Males compete among themselves for the ability to mate with female eastern grey squirrels. Females may mate with more than one male as well.
Mating System: polygynandrous (promiscuous)
Males start following females 5 days before estrus and may come from as far away as 500 meters. Estrus in the female is indicated by an enlarged pink vulva, a condition which usually lasts less than 8 hours. The vagina is closed in prepubescent and anestrous females. Copulation lasts less than thirty seconds. After ejaculation, a gelatinous white vaginal plug forms, preventing further sperm entry.
Breeding occurs in December-February and May-June and is slightly delayed in more northern latitudes. Gestation lasts 44 days. Most females begin their reproductive life at 1.25 years but can bear young as early as 5.5 months. Females may bear young twice a year for more than 8 years. Males usually are sexually mature by 11 months but maturity can be delayed by as much as two years if the young males are housed with a dominant adult male. Inactive testes weigh 1g, whereas active testes weight 6-7g. This cycle of testicular recrudescence and regression occurs twice a year.
Newborns are naked with the exception of their vibrissae and they weigh from 13-18g. Young are altricial. Weaning begins in the seventh week and is completed by the tenth. At this point, the juvenile pelage is lost. Adult size and mass are reached at 9 months. Two litters are born each year in late winter and midsummer with generally 2-4 young per litter (up to 8 young are possible).
Breeding interval: Eastern grey squirrels breed twice in a year, typically.
Breeding season: Breeding occurs in December-February and May-June and is slightly delayed in more northern latitudes.
Range number of offspring: 2.0 to 8.0.
Average number of offspring: 3.0.
Average gestation period: 44.0 days.
Average weaning age: 3.0 weeks.
Range age at sexual or reproductive maturity (female): 5.5 (low) months.
Average age at sexual or reproductive maturity (female): 15 months.
Range age at sexual or reproductive maturity (male): 5.5 (low) months.
Average age at sexual or reproductive maturity (male): 15 months.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); fertilization ; viviparous
Average birth mass: 15 g.
Average gestation period: 44 days.
Average number of offspring: 4.
Newborns are naked with the exception of their vibrissae. Vibrissae are small hairs around the nose and mouth that are used for touch, much like the whiskers of a cat. The newborns weigh from 13g to 18g. Young are altricial. They are cared for in the nest by their mother until they reach independence. Weaning begins in the seventh week and is completed by the tenth. At this point, the juvenile hair is lost. Adult size and mass are reached at 9 months old.
Parental Investment: no parental involvement; altricial ; pre-fertilization (Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female)