The importance of sagebrush in the diet of adult sage grouse is impossible to overestimate. A Montana study, based on 299 crop samples, showed that 62 percent of total food volume of the year was sagebrush. Between December and February it was the only food item found in all crops. Sage grouse select sagebrush species differentially. Among the big sagebrush subspecies, basin big sagebrush is less nutritious and higher in terpenes than either mountain or Wyoming big sagebrush.
Sage grouse are highly selective grazers, choosing only a few plant genera.
Insects are a minor diet item for adult sage grouse. Sagebrush made up 71 percent of the year-round diet. Their diet then switches to forbs, with sagebrush gradually assuming primary importance. Sage grouse apparently do not require open water for day to day survival if succulent vegetation is available. They utilize free water if it is available, however.