Like other squirrels, the courtship of Tamiasciurus douglasii consists of a mating chase in which the males and females call to and chase each other. This ultimately leads to coupling off and mating. Each Douglas squirrel has one mate per mating season.
Mating System: monogamous
Male Douglas squirrel testes become mature in spring. Reproduction occurs from January until mid-August with the greatest portion between March and May. Most females have only one litter per year, although occasionally a second litter is born in August or September. The gestation period ranges from 36 to 40 days. Females have eight mammae, and the litter size ranges from 1 to 8, with 4 to 6 on average.
Breeding interval: The majority of Douglas squirrels breed once a year.
Breeding season: Reproduction can occur from January through August, although it usually occurs from March to June.
Range number of offspring: 1 to 8.
Average number of offspring: 4-6.
Range gestation period: 36 to 40 days.
Range weaning age: 6 to 9 weeks.
Range time to independence: 4 to 7 months.
Range age at sexual or reproductive maturity (female): 8 to 9 months.
Range age at sexual or reproductive maturity (male): 8 to 9 months.
Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Douglas squirrels are born blind and without hair, weighing between 13 and 18 g. Fur covers the body by 18 days, and the eyes open at around 26 to 36 days. The young stay in their mother’s nest until they are one-half to two-thirds the size of an adult, usually around mid-July to early August. Siblings and the mother remain in close contact when they first leave the nest. Weaning starts at 6 weeks and is finished by 9 weeks. After this, the young become more independent, but families remain together until December. A juvenile Douglas squirrel will reach adult body size after around 8 to 9 months. Most will reproduce the following summer.
Parental Investment: altricial ; pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)