After 4 days, a pup’s ears are fully developed. After 10 days, their fur grows in. After 12 days, their eyes finally open, allowing them to see.
The young mice aren’t old enough to can’t have babies of their own yet. Their mothers, on the other hand, can get pregnant again just a few days after their babies leave.
Female mice can have 5-10 litters a year. That’s over 100 babies a year—if her litters are large enough! Unlike humans, mice don’t form families. Male mice don’t help raise their pups at all, and female mice stop caring for their pups completely after 21 days. Siblings from the same litter treat each other like strangers once they’re fully grown.
Mice can produce hundreds of babies during their short lives. This is why mouse populations can grow so quickly, especially in places where there are no predators to hunt them.
Lots of other animals have many babies at a time. Like mice, most of these animals are small, vulnerable to predators, and don’t live for very long. Having multiple babies at a time (and having babies many times per year) helps their species survive.
Bigger, stronger animals produce much bigger babies, requiring a lot more time and energy from their mothers. This is why larger animals produce fewer babies at a time, and why their pregnancies take much longer. A typical newborn human baby weighs about 7 pounds (just over 3 kg). That’s over 2000 times heavier than a newborn mouse. This is why it takes 9 months for a human baby to fully develop. [10] X Research source
Like mice, these rodents produce huge numbers of offspring to help their species survive. Given how many rabbits, rats, and squirrels there are in the world, it’s safe to say the strategy is working well!
