Brown Rat

CLASSIFICATION

Rat is the common name for about 1,000 species of rodents in 70 genera and eight families. These species include the kangaroo rats, Dipodomys, family Heteromyidae; wood rats, Neotoma, family Cricetidae; spiny rats, Proechimys, family Echimyidae; and the typical rats, Rattus, family Muridae. Most rodents called rats have an elongated body, a moderately pointed snout, approximately equal-length legs, and a long, sparsely haired or hairless tail. Rats are generally distinguished from mice by their larger size. A rat's incisors are open rooted which means they are continuously growing (hypsodontic). They may need to be trimmed with clippers if there is nothing for them to gnaw on. The space between the incisors and the moars is called the diastema. Rats have twelve molars which are permanently rooted and do not continuously grow (brachidontic).

An adult male rat weighs between 450 and 520 grams while the female is between 250 and 300 grams. They have a diploid chromosome number of 42. Their body temperature range is 35.9 to 37.5 C. They can grow to length of 32-46 cm (12-18 inches). They have a chubby body shape.

Rats are burrowers and are nocturnal most of the time. Escaped rats will often return to their cages. Rats have an excellent sense of balance, and will usually land on their feet like a cat.

RANGE
The Norway rat, also called the brown rat, probably originated in eastern Asia, possibly northern China. The first record of its appearance in Europe was 1553, and it is now found throughout the United States.

HABITAT
Since rats live on all continents, they also live in all the different environments. Therefore, they have no one specific niche.

They do however have special adaptations that allow hem to survive in their type of habitat. For example, the rat's eyes. Rats have poor eyesight and are color blind. They do well in dimly lit rooms or cages. They do have a highly developed sense of touch because of sensitive whiskers called vibrissae which compensates for the eyesight. They prefer to move along walls using their whiskers to guide them. Behind the rat's eyeball is the Harderian gland. This is a pigmented lacrimal gland. This red brown gland is larger than the eyeball and secretes a lipid and porphyrin rich secretion which lubricates the eyes and lids in stress situations such as restraint, swimming, acute illness ect... The red tears overflow and stain the face and nose. The dried red porphyrin crust fluoresces bright red under an ultraviolet light. The secretion contains little blood however.

DIET
Most rats prefer food of animal origin, such as fish, mice, and chickens, but are still highly omnivorous. As pets, they can be fed almost anything. Average daily food intake for a rat is 10 grams per 100 grams body weight. Average daily water intake is 10-12 ml per 100 grams body weight.

GESTATION
Rats often associate in packs of 60 or more animals, usually all closely related and often all descended from a single pair. Norway rats breed throughout the year. The breeding onset is between 65 and 110 days, and they have a gestation period of 21 to 23 days and produce a litter of 6 to 12 young. Young are communally raised with shared nursing. Rats often set up breeding harems of one male to 6 females. Newborn rats weigh between 5 and 6 grams.

Rats often associate in packs of 60 or more animals, usually all closely related and often all descended from a single pair. If a nursing female is killed, for example, other nursing females of the pack will raise her young for her.

LONGEVITY
Life expectancy for the rat is between 2.5 and 3.5 years in the wild.

BIBLIOGRAPHY
1. Barnett, S. A., The Rat, a Study in Behavior, rev. ed. (1976)
2. Biology and Medicine of Rabbits and Rodents, The; 2nd ed, by Harkness and Wagner, 1983, Lea and Febiger.
3. Greene, Eunice G., Anatomy of the Rat (1935; repr. 1971) Simon and Schuster's Guide to Mammals, by Boiyani and Bartoli, 1983, Simon and Schuster, Inc.
4. Hirschhorn, Howard, All About Rats (1974)
5.Rats- A complete Pet Owner's Manual, by Carl Himsel, 1991, Baron's Educational Series, Inc.
6. Rowett, H. G., Rat as a Small Mammal, 2d ed. (1965)
7. Simon and Schuster's Guide to Mammals, by Boiyani and Bartoli, 1983, Simon and Schuster, Inc.
8. Zinsser, Hans, Rats, Lice, and History (1935).