Identifying the sex of gerbils older than 7 weeks is relatively simple. Adult male gerbils have prominent testicles that can be seen under their tails. It is more difficult to determine the sex of gerbils that are less than 7 weeks old. Lifting the tail of a young gerbil reveals a small patch with no fur; this patch is farther away from the tail on males than on females. The easiest way to sex a gerbil under 7 weeks old is to compare it with another young gerbil whose sex is known. However, these methods are not always accurate.
Gerbils are generally monogamous, and paired gerbils will usually begin to mate at about 3 months of age. Mating can be identified by a ritual of chasing and mounting, with both gerbils checking their undersides after each round. Pregnancy lasts about 24 days, and a litter consists of 1 to 8 gerbil pups. Gerbils will begin mating again almost immediately after the female gives birth.
There are several causes of infertility in gerbils, including ovarian cysts, old age, sexual immaturity, exposure to pesticides or other toxins, nutritional deficiencies, and disease. Environmental causes of infertility in gerbils include overcrowding, incompatibility with a potential mate, environmental disturbances, and low temperatures. Ovarian cysts, which occur in many older female gerbils, are the major cause of infertility and small litter sizes.
Gerbils instinctively take good care of their offspring, and no owner intervention is required. In fact, touching the pups or changing the layout of the cage can be harmful, so unless something is wrong, do not interfere during the pups’ first few days of life. The male and female gerbil can both remain in the cage with the newborns.
Newborn gerbil pups can get lost or crushed under regular gerbil toys and exercise equipment. If you suspect that your female gerbil is pregnant, remove everything from the cage except food, water, nesting materials, and a reduced layer of bedding. Avoid cleaning the cage during the first few days of the pups’ lives.