In a single year a female may have five to ten litters of usually five or six young each. Young are born 19 to 21 days after mating and the young can start having their own babies in six to ten weeks. You do the math. That means a boat full of mice in a short amount of time. Effective mouse control involves sanitation, mouse proof construction and population reduction.
Sanitation involves cleaning up all spilled or unused pet food especially at night.
Grains or birdseed should be stored in glass, metal or heavy duty rubber tightly sealed containers. Mouse proof construction includes sealing any openings larger than one fourth of an inch. Steel wool mixed with caulking compound makes a good plug. Tightly seal cracks in building foundations and openings for water pipes, vents and utilities with metal or concrete. Plastic sheeting, wood or rubber are unsuitable for plugging holes.