Factors Influencing Productivity of Two Mule Deer Herds in Utah

Abstract

Highlight: Doe-fawn counts show that the mule deer herd on the LaSal Mountains of southeastern Utah produced over 38% more fawns per doe than the Henry Mountain herd over a 9-year period. Carcass weights of animals from the LaSal herd were generally greater for all age classes. Observed reproductive differences appear to be unrelated to the incidence of diseases, parasites, or predation. Furthermore, winter ranges are nearly equal in forage quantity and quality on the two ranges. Summer range vegetation on the LaSal Mountains, however, produced more forage of better quality than did similar community types on the Henry Mountains. LaSal summer ranges produced 2,149 kg/ha fresh weight of available forage while similar ranges on the Henrys produced only 1,314 kg/ha. Forbs account for 52% of the forage on LaSal summer ranges but only 12% of the forage on ranges of comparable elevation on the Henrys. The data suggest that the characteristics of the forage found on the summer range, especially the quantity and quality of forbs, exert important influences on productivity of these herds. During the 1950’s, Utah experienced high populations of mule deer (Odocoileus hemiorzus), and a general deterioration of habitat results. In an attempt to correct this condition, the Utah State Division of Wildlife Resources and federal land management agencies embarked on a program to reduce mule deer and livestock numbers to the carrying capacity of the range. Management tools implemented to reduce deer numbers included building access roads, issuing permits for special hunts, and extending hunting seasons. The effect of that program on herd size varied by herd unit. Some herds maintained a high reproductive rate and special controls are still being used to keep such herds in balance with their ranges. Other herds have not responded to reduced hunting pressure; production of fawns appears to be low and herd size has remained static. Because of such apparent differences in productivity, this study was initiated to quantify reproductive differences between two herds and identify factors that might be responsible for observed differences. The LaSal and Henry Mountain deer herds were selected for their apparent differences in fawn production. Both areas are geologically similar, and each is an isolated mountain system rising from the surrounding desert. There is little movement of deer into or out of either herd unit. Research objectives were to determine: (1) fawn production for the two herds; (2) carcass