Because mule deer (Odocoileus hemionus ) are an important game species throughout their range, an understanding of factors affecting mule deer populations is important for effective management. Desert mule deer (O. h. eremicus ) in southeastern California inhabit an arid region of North America where generally annual precipitation is <200 mm. Limited rainfall suggests a low abundance of plants for forage and cover. Consequently food and perhaps free water may be important limiting factors in populations of mule deer in deserts. The purpose of this study was to collect information about the resources upon which desert mule deer in a region of southeastern California rely, the factors that affect those resources, and the influence of the resources on mule deer population dynamics. This study addressed 6 components of deer ecology. Part 1 involved the use of long-term El Niño southern oscillation (ENSO), rainfall, and deer harvest records to investigate effects of ENSO and rainfall on long-term population trends of mule deer in the Sonoran Desert, southeastern California, USA. Part 2 reported the results of a microhistological analysis of fecal pellets to identify plant species in diets of desert mule deer in southern California and the seasonal changes in use of forage classes. The third part investigated at how rainfall, temperature, and plant characteristics affected biomass of deer forage. Part 4 involved an analysis of gradients in forage biomass and use by mule deer and bighorn sheep ( Ovis canadensis ) along dry riparian streams near catchments. The fifth part was a study of how rainfall, temperature, forage biomass, and forage growth are related to water content, crude protein, and in-vitro dry-matter digestibility of some common forage species of desert mule deer in the Sonoran Desert, California. The final section involved the use of radiocollared deer, remote photography at wildlife water developments, and mark-recapture techniques to estimate population abundance and sex and age ratios. Together, these studies provide an understanding of the resources on which desert mule deer in California depend, how those resources are influenced by environmental conditions and large herbivores, and the consequences of these interactions on the demography of mule deer.

Desert mule deer (Odocoileus hemionus crooki) abundance and distribution, deer activity and diet, fawn survival, and predation were studied in Big Bend National Park, Texas from 15 January 1980 to 9 December 1981. Deer abundance was correlated with total plant, forage, and succulent densities but was also related to perennial water abundance and bed site availability. Fawn production and survival were related to spring rainfall. Diurnal and annual deer activity were influenced by temperature where spring and winter had longer daily activity compared to summer. Daily activity by deer was highest during the morning and evening. Forage use varied seasonally with browse use decreasing from spring to winter with a corresponding increase in use of forbs. Diets of two deer herds were compared and during drought periods forb use decreased until summer rains occurred. Prior to the rains, deer relied on evergreen browse species. Additionally, deer within mesic areas had a higher use of forb species contrasted with deer within xeric areas. Predator diet significantly changed with a decline in the deer population determined from pellet-group transects. Mountain lions (Felis concolor) used smaller prey including javelina and lagomorphs. Coyotes (Canis latrans) fed opportunistically by increasing use of insects, birds, reptiles, and lagomorphs. Bobcats (Lynx rufus) increased use of lagomorphs with little change in other prey species. Given alternate prey species, predator populations remained relatively constant given the deer decline.