Inventory and Monitoring of Bald Eagles and Other Raptorial Birds of the Snake River, Idaho: 1998 Bald Eagle Territory Descriptions and Raptor Surveys and Bald Eagle Productivity 1998-2000

The Snake River Bald Eagle and Raptor Project, a five-year effort, was initiated in 1994 with two primary objectives: 1) to monitor bald eagle productivity in Southeast Idaho, and 2) to develop a monitoring program for raptorial birds in the Snake River study area. The South Fork Snake River study area in Southeast Idaho, including the lower Henrys Fork, is recognized for its highly productive bald eagle breeding pairs and diversity of raptors. This report covers work completed in the final year of the project, 1998. It also summarizes bald eagle productivity observations from 1998-2000.

In 1998, there were 47 known bald eagle breeding areas within the Southeast Idaho portion of the Greater Yellowstone Ecosystem, up from 39 breeding areas in 1994. In 2000, there are 51 known breeding areas and more are suspected.

Even though young bald eagle pairs are occupying new nests, we are witnessing the gradual loss of historically productive bald eagle nesting areas, primarily on private lands now being developed. This is particularly troubling because the newer territories are generally in the less productive habitat. Ironically, the nesting areas at greatest threat have historically been the most productive breeding areas on the South Fork. This loss of preferred bald eagle nesting habitat is most apparent in the South Fork reach from Palisades Dam to Conant Valley, and highlights the importance of protected habitats.

In 1998, we focused our raptor surveys on location of nesting raptors, both diurnal and nocturnal, on the upper South Fork from Palisades Dam to the Heise area. We have documented the high value of riparian cottonwood forests and nearby Douglas-fir forests for many nesting birds of prey. Of less noted but perhaps equal value, the cottonwood bottoms provide high quality winter habitat for several of the raptor species studied here.