Change of Seasons on the Blue Sage Prairie   A herd of antelope with newborns appears along a dry ridge line, their silhouettes visible against the light background of yellow-orange twilight; and as the cold void ends the winter grasslands release their hold on the blooming larkspur and native columbine.   Out among the fragrant blue sage the nervous prairie chickens gather in a dusty circle, greeting the descending darkness with a furious, collective dance, their frenzy revealing ritual meanings they alone understand.   High overhead flights of sandhill cranes call down, their long necks extended like the narrow-tubed clarion…