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ROOF AND NORWAY RAT

Rattus rattus and  Rattus norvegicus

INTRODUCTION

Management of rats and other rodents always begins with a systematic survey and evaluation of the potentially infested site. Estimates of pest numbers and a map of the infested site should be generated. The potentially infested site should be cleaned, removing all possible food sources for the rodents. The site should be altered to eliminate all favorable nesting habitat and to eliminate any passageways that might exist form outside points into adjacent structures. When a structure is infested, intense trapping, using large numbers of traps should be attempted along with the structural and habitat modifications. All park staff and visitors should be fully informed of the mission of the control effort and the reasons for the infestation. These cultural, mechanical, and physical methods of addressing a pest problem should always be carried out before the use of a chemical is considered.

BIOLOGY

Animal Color Size, weight, shape Other Features
House mouse

(Mus spp.)

Uniformly light brown to dark gray; occasionally a little lighter on the belly 5 to 7 inches, ½ to 1 ounce, slender, agile large ears, small feet and eyes in proportion to the body; sparsely hairy tail.
Norway Rat

(Rattus norvegicus)

Dark brown to black 12 to 18 inches (including tail), 12 to 16 ounces, stocky, ears are small and hairy. tail is shorter than its head and body length, is a larger, heavier rat, with smaller eyes and a blunter snout than the roof rat, dropping are large and ovoid.
Roof Rat

(Rattus rattus)

Dark brown to Black 13 to 18 inches (including tail), 5 to 9 ounces, slender, ears are large and nearly hairless. tail is longer than its head and body length, thinner and lighter than Norway rat, droppings are long and cylindrical.

Roof rats and Norway rats have similar Life Histories and habits. Where differences are important for management purposes, however, the differences will be highlighted. Rats have poor vision. Rats are wary of anything new that appears in their territory, avoiding the new object for a few days until the rats become familiar with it.

Life cycle: A mature female rat can give birth to about 20 young in a year (4 to 6 at a time). The average life span of a rat in the field is less than one year, with females living longer than males. The young are born in nests. They are hairless and their eyes and ears are closed. Within two weeks their eyes and ears open, they grow fur, and they begin exploring the nest area. In the three week they begin to switch to solid food, and imitate their mother to learn pathways to food, escape routes, and danger zones. If the mother rat has become wary of rodenticides or traps, many of her young will learn to avoid them. This learning experience can make management difficult in sites where long-term rodent suppression programs have been unsuccessful in the past.

Young are totally weaned when 4 or five weeks old. They then weigh about an ounce and a half. At three months the young are independent of their mother and able to mate and continue the cycle, either in the same location or after migrating to a new, unoccupied are.

Outdoor populations tend to peak in summer to early fall. Indoor populations may remain at the same levels throughout the year, limited only by periodic shortages of food, water, or nesting sites.

Social Behavior: Rats are social animals and live in colonies with well defined territories that they mark with urine and glandular secretions. Rats are aggressive, and social conflicts are most common at feeding sites, prime nesting sites, and territorial boundaries. Females fiercely defend their nest and young from other rats.

Environmental conditions that favor development: The Norway rat and the Roof rat have different nesting and feeding preferences that should be considered when management programs are formulated.

Animal Nesting Requirements Food Preferences Other environmental conditions needed
Roof Rat nest outside in trees, woodpiles and debris, and in dense vegetation. Inside, roof rats prefer to nest in the upper levels of a building in the attic and ceiling Have more vegetarian preferences. Typical food is fresh plant material, nuts and seeds, fruit and vegetables and tree bark. Quite, isolated nesting site near water and food sources.
Norway Rat nest either inside or out; Outside, they form burrows usually less than 18 inches deep. Also nest in sewers and storm drains. Nests inside are found in lower floors, crawl spaces, storage rooms and/or in any cluttered area that is little used. More likely to eat garbage than roof rats. High protein foods such as fish, meat, nuts, grains, pet food and insects. Good nesting sites within 100 feet of water and food sources.

Natural Enemies: Dogs, cats, snakes, birds of prey, and other rats.

MANAGEMENT

Medical importance: Rats can spread disease. Sometimes they transmit disease directly by contaminating food with their urine or feces or by biting people. Sometimes they transmit disease indirectly, as when fleas bite a disease-infected rat, then a person. Some of the important diseases associated with commensal rats are: Plague (not currently a problem in the NE USA), Rat-Bite Fever (a seldom serious bacterial infection that occurs occasionally after being bitten by a rat.), Salmonella Food Poisoning (a problem where rats have access to human food sources), and Leptospirosis (another disease that is spread to humans through contaminated food, water, and through cuts in the skin).

Potential Damage: Rat burrows can cause structural damage by undermining the foundations of buildings, roads, and walkways; can cause damage by gnawing, damaging plastic and lead pipes, door frames, upholstery, and electric wires; and cause damage through the destruction and contamination of food crops and stored foods.

Threshold: The Roof and Norway rats are not native to the United States and are thus considered to be exotic. For that reason, the sighting of just one Norway or Roof rat is adequate reason to initiate management efforts addressed at eliminating the rats. Management efforts should continue until all visible signs of the rats are absent. Monitoring for the detection of a new rat infestation should continue year-round.

