Quantitative data are presented on population size and structure, mortality, breeding, growth, movements, and activity during a 3-yr live-trapping study. The population reached a peak each autumn and declined to low numbers each spring. A few females survived to breed a second time but males suffered 100% mortality in each breeding season. Death after mating was not inevitable under laboratory conditions. Mating occurred only in the last 2 weeks of September each year in the field. Pregnancy lasted about 1 month, and lactation about 3 months. Juveniles attained sexual maturity at 11 months of age. Though A, stuavtii is usually nocturnal-crepuscular, some diurnal activity occurred; and extensive arboreal activity was recorded. Male home ranges were larger than those of females, and expanded farther during the breeding season. Mortality had a greater influence on population size than reproduction. Late sexual maturity and stereotyped reproductive pattern seem to preclude cyclical changes in population density.