Livestock grazing could affect the sage grouse population across 11 states in the western region of the United States and two Canadian provinces in western North America, according to a study.
Its effect, either positive or negative, is determined by the amount of grazing and when it occurs.
The study said some grazing could still be beneficial to chicken-like grouse if grazing occurred during the later part of the growing season, a team of scientists from the U.S. Geological Survey, Colorado State University, and Utah State University, said.
The researchers said grazing, particularly after the peak plant productivity, could also stimulate the growth of grasses that greater sage grouse eat and nest in.
Sage-Grouse Diet, Habitat
The greater sage-grouse (Centrocercus urophasianus) live on large expanses of grasslands feeding on wildflowers, insects, and forage crops. During winter, they depend mainly on sagebrush as the only available food source.
They have been known as the ambassador for the less known but critically important Sagebrush Sea from which many fish and wildlife species depend on for survival. The chicken-sized sage-grouse's declining population is distributed in Oregon, Idaho, Nevada, Montana, Wyoming, Utah and Colorado. A remnant population is also spotted in Washington, California, North Dakota, South Dakota, Alberta, and Saskatchewan. It is locally extinct in Nebraska and Arizona.
Understanding When And How Much To Graze
From a peak population of 16 million, there are around 200,000 to 500,000 sage-grouse species in the United States at present.
Biologists often blamed grazing and a host of other factors, such as diseases and oil and gas drilling among others, had contributed to the bird's population decline.
The study does not refute what the biologist had claimed.
It was observed that there was a decline in the sage grouse population when extensive grazing occurs during the early part of growing season while the same level of grazing after the growing season was associated with the increase of their population.
The authors said this finding may indicate that there are grasses that are sensitive when grazed upon during the early growing season. Conversely, there is a probability for additional plant growth if dead grasses are removed when grazed in the later part of the growing season.
"Increasing our understanding of how the amount of grazing and season of livestock use affect vegetation could help inform the short-term modifications to livestock management to benefit the sage-grouse populations and help sustain western ranching operations," Cameron Aldridge, a professor of CSU, USGS collaborator, and study co-author, said.
Study Is No One-Size-Fits-All
Study's lead author Adrian Monroe at CSU said the research could be a tool for land managers for them to help assess the impact of grazing at the local level.
"Managing the level of grazing and the timing of that grazing to reduce or avoid impacts to grasses and forbs could possibly affect the sage-grouse population levels through increased food resources and nesting cover that will support the reproduction and recruitment of another generation of birds," Monroe explained.
The study was the first to connect the conditions and trends of the grouse populations to livestock management, he added.
He admitted the findings were not meant to provide "one-size fits all" solution to the problem. The study is considered more applicable to Wyoming.
In conducting the study, the researchers had focused on more than 700 breeding sites for grouse in Wyoming. The site is one of the last remaining strongholds for sage grouse.
The study was published in the journal Ecological Applications on March 23.