The hawks of Gunsight Mountain, Alaska. Birding January 2011:31-36.

McIntyre, C. L. and S. B. Lewis. 2016. Observations of migrating Golden Eagles in eastern interior Alaska offer insights on population size and migration monitoring. Journal of Raptor Research 50: 254-264.

Learn More

Monitoring Golden Eagles

Acknowledgements

Thanks to Travis Booms, Alaska Department of Fish & Game wildlife biologist, for providing access to tracking data on the eagles telemetered at Gunsight Mountain; Ray Hander, project volunteer, for the untold number of hours he spent working on this project; Ike and Nuala Rego and Kyle Cutting for helping us count golden eagles; and Buck Mangipane, wildlife biologist at Lake Clark National Park and Preserve, for securing and overseeing the project funding.