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Mown on the range
Mar 3, 2014 - By Eric Blom, Staff Writer
Could one problem with the struggling sage grouse be too much sage brush? Researchers think it's possible.
Removing sagebrush may seem like an odd way to help sage grouse, but researchers think it might work. They are looking into the question with a study across 3,000 acres in southeastern Fremont County.
Fewer or smaller sagebrush could allow more forbs, wildflowers and other broad-leafed plants, to grow, the scientists hypothesize. Forbs are a major food source for young sage grouse, and they attract more insects, which make up almost the entire diet of grouse chicks.
Adults of the greater sage grouse species eat sage brush almost exclusively, build nests under sage brush plants, and hide from predators beneath their canopies.
The study is a collaboration between Wyoming Game and Fish and the University of Wyoming. Kurt Smith, a doctoral student in ecology at UW, is conducting the research.
The mowing study is on the cutting edge of sage grouse research.
Thinning the brush
Previous studies measuring how sage grouse used areas treated with prescribed burns, aeration or herbicides showed mixed results, Smith stated in a report. The studies lacked rigorous designs, Smith stated, but his would be more careful.
Smith has been studying the sage grouse in the treatment and control areas for several years. He will be able to compare the bird's success before and after thinning the sage plants.
"This is the first of its kind to gather pre-treatment grouse use and monitor post-treatment grouse use to see how it changes," said Wyoming Game and Fish biologist Harter.
He's working with Smith on the study.
Researchers have put radio collars and GPS locators on dozens of hens in the past several years, and Smith has used them to study their survival and success raising chicks.
The local investigation's findings could resonate well beyond the borders of Fremont County.
Sage grouse populations are on a downward trend in many locations, A report the local sage grouse working group released Jan. 27 shows the sage grouse population in Fremont County in 2013 was about one-third of its 20-year peak size in 2006 by several measures. It was still 50 to 100 percent higher than the 20-year low reached in 1996.
Weather patterns, such as droughts, cause the short-term changes, Harter said. Human-related impacts, such as habitat disturbance and invasive cheatgrass, are behind the long-term trend, he said.
The U.S. Fish and Wildlife Service is due to consider the species for listing under the Endangered Species Act, which would preclude most development in its habitat.
The researchers are removing sage brush both by mowing and with an herbicide.
"(Both treatments) are expensive, but if this turned out to be a real positive, we might be able to say...even though it's small scale, over time we can improve the viability of the species," Harter said.
Government agencies often require energy companies to offset disturbance they cause to sage grouse habitat by improving habitat elsewhere.
If thinning sagebrush is effective, it could be a way developers could offset habitat loss, Harter said.
For about a month this winter, investigators have been mowing swaths of sage brush up to 120 yards wide in nine locations near Cedar Rim and Dishpan Butte with a tractor and rotary cutter.
As of the end of February, about 1,500 acres had been mown into a mosaic of untouched sagebrush and 8-inch-tall stubble.
Researchers plan to scatter tebuthiuron, an herbicide sold under the trade name Spike, across another 1,500 acres in April. Spread thinly, the chemical pellets dissolve into the soil and kill individual plants, leaving other plants nearby unharmed, Harter said.
In both kinds of treatment, untouched sage brush plants are left near the mown or killed plants to provide cover for the birds.
Smith also will study a control area of undisturbed sagebrush habitat.
He plans to collect data first to measure the treatments' impacts on grouse population in the treatment area.
"We are monitoring adult female survival, nest success, and brood survival, before and after treatment in treated and untreated reference areas," Smith stated.
He also plans to evaluate chick diet in treated and untreated areas by measuring plant and insect food sources near nests, clipping and analyzing wings, and weighing infant birds, according to Smith's report.
UW plans to have students conduct similar research for the next 10 years to see impacts over time.
Sage brush out-compete other plants for water and nutrients in the soil, Harter said. The situation worsens as the dominant species ages.
"Some of these sage brush plants are getting 80 to 100 years old and starting to lose vigor," Harter said.
The older plants are larger, requiring more nutrients, but as their condition worsens they require more resources simply to survive, the biologist said. Consequently, they drew more moisture and nutrients from the soil, leaving other plants struggling.
Mowing and herbicide treatments are designed to mimic the effect of wildfires that would have naturally thinned the sagebrush in the past, Harter said. Burned sage brush take decades to recover, however, whereas those cut back start to regrow that same year.
Harter is helping perform the treatments and is following the investigation.
One cold, sunny morning in January, he drove a tractor towing a rotary cutter 20 feet wide through a sagebrush-covered plain.
He left behind tire tracks in the snow, gnarled shrubs cut to boot height, and the strong smell of sage in the air. Come spring, though, he hopes the shorn field will be thick with forbs and insects for sage grouse to feed on.