Rodents
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Rodent is an animal with front
teeth especially suited to gnawing hard objects. Squirrels,
beavers, and rats are rodents. Squirrels can break the shells of
nuts with their front teeth. Beavers can gnaw through tree
trunks, and rats can gnaw through some wood and plaster walls.
The many kinds of rodents include voles, hamsters, mice, and
porcupines. All rodents have two top and two bottom front teeth
called incisors. They wear away at the tips, but do not wear out
until late in the animal's lifetime because they keep growing
until the animal is old. The incisors wear faster in the back
than in front. As a result, they have a chisellike edge,
well-suited to gnawing. Rodents also have back teeth consisting
of molars and premolars that they use for chewing. The space
between the incisors and back teeth is called the diastema.
Rodents are mammals (animals that feed their young milk). There
are more individual rodents than there are individuals of all
other kinds of mammals combined. Rodents live in almost all parts
of the world. Mice are the smallest rodents and capybaras of
South America are the largest. Some capybaras are over 1 metre
long. Most rodents are herbivorous (plant eaters). But rats and
some other rodents will eat almost any food they can find.
Rodents are both helpful and harmful to people. Some rodents eat
harmful insects and weeds, and some have valuable fur. Scientists
use mice and rats in research. But some rodents damage crops and
other property. Many rodents also carry serious diseases, such as
plague and typhus. Scientific Classification. Rodents make up the
order Rodentia in the class Mammalia and the phylum Chordata.
Rat
Rat is a furry mammal that
looks like a mouse but is larger. The smallest kinds of rats grow
longer and weigh more than the largest mice. Rats, like mice,
beavers, and squirrels, are rodents. All such animals have
chisellike front teeth especially suited for gnawing. There are
about 120 kinds of rats, of which the best known are the black
rat and the brown rat. Both these species live in all parts of
the world. The Nile rat is a pest in North and East Africa. Most
other kinds of rats live in areas not inhabited by people. Black
rats and brown rats rank among the most serious animal threats to
people. They carry the germs of several diseases, including
bubonic plague, food poisoning, and typhus. Rats also damage or
destroy crops and other food products, and they kill poultry,
lambs, and baby pigs. On the other hand, scientists use rats in
research projects that have benefited people. The word rat is
often used for any long-tailed rodent that is larger than a
mouse. But most of these animals are not true rats. They include
the cotton rat, the rice rat, the kangaroo rat, and the wood rat.
The body of a rat. All species of rat have a slender, scaly tail
and long, sharp claws. But black rats and brown rats differ in
several ways besides colour. Black rats grow to 18 or 20
centimetres long, excluding their tail, and weigh about 280
grams. The tail is longer than the rest of the body. These rats
have large ears, a pointed snout, and soft fur. The fur of a
black rat may be black, greyish-brown, or smoky-grey. Grey,
white, or yellow fur covers the animal's underside. Black rats
are also called roof rats or ship rats. Brown rats measure from
20 to 25 centimetres long, not including their tail, and weigh up
to 485 grams. The tail is shorter than the rest of the body.
Brown rats have small ears, a blunt snout, and coarse fur. They
vary in colour from brownish-grey to reddish-grey. Other names
for the brown rat include barn rat, grey rat, house rat, Norway
rat, and sewer rat. The life of a rat. Black rats and brown rats
originally lived only in Asia. They reached Europe either by ship
or overland. From western Europe, the animals spread to North and
South America on ships. Both black and brown rats live in large
groups, with certain rats dominating (having control over)
others. Most members of each species build a nest in or near
buildings. Black rats live in the upper storeys of buildings or
in trees. Brown rats are found under floors, within walls, in
piles of refuse, or in the ground. If the two species live in the
same building, black rats usually occupy the upper levels, and
brown rats dwell on the ground level. Rats are cautious creatures
and generally avoid anything unfamiliar in their environment.
They have a keen sense of smell and can quickly detect
approaching danger. Both black and brown rats eat almost any kind
of plant or animal--even other rats of the same or a different
species. The brown rat is fierce and aggressive, compared with
the milder black rat. Rats feed mostly at night, and sometimes
they band together and attack such animals as chickens and pigs.
