Differences between male and Female
It is important to keep your gerbil groups in same-sex groups, for obvious reasons. Knowing that a pair can produce a litter of 3 to 10 babies every month, you should learn to differentiate between the two sexes before adopting, and to confirm yourself at the time of adoption. Unfortunately, many pet shops still leave both males and females together or misgender them, sometimes deliberately to be able to resell the babies.
With babies, we can know the sex around 12 days old. The hair has already begun to grow but not enough to cover everything. We can also see small holes on the stomach: it is about the nipples. They are more apparent in females but can sometimes be seen in males, so trust the scent gland to be certain!
We can see here a female on the left and a male on the right.
It is more difficult to differentiate between the genders in teenagers. Their fur is thick and covers the scent-gland. And even the genitals are not of much help, since the males testicles are still not developed. Our only clue is to compare the distance between the urethra and the anus.
Here is a female, on the left, and a male, on the right, of 3 weeks.
The easiest is when the gerbil is about 2 months old. It is now considered an adult and is sexually mature, which means that male testicles have dropped. In the male, the scent-gland is clearly visible on the belly and we can see the testicles well. The distance between the urethra and the anus is also greater.
Once again, the female on the left and the male on the right.