The Eastern Grey Squirrel (Sciurus carolinensis) is a widespread North American species that follows an annual reproductive pattern characterized by two distinct breeding periods. The ability to produce two litters each year allows them to capitalize on seasonal resource availability and is a significant factor in their successful adaptation to various environments.
The Dual Breeding Seasons
The grey squirrel’s reproductive year is divided into two separate breeding seasons, primarily determined by food availability and local climate. The first, and often most successful, mating period begins in the winter, typically running from December or January through February. This early season results in the first litters being born in late winter or early spring, when new food sources soon become abundant for the mother.
The second breeding window opens in late spring and extends into the summer, generally occurring from late May through July. This second cycle is often dependent on the female’s condition and the success of the first litter; in years with scarce food, fewer females attempt to breed a second time. Environmental factors, such as cold weather or latitude, can delay the start of both breeding seasons by several weeks.
Courtship Behavior and Mating Chases
Reproduction is preceded by a highly visible and competitive courtship spectacle known as the mating chase. A female is only receptive to mating for a very short period, sometimes lasting less than a single day. During this concentrated estrus period, she attracts multiple males, sometimes drawing a dozen individuals from an area up to 500 meters away.
The chase involves males pursuing the female on an acrobatic, high-speed dash through the trees and across the ground. This ritual tests the stamina and physical fitness of the competing males. A dominance hierarchy is established during this pursuit, and the largest, most dominant male generally wins the right to mate. Following copulation, a gelatinous vaginal plug often forms, which physically prevents further sperm entry.
Gestation and Rearing the Young
After successful mating, the female undergoes a gestation period lasting approximately 44 days. The mother constructs a nest called a drey, which is a bulky sphere of leaves and twigs high in the tree canopy, or she may utilize a tree cavity for shelter. The resulting litter typically consists of two to four young, though up to eight kits are possible.
The young are born helpless: blind, toothless, and nearly hairless except for their whiskers. The mother is the sole provider of care, as the male plays no role in raising the young. Weaning begins around seven weeks and is completed by ten weeks of age, when the young transition to a solid diet. Juvenile squirrels attain full independence and begin to leave the nest around 12 weeks after birth.