THE IMPORTANCE OF BIRDS

In nature. Each species of animal in a woodland, grassland, or other natural area depends on other living things in the environment for food. In a woodland, for example, some birds get their food mainly from plants. Others chiefly eat small animals, such as insects or earthworms. Birds and bird eggs, in turn, serve as food for such animals as foxes, raccoons, and snakes. The feeding relationships among all the animals in an environment help prevent any one species from becoming too numerous. Birds play a vital role in keeping this balance of nature.

Birds also serve other purposes in nature. Fruit-eating birds help spread seeds. The birds eat and digest the pulp of berries and other fruits but pass the seeds in their droppings. The seeds may sprout wherever the droppings fall. Hummingbirds pollinate certain flowers that produce nectar. Hummingbirds feed on nectar. As they visit flowers in search of it, they carry pollen from flower to flower. In these ways, birds help numerous kinds of plants reproduce and spread.

Many kinds of birds assist farmers by eating weed seeds, harmful insects, or other agricultural pests. Unlike birds that feed on fruits, seed-eating birds digest the seeds they eat. One bobwhite may rid a field of as many as 15,000 weed seeds a day. Many birds eat insects that damage farm crops. Some birds are especially helpful in keeping the number of certain kinds of insects under control. Robins and sparrows, for example, are highly effective against cabbageworms, tomato worms, and leaf beetles. Rats and mice can cause huge losses on farms by eating stored grain. Hawks and owls prey on these animals and so help limit such losses.

People consider a few kinds of birds to be pests. One such species, the common, or European, starling, was introduced into the northeast United States in the 1890's. The birds multiplied and spread rapidly. Today, starlings are so numerous in many North American cities that they have become a nuisance because of their noise and droppings. Moreover, starlings fight with certain native American birds, including bluebirds and swallows, over the tree holes in which they nest. Pigeons are also a nuisance in many cities because of their droppings. Flocks of starlings and pigeons leave masses of droppings on buildings where the birds have been roosting. The fungus Histoplasma capsulatum can grow on these droppings. The spores of the fungus may be carried in the air and cause the infectious disease histoplasmosis in people who inhale them. Some strains of influenza, another infectious disease, can be passed to human beings from infected domestic birds, including chickens and ducks. West Nile virus, which causes a flulike disease, is transmitted from infected birds to human beings and other animals through the bites of mosquitoes.

As a source of food and raw materials. People have always hunted birds for food. Some of the first birds used for food were ground-feeding birds, such as quails and turkeys, which were caught in traps and snares. Hunters captured pigeons, ducks, and other birds by placing nets where the birds normally flew. After the invention of guns, most people hunted large, meaty birds to save gunpowder and shot. The eggs of wild birds were also an important food for people in prehistoric times, and people in some parts of the world still eat such eggs. Because most birds' nests are hard to find, the eggs used for food have come chiefly from sea birds that nest in open places in large colonies (groups).

People eventually discovered that certain wild fowl could be domesticated (tamed). This discovery led to the development of poultry-that is, domesticated fowl that farmers raise for meat and eggs. Chickens are probably the oldest kinds of poultry. They were domesticated in Asia at least 3,000 years ago. Since then, farmers have developed other poultry, including ducks, geese, guineafowl, pheasants, and turkeys. Mallard ducks, geese, and pheasants were domesticated in Asia; guineafowl in Africa; and Muscovy ducks and turkeys in Mexico.

Today, chickens rank as the most widely raised poultry by far. Farmers throughout the world produce hundreds of millions of chickens annually for meat and eggs. Ducks and turkeys rank second and third in production worldwide. Ducks are raised for both meat and eggs. Turkeys are raised mainly for meat.

People use the feathers of certain birds to stuff pillows, mattresses, sleeping bags, coats, and quilting. Goose feathers are preferred because they are soft and springy. Manufacturers often mix goose feathers with down feathers, or down, to provide extra softness. Down feathers are small, fluffy feathers that some adult birds, especially water birds, have between their stiffer outer feathers. Most of the down used for stuffing comes from ducks and geese raised on farms.

People throughout the world use colorful bird feathers to decorate jewelry, clothing, and hats. Many countries forbid the use of feathers from wild birds. People may only use feathers from domesticated birds, such as turkeys, or from other birds raised in captivity, such as peacocks and pheasants.

Over the centuries, the droppings of ocean birds have formed huge deposits on certain islands where the birds nest in dry areas. This waste matter, which is called guano, provides an excellent source of nitrogen that people use to make fertilizer and explosives. The mining of guano for fertilizer was once an important industry in some countries.

