The Rodent Animal are mammals of the order Rodentia, which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws.
Rodent Animal Fact:
Scientific name: Rodentia
Lifespan: 4 – 8 years
Mass: 0.7 – 1.2 kg
Length: 20 – 25 cm
Height: 50 – 64 cm
Representing over per cent all mammal species, rodents from a successful and highly adaptable order. They are found worldwide (except Antarctica) in almost every habitat: lemmings, for example, favour the cold climate of the arctic tundra, while gundis prefer the heat of African desert regions. Despite the variety of lifestyles and habitats exhibited by members of this order, there are many common characteristics: most rodents are small quadrupeds with a long tail, clawed feet, long whiskers, and teeth (especially the long incisors) and jaws specialized for gnawing. Although generally terrestrial, some species are arboreal (such as tree squirrels), burrowing (mole-rats, for instance, live almost wholly underground), or semi-aquatic (such as beavers). Some species, such as the woodchuck, are solitary, but most are highly social and form large communities.
While the anatomy of rodents is more uniform than that of most other orders of mammals, some characteristics, such as a compact body and a long tail and whiskers, are shared by many species. The front foot usually has 5 digits (although the thumb may be vestigial or absent), the back foot has 3-5 digits, and the method of locomotion is generally plantigrade. Different species use their tail to perform distinct functions: beavers have a flat wide tail that is used for steering when swimming; while the Eurasian harvest mouse uses its prehensile tail when climbing in long grass. In some species, part of the tail skin, or the tail itself, will break off if caught, enabling the animal to escape. Because rodent anatomy is more generalized than that of other mammals, they can adapt easily and are able to thrive in many different habitats.
Most rodents enjoy acute senses of smell and hearing, which, in combination with their long and numerous touch-sensitive whiskers, provide them with a heightened awareness of their surroundings. Nocturnal species have larger eyes than diurnal species, to maximize the e amount of light received by the retina (the greater the amount of light, the brighter and clearer the image). Rodents communicate by smell (odours are secreted from scent glands on the body) and by an extensive range of vocalizations.
Well-developed sense organs are present in most rodents and may contribute to the adaptability of species, such as this brown rat. The large eyes and ears, elongated snout, and long whiskers are typical of many rodents.
Rodents have an enlarged chewing muscle (the masseter), which permits both a vertical and a back and forth motion of the lower jaw. In squirrel- and beaver-like rodents, the upper part of the masseter reaches the back of the skull, deep part extends to the zygomatic arch, and the temporal muscle is small. This system allows a strong forward motion when biting. In mouse-like rodents, the deep part of the masseter extends on to the upper jaw, the upper part is located forwards, and the temporal is large. This permits a versatile chewing action. In cavy-like rodents and the springhare, the deep part of the masseter extends in front of the eye, and the temporal is small. This gives a strong forward bite.
The 4 huge incisors (seen here in a marmot) distinguish rodents from most other mammal orders. These teeth are long, curved, and grow continually. Only the front surface these teeth has enamel, however-the back surface consists of softer dentine, which is eroded by constant gnawing ensure that the teeth remain sharp.
Most rodents have a plant-based diet that may include leaves, fruit, seeds, and roots. However, species have alternative diets: water rats many and the wood mouse eat snails, rice rats take young turtles: muskrats eat clams and crayfish; the southern grasshopper mouse eats ants and scorpions; while the black rat scavenges in human food supplies. To assist digestion, rodents have a large caecum, a blind-ending sac in the large intestine. This contains bacteria that break down cellulose, the main component of plant cell walls, into digestible carbohydrates. In some rodents, after food is processed in the caecum, it is ejected from the anus and is eaten again. Once in the stomach, the carbohydrates (amounting to 80 per cent of the energy contained in the food) are absorbed. This highly efficient process, known as refection, leaves only a dry faecal pellet to be excreted.
Rodents and people
Some rodents, mainly rats and mice, are considered pests by people because are often in direct competition with humankind they occupy the same habitats and eat the same food) and are highly adaptable. Rodents consume over 40million tonnes (39milliontons) of human food every year, contaminate stored food with their urine and faecal pellets, and are known to transmit more than 20 disease-causing organisms. Although some control of rodent populations is brought about by the use of traps and poisons, many species are sufficiently intelligent to learn to avoid such measures. Only a few of the 2,478 species of rodents, however, are genuine pests: many benefit people, for example, by destroying insects and weeds or by maintaining the health of forests by spreading fungi. Beavers and chinchillas are farmed for their fur, while rats, mice, and guinea pigs are kept as pets and are used extensively in medical research.
Most rodents are herbivorous, eating only plants. The European water vole shown here feeds on aquatic and land plants. Food may be stored for consumption during winter shortages.
The high rate among rodents enables them to maintain stable population levels in adverse conditions. This means that predation and human controls (such as poisoning) have little effect on the survival of a species, and in favourable brown conditions numbers may increase rapidly. A brown rat, for example, is able to breed at only 2 months of age and may yield litters of more than 10 young every month or so. Voles are also prolific breeders some species may produce more than 13 litters annually. Smaller rodents tend to produce more young than larger species (such as the capybara) -as a result, small rodents form the staple diet of a wider range of animals. In rodents, the complete cycle of reproduction, from sexual attraction right d through to raising young, is influenced by the emission of pungent glandular secretions. Female rats, for example, produce a pheromone about 8 days after giving birth. This scented chemical is secreted into the mother’s faeces and helps prevent the offspring from becoming separated from her.
Among rodents, many species live in organized communities, although some are solitary. These black-tailed prairie dogs, like most ground squirrels, are highly sociable. They live in a system of burrows called “towns”, each of which may cover an area up to 1 square km (square mile). The interconnected burrows in a town provide a refuge from predators and a safe place to rear young. Within the town, prairie dogs form subgroups known as coteries Members of a coterie act cooperatively; for example, to defend their territory.
Rodents are highly gregarious animals and have successfully colonized many habitats, especially those created by human settlement, such as refuse tips and sewers. These brown rats are scavenging for food among the rubbish.
All rodents use their well-developed incisor teeth to gnaw A beaver can fell trees, such as this birch, by gnawing through the trunk Branches and smaller trunks from the tree are used to build a lodge or to dam a river.
Not all rodent species breed as prolifically as mice and rats do. The capybara, for example, usually produces only one litter a year unless conditions are particularly favourable. Litter size varies between one and 8 but is usually 5. Capybara offspring are well developed at birth and are soon able to follow their mother and eat solid food.