NORWAY RATS

Damage Prevention and Control Methods

Exclusions

• Seal all openings larger than 1/2 inch wide

Habitat Modification

• Good sanitation practices reduce sources of food, water, and shelter
• Store foodstuffs in rodent-proof structures or containers
• Store and dispose of refuse and garbage properly
• Control weeds and remove debris from around structures

Trapping

Identification
The Norway rat is a stocky burrowing rodent, unintentionally introduced into North America by settlers who arrived on ships from Europe. This rat is also known as the brown rat, house rat, barn rat, sewer rat, gray rat, or wharf rat. Their fur is coarse and usually brownish or reddish gray above and whitish gray on the belly. Blackish individuals occur in some locations

Range
First introduced into the United States around 1775, the Norway rat has now spread throughout the contiguous 48 states. It is generally found at lower elevations but may occur wherever humans live.

Habitat
Norway 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. On farms they may inhabit barns, granaries, livestock buildings, silos, and kennels.

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.

Food Habits
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 of water daily when feeding on dry foods but need less when moist food are available..

General Biology, Reproduction, and Behavior
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. 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. Nests may be lined with shredded paper, cloth, or other fibrous material. Litters of 6 to 12 young are born 21 to 23 days after conception. Newborn rats are hairless and their eyes are closed, but they grow rapidly. They become completely independent at about 3 weeks and reach reproductive maturity at 3 months of age. Breeding often peaks in the spring and fall, with reproductive activity declining during the heat of summer and often stopping completely in winter, depending on habitat.

Norway rats usually construct nests in below-ground burrows or at ground level. Nests may be lined with shredded paper, cloth, or other fibrous material. Litters of 6 to 12 young are born 21 to 23 days after conception. Newborn rats are hairless and their eyes are closed, but they grow rapidly. They become completely independent at about 3 weeks and reach reproductive maturity at 3 months of age. Breeding often peaks in the spring and fall, with reproductive activity declining during the heat of summer and often stopping completely in winter, depending on habitat.

Damage and Damage Identification
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 railroad 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.

Among the diseases rats may transmit to humans or livestock are murine typhus, leptospirosis, trichinosis, salmonellosis, and ratbite fever.

Detecting rats
The presence of rats can be determined by a number of these signs:
Droppings; Tracks; Urine; Runs or burrows; Smudge marks; Gnawing; and Sounds

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ACKNOWLEDGEMENTS
The above information was adapted from PREVENTION AND CONTROL OF WILDLIFE DAMAGE with permission of the editors, Scott E. Hygnstrom, Robert M. Timm, and Gary E. Larson (Cooperative Extension Division, Institute of Agriculture and Natural Resources University of Nebraska-Lincoln, United States Department of Agriculture Animal and Plant Health Inspection Service, Animal Damage Control, Great Plains Agricultural Council Wildlife Committee). It is will great gratitude and appreciation that we are able to pass along this useful information.