The Norways are usually more aggressive, driving roof rats from the territory. Both species are seldom found in the same building. Rats and mice frequently gnaw on their surroundings. Rats and mice are active mostly at night. Rats show greatest activity the first half of the night, if food is abundant.
Mice usually are active at night both right after dark and between midnight and dawn.
Both rats and mice will be active during daytime hours when food is scarce, when there is an overpopulation of rats, or when a poison has been used and the population is sick. Since rats and mice are active at night and are rarely seen during the day, it is necessary to recognise signs of their activity. Rodents usually have favourite toilet areas but will void almost anywhere. Old droppings are grey, dusty, and will crumble. Fresh droppings are black, shiny, and puttylike.