The Roof Rat is one of two introduced rats found in throughout the United States. The Norway rat is the other species and is better known because of its widespread populations. The Roof Rat is commonly known as the, black rat, and ship rat. Roof Rats were common on early sailing ships and apparently arrived in North America by that route. This rodent has a long history as a carrier of bubonic plague.
Roof Rats are more aerial than Norway rats in their habitat selection and often live in trees or on vine-covered fences. Landscaped residential or industrial areas provide good habitat, as does, vegetation of riverbanks and streams. Parks with natural and artificial water features, or reservoirs also, may be infested. Roof Rats will often move into citrus groves. These rodents are commonly found living around poultry or other farm buildings as well as in industrial sites where food and harborage are available.
Roof Rats frequently enter buildings from the roof or from accesses near overhead utility lines, which they use to travel from area to area. They are often found living on the second floor of a warehouse in which Norway rats occupy the first or basement floor. Once established, they readily breed and thrive within buildings, just as Norway rats do.
Control methods must reflect an understanding of the Roof Rat’s harborage requirements, reproductive capabilities, diet, life history, behavior, senses, movements, and the inner workings of its population structure. Without this knowledge, both time and money are wasted, and the chances of failure are increased.
The young are born in a nest about 21 to 23 days after conception. At birth, they are hairless, and their eyes are closed. The 4 to 9 young in the litter develop rapidly, growing hair within a week. Between 9 and 14 days, their eyes open, and they begin to explore for food and move about near their nest. In the third week, they begin to eat solid food. The number of litters depends on the area and weather conditions, availability of nutritious food, density of the local rat population, and the age of the rat. Typically, three or more litters may be produced annually, per female.
The young may continue to nurse until 4 or 5 weeks old. By this then, they have learned what is good to eat by experimenting with potential food items and by imitating their mother.
Young rats generally cannot be trapped until about a month old. At about three months old, Roof Rats are completely independent of the mother and are able to reproduce.
Breeding seasons vary in different areas. In tropical or semi-tropical regions, the season may be nearly year-round. Usually the peaks in breeding occur in the spring and fall. Roof Rats prefer to nest in off the ground nests.
Roof Rats usually begin searching for food shortly after sunset. If the food is in an exposed area and too large to be eaten quickly, they will usually carry it to a hiding place before eating it. Roof Rats may hoard considerable amounts of solid food, which they eat later. Such caches may be found in a dismantled wood pile, attic, or behind boxes in a garage.
When necessary, Roof Rats will travel considerable distances (100 to 300 feet) for food. They may live in the landscaping of one residence and feed at another. They often are seen at night running along overhead utility lines or fences. They may live in trees, such as palm and citrus, or in attics, and climb down to a food source. Traditional baiting or trapping on the ground or floor may prove to be futile, unless bait and/or traps are placed at the points that rats travel from above to a food resource. Roof Rats have a strong tendency to avoid new objects in their environment and this can influence control efforts, for it may take several days before they will approach a bait station or trap. All Roof Rat populations are skittish and will modify their travel routes and feeding locations if frequently disturbed. Disturbances such as habitat modifications, are to be avoided, until the population is under control.
their greater climbing ability. Eliminate vines growing on buildings and, when feasible, overhanging tree limbs that may be travel routes.
Harborage Modification and Sanitation
The elimination of food and water through good sanitation practices can do much to reduce rodent infestation. Store pet food in sealed containers and do not leave it out at night. Use proper garbage disposal containers and implement exterior sanitation programs. Emphasize on the removal of as much harborage as is practical.
Dense shrubbery, vine-covered trees and fences, and vine ground cover make ideal harborage for Roof Rats. Severe pruning and/or removal of certain ornamentals are often required to obtain a degree of lasting rat control. Remove fruits or nuts that drop in backyards. Strip and destroy all unwanted fruit when the season is over.
In tree crops, some cultural practices can be helpful. When practical, remove extraneous vegetation adjacent to the crop that may provide shelter for Roof Rats. Citrus trees, having very low hanging skirts, are more prone to damage because they provide rats with protection. Prune to raise the skirts and remove any nests constructed in the trees.
Products sold as general animal repellents, based on taste and/or odor, are sometimes advertised to repel animals, including rats, from garbage bags. The efficacy of such products for rats is generally lacking. No chemical repellents are specifically labeled for Roof Rat control.
registered. Their use for Roof Rats is limited to control within structures because Roof Trapping
Trapping is an effective alternative to pesticides and recommended in some situations. It is recommended for use in homes because, unlike with poison baits, there is no risk of a rat dying in an inaccessible place and creating an odor problem.
The common wooden snap traps that are effective for Norway rats are effective for Roof Rats. Raisins, prunes, peanut butter, nutmeats, and gumdrops make good baits and are often better than meat or cat food baits. The commercially available, ‘Rat Traps’, are particularly effective if properly located in well-traveled paths. Traps should be placed where they will intercept rats on their way to food, such as on overhead beams, pipes, ledges, or sills frequently used as travel routes. Several traps to be placed on the floor, but more should be placed above floor level (for example, on top of stacked commodities)