Squirrel Breeding Cycles
By Chris Williams on October 19, 2011.
Q. The squirrel that lives in the tree in front of our house just had another batch of babies. Don’t they normally have their young in the spring, not in the fall? Guess this means we’ll have even more squirrels chewing on our porch furniture!
A. You’re probably talking about the common eastern gray squirrel, although we do also have red squirrels in our area. Gray squirrels begin breeding at about one year old. Yearling female gray squirrels usually have only one litter a year, but older female gray squirrels usually breed twice a year. Winter breeding is from January to February and summer breeding runs for a longer period, from May to July. Whether or not a female has a second litter usually depends on the availability of food.
Usually 3 or 4 young are born after a 44-45 day gestation period. At first they look like hairless mice. It takes about 4-5 weeks for their eyes to open. They start straying from the nest and gathering their own food when they are 5 to 8 weeks old, although they are not completely weaned until they are 8 to 10 weeks old. Young squirrels are about half of their adult weight when they are weaned and look like slightly smaller versions of the adult.
Those babies born in the winter would be making their appearance in spring, but babies born in late summer would be showing up about now. Let’s do the math. If your momma squirrel mated in early July and gave birth in mid August, the young would be making their appearance about early October. This is somewhat later than the usual breeding time, but within the bounds of normal.
Gray squirrels usually have two types of nests: leaf nests that they use in the summer, and more desirable den holes in trees that they use in winter, but that can also be permanent nests. Spring litters are usually born in a tree cavity while summer litters may be born in leaf nests. Survival of young in tree cavities is higher than for those in leaf nests. Female squirrels are very territorial in protecting their nest when they have young, but will sometimes nest with close relatives during the winter.
When squirrel babies are ready to leave the nest, they do so gradually. They may spend a couple of days practicing running up and down their den tree and in and out of the nest, before they ever take that first big jump to the ground. When young squirrels finally disperse to go out on their own, they usually remain within two miles of where they were born. You just have to hope they don’t choose to nest in your attic!