Riding thermals high above the canyon on 3-foot wings, the falcon looks for the slightest movement of prey in the sagebrush below. The bird's predatory wheeling shows unconcern for the man peering up from the rim of the gorge.
The three — Falco mexianus, Homo sapiens and that prey, usually Rodentia — are, for the moment, confronting the same menace: a Eurasian invader that biologists and ranchers call "cheatgrass."
The weedy plant is changing the Western landscape from sage blue to brown stubble. It has spread across the Great Basin, penetrating even this remote section of the Snake River Gorge in Idaho.
More raptors nest at the Snake River Birds of Prey National Conservation Area than anywhere in the lower 48 states. The basalt gorge, a 30-minute drive south of Boise, is honeycombed with ledges and shallow caves that falcons, eagles, hawks and owls use to raise young.
This perfect raptor nursery is where Tom Sullivan, who oversees the natural area for the U.S. Bureau of Land Management, is making a stand against cheatgrass.
"Where birds will normally nest a half-mile from each other," Sullivan says, "we'll have a golden eagle nesting, and right below it you'll have a prairie falcon nesting. It's amazing."
About 700 to 800 pairs of raptors come here each year because deep soil above the canyon harbors the world's largest concentration of ground squirrels and other rodents, Sullivan says. "It's kind of like having the kitchen right next to the bedroom," he says. A nesting falcon or eagle simply has to hop out of its high-rise nest, catch the nearly constant updrafts that lift it above the canyon, find dinner on the level uplands, then glide back home to feed the kids. It is one of the closest things to a free lunch in nature.
But cheatgrass is changing the chuck wagon.
An annual grass inadvertently brought to North America in 19th century grain shipments, cheatgrass (Bromus tectorum) is a kind of vegetative firestorm. All over the Great Basin, it sneaks into native sagebrush communities, sprouts, goes to seed and turns quickly to tinder.
One spark can ignite thousands of acres in flame. And because high desert plants aren't adapted to frequent fire, the invasive foreigner takes over the land.
In the Great Basin, more than 3 million acres of public land are now dominated by cheatgrass. Nearly 70% of the 485,000-acre Birds of Prey National Conservation Area is infested with cheatgrass, upsetting the food chain, from rodents to raptors.
"Now, ground squirrels are grazing a grass they didn't evolve with, [a type] that doesn't have as much nutrition when they need it," Sullivan says. "And since they're basically the foundation of the food chain, the whole food chain doesn't operate like it did before."
As prey species decline, studies show that both prairie falcons — the most numerous of the conservation area's nesting raptors — and golden eagles have also declined.
"Historically, there were around 36 pairs of golden eagles that would nest along this stretch of the canyon," Sullivan says. "That number has declined to about 28. We think it's because of a loss of sagebrush."
Sullivan and others are now trying to save native plants to save raptors.
At a test plot once overgrown with cheatgrass, Sullivan walks through tufts of bunch grass that seem to be holding their own against the invasive weed. He points to another area thick with young sagebrush, restored by dropping seed from the air. And not far from here, farmers are growing Great Basin plants to increase the supply for further restoration.
But it's an uphill battle. Funding is a constant problem, planting on arid ground often fails, and fire can erase restoration.
Sullivan shrugs, then something catches his eye. "Prairie falcon," he whispers as a bird glides across the sky. Signs of hope can be hard to find when you're fighting cheatgrass, but Sullivan knows that's one of them.