There is no available information on mating systems in northwestern deer mice. Mating systems in Peromyscus are variable, and include monogamous, roving, or polygynous mating behaviors. At high female densities, males become more territorial and defend a small number of females or maintain a monogamous relationship with one female. In areas with low female densities, females become solitary and males develop a less territorial, roving strategy where they mate with multiple females. Females generally maintain small, solitary home areas in all mating systems.
During the breeding season, northwestern deer mice females with mates have short breeding intervals and exhibit postpartum estrus. Breeding intervals are increased among females that do not have established mates. In wild populations, many adults only live long enough to reproduce during one breeding season. Adult males enter breeding condition prior to adult females and all females average 2 to 3 litters per breeding season. Females give birth to 2 to 5 young after a gestation period of 23 to 25 days. Gestation periods are shorting when females are nursing a previous litter. Litter size is positively correlated with relative litter mass: larger litter sizes result in smaller body sizes of young in that litter. Young are weaned and independent at 3 to 4 weeks old and may be able to breed as early as 5 to 6 weeks old. Males have a lifetime reproductive success that is twice that of females.
Breeding interval: Female northwestern deer mice breed two to three times per breeding season.
Breeding season: Breeding occurs from February to October.
Range number of offspring: 2 to 5.
Average number of offspring: 4.3.
Range gestation period: 23 to 25 days.
Range weaning age: 3 to 4 weeks.
Range time to independence: 3 to 4 weeks.
Range age at sexual or reproductive maturity (female): 5 to 6 weeks.
Range age at sexual or reproductive maturity (male): 5 to 6 weeks.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous ; post-partum estrous
Parental investment in northwestern deer mice has not been well-studied. Like all mammals, females invest substantially in young through gestation and lactation.
Parental Investment: altricial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female)