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The effects of chemical manipulation of big sagebrush (Artemisia tridentata) on sage grouse (Centrocercus urophasianus) were studied in Montana during the summers of 1962 through 1964. The principal study was conducted on 1,900 acres, of which 1,710 had been strip-sprayed in 1961 with 2,4-D. Vegetation analyses revealed about 80 percent grasses and 20 percent forbs in the sprayed strip, and 60 percent grasses and 40 percent forbs in the unsprayed strip. Eight and 97 percent of the individual big sagebrush plants were entirely dead in the unsprayed and sprayed strip, respectively. Only 4 percent of 415 sage grouse observations were made on the sprayed strips of the 1,900-acre study area. Canopy coverage of herbaceous vegetation at 137 sage grouse locations consisted of approximately 60 percent grasses and 40 percent forbs. Ninety-two percent of the big sagebrush plants evaluated at grouse locations were living. The similarity of vegetation at grouse locations and in the unsprayed strip led to the conclusion that differences in numbers of sage grouse observed in sprayed and unsprayed strips were related to vegetation composition. Measurements of big sagebrush at 159 grouse locations showed young broods using areas having a lesser density and lower percent crown coverage than older broods and adults. Analysis of 35 sage grouse crops revealed that sagebrush and three forbs together constituted 94.6 percent of the total volume. Dandelion (Taraxacum officinale) and sagebrush had the greatest total frequency of occurrence of all food items. Favored food plants were more abundant in the unsprayed than in the sprayed strip, supporting the conclusion that differences in numbers of sage grouse observed in unsprayed and sprayed strips were related to vegetation composition.
The Journal of Wildlife Management © 1970 Wiley