Photo Credit: (c) Larry Jon Friesen, saturdays.net
SCIENTIFIC NAME: Rattus rattus
OTHER NAMES: Alexandrine rat, house rat, Old English rat, black rat, and ship rat
STATUS: Exotic. Breeder. A commensal ("sharing the table") rodent brought to the United States by early European colonists. Often displaced by Norway rat, but when co-inhabiting same areas, usually spatially seperated vertically. Often targeted for eradication because of potential economic damage and health concerns.
DESCRIPTION: A typical adult roof rat is 12.75–18.25 inches long, including a 6.5–10 inch tail, and weighs 4–12 oz. Despite its name, the black rat exhibits several color forms. It is usually black to light brown with a lighter underside. The roof rat also has a scraggly coat of black fur.
DISTRIBUTION: The roof rat originated in India and Southeast Asia, and spread to the Middle East and Egypt. It eventually spread throughout the Roman Empire, reaching England as early as the first century. Europeans consequently spread them throughout the world through shipping. The roof rat is largely confined to warmer areas, having been outcompeted in cooler regions and urban areas by the brown rat (Rattus norvegicus), also known as the Norway rat.
HABITAT: The roof rat is one of the most widespread animal species in the world due to their adaptability to a wide range of habitats. In urban areas, they are found around warehouses, residential buildings, and other human settlements. They prefer to live in dry upper levels of buildings, so they are commonly found in wall cavities and false ceilings. They also are found in agricultural areas, such as barns and crop fields. In the wild, roof rats live in cliffs, rocks, underground, and trees. They are great climbers and prefer to live in trees, such as pines and palm trees. In the absence of trees, they can burrow into the ground. Roof rats also are found around fences, ponds, riverbanks, streams, and reservoirs. Their nests are typically spherical and made of shredded material, including sticks, leaves, other vegetation, and cloth.
FEEDING HABITS: Roof rats are predatory animals and adapt to different micro-habitats. They often meet and forage together in close proximity within and between sexes. They tend to forage after sunset. If the food cannot be eaten quickly, they will search for a place to carry and hoard their food to eat at a later time. Roof rats are omnivores and eat a wide range of foods, including seeds, fruits, stems, leaves, fungi, and a variety of invertebrate and vertebrate animals. Although roof rats eat a broad range of foods, they are highly selective feeders; only a small number of the foods they eat are foods that are prominently found. When there is a wide variety of food, roof rats eat only a small sample of each available food. This allows them to monitor the quality of foods that are present year-round, like leaves, and seasonal foods, such as herbs and insects. This method of operating on a set of foraging standards ultimately determines the final composition of their meals. By sampling the available food in an area, the rats maintain a varying food supply, balance their nutrient intake, and avoid intoxication by secondary compounds. They are generalists and thus not very specific in their food preferences. This is seen in their tendency to feed on any meal provided for cows, swine, chickens, cats, or dogs, but, like squirrels, they prefer fruits and nuts. They eat about 0.5 oz. per day and drink about 0.5 oz per day. Their diet is typically high in water content. They are a threat to many natural habitats because they feed on native birds and insects. Roof rats also are a threat to many farmers since they feed on a variety of agricultural-based crops, such as cereals, sugar cane, coconuts, cocoa, oranges, and coffee beans.
LIFE HISTORY AND ECOLOGY: In a suitable environment, the roof rat will breed throughout the year, producing 3–6 litters of up to 10 young. Females may regulate their production of offspring during times when food is scarce, producing as few as one litter a year. The roof rat lives for about 2–3 years and social groups of up to 60 can be formed. Roof rats (or their ectoparasites) are able to carry a number of pathogens, of which bubonic plague (via the rat flea), typhus, Weil's disease, toxoplasmosis, and trichinosis are the best known.
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AUTHOR: Thomas Harms, Wildlife Biologist, Alabama Division of Wildlife and Freshwater Fisheries