Landscape Collaborative Grazing and Greater Sage Grouse Survival

Landscape Collaborative Grazing and Greater Sage Grouse Survival

Summary

Our original study objective in 2014 was to capture and radio-collar sage-grouse hens from five leks and test the effects of cattle grazing on nest survival, brood survival, and hen survival. Unfortunately, the hens failed to nest and raise broods in sufficient numbers where we controlled grazing on 10,000 acres of land. In the second year of our study (2015), we captured hens from three additional leks and attempted to increase our chances of having sage-grouse in areas occupied by cattle. We also expanded our objectives to include other factors which would influence sage-grouse survival. Cattle in our study area are not grazing in sagebrush habitats frequently used for sage-grouse nesting. Cattle grazing appears to have little to no effect on grass utilization and sage-grouse home range size in the brood rearing stage. Nesting success was greater in mountain big sagebrush (47%), medium in three-tip sagebrush (37%), and lowest in basin big sagebrush (13%). We have not completed a thorough analysis on the direct and indirect effects (fences, water tanks, and roads) of cattle grazing on sage-grouse survival. Management practices which maintain unfragmented blocks of mountain big sagebrush and three-tip sagebrush habitat types appear to have the greatest potential to maintain sage-grouse populations in the Centennial Valley, MT.

Objectives/Performance Targets

Objective: Expand capture design to include more birds in grazed areas

In 2014, 51 females were captured from five leks and radio collared. These birds dispersed to 50,000 acres. In 2015, 58 sage-grouse hens were captured from eight leks and dispersed to 97,581 acres.

Objective: Estimate cattle grazing influences on sage-grouse nesting

Cattle grazing in our study area of the Centennial Valley generally does not occur until most of the sage-grouse have completed nesting. Across the two years of our study, we only had two nests (2%) that experienced grazing effects by cattle (Table 1). Most producers do not graze their cattle in the valley until later in the summer after most sage-grouse have nested.

Objective: Estimate influence of habitat type on nesting success

At the end of the 2015 season, sage-grouse used 3,667 acres of low sagebrush, 7,331 acres of basin big sagebrush, 24,722 acres of three-tip sagebrush, and 61,861 acres of mountain big sagebrush.

Nesting success (Table 2) was highest in mountain big sagebrush (47%), medium in three-tip sagebrush (37%), and lowest in basin big sagebrush (13%). Sage-grouse did not nest in low sagebrush. Nesting success is usually dependent on factors that reduce predation rates. Mountain big sagebrush plants provide the most cover for nests which would reduce predation due to increased concealment of the nest.

The effect of distance to water tanks on nest survival was dependent upon sagebrush type. Successful nests in mountain big sagebrush were closer to water tanks, whereas successful nests in three-tip sagebrush were farther from water tanks.

Successful nests were farther from roads in mountain and basin big sagebrush than unsuccessful nests, whereas successful nests in three-tip sagebrush were closer to roads than unsuccessful nests. It appears that the indirect effects of grazing may influence nest success but our analysis is incomplete at this time.

Objective: Sage-Grouse Brood Survival Influences (2014-2015):

There were seven hens with broods in pastures grazed by cattle, and 17 hens with broods in pastures without cattle in 2014 and 2015 (Table 3).

There were no differences (P = 0.39) in grass heights between 2014 and 2015 (Table 4).  This suggests growing conditions in both years were similar and differences in sage-grouse nest and brood survival were not due to environmental factors, but we have not tested this hypothesis.

Grazing did not reduce (P = 0.18) average grass height in pastures with and without cattle for both years (Table 5). This provides evidence that grazing levels in our original and expanded area did not alter grass height. Since most studies have indicated increased grass height will increase sage-grouse survival, it is unlikely that grazing altered brood survival, but we have not analyzed this.

Grass heights did not differ (P = 0.89) between mountain big sagebrush and three-tip sagebrush habitat types in both years (Table 6). This would suggest that these two shrub types have similar site potentials to produce herbaceous vegetation (grasses and forbs), so differences in sage-grouse brood survival would not be due to differences in herbaceous vegetation production.

Eighty four percent (16/19) of sage-grouse hens with broods used mountain big sagebrush and three-tip sagebrush vegetation types (Table 7). No hens with broods were found in low sagebrush. Brood survival to 30-days of age was highest in three-tip (60%) followed by mountain big sagebrush (39%).

Objective: Grazing influences on sage-grouse home range size:

Grazing utilization levels averaged 4% in brood home ranges across both years of the study (Table 8). The maximum utilization level recorded in a brood’s home range was 14% (Table 8). Therefore, utilizations levels were very low in brood home ranges.

There was no year effect (P=0.66) in brood home range size, and brood home range size did not differ between grazed and ungrazed pastures across the two habitat types the broods used (e.g. mountain big sagebrush and three-tip sagebrush; Table 9, 10, 11). The sample size for broods in pastures with cattle (n=7) was low, but two broods traveled >1 km into a pasture with cattle were they remained for over 2 weeks (Table 10).

Current grazing practices in the Centennial Valley appear to have minimal effects on sage-grouse reproduction and survival during the nesting season. Average nesting success was 36% for both years.  Cattle and sage-grouse generally overlap during the brood-rearing period. Cattle had little effect on vegetation during the nesting and brood rearing seasons for sage-grouse. Cattle utilize only a small portion of the total landscape, which minimizes the chances of conflict between cattle and sage-grouse. We did not detect an influence of cattle on brood home range size though the sample size was small. The only grazing effect we detected was that unsuccessful nests were closer to water tanks than successful nests in three-tip sagebrush, but we have not completed a thorough analysis of these relationships.  Sagebrush type appeared to have a stronger influence than livestock grazing on sage-grouse survival.

• Objectives/Performance Targets Tables 1-11

Accomplishments/Milestones

1. Captured 58 sage-grouse hens
2. Marked location of hens with and without cattle grazing
3. Delineated habitat type use by hens and estimated nesting success
4. Estimated brood home range size with and without cattle
5. Estimated grazing effects on herbaceous vegetation and sage-grouse survival
6. Estimated effects of habitat type on brood survival
7. Meeting to discuss sagebrush habitat grazing management with U.S. Forest Service, U.S. Fish and Wildlife Service, Montana Fish, Wildlife & Parks, Greater Yellowstone Coalition, and cattle and sheep producers. August 6, 2015, Dillon, MT.
8. Presented preliminary findings to scientists (Greater sage-grouse Grazing Research Meeting, hosted by Montana Fish, Wildlife & Parks and attended by researchers from Montana State University, Idaho Fish and Game, Idaho State University and Utah State University; November 4-5, 2015, Helena, MT.)
9. YouTube video of project completed December 2015, Link sent to WSARE for approval. (https://www.youtube.com/watch?v=AVGeIBjHnqY)

Impacts and Contributions/Outcomes

Preliminary results indicate the current grazing practices are compatible with sage-grouse nesting and brood rearing in the Centennial Valley, MT.  Management of livestock grazing should focus on habitat types with the greatest potential for success.  General grazing guidelines used by agencies should be modified by habitat type.

Collaborators: