Tell Me More About Rats

Problems

Rats damage human food more through contamination with their urine and feces than by consumption, and can cause structural damage and disfigurement in many ways. Burrowing is potentially damaging, although usually the problem is more cosmetic than structural because burrow systems are instinctively built to remain stable and to not allow water to enter. Gnawing can be a dangerous problem when electrical wires are attacked. Rats can and do gnaw through materials as dense as lead pipe, meaning that most woods are not impediments to them at all.

Solutions

>Exclusion: Rats can access buildings through holes as little as 1 inch wide – about the size of a quarter. All such holes and opening should be sealed with heavy-weight material (1/4-inch hardware cloth or heavy-gauge screening is recommended). Heating vents often are overlooked as points of entry, and they should be checked to ensure that access through them by rats is not possible. Anywhere electrical conduits, utility or air conditioning lines enter a building, the hole that has been made needs to be checked for gaps that will allow entry. Wire mesh can be used to plug openings in walls and floors through which rats might gain entry. Aluminum window screen can be wadded and stuffed into openings to deter rat entry. Caulking or foam sealants can be used to seal openings also, but because rats can gnaw through them, they are best when combined with screening or wire mesh.

>Habitat Modification: Proper sanitary techniques constitute the most economic and effective method to limiting rat presence. Mow grass and clear debris close to buildings to reveal burrows as well as openings that rats might use to get inside. Store food in rat-proof containers. Remember that birdseed, grass, and other potential foods are stored in garages and buildings frequently attract these animals. Store and dispose of garbage properly so that rats cannot gain access. Do not leave pet food outside. If pets are fed outside, leave the food out for twenty minutes and then remove it. Remove old wood or debris piles if rats are a problem – these are frequent havens for these animals.

Where rat infestation has been and continues to be a problem around buildings, the long-term solution to preventing burrowing along foundations can be addressed by creating an L-shaped footer of either hardware cloth or concrete. Bury the footer about 12 inches and extend it from the foundation about another 12 inches. Although rats may begin to dig at the foundation, they will encounter this obstacle, dig down and get frustrated, and then give up.

Physical Appearance

The Norway rat is slightly larger than the black rat, averaging 10 to 16 ounces, while its smaller cousin runs between 8 and 12 ounces. Black rats are more slender than Norway rats and have more pointed muzzles and larger eyes relative to body size. The Norway rat’s tail is shorter than its head and body combined, while the black rat’s tail is longer.

Physically, rats do not appear more imposing than many mammals, but they are incredibly hardy and capable of physical feats that would seem beyond the ability of creatures so small. An opening no larger than a quarter is sufficient to allow an adult rat to gain entry to a building, and both species climb well enough to use a pipe or conduit within 3 inches of an outside wall to gain access at any level. Rats are capable of vertical leaps of as much as 3 feet and horizontal leaps of 4 feet. They are excellent swimmers and the tales of Norway rats emerging in toilet bowls after swimming up through plumbing, while rare, appear to be true.

Habitat

Norway rats arrived in Denver in the 1880s and occur mostly in urban areas (ill-kept alleys, storm sewers, unsanitary dumps), around livestock feedlots and under outbuildings. Neither species apparently copes well with natural grass or woodlands, where predators abound and competition from native species is keen. In cities, Norway and black rats favor small municipal parks where humans inadvertently leave food in trash containers. Older industrial areas, rail yards and back alleys provide excellent habitat. The common Hollywood image of hordes of rats in sewers or abandoned warehouses is not realistic unless highly unusual environmental conditions exist, including super abundant food resources provided by humans through improper trash management.

Norway rats prefer to live in burrows that are usually around 18 inches deep and 3 feet long. Burrow systems may have multiple openings that, if possible, are placed so that the entrance abuts a solid structure – building foundation, sidewalk edge, rock, tree root, or any other physically stable platform. Some entrances serve as escape or bolt holes and may be loosely closed with soil or located in dense vegetation to foil easy detection. The main entrances are usually marked by a well-worn path that leads up to them. In buildings, Norway rats will live inside walls, under stacked lumber or other construction material and anywhere human clutter is allowed to build up. Black rats are accomplished climbers and are found in the upper levels of buildings more often than Norway rats. They often build loose spherical nest of shredded material in trees or vines well above ground.

Feeding Habits

Rats will eat a wide range of plant and animal foods. Adults require about 1 ounce of food a day and need access to some supply of water. In the winter, seed spilled from bird feeders can be an important source of food, as can pet food left outside. Norway rats tend to eat more animal matter than do black rats and will consume insects, meat refuse, bird eggs, and even pounce on small mammals such as mice.

Mating & Breeding

Rats breed year-round, although peak breeding occurs in the spring and fall. Breeding age is reached at 2 to 3 months, and litter size averages 8 to 12 in the Norway rate and 5 to 6 in the black rat. One female can wean about twenty young a year.

Behavior

Rats are wary of new objects in their environment, which makes them difficult to trap. Norway and black rats utilize areas of about 75 to 500 feet in diameter as a typical home range, although this might vary greatly depending on the location and availability of necessary resources such as food. We know that Norway rats will travel a half-mile or more in a single night to use a reliable source of food. Black rats live more off the ground than do Norway rats, nesting in trees and other structures above ground and using electrical and telephone wires to move about as squirrels do. Both species are mainly active at night. Rats seen during the day are said to reflect a high population density, and usually are juveniles that must take the risk of exposure because they cannot compete with adults.

Predators

Large house cats and dogs kill rats, and so do owls and a variety of native mammalian carnivores.

Public Health

Rats are implicated as carriers or transmitters of more diseases of importance to humans than any other organism, except possibly the mosquito. They are bold and aggressive animals and are known to bite children. Physical attacks in the form of rat bites exceed fifteen thousand annually in the United States and often involve very young, old, or incapacitated people. Rat bites should be treated by a physician. Among the diseases that can be spread from rats to humans are bubonic plague, salmonella, leptospirosis, hantavirus, and tularemia.

- Information provided by the Colorado Division of Wildlife

- Information also provided by The Humane Society of the United States

Humane Society of U.S.| CO. Dept.of Health & Environment
Animal Control Home | Colorado Div. of Wildlife
Urban Wildlife Rescue | Table Mountain Animal Shelter