Habitat use by mule deer of the Armstrong Winter Range, Bridger Mountains, Montana

A study of winter habitat usage by mule deer was conducted on the Armstrong Winter Range in the Bridger Mountains of southwestern Montana during the winters of 1976-77 and 1977-78.Objectives were to ascertain the extent of individual variability in habitat use and to evaluate the reliability of conventional estimates of winter range use.A total of 19 deer wearing radio transmitter collars were monitored from the. ground, and from the air during weekly surveys in a Supercub aircraft.Conventional ground observations were obtained of neckbanded and unmarked deer.The number of marked deer on the winter range totaled 58 and 76 for the 1976-77 and 1977-78 winters, respectively.Relocations of instrumented and neckbanded individuals indicated the existence of three major winter range units.Instrumented animals exhibited larger home ranges during the first, mild winter than during the second, more severe winter, and north unit deer were characterized by more extensive movements than middle unit deer both winters.A substantial bias toward open habitats in observations of neckbanded and unmarked deer favored the use of instrumented deer for habitat use assessment.During the 1976-77 winter, deer use was concentrated on the forested upper portion of the winter range with only 19% of the total use by instrumented deer occurring in shrub/grass types.Percent total use of shrub/grass and forest types by instrumented deer during the 1977-78 winter was 39% and 54%, respectively.Core home range preference ratios for individual habitat types and for shrub/ grass and forest habitat categories varied widely among individuals.But preference ratios less than 1 for total shrub/grass types and greater than 1 for total forested types were common to all instrumented individuals of the north and middle range units, indicating a common preference for forested types.Habitat types most selected were the JUSC-PUTR/FEID and PSME/FEID types of the north unit and the PSME/SYAL and PSME/PRVI types of the middle unit.Temporal variation in habitat usage and home range size during the 1977-78 winter reflected snow depth and crust conditions.Snow depths of 36-48 cm with a non-supportive surface crust prompted deer congregation in forested habitats offering less severe snow conditions.Habitat use patterns iii