Peromyscus maniculatus is polygynous (Kirkland and Layne 1989).
Mating System: polygynous ; polygynandrous (promiscuous)
Female Peromyscus maniculatus are seasonally polyestrous with an estrous cycle of about five days. In the wild, reproduction may not occur during winter or other unfavorable seasons (LTER 1998). Females exhibit post-partum estrus and are able to become pregnant shortly after giving birth (Baker 1983). The gestation period of a nonlactating female deer mouse lasts from 22.4 to 25.5 days and 24.1 to 30.6 days in a lactating female (Kirkland and Layne 1989). Litter size is highly variable between populations. Peromyscus maniculatus may have litters containing from one to eleven young with typical litters containing four, five, or six individuals (Baker 1983). Litter size increases with each birth until the fifth or sixth litter and decreases thereafter (LTER 1998).
Peromyscus maniculatus is very altricial at birth but develops quickly. At birth, the deer mouse has a mass of about 1.5 g. The young are born hairless with wrinkled, pink skin, closed eyes, and folded over ear pinnae. Juvenile hair begins to develop on the second day after birth. On the third day, the pinnae unfold with the ear canal opening on the tenth day. Eyes open on the fifteenth day, and the young are weaned between day 25 and 35.
Conception can occur as early as 35 days, but the first estrus typically occurs around 49 days (King 1968).
Breeding interval: Deer mice breed every three to four weeks during the warmer months and less frequently during the winter.
Breeding season: Deer mice breed year round, but most breeding occurs during the warmer months.
Range number of offspring: 1 to 11.
Average number of offspring: 4 to 6.
Range gestation period: 22.4 to 30.6 days.
Range weaning age: 25 to 35 days.
Average time to independence: 35 days.
Range age at sexual or reproductive maturity (female): 35 (low) days.
Average age at sexual or reproductive maturity (female): 49 days.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous ; post-partum estrous
Average birth mass: 2 g.
Average number of offspring: 5.
While nursing, the mother carries her young clinging to her nipples or one at a time in her mouth (Baker 1983). Once weaned, the young usually leave the nest and become independent of their mother, although sometimes the mother will tolerate their presence for longer periods. Often when the mother has a second litter, she forces the first litter out of the nest (King 1968).
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)