Behaviour and Biology
Rats live in close association with people. In urban or suburban areas they live in and around residences, in cellars, warehouses, stores, slaughterhouses, docks, and in sewers and more frequently I have found many infestations in domestic lofts.
On farms they may inhabit barns, granaries, livestock buildings, silos, and kennels.
Among the diseases rats may transmit to humans or livestock are weils disease, murine typhus, leptospirosis, trichinosis, salmonellosis (food poisoning), and ratbite fever.
They may burrow to make nests under buildings and other structures, beneath concrete slabs, along stream banks, around ponds, in garbage dumps, and at other locations where suitable food, water, and shelter are present. Although they can climb, Norway rats tend to inhabit the lower floors of multistory buildings.
Norway rats are primarily nocturnal. They usually become active about dusk, when they begin to seek food and water. Some individuals may be active during daylight hours when rat populations are high. Rats have poor eyesight, relying more on their hearing and their excellent senses of smell, taste, and touch. They are considered color-blind. Therefore, for safety reasons, baits can be dyed distinctive colors without causing avoidance by rats, as long as the dye does not have an objectionable taste or odor. Rats use their keen sense of smell to locate food items and to recognize other rats. Their sense of taste is excellent, and they can detect some contaminants in their food at levels as low as 0.5 parts per million. Norway rats usually construct nests in below-ground burrows or at ground level and also in loft insulation.
Norway rats will eat nearly any type of food. When given a choice, they select a nutritionally balanced diet, choosing fresh, wholesome items over stale or contaminated foods. They prefer cereal grains, meats and fish, nuts, and some types of fruit. Rats require 1/2 to 1 ounce (15 to 30 ml) of water daily when feeding on dry foods but need less when moist foods are available. Food items in household garbage offer a fairly balanced diet and also satisfy their moisture needs. Norway rats consume and contaminate foodstuffs and animal feed. They may damage crops in fields prior to and during harvest, and during processing and storage. Rats also damage containers and packaging materials in which foods and feed are stored.
Rats cause structural damage to buildings by burrowing and gnawing. They undermine building foundations and slabs, cause settling in roads and rail-road track beds, and damage the banks of irrigation canals and levees. Rats also may gnaw on electrical wires or water pipes, either in structures or below ground. They damage structures further by gnawing openings through doors, window sills, walls, ceilings, and floors. Considerable damage to insulated structures can occur as a result of rat burrowing and nesting in walls and attics.