KAREN STEENHOF Boise, Idaho District Office

Each spring, as cheatgrass and ground squirrels emerge from the thawing desert soil, more than one thousand birds of prey congregate in the sheltered canyonlands along a seventy-five mile stretch of the Snake River in southwestern Idaho. The Snake River Birds of Prey Natural Area, less than an hour's drive from the city of Boise, provides a valuable and unique nesting area for birds of prey. Here, golden eagles, prairie falcons, red-tailed hawks and ten other species of raptors find suitable nesting sites in the crevices of towering volcanic cliffs.

The Natural Area and an adjacent canyon 42 miles upstream host the densest known nesting population of raptors in the world, and 80 percent of this nesting population is administered

by the Bureau of Land Management. BLM became actively involved in raptor habitat preservation and management in 1971 when the Secretary of the Interior signed Public Land Order Number 5133 forming the Snake River Birds of Prey Natural Area. This protective withdrawal preserved nesting habitat along 33 miles of the Snake River Canyon.

Prairie falcons are the most numerous of the 13 raptor species nesting within the southwestern Idaho sanctuary and further upstream. Last year 202 pair, approximately ten percent of the prairie falcons left in the world, nested along the 75 mile stretch of the river. Thirty golden eagles and 61 pair of red-tailed hawks also reared their young within this stretch of the Snake River Canyon Law LEN in 1977.

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Kestrels, marsh hawks, turkey vultures, Swainson's hawks, and ravens also select nesting sites within the canyon. Ferruginous hawks, the largest buteos in North America, nest in the cliffs and desert shrub surrounding the canyon. Bald eagles, rough-legged hawks, ospreys, sharp-shinned hawks, and Cooper's hawks use the area during the non-breeding season. The Natural Area also hosts six species of nocturnal birds of prey; the great horned owl, the barn owl, the screech owl, the short-eared owl, the long-eared owl, and the burrowing owl.

The canyon shelters raptors from the elements and predators. The canyon alone, however, is not adequate to sustain the birds, and the canyon is not the sole reason for the bird's intensive use of the area. The surrounding desert provides abundant prey and comprises the essential hunting grounds for all raptor in the area. For example, prairie falcons, who feed almost

exclusively on the Townsend ground squirrel, range more than ten miles from their nests to secure adequate food. Golden eagles must also hunt large desert expanses to secure their favorite food, the black-tailed jackrabbit.

Although the nesting sites of the raptors in the Natural Area had been preserved, the habitat that supports their prey just outside the Natural Area had not. Each year, more land was being planted in sugar beets, potatoes, alfalfa, and wheat under such public land disposal laws such as the Carey Act and the Desert Land Act. Unfortunately, jackrabbits and ground squirrels are not compatible with agriculture.

The competition between men and raptors for the same piece of real estate was underway in 1972 when BLM hired Mike Kochert as a raptor research biologist. Some of the questions facing BLM then

were:

How much prey is required to sustain a nesting pair of raptors and their young?