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The Animals of Eurasia (реферат)

Eurasia is the largest land mass on earth, stretching halfway around the globe from the British Isles to the Pacific Ocean, and from the Bering Sea south to the tip of Malaysia, an area of 54 million sq km (21 million:sq -л»ХА few of its animal species, especially those in the north, are closely related to, and in some instances are the same as, those of North America.

Relatively recently, as earth time is measured, Eurasia was linked to America by a land bridge which spanned what is now the Bering Straits. This causeway existed for thousands of years during the Ice Ages, when much of the earth's water was locked up in glaciers, thus lowering sea level. Animals crossed back and forth between the two continents on the land bridge, and the first human settlers in America prob­ably arrived via this route.

About ten thousand years ago, the latest in a series of ice ages came to an end. The ice melted; the seas rose, and the Bering land bridge was submerged. An­imal species which had wandered west into Eurasia or east to America were isolated from their native home­lands. But because ten thousand years is a mere eye wink in evolutionary timekeeping, very few changes have had time to take place in these exiles. For exam­ple, the largest member of the deer family lives in the taiga of both Eurasia and America. In Eurasia it is called an elk, in America, a moose. But it is one and the same animal. This is also true of another deer, the caribou, or reindeer. The former is a wild animal of America; the latter has been domesticated for cen­turies by the Lapps of northern Europe.

The Bering land bridge was probably responsible for the survival of at least one species — the horse. This animal originated in the western hemisphere, where it developed from a tiny, three-toed creature, to the form very much like the one we know today. During the Ice Ages, it migrated across the land bridge into Asia, where it thrived. In America the horse be­came extinct and didn't reappear here until the Spaniards brought it back as a domesticated animal in the 16th century.

The Spanish horses, as are all domestic breeds, were descendants of the wild horses which migrated from America. That original breed still exists. It is called Przewalski's horse, named for the naturalist who first brought specimens to Europe from the grasslands of Mongolia. This is the only true wild horse left in the world. All other so-called "wild" horses are feral ani­mals, that is, horses descended from domestic animals which escaped from or were released by their owners. Przewalski's horses once existed in large herds, but human intrusion into their habitat pushed them farther and farther back into a harsh environment where even these tough animals could not survive.

They were last seen in the wilderness in 1967. Fortu­nately breeding groups existed in zoos and reserves. Captive propagation brought the population up to about 700 by 1985, and four dozen Przewalski's horses have been born at the San Diego Zoo and the San Diego Wild Animal Park. Several of the Zoological So­ciety's Przewalski's horses are on breeding loans to other zoos.

The Eurasian bison, called a wisent, is closely related to the American bison. Although never so numerous as the American member of the species, wisent used to roam the forests which covered western Europe. Cen­turies of cutting destroyed all but a small remnant of these forests and came within 17 animals of exter­minating the wisent. A captive breeding program saved them and today a few hundred live in the Bialowieza Forest in eastern Poland. The San Diego Zoo has produced 25 calves.

If the felling of Europe's forests meant the destruc­tion of many wild animal species, it worked to the advantage of others. Deer, for instance, have thrived and live from the British Isles eastward. Red, roe and fallow deer live in western Europe, sika deer in Japan. Pere David's deer, formerly a native of marshy areas in central China, is extinct in the wild. It exists only in zoos and reserves.

The hedgerows of western Europe house many small animal species. There are foxes, rabbits, hares, badgers, ferrets, squirrels and birds. These and other animals have adapted to life in a human-dominated environment. Starlings and sparrows, for example, do so well that they are considered "pest" birds. Until recently, one of Europe's largest birds, the white stork, even nested in the smaller towns and villages. The bird was considered a symbol of good luck, and home-owners built platforms on rooftops for its nests. This practice is no longer common and the stork avoids the towns.

