Squirrels are among the most common wildlife that we see in urban environments and they generate a lot of curiosity with their behavior and antics. People are especially fascinated with baby squirrels because, let’s be honest, they are absolutely adorable! If you are excited about the thought of seeing some of these delightful itty bitty fur balls then you are probably wondering, “When do squirrels have babies?”
Squirrels have a litter of 2-4 babies, called kits or kittens, in February and March. Older female squirrels will produce a second litter in August. The timing of the births will vary based upon latitude and availability of food. The babies will leave the nest at three months of age and reach full size nine months after being born.
The Months That Squirrels Have Babies
We are going to be specifically looking at the Eastern Grey squirrel for this article as it is one of the most common squirrel seen and asked about in urban environments. Other species of squirrels (Fox, Red, Flying) follow similar patterns of reproductive behavior but with different breeding dates and gestation periods.
Eastern grey squirrels breed in late December through February in warm climates. In colder climates the breeding season is delayed and occurs in January through March. Grey squirrels have a second breeding season in May through June which extends into July in colder climates.
Grey squirrels will carry their babies for 44 days which results in the earliest baby squirrels being born in late January and the latest being born in April. In the fall breeding season the babies will be born in June and July.
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By taking the differences in climate into account you can see that squirrels in Florida will have babies in late January and June while squirrels in Michigan will have babies in April and August.
The numbers and dates presented above are general ranges but they can vary dramatically based on environmental conditions. An article published in the Journal of Ecology by John Gurnell in 1996 showed a strong statistical correlation between both food availability and winter severity with the breeding patterns of grey squirrels. To quote from the article’s abstract:
“In good seed years, breeding starts in December, in poor seed years the start of breeding is deferred until the spring. There was no or very little spring breeding in 5 years when food supplies were poor.”
Here is a more detailed article describing what squirrels eat that shows the importance of different food sources.
How Many Babies Are in a Litter?
Grey squirrels average three babies per litter with a maximum liter size of eight. These babies, called kits or kittens, are born blind, deaf, and furless, like most other species of rodents. Their ears are also folded against their skull and they are completely helpless. The kits weigh about 15 grams which is about the same weight as two tablespoons of flour.
The mother remains in the nest with the babies, where she cares for them by herself. They are fed every few hours and require constant care by their mother for several weeks.
When Do Baby Squirrels Leave the Nest?
The timeline for the development of young squirrels can be described as follows
- 1-2 weeks old: Pink skin, eyes and ears closed. Kits are nursing.
- 2-3 weeks old: Dark skin, eyes and ears closed. Kits are nursing.
- 3-4 weeks old: Fuzz type fur, eyes and ears closed. Kits are nursing.
- 4-5 weeks old: Fur development, eyes and ears open. Kits are nursing.
- 6-7 weeks old: Bushy tail and looks like a miniature adult. Kits are nursing.
- 7 weeks old: Weaning begins and solid food is introduced.
- 10 weeks old: Weaning is complete.
- 11 weeks old: Young squirrels leave the nest and are independent.
Baby squirrels become fully independent and are able to leave the nest roughly three months after being born. This means that the squirrels that are born in late January will start running around your yard towards the end of April while ones born from the summer breeding season will emerge in the September/October timeframe.
Depending on the number of squirrels in the immediate area and available nesting sites, the young squirrels may try to build their nest close to their mother. Grey squirrels are not territorial and most stay within two miles of their home nest. If the area is crowded with other squirrels, the young squirrels may be forced to travel further away to establish their nest.
Squirrels born from the summer mating season have little time to prepare for winter by fattening up and caching nuts than squirrels born in the spring. As a result, the long term survival rate for summer babies is typically lower than spring babies. The other major factor that influences how long squirrels live is the abundance of predators.
How Old Are Squirrels When They Mate?
Young squirrels reach their full adult size and mass around 9 months of age but sexual maturity takes longer to obtain.
Females grey squirrels typically reach sexual maturity when they are about 15 months old while male squirrels are sexually mature closer to 12 months old but will be delayed if in the presence of dominate males. This means that a female squirrel born in November would be ready to mate in the following summer season.
The reproductive cycle of male grey squirrels is interesting and is defined through testicular development. Sexually active male squirrels have very pronounced testicles that go through two seasons of testicular regression where the size of their testicles shrink by up to 90%. These times of regression correspond to seasons where females are not breeding and are thought to be a way to conserve energy.
The thought that testicular regression is an energy conservation mechanism is supported by a study that showed males which were extremely well fed in an enclosed environment did not undergo regression. Further supporting this idea is another study which showed regression was prolonged when food was scarce.
Squirrels do not mate for life and are quite promiscuous. Males will mate with multiple females and females will mate with multiple males. It is not uncommon for a female squirrel to have a litter where the kits are sired by multiple fathers. The mating process involves elaborate chases where males pursue the females and scare away other males.