The loss of sagebrush and the disappearance of food species for raptors are reducing the golden eagles and prairie falcons in the Snake River Birds of Prey National Conservation Area, according to government research.
A study that began in 1990 has been released on the 485,000 acres along an 81-mile stretch of the canyon south of Boise. It has the highest known density of nesting raptors on the continent, as well as many wintering and migrating birds of prey.The research was done by the U.S. Geological Survey's Biological Resources Division, Boise State University and others.
It was funded by the U.S. Bureau of Land Management and the Idaho Army National Guard to address concerns raised in the 1980s about military training on the table land above the canyon, the feeding area for raptors.
The most important change is the loss of half of the native shrub lands since 1979. Larger fires are more frequent. The complete destruction of shrubs could occur within 25 to 50 years without fire suppression, while it would take up to 80 years to restore them.
Area Manager John Sullivan said the study showed "exotic" grasses such as cheatgrass were making inroads.
It results in greater fluctuations in Townsend's ground squirrel populations and a reduction in jackrabbits. And that means fewer eagles and prairie falcons, for which the conservation area is well known.
"The complex balance of nature in the NCA is shifting. The research tells us that we must restore native shrubs and perennial grasses to avert long-term declines in important wildlife populations," Sullivan said.
"The research also has some good news," he added. "Four species of birds of prey are essentially unaffected by wildfire and military training. Northern harriers, burrowing owls, shorteared owls and ferruginous hawks are doing really well in the grasslands."
Military training with tracked vehicles such as tanks disturb the soil. It also alters the foraging behaviors of prairie falcons and other birds when it occurs during their breeding seasons.
Gen. Jack Kane, adjutant general of the Idaho Army National Guard, said the study directs the military to conduct its training so it minimizes environmental impacts.