Sage Grouse Nest Success Study
by University of Wyoming Extension
December 22, 2014
Scientists whose study found a positive relationship between taller grass and sage-grouse nest success are concerned environmental groups are using findings to incorrectly label livestock producers as responsible for the birds’ decline.
The study is described in "Linking conservation actions to demography; grass height explains variation in greater sage-grouse nesting survival" published earlier this month in the journal Wildlife Biology. (The study is linked below.)
Dave Naugle, the study’s principal investigator and professor in the Wildlife Biology Program at the University of Montana, said the Center for Biological Diversity in a media release this week used the study to call for a uniform 7-inch stubble height requirement across sage-grouse range as a regulatory mechanism to shut down public lands grazing.
"The center’s messaging is an abuse of science," said Naugle. "Twisting the facts to further an agenda only alienates partners and slows defensible policy making."
The study period was 2003-2007. The scientists found a strong correlative relationship between grass height and nest success in northeast Wyoming and southeast Montana study sites, which has helped prompt new research, said lead author Kevin Doherty of the U.S. Fish and Wildlife Service in Colorado.
"Our research has helped to spur new research projects that are experimentally designed to evaluate if grazing systems can be used as a tool to increase sage-grouse populations," he said.
Brett Walker, author and sage-grouse research biologist, Colorado Parks and Wildlife, said the study doesn’t address the role of livestock grazing as a factor in sage-grouse declines: the study 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," he 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."
Grazing is but one of many factors influencing grass height with others including precipitation, soils and temperature, said Jeff Beck, co-author and associate professor, University of Wyoming.
"For instance, an early, wet spring in 2003 resulted in the highest nest success observed in the five-year study," said Beck.
The study occurred in some of the wettest and most grass-dominated sagebrush habitats in the 165-million acre range of sage-grouse, said Doherty.
He cautions against applying the findings to drier regions, including the Great Basin.
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Editor's Note: There are some important considerations in the research paper, including this: "Managing grass height in large and intact landscapes with grazing is a tool that may benefit populations in eastern Montana and northeast Wyoming. Positive effects of grass height in our study areas explained variation in nest success between years with large and precise effect sizes. Differing intercepts prohibit extrapolating of results to novel sagebrush systems because absolute effects likely depend upon regional conditions that influence grass and shrub composition. South and west of our study areas where sagebrush rather than grass provides most hiding cover, grass height had only a weak effect on nest success, and nest fates were dominated by year and site effects."
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