Reproduction
Spermophilus tridecemlineatus’ breeding season occurs two weeks after their arousal from hibernation in the spring starting in April or early May and is sexually active for the following two weeks. Ovulation is stimulated 1 to 2 days after copulation. Their gestation period lasts 28 days on average, and each year a female squirrel gives placental birth to one litter containing between five and 13 young pups. Rarely, some female can give birth to a second litter later in the summer.
Maturation
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The pups are born blind, toothless, hairless, and weigh only three or four grams at birth. Hair and stripes are noticeable 12 days after birth and by 21 days the young begin walking. Within 28 days the young open their eyes and the weaning process begins. The female mothers care for and nurse the pups with their ten nipples for six weeks and thereafter, leave their nest to become independent squirrels. One month after birth, the young start actively exploring the area out from their burrow they were born in. After a month and a half old, the squirrels are able to provide for themselves but do not venture far from their mothers. On average they only move 100 meters of where they are born to dig their own personal burrow. The young are full grown adults by the age of three months. The large litter size is produced due to the high risk of predation that occurs before the hibernation season even begins. Only 10% of the offspring make it to hibernation. After a year both male and female squirrels are reproductively mature and will produce young after their first hibernation period. Each squirrel on average goes on to live only a few years, due to predation, but in captivity is able to survive for almost eight years.
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