The females come into season for at least 4 hours every 4 days throughout the year, and immediately after giving birth. Being nocturnal, they are likely to be receptive to a male only at night. Even experienced breeders don’t know a definitive way of telling when a female is in season. Only a hamster in good health is capable of bearing a large litter and they quickly become exhausted by having many litters. No hamster should be expected to have more than 3-4 litters in her life.