Breeding
In Tuva, the breeding season of Campbell's dwarf hamster begins in April and in Mongolia, it begins in May. However in all distribution ranges, it ends in late September or early October. In captivity, Campbell's dwarf hamster breed throughout the year and there is no fixed breeding season, but a large number are born in the summer months. In the wild, three to four litters are produced each year, with an average of eight offspring per litter. In captivity, females can have between one and 18 litters per year, with one to nine offspring per litter. In captivity, the gestation period for Campbell's dwarf hamster is between 18–20 days and the shortest gestation period recorded for a captive female was 13 days. The male hamster is likely to assist the female during birth. The male may pull the offspring from the birth canal, clean them or collect food for the mother and offspring.
When the offspring are born, they are hairless and have a body mass of approximately 1.5 grams (0.053 oz). Incisors and claws are already formed, but the digits, eyes and pinna are closed and cannot be used. The rate at which the young develop differs depending on the distribution range. However, the differences are usually no longer than a day. In Tuva, the pinna open on the first day of birth and are completely open after three days of development. However, in Mongolia, the same process occurs between two and four days of development. Fur first grows on the crown, back and abdomen. The young are usually have a full coat of fur after seven days of development. Offspring born in captivity have a shorter development time than those born in the wild. Specifically, the growth and development of the head and body, tail, hind foot and pinna can is up to a day quicker than those found in the wild. After 28 days of development in captivity, the young are already around half the mass of their parents.
In captivity, females become sexually mature at two months of age. The ovarian follicle forms approximately 16 days prior to the birth of the offspring. Female hamsters that live with the male hamsters after mating typically have larger uteri, ovaries and adrenal glands compared to females who live alone or with other females. Also, these females have a shorter gestation period, of approximately four days, where oher females have a gestation period of approximately five days.
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