Thirty-two years of counts of Sage Grouse (Centrocercus urophasianus) males on leks in southern Idaho revealed major population peaks about every 10 years. Lek counts from northern Utah and western Nevada and harvest data from Idaho and Utah all show strong synchrony in this cycle. Individual lek counts within each region tended to fluctuate together despite being located in different habitats or at different elevations. Eight of nine monthly weather variables having significant correlations with lek counts in Idaho were precipitation, rather than temperature, variables. However, weather variables were not useful in predicting mean lek counts through linear-regression analysis. In Idaho 79% of the variation in mean lek count could be explained by knowing the mean lek count of the previous spring and the juvenile/adult ratio in the preceding autumn's harvest. About 65% of the variance in the juvenile/adult ratio could, in turn, be explained by knowing the amount of precipitation in July and August. There is no evidence that Sage Grouse populations decline as a result of being alternate prey in a predator-prey system involving coyotes (Canis latrans) and cycling black-tailed jackrabbit (Lepus californicus) populations.
In this paper I propose to test the hypothesis that Sage Grouse (Centrocercus urophaisnus) populations in three western states are oscillating together annually and that their oscillations are similar to the 2 well-known 10-year cycle of the boreal forest of Canada (Keith 1963, Bulmer 1974, Finerty 1980). Such a population cyclicity in the Sage Grouse was suspected by Patterson (1952) but no data analysis was presented. I further examine several weather and population variables through multiple linear-regression analysis in order to identify variables that might be useful in a population model for this species.
Currently among the tetraonids, evidence for a 10-year population cycle exists for the territorial Willow Ptarmigan (Lagopus lagopus) (Bergerud 1970, 1971), Rock Ptarmigan (h mutus) (Gudmundsson 1960, 1972; Weeden and Theberge 1972), and Ruffed Grouse (Bonasa urnbellus) (Bump et al. 1947, Keith 1963). Less evidence is available for the lekking Sharp-tailed Grouse (Tympanuchus phasianellus) and Greater Prairie-chicken (L_ cupido) (Hamerstrom and Hamerstrorn 1954, Lack 1954, Williams 1954, Keith 1963). The Sage Grouse is a lekking species.