As pets. People have long kept birds as pets. Favorite bird pets include canaries, parrots, finches, and parakeets called budgerigars, or "budgies." Budgies and parrots are especially popular because they can be trained to imitate human speech and even to whistle.

Most birds sold as pets have been raised in captivity. The birds are hatched in cages and sold to the public by pet stores. After years or centuries of captive breeding, some of these birds look much different from their wild ancestors. For example, wild budgerigars are green, but breeders have produced white, yellow, blue, and even violet budgerigars. In the past, most of the parakeets and parrots sold as pets were caught in the wild. Over the years, this practice wiped out some species. To help protect such birds, many countries have made it illegal for wild birds to be caged except in zoos. However, many wild parakeets and parrots are still captured and sold illegally throughout the world.

Bird is an animal with feathers

All birds have feathers, and they are the only living animals that have them. When people think of birds, they usually think first of their flying ability. All birds have wings. The fastest birds can reach speeds well over 100 miles (160 kilometers) per hour. No other animals can travel faster than birds. Yet not all birds can fly. For example, ostriches and penguins are flightless. Instead of flying, ostriches walk or run. They use their wings only for balance and to attract mates. Penguins swim. They use their wings as flippers.

People have always been fascinated by birds. Birds' marvelous flying ability makes them seem the freest of all animals. Many birds have gorgeous colors or sing sweet songs. The charms of birds have inspired poets, painters, and composers. Certain birds also serve as symbols. People have long regarded the owl as a symbol of wisdom and the dove as a symbol of peace. The eagle has long represented political and military might.

There are about 9,700 species (kinds) of birds. The smallest bird is the bee hummingbird, which grows only about 2 inches (5 centimeters) long. The largest living bird is the ostrich, which may grow up to 8 feet (2.4 meters) tall. The largest bird that ever lived was the elephant bird, which died out hundreds of years ago. It weighed about 1,000 pounds (450 kilograms). Birds inhabit all parts of the world, from the polar regions to the tropics. They are found in forests, deserts, and cities; on grasslands, farmlands, mountaintops, and islands; and even in caves. Some birds, including albatrosses and certain ducks, always live near water. Most such birds can swim. Other birds, especially those in the tropics, stay in the same general area throughout life. Even in the Arctic and the Antarctic, some hardy birds stay the year around. But many birds of cool or cold regions migrate each year to warm areas to avoid winter, when food is hard to find. In spring, they fly home again to nest.

All birds hatch from eggs. Among most kinds of birds, the female lays her eggs in a nest built by herself or her mate or by both of them. The majority of birds have one mate at a time, with whom they raise one or two sets of babies a year. Some birds keep the same mate for life. Others choose a new mate every year. Most baby birds remain in the nest for several weeks or months after hatching. Their parents feed and protect them until they can care for themselves. Other kinds of baby birds, including chickens and ducks, become active and able to walk and feed themselves soon after hatching. Most birds leave their parents after only a few months.

 

Birds belong to the large group of animals called vertebrates. Vertebrates are animals with a backbone. The group also includes fish, reptiles, and mammals. Birds have two forelimbs and two hindlimbs, as do cats, frogs, lizards, and many other vertebrates. But in birds, the forelimbs are wings rather than arms or front legs. Like mammals, and unlike amphibians and reptiles, birds are warm-blooded-that is, their body temperature always remains about the same, even if the temperature of their surroundings changes. Unlike most other vertebrates, living birds lack teeth. Instead, they have a hard bill, or beak, which they use in getting food and for self-defense. A number of the earliest birds possessed teeth, but these species no longer exist.

Many birds have great value to people. Such birds as chickens and turkeys provide meat and eggs for food. Some kinds of birds help farmers by eating insects that attack their crops. Others eat farmers' grain and fruit. But in general, birds do much more good than harm.

Since the 1600's, about 80 kinds of birds have died out. People have killed off most of these species by overhunting them and by destroying their environment. Today, most countries have laws to protect birds and help prevent any more kinds from dying out.

This article discusses the importance of birds, their distribution throughout the world, how they live, and how they raise a family. The article also describes bird migration, the bodies of birds, bird study and protection, and the evolution of birds.

Where Animals Live

Animals live in many kinds of places. The place where an animal lives is called its habitat. Each type of habitat presents a special challenge to animals. For example, animals that live in polar regions must withstand bitter cold. Those that inhabit the tropics face extreme heat. In spite of these challenges, animals can be found everywhere on Earth. They live on the highest mountains and in the deepest oceans. They roam the driest deserts and the wettest rain forests. They swim in fresh water and salt water.