The most regal of Eurasia's raptors is the golden eagle, and the bird has figured in history for centuries. Its image was carried by Roman legions as they con­quered much of the continent. During the Middle Ages, lesser members of royalty were free to use other raptors for falconry, but the eagle was reserved for the king. Today, in more remote parts of Asia, the golden eagle is used to hunt wild goats, gazelles, foxes, and wolves. The bird occurs in the United States, where it is under federal protection. It can be seen in San Diego's back country and often is observed soaring over the San Diego Wild Animal Park.

Several other northern Eurasia predators are found in North America — falcons, hawks and owls; mam­mals including wolves, wolverines and foxes. a However, two mammalian predators are unique to I the Old World — leopards and tigers. Leopards range i from northern Asia into Africa; tigers live only in Asia I from Manchuria southward into India and Malaysia. There are five races of this great cat; all of them are endangered. The Zoo enjoys considerable success breeding and raising Siberian tigers, of which the total world population is only about 750 individuals. More than two dozen cubs have been born and raised at the Zoo.

South of the taiga, Eurasian biomes become less clearly defined. Much of the area is flat and treeless. In the west, where rainfall is adequate, grass grows thickly. But deep in the continent's interior, the land becomes a desert. Here, thousands of miles from the moderating effects of the ocean, temperatures can climb well above 38°C (100°F) in summer, and plum­met far below freezing in winter.

Animals must make drastic adjustments to these climatic extremes. One of the most common is migra­tion. Herders move their domestic herds and flocks, following the seasons, and many of the wild grazers also make similar journeys, with predators following along.

The animals which are permanent residents have adapted to the heat, cold and aridity of this area. The saiga, an antelope-like animal, has nostrils pointing downward to help keep out dust. Inside each of its nostrils the saiga has a sac which is believed to warm and moisten the air.

The Bactrian camel of Mongolia and China has adapted to its environment by growing a thick, shaggy, winter coat; broad, split hooves to keep from sinking into the sand; and two humps for storing fat when foraging is poor.

Several species of wild asses are native to the inte­rior of central Asia. Among these are the Mongolian kulan and Iranian onager. Asses are smaller than true horses and characterized by long ears, deep-set eyes coarse, wiry manes, small feet and tails tipped with long hairs. They can survive longer without water than other members of the horse family and are able to get along on a small amount of food. Because of their sure-footedness and endurance they are valuable beasts of burden and have been domesticated for centuries.

The Eurasian grassland is home to the heaviest of all flying birds, the 20 kg (45 lb) great bustard. And the world's smallest crane, the demoiselle which stands just 1 m (39 in) tall, breeds on grasslands from south­eastern Europe into central Asia.

Several species of wild sheep and goats live on the grasslands and adjacent mountains. Markhors and turs, both goats, range from Spain to India and northward into Mongolia and Siberia. The tahr, a goatlike animal, is found in the high Himalayas. Goats differ from sheep in that they have beards, feet with scent glands, convex foreheads, and a definite odor among the males.

Some of the world's most unusual mammals live in the mountains which separate central Asia from India. One of the best known is the giant panda, once considered a member of the raccoon family and now thought to be related to bears. This animal lives on a diet consisting mainly of bamboo shoots. For un­known reasons the bamboo is dying, which threatens the pandas' future. The Chinese government has commissioned a team of biologists to study the situa­tion. Although giant pandas have rarely reproduced in western zoos, a number of babies have been born in the Beijing zoo through natural conception, and artifi­cial insemination has recently been successful.

The giant panda shares its bamboo forest with the lesser panda. This animal looks like a raccoon but is related to the giant panda.

Central Asia is isolated from India and Burma by the Himalaya mountain range, the highest mountains on earth. The area is so remote that little is known about the behavior of many of its animals. It is the home of a collie-sized gazelle, several species of wild sheep, and a member of the cow family, the yak. The yak is also domesticated and has been a beast of burden and supplier of milk, wool and fuel for many centuries.

One of the most beautiful of all Himalayan animals is the snow leopard, or ounce. Its fur is in great demand and poaching has placed it in grave danger of extinction.

