Naugle, Montana State research disproves stubble height necessity for sage grouse
Casper – When the Bureau of Land Management and Forest Service released their plans for Sage Grouse Management Resource Management Plan (RMP) Amendments, an objective for seven inches of stubble height on grass immediately emerged as a concern for ranchers across the West.
“In 2000, a document that came to be known as the Connelly guidelines was released,” said Dave Naugle of the Sage Grouse Initiative.
Naugle explained that the research showed higher sage grouse nest success for areas with more grass cover.
“The paradigm that prevailed was that the grass hides the nest,” he said. “Nest survival drives population growth. We built a bunch of models, and it looked like an eight percent increase could be seen in nest success with additional grass height in cover.”
As a result of the research, the Natural Resources Conservation Service began to offer additional incentives for sustainable grazing practices, wet meadow riparian restoration and more.
“We worked with over 1,600 producers in 11 western states that have sage grouse,” Naugle says.
Then, early in 2017, Gibson from the University of Nevada-Reno published a paper that disrupted assumptions about grass height, nest cover and sage grouse nest success.
“The title of the paper was, ‘Evaluating vegetation effects on animal demographics: The role in plant phenology and sampling bias,’” Naugle said, adding that Gibson’s work pointed out an important oversight from the Connelly guidelines.
In short, Naugle explained that, for many years, sage grouse were trapped in the early spring and collared. Researchers then located grouse nests.
“If the nest was unsuccessful early, then technicians would go out and measure grass height at the nest,” he says. “For successful nests, technicians returned to the nests about a month later to measure grass height. The idea was, if we disturbed the female while she was incubating the eggs, she might abandon the nest.”
Naugle continued, “It finally hit Gibson, in a big, long-term data set, the phenology – or the seasonality of growth patterns – plays a role. The grass is growing while the nest is incubating.”
Gibson looked at the data set and looked at grass height at the time when the nests were deemed successful or unsuccessful, and the relationship between grass height and nest success disintegrated.
“There’s no relationship to stubble height from his research,” Naugle said.
At the same time, Naugle had a graduate student working on the same concept, so they opted to affirm and enhance Gibson’s research by replicating it.
“In science, replication is big,” Naugle said. “We used Gibson’s algorithm for correcting nesting date and put everything on an even framework to see if his theory held.”
Their research was published in Ecology and Evolution and, in short, noted that usually, the relationship between grass height and nest success disappears when corrected for fate date.
“The relationship goes away in studies from Nevada, central Montana and Utah,” Naugle said. “In an older set of data from the Powder River Basin, the relationship held, but it was weakened. For the majority of data sets, once we correct for grass height measurement timing bias, the story about grass height and sage grouse nest success has been overblown.”
Looking at 1,500 nest sites over four states and pooling the data to determine which nests failed, which hatched and the grass height at both, Naugle noted the difference in grass height between successful and unsuccessful nests was 0.05 inches.
“That is the height of a penny,” Naugle said. “Evidence for the ubiquitous effect of grass height is lacking.”
“These findings could have implications during the Department of the Interior’s revisions to RMPs as it relates to public lands grazing,” Naugle emphasizes.
A number of other grazing interaction studies are simultaneously occurring across the West, which may help to further improve the assertion that grass height negligibly impacts sage grouse nest success.
A study in Idaho has been replicated at five sites across the states. In the study, one site has 17 pastures and 80 radio-collared birds and another has 23 pastures with 90 birds collared. The study has been ongoing over the past decade.
“No grazing for four years lower nest survival, and higher nest survival was seen where spring grazing occurred,” Naugle said.
He added, “We also have to stop measuring grass just around the nest.”
Naugle explained sage grouse pick their nest location in area that fit their needs.
“Right now, we’re measuring only around the nest and then apply that measurement blindly, regardless of economic site. We’ve got to stop doing that,” he said. “Things aren’t the same when we move from small to larger scales.”
For ranchers, Naugle said, “Good grazing management is still important for a huge number of reasons. The importance of boosting hiding cover has been over-emphasized, however.”
He further noted that getting back to good range conservation practices will be important over the long-term.
“At the Sage Grouse Initiative, we might make updates based on the new science,” Naugle said. “We need to work on grazing management, but we have to have that conversation in the context of science.”
Naugle spoke during the 2017 Wyoming Natural Resources Rendezvous, held in late November in Casper.
Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org.