Pregnancies then occur from May to July. Gestation lasts 21 to 25 days. When there is an abundance of food, females have an average of two litters per year. Some have even been found to have three litters. Otherwise, an average of 1.1 litters is produced.
Litters vary from three to eight mice.
Behavior Most individuals remain underground from December to March, but for the rest of the year they emerge for an average of sixty days to ninety days, depending on the abundance of food. Great Basin pocket mice are nocturnal and stay in their burrows during the day. It has been found that the peak population in south-central Washington during autumn was an average of 320 individuals in a 2.7 ha. study area. Because they are able to retreat to underground burrows, these mice are not in much immediate danger from fires in sagebrush and bunch grass habitats. References Britannica Online.