Most rats live within an area that may be no more than 45 metres
in diameter. But if a food shortage occurs, rats may travel long
distances in search of food. Most black and brown rats mate the
year around, and the females give birth to three to six litters
annually. A female rat carries her young in her body for about
three weeks before they are born. Most black rat litters consist
of six or seven babies. Most brown rat litters have eight or
nine. Newborn rats are blind and deaf. They remain in the nest
for about three weeks. Few rats live more than a year in their
natural surroundings because they have so many enemies. Animals
that prey on rats include cats, dogs, hawks, owls, snakes, and
weasels. In captivity, some rats live more than three years. Rats
and people. Both black and brown rats destroy eggs, fruit, stored
grain, vegetables, and other foods and attack various farm
animals. Rats also cause considerable additional damage by
gnawing on such objects as furniture and lead pipes. They
sometimes cause fires by chewing the insulation off electric
wires. In addition to spreading disease, rats sometimes attack
human beings, including babies in cots. Their bite may cause
ratbite fever. Some people fight rats by destroying the food
sources or homes of the animals. Others kill rats by poisoning,
shooting, or trapping them. Rat poisons must be used carefully to
prevent accidental poisoning of human beings or of other animals.
Rats may also be controlled by placing specially treated food in
areas where they live. Such food contains chemicals called
antifertility drugs. These drugs make the rats incapable of
reproducing. Domesticated varieties of brown rats, especially the
white rat, play an important role in many scientific experiments
and research projects. Researchers use white rats in studies of
disease, drug effects, heredity, nutrition, and learning and
other aspects of behaviour. They also use rats in the preparation
and testing of new drugs. Many zoos maintain colonies of rats as
food for snakes and other animals. Some people keep domesticated
rats as pets. Scientific Classification. Rats belong to the
family, Muridae. Black rats are Rattus rattus, brown rats are R.
norvegicus and the Nile rat is Arvicanthis niloticus.
Guinea Pig
Guinea pig is a small South
American mammal. It is a domesticated (tamed) form of the wild
cavy. Scientists have used these animals in experiments that have
led to the development of many drugs. Guinea pigs also have been
used in research in the fields of behaviour, heredity, and
nutrition. Guinea pigs make good pets because the animals seldom
bite and are easy to care for. Guinea pigs are not really pigs.
They are rodents, as are beavers, rats, and squirrels. Guinea
pigs measure from 25 to 35 centimetres long and weigh about 0.5
kilogram. They have a large head, small ears, and short legs.
Most guinea pigs that live in their natural surroundings have
long, coarse, brown or grey fur. Guinea pigs bred by animal
breeders may have long or short fur of varying texture. The
animals may be coloured black, brown, red, or white, or a
combination of colours. In some countries, guinea pigs are
popular as show animals. Cavies, wild relatives of guinea pigs,
live in groups of from 5 to 10 animals. They make their home on
grassy plains and the edges of forests and in marshes and rocky
areas. They dig burrows in soil or among rocks and stay there
during the day. They sometimes take over burrows abandoned by
other animals. They are active mostly at night, when they feed on
plants. They are timid and utter loud whistlelike screams when
frightened. After mating, a female guinea pig carries her young
in her body for about 70 days. Most wild female cavies have from
one to four young. In captivity, as many as eight babies may be
born. The young weigh about 85 grams at birth and are well
developed. The mother cares for them for about three weeks.
Domestic guinea pigs may live up to eight years. Guinea pigs have
been hunted for food for hundreds of years. The Inca Indians of
Peru had domesticated them when Spanish explorers arrived in the
1500's. Dutch traders later brought guinea pigs to Europe. Pet
guinea pigs should be kept in a well-ventilated cage and given
dry grain, greens, and hay to eat. Food and clean water should be
available at all times. The front teeth of guinea pigs, like
those of other rodents, continue to grow all their lives. For
this reason, guinea pigs should have a nonpoisonous piece of wood
to gnaw on in order to wear down their teeth. The animals are
healthiest at temperatures above 18 °C. They are sensitive to
dampness and rapid temperature change. Scientific Classification.
The guinea pig belongs to the family Caviidae and the genus
Cavia. Most pet guinea pigs are C. porcellus.
Chinchilla
Chinchilla is a small animal
prized for its soft, thick fur. It is a rodent, a small mammal
with teeth specially suited for gnawing. Chinchillas grow about
half as big as rabbits and have bushy tails like squirrels. Their
thick, shiny, blue-grey fur is 2.5 centimetres or more deep. The
pelts can be made into soft, luxurious coats. A typical pelt
measures 30 to 35 centimetres long and 10 centimetres wide. From
120 to 150 pelts are needed to make a full-length coat.
