Sage Grouse ( Centrocercus urophasianus) are the largest North American grouse, both in body dimensions and weight. Their weight differs between sexes and varies strikingly among regions and seasons (Table 1). Weight has been used as a criterion for sex determination (June 1967). However, there is little systematic information on seasonal weight change. Before weight can be assessed as a physiological index, a taxonomic criterion, or a factor in behavioral development the seasonal pattern of weight change must be documented.