As one of the most common animal species in the world, rats have long adapted to living alongside people, although they are not always the most welcome of neighbors. One of the reasons rats have been a particularly successful species is that they can live in a wide range of different habitats, including attics and loft spaces. They also reproduce in high numbers and are social animals, which means that if they are living on a property, there will often be several rats present together.

How Often do Rats Reproduce?

Rats become sexually mature after about five weeks from birth. Once an adult, a female rat can give birth to up to five litters of baby rats every year. If there are plenty of food sources and a safe area for the rats to live, (as is often the case when they are found in an attic), a rat population can grow almost exponentially. Another advantage for female rats when it comes to how quickly they can reproduce is that once they have given birth, there is no physical restriction that stops them from immediately becoming pregnant again.  

Mating, Gestation, and Rat Babies

The rat population is not monogamous, so male rats will usually mate with several different females. As they often ejaculate multiple times during mating, chances of successfully impregnating the female are high.

In most cases, the gestation period is around 21 days. A female rat will usually give birth to a litter of around seven baby rats, although the number of babies depends on external factors such as climate, food sources and rat species.

From birth, a litter of baby rats will grow from hairless pinkies to juveniles quickly. Within five weeks, they will leave their mother and become independent. This means that if a female rat gives birth to five litters a year, she will have a nest of babies with her for up to half of the year.

Is Rat Breeding Seasonal?

This is a more nuanced question, as the answer is not strictly yes or no. For larger brown rat populations in towns or cities where good food sources are accessible all the time, the rats can breed throughout the entire year. (The size of the litter can be a little smaller in winter, though.) However, other rat species that live in different habitats will sometimes breed seasonally, in order to give litters the best chance of survival.

What to Do If You Find a Nest of Baby Rats While Dealing With an Infestation

A very challenging situation that many people find themselves in while dealing with a rat infestation is that they may have trapped and removed the mother, but left a small nest with a litter of baby rats. Depending on how old the babies are, they can be quite docile and not moving, or they may already be crawling around the nest.

Dealing with this situation humanely can be a dilemma. If you leave the nest alone, the babies will die of starvation without their mother. The nest can then cause odor and other problems as the baby rats decompose. You will not usually be able to take them to a wildlife rehabilitation specialist, because they are very common and also a pest species. One solution is to place the baby rats in a sealed plastic bag or small container to suffocate them quickly.