Chinchillas are native to the snow-capped Andes Mountains of
South America, living in the high valleys from Peru and northern
Bolivia to southern Chile. By the 1940's, hunters had nearly
exterminated the animal in the wild. Today, most pelts come from
animals raised on ranches in Canada, Europe, South Africa, South
America, the United States, and Zimbabwe. The chinchilla eats
roots and grasses. In captivity, its diet consists of grains,
barks, scientifically prepared pellets, and alfalfa, bean, oat,
and timothy hay. Chinchillas are kept in pens. The rack of pens
used on most chinchilla ranches is 0.5 by 2 metres and 2.5 metres
high, and houses 32 adult animals. Most breeders place a nest box
in the pen. Chinchillas begin breeding at about 9 months of age,
and the female usually has two litters a year. The average litter
has two babies, but a litter may have as many as seven. The
babies weigh about 35 grams each and are born with their eyes
open, fully furred, and with all their 20 teeth. The young
chinchillas are taken from the mother when they are 45 to 60 days
old, and they reach maturity in 12 to 18 months. Fully grown,
they weigh from 500 to 1,000 grams and are about 30 to 35
centimetres long. The Chincha and Inca people ate chinchillas and
used their fur for clothing. Spaniards who went to South America
in the 1500's named the animal after the Chinchas. They
introduced the fur into Europe, and the demand became so great
that the chinchilla was almost wiped out. Scientific
Classification. Chinchillas belong to the chinchilla family,
Chinchilladae. There are two species, Chinchilla brevicaudata,
and C. langigera.
Beaver
Beaver is a furry animal with a
wide, flat tail that looks like a paddle. Beavers are known for
their skill at cutting down trees with their strong front teeth.
They eat the bark and use the branches to build dams and lodges
(homes) in the water. Beavers live in rivers, streams, and
freshwater lakes near woodlands. They are excellent swimmers and
divers. A beaver can swim underwater for nearly one kilometre,
and can hold its breath for 15 minutes. Beaver fur is soft and
shiny and wears well. Clothing manufacturers use it to make fur
coats. They also use it to trim the collars and cuffs of cloth
coats. Beaver fur may be squeezed together with other kinds of
fur to make a cloth called felt. Beavers, like many other
animals, may be trapped only at certain times of the year.
Beavers are found in the Northern Hemisphere in central Europe,
southern France, Russia (as far east as Lake Baikal),
Scandinavia, Canada, and the United States. The body of a beaver.
Beavers are about 90 to 120 centimetres long, including the tail,
and weigh from about 20 to 45 kilograms. They are the largest
rodents (gnawing animals) in the world except for the capybara of
South America. Head. The beaver has a broad head, with large and
powerful jaws. Its rounded ears and small nostrils can close
tightly to keep water out. A beaver has three eyelids on each
eye. Two outer eyelids, one upper and one lower, fit around the
eye. A transparent inner eyelid slides down over the eye and lets
the animal see under water. On land, it protects the eye from
sharp twigs when the animal cuts trees. The beaver cannot see
well, and depends on its keen hearing and sense of smell to warn
it of danger. Teeth. A beaver has 20 teeth--4 strong, curved
front teeth for gnawing, and 16 back teeth for chewing. The front
teeth, called incisors, have a bright orange outer covering that
is very hard. The back part of the incisors is made of a much
softer substance. When a beaver gnaws, the back part of its
incisors wears down much faster than the front part. As a result,
these teeth have a sharp, chisel-like edge. The incisors never
wear out because they keep growing throughout the animal's life.
A beaver uses its strong front teeth to cut down trees and to
peel off the bark and the branches. There are large gaps between
the beaver's incisors and its back teeth. Flaps of skin, one on
each side of the mouth, fold inward and meet behind the incisors.
These skin flaps can seal off the back of the mouth. They let the
animal gnaw wood on land or be in the water without getting
splinters or water in its mouth. The flaps open when the beaver
wants to eat or drink. Feet. The back feet are larger than the
front ones, and may be 15 to 18 centimetres long. The toes are
webbed and end in strong claws. Two claws on each foot are split.
