Mice are very social. Related males and females are compatible and live in and maintain territories by marking the area with urine and droppings which can cause health concerns. The house mouse will begin reproducing within 35 days and average 8 litters a year, each of which average 6 young. Thus populations build up rapidly. They are good climbers and can jump 12 inches high and 8 feet down. House mice easily squeeze through holes and gaps of 1/4 inch or more.