The refractory period lasts for about an hour, and full sperm count is not built up again for two days, but a male may mate with up to three females in one night. Before giving birth, females construct nests for their young, ranging in complexity from no nest, a platform nest, a bowl-shaped nest, to an enclosed chamber . Which type of nest a female constructs depends on the ambient temperature indicating that nests function as a thermoregulatory device for young. Also, pups from post-partum litters are heavier than first litters and are male biased . Mice are considered to be adults at 60 days.
Adults are sexual dimorphic with males being larger than the females and having larger scent glands.
Mice can live for nearly three years in captivity, but they rarely live for more than a year in the wild. Females in the wild will only produce two surviving offspring in her lifetime if the population size is stable. Male Behavior Males establish dominance and territorial status by severe aggression . Our behavioral observations and genetic data both indicate that territorial males obtain nearly all matings, with subordinates only occasionally successfully mating. When fighting over territories, larger males have an advantage over smaller males , residents have an advantage over non-residents , and unparasitzed males have an advantage over parasitized males .