Food may be cached. Burrow entrances are multiple, and may be plugged lightly with vegetation or soil. A nest lined with shredded plants, or other soft material, is constructed in the burrow. Generally associated with unsanitary human habitation, with accessible garbage and sewers. Often none, but Norway rats occupying agricultural habitats may move to buildings during cold weather, returning in the spring.
Colonies consisting of several families share nesting and feeding areas.
Breeds year-round, with peaks in spring and fall. Gestation period is 21-22 days. The Norway rat is an aggressive, omnivorous, moderate-sized rodent. Prey to humans, hawks, owls, foxes, dogs, cats, mustelids, and snakes. These diseases can decimate dense rat populations, and they can be transmitted to humans.