Each habitat supports many kinds of animals. In most cases, the animals are the same kinds that have lived in those surroundings for thousands of years. As a result, the animals have developed bodies and ways of life that suit them to that particular habitat. No single species of animal can survive everywhere. For example, tropical fish from the Amazon River thrive in warm water but cannot withstand the cold streams of the Andes Mountains. On the other hand, many kinds of fish that live in the Arctic Ocean would die if they were exposed to the warm waters of the Caribbean Sea. However, some animals may travel between habitats from time to time. For example, African elephants eat both grass and tree parts and so move between grassland and forest. But these animals would not be able to withstand the freezing temperatures of the polar regions.

Some habitats, including many forests and grasslands, are being destroyed by human beings. The destruction of these habitats usually causes the death of many animals. When people convert grassland to farmland, for example, they destroy the homes and source of food of many species. Without these necessities, some animals will die immediately. Others may try moving to another grassland. But the new area may not have enough food and shelter to support the additional wildlife. As a result, many more animals will die.

Some of the major animals, grouped according to seven types of habitats: (1) mountains, (2) grasslands, (3) temperate forests, (4) tropical forests, (5) deserts, (6) polar regions, and (7) oceans.

Animals of the mountains

Mountains support a variety of animal life. The numbers and kinds of animals found on mountains vary with altitude. More animals and more kinds of animals live at lower altitudes than at higher ones, largely because of the differences in climate between elevations. Generally, mountain climates become colder, wetter, and windier with increasing altitude. The air also gets thinner and has less oxygen. In addition, fewer plants are found at higher elevations, and therefore less food is available for animals.

Bears, deer, elk, and mink make their homes on the forested lower slopes and in the wooded or grassy valleys of mountains. Rainbow trout and graylings swim in mountain streams. Many mountains have meadows of grasses and herbs. These meadows are home to chinchillas, ibexes, llamas, vicunas, and yaks. Butterflies, grasshoppers, and spiders also live there.

Above the timber line-that is, the line beyond which trees will not grow because of the cold-stand rocky cliffs and peaks dotted with shrubs, mosses, and other plants. Small meadows are also found there. Sure-footed bighorn sheep and mountain goats dwell among the windswept rocks, as do furry marmots and pikas. High on the snow-capped peaks, only a few insects, spiders, and ice worms can survive. Golden eagles and some other birds fly above the mountains. A large African vulture, Ruppell's griffon, has been known to soar as high as 36,600 feet (11,150 meters).


Animals of the grasslands

Grasslands include the prairies of North America, the pampas of South America, the plains of Europe, and the steppes of Asia. The savannas of east Africa have more grassland animals than any other area.

Rainfall in grasslands is seasonal, and animals sometimes travel great distances to find green grass. Gazelles, gnus, and zebras migrate by the thousands through the African savannas. Smaller groups of elephants and rhinoceroses also feed on the grasses there. Such meat-eating mammals as cheetahs, hyenas, and lions roam the savannas in search of prey. The savannas are also home to giraffes, jackals, ostriches, secretary birds, and termites. In addition, hippopotamuses live in and near bodies of water in African grasslands. Animals of other grasslands include the kangaroos and wombats of Australia, the cavies and rheas of South America, and the coyotes and prairie dogs of North America.

Many animals of the grasslands have become endangered due to loss of their habitat and to overhunting. The rich soils of grasslands are ideal for farming, and people have converted many such areas to farmland. Many of the large grassland animals are favorite big game for hunters. For example, the once-plentiful pampas deer of South America have become extremely rare. As the pampas are converted to farmland, the tall grass that grows there disappears. Without this grass, the pampas deer have no shelter and become easy prey. Bison once grazed in huge herds in the Great Plains of North America. But so many of these animals were killed by hunters or died as their grassland habitat was converted to farmland that they were nearly wiped out.

Animals of the temperate forests

Temperate forests consist largely of deciduous trees and evergreen trees. Deciduous trees shed their leaves in the fall and grow new ones in the spring. Evergreen trees have leaves that live two or more years. Some evergreens have needle-shaped leaves. Most temperate forests are in Asia, Europe, and North America. Australia also has some temperate forests. 

Many forest animals have small bodies that allow them to move easily through the underbrush. Forest mammals include chipmunks, mice, opossums, porcupines, raccoons, skunks, and squirrels. Bears, deer, and wild boars also live in temperate forests. Bobcats and wolves were once common in woodland areas. However, so many of these predators have been hunted and trapped through the years that they have become rare.

Salamanders are often plentiful in temperate forests. They hide in the leaf litter or under rocks, where they feed on insects and other small organisms. In wet forests, slugs and other snails are common. Beavers, fish, frogs, muskrats, otters, salamanders, and turtles live in or near woodland streams, ponds, and lakes. Great numbers of birds nest in the trees and shrubs.