The beaver uses these split claws to comb its fur. The webbed
feet serve as flippers, and help make the animal a powerful
swimmer and diver. Tail of a beaver is one of the animal's most
interesting features. The stiff, flat tail looks like a paddle.
It is about 30 centimetres long, up to 18 centimetres wide, and
about 2 centimetres thick. A small part of the tail nearest the
beaver's body has the same kind of fur as the body. The rest is
covered with black, scaly skin and has only a few stiff hairs.
The beaver uses its tail to steer when it swims. The tail is used
as a prop when the animal stands on its hind legs to eat or to
cut down trees. A beaver slaps its tail on the water to make a
loud noise to warn other beavers of danger. Fur. Beaver fur
varies from shiny dark brown to yellowish brown. It looks black
when wet. A beaver's coat consists of two kinds of fur: (1)
short, soft underfur; and (2) long, heavy guard hairs. The guard
hairs lie over the underfur and protect it. The underfur helps
keep a beaver comfortable in the water. This fur traps air and
holds it close to the animal's skin. The trapped air acts as a
blanket that keeps the beaver warm, even in icy water. The life
of a beaver. Beavers usually live in family groups. As many as 12
beavers may make up a family, but generally there are 6 or fewer.
The group includes the adult male and female, the young born the
year before, and the newborn. A newborn kit is about 40
centimetres long, including its tail, and weighs about half a
kilogram. The tail is about 9 centimetres long. A kit has soft,
fluffy fur at birth, and its eyes are open. Food. Beavers eat the
inner bark, twigs, leaves, and roots of trees and shrubs. Poplar
trees, especially aspens and cottonwoods, and willow trees are
among their favourites. Half a hectare of poplars can support a
family of six beavers for one or two years. Beavers also eat
water plants, and especially like the roots and tender sprouts of
water lilies. Beavers store food for winter use. They anchor
branches and logs in a cache under the water near their lodge.
Building dams and lodges. The beaver's habits of building and of
storing food seem to be instinctive (unlearned). A beaver cuts
down trees even if it has no place to build a dam or a lodge, and
even if it has more than enough food. A whole beaver family, and
sometimes beavers from other families, may join in building.
Beaver dams and lodges are made of logs, branches, and rocks
plastered together with mud. Beavers use mud and stones for the
base. Then they add brushwood and log poles. Beavers build dams
in order to produce lakes where they construct their island-like
lodges. The lodges are built in the centre of the created lakes,
out of reach of predators. Each lodge has several underwater
entrances and tunnels, all of which lead to an inside chamber.
The floor of the chamber is 10 to 15 centimetres above the water.
Here, young beavers can stay warm and dry in winter, and the
adults can dry off after bringing in food. Holes between the
branches in the ceiling let in fresh air.
Hamster
Hamster is any of
several kinds of small, chunky, furry rodents that live in Europe
and Asia. Most kinds of hamsters have a short tail and large
cheek pouches in which they can carry a great amount of food.
There are about 15 kinds of hamsters. The best-known species are
the golden hamster and the common hamster. The golden hamster,
also called the Syrian hamster, has light reddish-brown fur on
its back and white fur on its underside. Golden hamsters measure
about 18 centimetres long and have a short tail that is 13
millimetres long. They weigh about 110 grams. The common hamster
is also called the black-bellied hamster because it has black fur
on its underside. Common hamsters measure about 28 centimetres
long and weigh up to 900 grams. Golden and common hamsters live
alone and are active mostly at night. They dig burrows that have
separate compartments for nesting, food storage, and body wastes.
Hamsters eat many kinds of food, including fruits, seeds, green
vegetation, and some small animals. A female golden hamster
carries her young in her body for 16 days, and the common hamster
carries hers for 16 to 20 days. Both species generally give birth
to six or seven young. Wild females usually have two litters a
year, but they may give birth as often as once a month in
captivity. Newborn hamsters are completely helpless and are cared
for by their mother for about three weeks. Golden hamsters are
popular pets. Pet hamsters should be kept in metal cages or in
glass or plastic enclosures. Wood shavings, dried grass, or some
other absorbent material should line the cage floor. Hamsters may
be given many kinds of food, including fruit, raw vegetables,
small grains, whole or rolled oats, and some meat. They need
fresh water. Pet hamsters live three to four years. Scientific
Classification. Hamsters belong to the rodent family Cricetidae.
The golden hamster is Mesocricetus auratus, and the common
hamster is Cricetus cricetus.
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