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Empirical descriptions of spatial overlap of coexisting herbivores are difficult to interpret in terms of functional interaction. In an attempt to obviate some of these difficulties, partial correlation analysis was applied to the study of habitat use behavior of whitetail deer, mule deer, elk, and bighorn sheep on an important wildlife winter-spring range in southeastern British Columbia. A probe was made of the basic determinants of habitat selection in order to isolate the response of represented species to the physical and vegetational environment and to summer grazing by cattle. Distinct patterns of habitat utilization were exhibited by each species. Whitetail and mule deer habitat preferences were distinguished from one another by elevation, ruggedness of terrain, and openness of forest and shrub vegetation. Elk were most widely distributed and showed the least apparent response to measured environmental parameters, whereas bighorn sheep were most localized and specific in their response to environment. Distributions of all species were only weakly influenced by the activities of grazing cattle at the level and pattern found on the study area. Partial correlation techniques appeared to offer some potential for analyzing resource division in mixed grazing systems. However, a number of technical and conceptual difficulties may limit their value in systems where reciprocal feedbacks, thresholds, and optima exist in the response of animals to environment. Numerous studies have attempted to provide measures of competition or ecological overlap among coexisting herbivores. Generally, competition has been described in terms of the extent to which members of a multispecies assemblage graze common areas during the same season and the extent to which they utilize common forage species (Julander, 1958). These parameters, in certain situations, may adequately describe the basic elements of competition when they are interpreted in relation to existing levels of

Studies were undertaken to determine if approximations of herbage productivity could be made from estimates of tree-crown cover, also whether or not estimates from aerial photographs would be accurate enough for this purpose. Results suggest that there is a sufficiently close relationship between herbage production and crown cover in coniferous stands to make the technique useful in range surveys. Estimation of herbage yields from the ground is too slow to be useful in surveys where large acreages have to be covered in a very short time. Similar results were obtained from ground estimates of crown canopy and those made from aerial photographs. Estimates of herbage yields on a pasture made as a result of the survey were almost identical to those established from an earlier grazing trial.