Norway rats, scientifically known as Rattus norvegicus, are a globally distributed rodent species. They are often referred to as brown rats, sewer rats, or wharf rats due to their frequent association with human environments. These animals are relatively large, typically measuring up to 28 centimeters (11 inches) in body length with a slightly shorter tail. Their fur is generally coarse, ranging from brownish to reddish-gray on their backs and lightening to whitish-gray on their bellies. Originally native to northern China, Norway rats have demonstrated remarkable adaptability, successfully spreading across every continent except Antarctica, thriving in diverse environments alongside human populations.
Urban Habitats
Norway rats frequently inhabit urban environments, living in close association with people and their structures. They are commonly found in basements, crawl spaces, and the lower levels of buildings. These rodents also utilize concealed areas like wall voids, attics, and storage rooms. Their presence extends to commercial sections of cities, particularly in areas with abundant food sources like restaurants and grocery stores.
Urban Norway rats rely heavily on human activity for sustenance and shelter. They are frequently observed near garbage disposal areas, dumpsters, and industrial zones, where discarded food provides a consistent supply. The sanitary sewer system offers another significant habitat, where they feed on human wastes and can even gain entry into buildings through compromised pipes or toilets. Nests within these urban settings are located near available food and water sources.
Rural and Outdoor Habitats
Beyond urban settings, Norway rats also inhabit rural and outdoor environments. Agricultural areas, such as farms, barns, granaries, and livestock buildings, provide ample resources. They often reside in silos and kennels, benefiting from stored feed and shelter.
In natural outdoor spaces, Norway rats extensively burrow. They construct complex tunnel systems along riverbanks, under building foundations, and beneath concrete slabs. These burrows, 2-4 inches wide, offer protection and nesting sites. They also inhabit fields, wooded areas, and vacant lots, utilizing dense vegetation, woodpiles, and debris piles for cover and nesting.
Factors Influencing Habitat Choice
Norway rats select habitats based on the availability of food, water, and shelter. They are opportunistic omnivores, eating nearly any food, but prefer cereal grains, meats, fish, nuts, and fruits. In urban areas, their diet largely consists of discarded human food, while in rural settings, they forage for seeds, grains, and agricultural produce. A single Norway rat needs approximately 110 calories per day.
Access to water is a determining factor. They can obtain moisture from moist foods, but also seek consistent water sources like leaky pipes, puddles, natural bodies of water, and sewers. Secure, hidden places for nesting, breeding, and protection from environmental elements and predators are essential. Nests are built in burrows or at ground level, often lining them with shredded materials like paper or cloth.
Temperature regulation also plays a role in their habitat preferences. Norway rats do not hibernate and seek warmer indoor accommodations during colder months to maintain body temperature. They prefer stable temperatures and move to cooler areas during hot weather. Their nocturnal activity helps them avoid predators in open, well-lit spaces.