Monitoring: Monitoring is a systematic survey conducted at regular intervals.

  1. Keep good monitoring records of what you see, smell, hear, and when you saw it, and under what conditions you saw it. These records are important in determining how to best manage a pest.
  2. Visual Sightings - an inspection using a powerful light, just after dark, is the best way to see rats. If you see rats during the daytime, population levels are very high!
  3. Sounds - when it is quiet in a building, you can sometimes hear squeaks, fighting noises, or clawing and scrambling in the walls. A stethoscope can help pinpoint activity.
  4. Droppings - A single rat may produce 50 droppings daily. One way to determine if a rat population is active is to sweep up old droppings and reinspect a week later for new droppings. Fresh rat droppings are black or nearly black, wet and may glisten, and soft. Older droppings lose the black coloration.
  5. Urine - Both wet and dry urine stains will glow blue-white under an ultra-violet light (blacklight). Blacklight inspections work best at night and in dark rooms.
  6. Grease marks - Oil and dirt rub off of a rat’s coat when it rubs against things. These grease marks build up in often used runways and soon become noticeable. These marks are commonly found along wall/floor junctions, on pipes and ceiling joists, and on sill plates.
  7. Runways - Outdoors, runways tend to appear as beaten paths on the ground where rats constantly travel the same route. These can be found next to fences, under bushes, and along buildings.
  8. Tracks, Gnawing damage, burrows - physical signs or damage are important indicators of the presence of rats, the size of the population, and the location of the infestation. A tracking patch (a light dusting of an inert material such as clay, talc, or limestone) can be place in sites where you suspect rat activity. The rats walk through the dust and you will be able to track the pests movement. The size and number of burrows is a useful indicator of the significance of the infestation.

Tools needed for Monitoring: A flashlight; ultraviolet light; talc; map of the site showing important observations; monitoring record form or sheet.

Management Strategies:

Tactic Comments When By Whom
Cultural Control Use any or all of these recommendations as needed
Public Education Provide instructional information and guidance in the area of Rodent pest management, including garbage and trash handling and proper site maintenance and sanitation. Ongoing Park IPM Coordinator

 

Physical Control Comments When By Whom
Harborage Reduction Rats avoid open areas!

Keep grass mowed to about 2 ½ inches.

Remove woodpiles, piles of building materials, and other items that might serve as a hiding or nesting site.

Keep shrubs and other low plants pruned, so monitoring is easy.

Make sure all trash and garbage storage cans and container are metal with tight fitting metal lids.

To decrease rat harborage inside an infested structure, clean out all food, clutter and debris that might exist inside the building. After cleaning the structure, make sure that all food residues are removed and that any remaining foods are stored in rat proof containers.

As needed!

During the initial stages of the Rodent IPM effort.

 

 

As needed!

 

During the early stages of the Rodent IPM effort.

Rat Proofing The most effective form of rat management in structures is "rat proofing"; fixing a building so that there are no easy paths for the rats to enter.

Young rats can squeeze through a slot-like opening ½ inch high.

To rat proof a structure:

  1. Block all opening around pipes, utility lines, and air vents.
  2. Doors and windows should be tight fitting.
  3. Seal holes and cracks in the foundation.
  4. Repair roof soffits and seal all openings on the roof.
  5. Repair gnaw holes as they occur, using steel wool to plug the hole before filling it.
  6. Cover all floor drains with mesh.
  7. Fill all interior and exterior holes to prevent movement of rats in walls.
Compliance Needs Work with the park cultural resources personnel to assure that all compliance issues are addressed before beginning any site modification activities on a Historic structure Before Rat proofing activities begin Park IPM coordinator.

 

Mechanical Control Comments When By Whom
Trapping The snap trap is an effective method of managing rats when properly placed.
  1. Leave traps unbaited for a few days to allow the rats to get used to them.
  2. For Norway rats, used peanut butter, bacon, fish, or nut meat as a bait.
  3. Roof rats can be baited with dried fruits and nuts or fresh fruits such as banana or apples.
  4. If one bait does not seem to be working, try another.
  5. Place traps where ever you have seen signs of rats (along runways, at the site of droppings, along the wall where markings are seen). Place the traps in groups of threes, with about ten feet between groups.
  6. Traps should be placed wherever runways exist, including over head if pipes and rafters are being used.
  7. Continue trapping for about two weeks.
  8. EMPTY TRAPS AT LEAST ONCE A DAY!
After examining the infested site to determine runways, and other sites for trap placement. The site should also be cleaned up before can be expected to work. Park IPM Coordinator
Live Trapping Live trapping not usually a option with rats. However, if non-target species are potential threatened, Live traps can be used.

Chemical Control

Rodenticides should not be used indoors in NPS facilities, particularly in historic buildings, except under extreme circumstances. Rodents that have ingested a toxic dose of a rodenticide may crawl into wall voids and other inaccessible areas to die. The decaying carcass can produce foul odors and attract insects such as dermestid beetles or blowflies, which feed on the dead animal. Once they have consumed the carcass, the insects will seek other food sources, and may become pests themselves, feeding on fabrics, furs, stored foods, and historic artifacts.


                                 
Last Update:
Feb. 3, 2011
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