Current Project Status

Results of the 2016 Field Season

In February and March of 2016, we collared 117 female sage grouse across five sites, as we added Pahsimeroi Valley (in Custer and Lemhi Counties) to the four existing study sites. In addition, 78 hens that had been captured the two previous years were still alive and had active radio-transmitter collars. That brought the total to 195 hens tracked in 2016; 77% were adults and 23% were yearlings.

We found 150 nests across all five sites in 2016, including nests located inside and outside the experimental pastures where we are manipulating grazing. Of the 150 nests we located, 137 were initial nest attempts and 13 were re-nest attempts.

Nest Success and Chick Survival

Apparent nest success was slightly lower in 2016 compared to 2015 except at Sheep Creek in Owyhee County, where nest success was 33% in both years. The percentage of nests where chicks hatched successfully ranged from 23% at Pahsimeroi to 38% at Brown’s Bench.

After clutches hatched, we conducted 125 brood flush surveys and 20 spotlight surveys on 30 different sage-grouse hens. Brood survival to 42 days of age ranged from a high of 73% at Browns Bench to a low of 20% at Sheep Creek.

We documented 20 mortalities among radio-collared birds during the 2016 field season. Sixteen were adults and 4 were yearlings.

Vegetation Measurements

We took vegetation measurements at nest sites, nest-patch plots near nests, and random plots across the pasture to document the plant species and amount of cover in areas used by grouse compared to random areas. Vegetation measurements taken from mid-April to early July revealed differences between nest sites and random sites throughout the pastures. Nest sites had more sagebrush cover but less total shrub cover than random sites. Forty percent of nests were under Wyoming big sagebrush, with another 22% located under low sage and 12% under basin big sage.

Successful nests had more sagebrush cover and more total shrub cover than failed nests. Shrubs selected by nesting sage-grouse were taller than those at random plots. Hens tended to nest under sagebrush ranging from 16 to 30 inches (40-76 cm) tall, which is consistent with numerous other sage-grouse studies.

Grass Height

Grass height is an aspect of sage-grouse habitat that is commonly measured, and grazing practices commonly prescribe maintaining grass height exceeding 7 inches. In our study, grass heights varied greatly among study sites, even within grass species. The amount of ground covered by grasses was higher at nests sites compared to random sites, and grass height generally exceeded the seven inches typically recommended for grouse nesting habitat.

Grazing Intensity

We used three methods to estimate the percent utilization across the experimental pastures: ocular method, landscape appearance, and percent height reduction.

Utilization varied spatially within individual pastures, which highlights the need for spatially explicit methods of mapping utilization. By accounting for and mapping this spatial variation, we will be able to investigate how utilization patterns may affect nest site selection of sage-grouse within our study pastures.

Certain methods of measuring utilization may be more beneficial for answering particular questions, and further investigation into the most appropriate method is warranted. It will be essential to select the most appropriate method(s) of assessing utilization in order to ascertain how changes in spring grazing affect greater sage-grouse, habitat and wildfire.

Insect Abundance

In the first two weeks after hatching, sage-grouse chicks depend on a high-protein diet. To determine what’s on the menu, we used sweep nets, pitfall traps and ant mound surveys to collect and record the species and biomass of arthropods present. Through the 2015 and 2016 field seasons, crews counted and identified more than 25,000 insects. About 89% of that biomass was made up of grasshoppers and crickets, ants and bees, and beetles. These are also the arthropods most common in the diets of sage-grouse chicks.

 Next Steps

For the 2017 field season, we plan to study our existing five research sites and hope to add one or two more study sites as partners and funding become available. We began implementing  4 grazing treatments on  pastures at two of our study sites: 1) spring-only grazed in odd years, 2) spring-only grazed in even years, 3) no grazing, and 4) alternating years of spring-only grazed and non-spring grazed. We define spring grazing as March 1 through June 15.

Since the beginning of our study, we have conducted vegetation sampling at 1,756 plots (breeding and post-breeding season surveys combined) and taken utilization measurements at 8,601unique locations. With this continued effort and large sample size, we will be able to make powerful inference regarding the specific effects of spring cattle grazing on sage-grouse populations and habitat in Idaho, and these results will be relevant throughout the species’ range.