DESERT MULE DEER SURVIVAL IN SOUTHWEST TEXAS

Abstract

We studied population structure and limiting factors within a desert mule deer (Odocoileus hemionus eremicus) population in Brewster County of the Trans-Pecos Region in Texas, USA. We estimated and compared annual survival and pregnancy rates from March 1990–February 1993 for 121 adult (>33 months old) male and female, 61 subadult (21–33 months old), and 77 young (8–20 months old) deer. Variation in weather patterns (i.e., drought) was associated with—if not causative of—annual variation in survival patterns. Adult female and young survival had the strongest correlation with drought. Pregnancy status of young (≤1.5 yr) and old (≥6.5 yr) deer appeared most affected by drought. Seasonal periods of natural stress differed for adult sex classes, with most female mortalities occurring during months associated with parturition and lactation, and most male natural stress losses occurring during late winter and early spring. The major mortality sources were hunting and natural stressors for adult males, natural stressors and predation for adult females, and predation and natural stressors for young. Subadult mortalities were too few to identify significant mortality agents. The significance of natural stress-related survival and fecundity impacting herd productivity and stability warrants further consideration of poorly understood causative mechanisms. Ideally, replicated treatment areas would be used to address compensatory and additive mortality issues relative to predator abundance, harvest, and natural-stress losses.