Bird v. bird: The complicated relationship between sage grouse and their avian predators

Rancher Truman Julian says he has “a place in his heart” for greater sage grouse. A former wildlife biologist who still works land his family homesteaded near Kemmerer, Wyoming, around the turn of the 19th century, Julian has piped spring water to troughs at the dry edges of his private ground that he says benefit both sage grouse and livestock, and has installed special ramped screens the birds can climb to escape drowning

should they fall in.

Sage grouse, best known for males’ elaborate chest sac-puffing mating displays, need all the help they can get. Though the species persists in 11 western states and two Canadian provinces, it occupies

less than half its historic range; its numbers have fallen from historic estimates in the millions to as few as 200,000 today. Environmentalists, ranchers, government officials, sportsmen, scientists, and others have been rushing to bolster sage grouse populations in advance of the U.S. Fish and Wildlife Service’s decision this fall about whether the bird deserves special protections under the Endangered Species Act.

Because sage grouse declines stem from habitat fragmentation and loss, much of the recovery work has focused on protecting and restoring what’s left. But Julian wondered about another variable. “Over the last 10 to 15 years, we’ve built up a lot of ravens,” he says—whole fields black with them. “They raid everything. They kill our lambs. We had a rancher that lost five calves when ravens pecked into their hind-leg joints.” Local producers were increasingly calling on Wildlife Services—a federal agency tasked with managing human-wildlife conflicts—to poison ravens at calving and lambing time. Since ravens also gobble sage grouse eggs, Julian thought, why not ask researchers to look into whether the agency’s effort to protect livestock boosted local sage grouse as a side effect?

Jonathan Dinkins ended up with the project as a Utah State University PhD student in 2008. It’s normal for sage grouse to get eaten, says Dinkins, now a post-doc at University of Wyoming: they’re the natural prey of many different species, including ravens. But a raven boom could be contributing to a grouse bust. So in part, he would try to determine whether killing ravens actually helped more sage grouse nests succeed—that is, let more eggs hatch into chicks. It was a good opportunity, he says, “to look at management as it would occur.”

He also wanted to investigate whether avian predators in general—ravens and magpies as well as raptors that kill adult grouse—had broader impacts by affecting sage grouse behavior. Could they change how the birds used the landscape? Even make otherwise choice nesting and brooding habitat unusable by scaring sage grouse away?

In other words, could the mere threat of predation be eating away more of the habitat the already struggling grouse so desperately needed? More…