Naugle clarifies grass height research at SGITWritten by Saige Albert
Cheyenne – The Sage Grouse Implementation Team (SGIT) met to discuss the latest challenges related to sage grouse in Wyoming on Jan. 28. The team heard from a wide variety of speakers, including University of Montana’s Dave Naugle.
Naugle, along with Kevin Doherty of U.S. Fish and Wildlife Service, Jason Tack of Colorado State University, Brett Walker and John Graham of University of Montana and Jeff Beck of the University of Wyoming, released a research paper, titled, “Linking conservation actions to demography: Grass height explains variation in greater sage grouse nest survival,” last year.
The paper looked at the relationship between grass height and sage grouse nesting success and resulted in some controversy.
“The paper found a relationship between the height of grass at sage grouse nest sites and the nesting success of radio-marked individuals,” Naugle explained. “For two study sites, as the grass height increased, nest success was elevated.”
The study, published in Wildlife Biology, noted, “Findings show grass height is a strong predictor of nest survival inside intact landscapes, and increasing hiding cover can increase nest success.”
However, it also added, “Positive effects of grass height should be evaluated on other important demographic rates including adult female and chick survival to see if benefits extend beyond what is now known.”
Shortly after the release of the paper, the Center for Biological Diversity (CBD) issued a press release claiming that the study was biological justification to initiate uniform grass height requirements in planning documents.
“The authors of the paper came together and issued a release saying that we did not agree with the way our findings had been used in the political arena,” Naugle said. “CBD’s messaging is an abuse of science. Twisting the facts to further an agenda only alienates partners and slows defensible policy making.”
Grazing is but one of many factors influencing grass height, with others including precipitation, soils and temperature, added Beck, a co-author.
“There is a bigger conversation going on in the sage grouse arena about putting grazing restrictions on public lands and possibly policy that would use a uniform residual grass height as the metrics,” Naugle continued. “Our message was that the paper we authored is not the paper that can be used to champion that idea because it did not investigate the question of grazing.”
Naugle clarified that the team’s paper simply studied the relationship between grass height and nest success.
Walker, author and sage grouse research biologist, said in a press release the study doesn’t address the role of livestock grazing as a factor in sage grouse declines, and it was not designed to answer that question.
“The study did not say overgrazing was a problem or that livestock grazing is contributing to the declines in sage grouse populations,” Walker said. “Maintaining sufficient grass height within sagebrush landscapes is important for nesting sage grouse in the Powder River Basin, but that’s important to ranching operations, too, so there’s a common, long-term goal.”
“CBD’s press release also said we should apply this research across 165 million acres,” Naugle continued. “Even though there is a relationship, there are also 20 other published papers on the subject.”
Erik Molvar, formerly of CBD, noted during the Jan. 28 meeting, “The findings don’t say anything about grazing, but I’m willing to make the legal inferences and will stand behind those claims with my professional accreditation as a wildlife biologist.”
“The real news is that grass height can have an effect on sage grouse populations in Wyoming, and in previous examinations of the things impacting sage grouse, many things are impacting the grouse,” Molvar continued. “Many folks discounted the possible impact of livestock grazing and other things that affect grass health. At this point, it is becoming obvious that we ought to be looking at livestock grazing and perhaps having standards for grass height.”
Naugle responded that more research is necessary, and he is not willing to extend the grass height data to prescriptive management decisions across the range of the sage grouse.
“Even though we know relationships at the nest site exist, I don’t think we have done all the heavy lifting on this research,” Naugle said. “More research is needed if we desire a biological response to grass height. What is the time, timing and intensity of grazing that would yield the desired biological response? I don’t think we know that yet.”
The physical potential of rangelands, as well as a wide array of other factors, must be considered in managing the range, Naugle said, noting that some areas of the range cannot reach those heights even if they are never touched.
He further noted that in some areas where there is greater precipitation, herbaceous cover provides a higher percentage of the range, whereas in the West, there is more bare ground and sagebrush plays a larger role in the percentage of cover, meaning moret han grass height impacts grouse.
Naugle continued that environmental gradients across the 11 western states that represent sage grouse habitat vary greatly.
“We have to understand how to impact the biological response of birds through management and treatments,” he said.
For example, Naugle noted that their research found a 20 percent increase in grass height resulted in 40 percent increased nest success at one site but over 60 percent nest success at a different location.
“The massive variability speaks volumes on how one uniform policy is not going to yield the expected outcomes,” he said.
Bob Budd, SGIT chairman, mentioned, “It is all of the components of the habitat that make grouse survival successful or not successful. We are trying to get to the point where we have parameters for what is advantageous to the bird. This is just one piece.”