A study of range use, food habits, and interspecific relationships of mule deer (Odocoileus hemionus) and cattle was conducted in the prairie habitat of north-central Montana during summer and winter. Among vegetation types, the big sagebrush and grassland types, combined, received 81 and 99 percent of the use by mule deer in summer and winter, respectively. Sixty-four percent of the observations of cattle for the period June-September occurred on the silver sagebrush type compared to 31 percent in the grassland type. Both mule deer and cattle used the silver sagebrush type, which occurred in bottoms of major drainages, during late summer. Browse plants averaged 43, 81, 60, and 59 percent of total volumes of rumens for mule deer for summer, fall, winter, and spring, respectively. Yellow sweetclover (Melilotus officinalis), snowberry (Symphoricarpos spp.), rubber rabbitbrush (Chrysothamnus nauseosus), and creeping juniper (Juniperus horizontalis) were the most important items in the diet for the respective seasons. Grass accounted for 67 and 85 percent, respectively, of summer and early fall diets of cattle as determined from the examination of feeding sites. Forbs, including yellow sweetclover, were important during early summer. Evaluation of food habits indicated no significant forage competition between mule deer and cattle. Reproductive performance of the deer seemed to verify this conclusion. An average incidence of ovulation of 2.0 and a conception rate of 90 percent were determined for females collected from January to April.
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