The Bridger Mountains fall raptor migration is particularly noteworthy for large concentrations of Golden Eagles. With a long-term average annual count of more than 1,500 birds, the Bridger flight is the largest known concentration of migratory Golden Eagles in the U.S. The Bridger flyway, a component of the regional Rocky Mountain Flyway, also attracts many other migrating raptors, with 18 species recorded since HawkWatch International (HWI) began monitoring the flight in 1991. Overall, combined-species counts typically range between 2,000 and 3,500 migrants per fall season.

Besides Golden Eagles, the other most commonly recorded migrants in the Bridgers include Sharp-shinned Hawks (average count 332), Cooper's Hawks (164), Red-tailed Hawks (102), Bald Eagles (81), American Kestrels (77), Northern Harriers (49), Northern Goshawks (36), and Rough-legged Hawks (34). Other species seen every year in smaller numbers include the Osprey, Broad-winged Hawk, Merlin, Prairie Falcon, and Peregrine Falcon, with Swainson's and Ferruginous Hawks also seen in most years. Although not usually seen in the lower states before November, HWI observers are also always on the look out for another sighting of the rare Gyrfalcon, seen once at the site in 1999.

Recent satellite tracking of Golden Eagles born in Alaska and of migrants outfitted at several locations in the western U.S. has confirmed that the Rocky Mountains comprise a primary migration corridor for Alaskan and Canadian eagles. Winter destinations range throughout the Rocky Mountain front-range and western Great Plains, in some cases extending into Mexico. Southeastern New Mexico and adjacent areas of western Texas have proven to be hotspots of winter range activity for eagles tracked by HWI from summer ranges in western Canada and along routes running through the Bridger Mountains region. Similar satellite tracking of Rocky Mountain Red-tailed Hawks has revealed summer ranges throughout the northern Rocky Mountains and typically winter ranges in various regions of Mexico from Sonora/Chihuahua to Oaxaca and east to the Gulf Coast. Extensive band-return data has revealed similar patterns for Rocky Mountain Sharp-shinned and Cooper's Hawks, except that most winter in far southwestern Mexico.

HWI observers monitor the Bridger migration daily from 27 August through 31 October each year. October is the peak activity period for both Golden and Bald Eagles, with Rough-legged Hawk activity mostly confined to the latter half of October. In contrast, the migrations of a few other species, such as Ospreys, Broad-winged Hawks, and Swainson's Hawks, are generally confined to September. For most other species, however, activity begins to pick up markedly in mid-September and generally peaks during the period spanning the last 10 days of September and first 10 days of October. Weather permitting, late September and early October are therefore the most productive times for visiting the site to see many species, with mid-October the best time for seeing lots of eagles. Peak daily activity periods vary with weather conditions, but generally extend from late morning to mid-afternoon.

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