The snow leopard's main prey is the bharal, or blue sheep, which lives in the Himalayas and other high mountains in eastern Asia.

As one moves south from the high country, the character of the land and its animals change. Rugged mountains give way to forested foothills. This country is the northern edge of the sloth bear's range which also includes other parts of India and Sri Lanka (Ceylon). Termites are a part of the sloth bear's diet, and it sucks them in by a "vacuuming" process. The bear rips open the termites' nest with its claws, then blows away the dirt and dust, and starts sucking. Its lips protrude; its nostrils close to keep out dirt.

Beyond the foothills, seasonal forests give way to semi-arid plains and desert in India. Axis deer, nilgai (India's largest antelope) and blackbuck live here. In the Gir Forest is the last remnant population of the lions which once roamed from the Atlantic through the Near East and into Asia. But lions have been gone from most of this range for many centuries and exist today only in a protected reserve in the tiny Gir Forest in western India, where a few hundred individuals survive.

Where one finds lions and other predators, scaven­gers will also be found. In India they include striped hyenas, foxes, dholes (wild dogs), and Indian white-backed vultures. These animals perform a vital func­tion in the balance of nature, cleaning up carrion left by the hunters, thus helping to prevent the spread of disease.

Still farther south lies India's tropical forest, actually two of them — a rain forest and a seasonally decidu­ous forest. They are home to a large variety of mon­keys, mainly of two groups — the short-tailed, stout-bodied macaques, which are primarily terrestrial, and the long-tailed, slender-bodied arboreal langurs.

The macaques include the rhesus monkey of India, sacred to the Hindus, and critical to science. The exis­tence of the Rh blood factor was first demonstrated in rhesus monkeys, and a rhesus was the first living being shot into space in the United States' space program. In Europe, the only wild monkeys are the Barbary apes, actually macaques, of Gibraltar. Legend has it that when these animals disappear — there are approximately 30 of them — Britain's reign over the Rock will come to an end.

The second large group of Asian monkeys, the lan-gurs, are also called leaf-eating monkeys. There are more than a dozen species, among which the douc langur is considered to be one of the most beautiful of all monkeys. The word "douc" means "monkey" in Vietnamese.

Three of the surviving five species of rhinoceroses live in southeastern Asia. Two, the Sumatran and Javan rhinos, could be extinct in the wild. The third, the Indian rhino, exists in small numbers in Assam. Be­cause of the heavy folds of skin and the bumps, called tubercules, on its hips and shoulders, this rhino ap­pears to be wearing a suit of armor.

The Chinese believe that rhino blood, urine, and horn (which is not a true horn at all, but is composed of hair-like material) have medicinal and aphrodisiacal powers. This superstition has resulted in heavy poach­ing of rhinos, placing them in grave danger.

Among the better-known snakes of southeastern Asia are the Indian and king cobras and the pythons. A king cobra can measure 3.5 m (12 ft) or more. It feeds mainly on other snakes. The closely related Indian, or Asian, cobra is appreciably smaller. The pythons are non-venomous constrictors. Contrary to popular be­lief they do not crush their victims to death but, through constriction, cause death through suffocation.

Southeastern Asia is the home of some of the showiest of all birds — the pheasants. Although native to Asia, they have been introduced elsewhere and now are among the most widely distributed of birds. One of the most widespread is the ringneck pheasant. An old legend claims that ringnecks were introduced into Greece by Jason, famous for his quest of the golden fleece. Ringnecks were brought to the United States in the mid-1800's and are now game birds. Several spe­cies of pheasants are exhibited at the Zoo, two of them roaming freely on the grounds.

The first is the blue peafowl. The male, called a peacock, is the traditional symbol of vanity and false pride because of its almost constant displaying and strutting. The peafowl has been semi-domesticated for ages. A Greek myth relates how the bird got the eye-like spots on its tail. The peacock was a favored pet of Juno, wife of Jupiter. She became angry at her one-hundred-eyed servant, Argus, because of a misdeed on his part. To punish him and to make sure the world remembered his offense, she snatched out his hun­dred eyes and scattered them on the tail of her pet peacock. There they remain to this day.

