We are now having an infestation of mice in South Australia and Western Australia. Even up at "The Camp" in western NSW we've been catching mice - I caught 7 mice and a grey rat in one night.
The recent rains and the subsequent boom in grain crops have proven ideal for mice to breed. Mice reach sexual maturity by 4-6 weeks. However, females should not be bred for the first time until they are 8 to 12 weeks old. Female mice come into estrus (heat) every 4-5 days (this is the time they will be fertile and receptive to a male). They will have a fertile estrus within 12-28 hours after giving birth, and within a couple of days of weaning a litter.
The gestation period of mice is usually 19-21 days. Mice can breed shortly after giving birth. If they breed while already nursing a litter, the gestation period can be longer (around 28 days).
The above video was made 2 months ago.
The following video is one from the 1993 mice plague!