Meadow jumping mice (Zapus hudsonius) reduce their metabolism substantially during hibernation and use stored fat reserves for overwinter energy needs. Preble's meadow jumping mouse (Z. h. preblei; PMJM) occurs along the Front Range of Colorado, north into southeastern Wyoming, and is listed as a threatened species under the Endangered Species Act because of the conversion and degradation of riparian habitats. To better understand how increasing fat and body mass before hibernation impact overwinter survival, we conducted a mark–recapture study of PMJM at the United States Air Force Academy, El Paso County, Colorado. We used environmental covariates and individual covariates, such as body mass and fat mass, to improve survival estimates. Overwinter survival of female PMJM was higher during long, cold winters, whereas overwinter survival of males was lower during winters with much snowfall. For both sexes, heavier individuals had higher overwinter survival. A combination of large body mass and colder winters may allow PMJM to conserve valuable fat resources. Because periodic arousal from hibernation is the most energetically expensive activity over winter, increasing body size (reducing surface area-to-volume ratio) should increase energy conservation and probability of survival.