Carol Ryan Dumas/Capital Press
TWIN FALLS, Idaho — While the debate continues over whether grazing is detrimental or beneficial to sage grouse populations, both proponents and opponents of grazing are convinced a long-term study led by the University of Idaho will prove their case.
But it is still too early to have any definitive answers, said Karen Launchbaugh, a professor of rangeland ecology at the University of Idaho and director of the collaborative Rangeland Center.
Speaking at the Rangeland Livestock Symposium on Jan. 10, Launchbaugh said preliminary and correlative research indicate livestock grazing influences sage grouse habitat and nest success in ways that may be both beneficial and detrimental.
Past studies have taken a correlative approach and included little replication and variation in plot sizes. What is needed is a series of replicated studies across huge landscapes, which is what the university-led study is doing, she said.
That project, initiated in 2012, is looking at the effects of spring grazing on sage grouse nesting and includes such collaborators as the Bureau of Land Management, Idaho Fish and Game and ranchers.
Spring — when sage grouse are nesting and raising broods — is considered a crucial time for sage grouse survival. While fire and invasive grasses are the primary threats to sage grouse survival, some people view livestock grazing as a significant threat to nesting sage grouse, Launchbaugh said.
The direct effect of cattle trampling nests is uncommon because nests are under shrubs. Cattle flushing nesting birds is possible but doesn’t happen much, she said.
The rub is in the indirect effect of livestock eating grass and reducing nesting cover. Research has shown that nesting success improves when grasses around the nest are 7 inches or taller, and cattle do eat grasses. But grass under shrubs is taller than between shrubs, and cows eat between shrubs, she said.
On the other side of the debate is that spring grazing can reduce fuel loads and increase forbs and insects, providing food for hens and chicks, she said.
The study is measuring the effects of spring grazing on sage grouse demographics, such as eggs per nest and number of eggs hatched. It is also monitoring habitat vegetation and the abundance of insects and other bird species.
Researchers are collaring about 200 hens a year and monitoring hens and nests. They saw fewer nests in 2017 than in the previous three years and consider it a yearly variation. Nesting followed a cold winter, and hens had lower weights and body condition, she said.
Perhaps not a surprise was that the height of grass and forbs was taller and shrubs were denser at successful nests than at failed nests. More interesting is that nests in grazed pastures had higher success than in ungrazed pastures, and that spring-grazed pastures had higher success than fall-grazed pastures.
The shorter the time from when the pasture was grazed had greater success. In addition, insect biomass was higher in grazed pastures, she said.
The research is generating valuable data, but the results are still a few years away, she said.