The other pheasant that wanders the Zoo grounds is the junglefowl. It looks much like a domestic chicken — understandably since it is the chicken's ancestor.

Anthropologists think the chicken was first domesti­cated about 4000 B.C. as a fighting bird. Evidence suggests that the first chickens in the New World came with Polynesian sailors. The most ornamental of all domestic chickens are the long-tailed birds bred by the Japanese, some having tail feathers 6 m (20 ft) long.

The hot, humid rain forests of southeastern Asia hold a profusion of wildlife, much of it arboreal. Among these tree dwellers, primates reign, and within this group, the anthropoid — manlike — apes are royalty. Two of earth's four kinds of manlike apes live in southeastern Asia.

The smallest and most agile of these are the gibbons and siamangs. These apes are light-bodied, long-armed and have long, slender hands. Their generic name, Hylobates, means "tree dweller." They are truly champion acrobats, swinging hand over hand and leaping more than 9 m (30 ft) from one branch to the next. On large branches they usually walk upright, holding their arms aloft for balance. Gibbons live in family groups of two to six animals within well defined territories. Their morning whooping, often heard at the Zoo, is a territorial call to warn off other gibbons. The second anthropoid of southeastern Asia is the slow, retiring orangutan. Its name means "old man of the forest," and the orang does seem the most human of the apes. Unlike the gibbon, it is a loner. The species used to be widespread throughout the islands of southeastern Asia but extinction came early on all but Borneo and Sumatra. If we read the evidence cor­rectly, prehistoric man hunted orangutans for food and could have been partly responsible for their dis­appearance from most of the range. Today fewer than 5,000 individuals remain, and despite strenuous efforts to save them, their numbers continue to drop. The forests they need are falling to the ax, so if the species survives, it will be in zoos and wildlife reserves.

Among the rain forest's arboreal creatures, there are a number of interesting "flying" animals — snakes, frogs and lizards. None of these animals actually flies. They glide with varying degrees of aerodynamic facil­ity. The snake spreads its ribs and arches its body to produce a crude airfoil that allows it to glide at a steep angle. The other animals have folds and strips of skin which, when stretched, produce taut membranes that slow descent.

The second largest of all land animals, the Asian elephant, lives in the tropical forest. A bull can weigh 5,000 kg (11,000 Ib) and stand 2.5 to 3 m (8 to 10 ft) tall at the shoulders. Asian elephants have been domesti­cated for centuries — for riding, war, and as beasts of burden.

The Asian elephant's only natural enemy is the tiger. Although this cat attacks elephants, especially calves, it also preys on just about anything it can catch, includ­ing the crocodiles that live in the forest's sluggish rivers. One of its chief prey is the Malay tapir.

Tapirs originated in the New World, crossed on the land bridge into Asia and now exist on both conti­nents. The obvious difference between Old World and New World tapirs is the large, white saddle-shaped patch of hair on the Malay tapir's body. American tapirs are a solid brown color.

Of the many species of birds in the tropical forest, among the most bizarre are the hornbills. There are 45 species, distributed throughout tropical and subtropi­cal Africa and Asia. One of the bird's more fascinating behavioral habits is the manner of nesting. In most species of hornbills, when the female is pregnant and ready to lay, she enters a natural cavity in a tree. She and the male plaster over the cavity's opening with a mixture of droppings, mud and regurgitated food. They leave a narrow opening just wide enough for the female to poke her beak through, but too small for predators to enter. The plastered wall hardens, and the female, her eggs, and later the chicks, are safe. The male spends the time feeding his mate. When the nestlings are half-grown, both parents chip away the wall and the female emerges. She then helps her mate feed the baby birds, which remain in the nest until they are fledged. During the time the nest is occupied, it is kept clean and disease-free by insects and micro­scopic scavengers.






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