Many temperate forests have been cleared for farms and cities, and many others have been cut down for fuel and lumber. This deforestation (destruction of forests) places woodland animals in danger. Extensive logging in the Pacific Northwest of the United States, for example, has destroyed much of the habitat of the spotted owl, threatening the existence of that species.


Animals of the tropical forests

Tropical forests stay warm all year and receive plentiful rainfall. These forests are found in Africa, Asia, Australia, Central and South America, and the Pacific Islands. More kinds of animals live in tropical forests than in any other habitat. Scientists estimate that perhaps as many as 30 million species of tropical animals have not even been discovered yet.

Insects make up the largest single group of animals that live in tropical forests. They include brightly colored butterflies, huge colonies of ants, mosquitoes, and camouflaged stick insects. Spiders are also plentiful.

Many tropical birds, such as quetzals and parrots, are spectacularly colored. The broad leaves of trees in tropical forests form a thick overhead covering called a canopy that blocks nearly all sunlight from reaching the forest floor. 

Many kinds of animals live in the canopies of tropical forests. They include harpy eagles and toucans; tree frogs; flying dragons; spider monkeys and howlers; gibbons and orangutans; sloths; slow lorises; tree boa constrictors; bats; and wasps, beetles, and leaf-cutting ants.

Kinds of Animals

People often divide animals into various groups based on certain similarities the animals share.


For example, some animals can be kept as pets, but others are wild. Arranging animals according to their similarities is a handy way of remembering and understanding them.


Some common ways of grouping animals. Animals can be grouped in many ways. They can be arranged according to whether they live on land or in water.


Animals that live on land are known as terrestrial animals. They include cats, dogs, lizards, mice, and worms. Animals that live in water are called aquatic animals. They include eels, fish, lobsters, octopuses, and whales.

Animals can be arranged by the number of legs they have. Dogs, frogs, and lizards have four legs. Bats and birds have two legs. Insects have six legs, and spiders have eight. Snakes and worms have no legs.


Another way to group animals is according to how they move. Bats, most birds, and many insects fly. Whales, fish, and squid swim. Snakes and worms crawl. Antelope and cheetahs run. Frogs, kangaroos, and rabbits hop. Some animals are cold-blooded, and others are warm-blooded.


The bodies of cold-blooded animals are warm when their surroundings are warm and cool when their surroundings are cool. Warm-blooded animals, on the other hand, almost always have the same body temperature, regardless of the warmth of their surroundings.


Birds, mammals (animals whose babies drink the mother's milk), and a few species of fish and insects are warm-blooded. All other kinds of animals are cold-blooded. Animals are also commonly divided into groups according to whether they have backbones. Invertebrates do not have backbones, but vertebrates do.

The vast majority of animals are invertebrates. They include clams, insects, jellyfish, sea urchins, snails, spiders, sponges, and worms. Birds, fish, mammals, and reptiles are vertebrates. So are amphibians-frogs, salamanders, and other animals that spend part of their lives in water and part on land. The scientific classification of animals involves grouping animals according to the biological relationships among them. This orderly arrangement of animals depends in part on the features the animals share.


In general, the more features they share, the more closely they are related. However, the scientific classification of animals is based mainly on the belief that certain animals share a common ancestor. Animals with a more recent common ancestor are more closely related than those who share an ancestor further back in time. In a somewhat similar way, brothers and sisters are more closely related than are cousins. Brothers and sisters share parents.





First cousins share grandparents. In classifying animals, zoologists (scientists who study animals) divide them into ever-smaller groups that have more and more features in common. The largest group is the kingdom Animalia itself, which includes all animals. Next, each animal is placed in a group called a phylum. Each phylum is divided into groups called classes. The classes are broken down into orders, and the orders into families.


The families are split into genera, and the genera into species. The singular form of genera is genus, but the word species may be either singular or plural. Among the animals that scientists have classified are about 13,000 species of flatworms; 50,000 species of clams, oysters, and other mollusks (soft-bodied animals, most of which have a hard shell); 1,000,000 species of insects; 30,000 species of spiders; 21,000 species of fish; 4,000 species of amphibians; 6,500 species of reptiles; 9,700 species of birds; and 4,500 species of mammals.

Each species belongs to one phylum, one class, one order, one family, and one genus. For example, tigers belong to the kingdom Animalia, the phylum Chordata, the class Mammalia, the order Carnivora, the family Felidae, and the genus Panthera. They are members of the species Panthera tigris. Lions are related to tigers. They belong to the same kingdom (Animalia), phylum (Chordata), class (Mammalia), order (Carnivora), family (Felidae), and genus (Panthera) as tigers. But lions are classified in a different species-Panthera leo, also written simply as P. leo.  Next >>>