Twenty-five years ago, the only documented raptor migratory “hot spots” in the United States were in the east: Cape May, New Jersey, Hawk Mountain, Pennsylvania, and Hawk Ridge in Duluth, Minnesota, to mention a few. Raptors were thought to congregate over distinct flyway sites in the East but were too scattered in the West to show in considerable numbers over any one location. And, as far as anybody knew, Golden Eagles were not seen in the lower 48.
However, a few years later, Fred Tilly, a biologist with a particular interest in raptors, was visiting friends in Bozeman, Montana, and decided to go into the Bridger Mountains to observe what was flying. He understood he had hit the hawkwatcher’s equivalent of the mother lode at the top of the mountain, about 9000 feet above sea level.
The Bridger Mountains are aligned north-south near the western end of the Great Plains, when the Rockies begin to appear in somewhat isolated ranges. Between those ranges lie vast swaths of undeveloped territory teeming with rodents, snakes, birds, and carrion—essential components of the Golden Eagle’s diet. With prevailing winds from the west, the Bridgers offer an almost continuous updraft over their 42-mile length—ideal for migratory raptors, particularly eagles. During migration, huge raptors like eagles and buteos take use of the wind as much as possible, taking advantage of updrafts so they don’t have to lose energy flapping their wings to remain aloft.
In the fall of 1979, Fred noticed that migrating Golden Eagles were using the Bridger Range as a freeway, skimming along on the steady updraft and sometimes dropping down into the valleys on either side to look for food. That first year, he counted 342 Golden Eagles as well as 12 other species of raptors, including the first observation of a Broad-winged Hawk in western Montana. When he submitted his results to the Hawk Migration Association of North America (HMANA), the chairman, Mike Harwood, described the discovery of the migratory point as a significant advance.
Tilly returned in the autumn of 1980 and discovered similar activities. He saw 563 raptors in 75 hours, including 211 Golden Eagles and a handful of Broad-winged Hawks, as well as Bald Eagles, Sharp-shinned Hawks, Northern Goshawks, Turkey Vultures, Red-tailed Hawks, Rough-legged Hawks, Ferruginous Hawks, Northern Harriers, Peregrine Falcons, Prairie Falcons, and American Kestrels.
A decade later, Hawkwatch International, a non-profit raptor conservation organisation located in Salt Lake City, launched an official count of the raptors travelling across the Bridger Mountains. Every year, from the beginning of September through the end of October, two observers spend as much time as they can, in all weather, at the observation position on the ridge above Bridger Bowl Ski Resort. They have documented an astonishing number of raptors in the previous 10 years, but the most valuable prize has been the knowledge they have obtained regarding Golden Eagles. The Bridger Range is the most major concentration location for Golden Eagles in the continental United States, with about 2000 of the enormous birds tallied each season.
During the spring migration, Fred Tilly has been monitoring another Golden Eagle migratory location in the front range of the Rockies at Rogers Pass, northwest of the Bridger mountains, since 1987. The Bridger and Rogers Pass project sites complement each other well since the autumn Bridger count is largely made up of juvenile golden Eagles, while the spring Rogers Pass count is mostly made up of adults. (After the census, adult Goldens move through the Bridger site in November.)
Five years ago, the US Forest Service’s local office collaborated with the Sacajawea Audubon Society, Big Sky Wildcare, and Bridger Bowl Ski Resort to present the inaugural annual Bridger Raptor Festival, an event encouraging public education about, and enjoyment of, raptor migration in the area. Talks by local and regional raptor experts, identification workshops, and a live raptor display by Big Sky Wildcare, a local nonprofit committed to raptor rehabilitation and release, are all part of the Festival.
The Festival’s high point, so to speak, is guided raptor watching at the Bridger Mountains observation point (weather conditions permitting). For more information on this year’s Bridger Raptor Festival, call the Forest Service’s Bozeman headquarters at 406-522-2520. However, you don’t have to wait until the Festival to see the raptor migration. Though Golden Eagles may be seen soaring over the Bridgers at any time after late August, the peak of the migration is in early October. If the weather cooperates, a diligent watcher may witness up to 100 Goldens each day for two weeks. Because of the tremendous height, many of the eagles and other raptors soar over at eye level, making viewing both simple and fascinating. Few birding experiences can compare to seeing a Golden Eagle so close you can look it in the eyes!
By the end of October, the Bridger ridge is normally covered in snow, making the hour-and-a-half trek to the summit, which takes an hour and a half under normal circumstances, impracticable, if not impossible.
The hawkwatchers grudgingly pack their equipment and data sheets and return to town, despite the eagles continue to soar for another several weeks, wending their way down to the southern United States and Northern Mexico, where they spend the winter months.
The Bridger Mountains eagle migration studies conducted by Hawkwatch International would not be possible without the support of its members and sponsors. Thank you from the bottom of my heart for financing this project:
- Gallatin National Forest
- Inter Fluve, Inc.
- Sacajawea Audubon Society
- New Belgium Brewing Company
- LaSalle Adams Fund
- National Fish and Wildlife Foundation
Thanks and appreciation also to the following Bozeman businesses and organizations for their logistic, material and moral support:
- Wild Birds Unlimited (406-586-8861)
- Big Sky Wildcare (406-585-1211)
- Museum of the Rockies (406-994-2251)
- Bridger Bowl Ski Area (406-582-0526)
- Bridger Outdoor Science School (406-587-2111)
Jeff Pentel is a freelance writer, photographer, and birding guide in Bozeman, Montana. He can be reached at [email protected].