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The animals of Americas - Реферат

km (25,000 sq mi) and contained approximately 400 million animals. With the coming of civilization, the burrows were plowed under and the animals poisoned. Few prairie dog towns still exist.
As the prairie dogs disappear, they are taking with them at least one of their predators, the black-footed ferret. This member of the weasel family has prairie dogs as its prime food. It has become overspecialized and is caught in an evolutionary trap.
North America's arid areas occur in the southwestern United States and parts of Mexico. Large grazers and browsers include bighorn sheep, mule deer and javelinas, also called peccaries. Hawks, foxes, owls, coyotes, and several species of reptiles are among the carnivores. Among them, the coyote is one of the few which has thrived in the face of human intrusion into its habitat. Not only has it maintained its former range; it has expanded it.
One of the resident birds of the North American southwest is the roadrunner, a member of the cuckoo family. Primarily a ground bird, it can run at speeds of up to 24 kmph (15 mph). Its diet consists of lizards and other reptiles which it kills by repeated blows from its heavy beak. If prey proves too large to swallow, the roadrunner ingests a bit at a time. The birds can be seen dashing along the desert with snakes or lizards hanging from their mouths.
The world's smallest owl, the 14 cm (5 1/2 in) high elf owl, also is a resident of the American desert. This tiny predator uses the hollowed-out nests of woodpeckers, located in cactuses, as its home.
The desert also has its reptiles, including many species of lizards, plus two of the four poisonous snakes of North America - the rattlesnake and coral snake.
Rattlesnakes are pit vipers, a group of reptiles which also includes the fer-de-lance, bushmaster, water moccasin, and the copperhead The pit is an opening below the snake's eyes which contains a heat-sensing organ.
Only two of North America's lizards are poisonous - the gila monster and Mexican beaded lizard. Unlike poisonous snakes which inject their venom through hollow fangs, these lizards bite their victims, hold on, and allow poison to flow into the open wound from fangs which are grooved at the rear.
The coastlands and adjacent lands of the United States are the habitat of a wide variety of reptiles, birds and mammals. Water moccasins and copperheads are found in the warmer portions, and the largest of all North American reptiles, the alligator, lives in the rivers and bayous of the southeast.
Alligators can be distinguished from the closely related crocodiles by their broader heads and the lower teeth which are out of sight when the mouth is closed. A crocodile's teeth are visible at all times.
There are no authenticated cases of wild alligators attacking humans. Crocodiles, on the other hand, can attack people.
Many species of shorebirds live in North America. One of them, the brown pelican, came close to extinction on the continent because of DOT. The pesticide was sprayed and dusted on croplands, then percolated into the ground water and was carried to sea where it entered the ocean's food chain. The pelicans, being ultimate consumers, got heavy doses. Although the chemical didn't kill them, it did weaken the shells of their eggs. The result was few pelican hatchlings. After DDT was banned the pelican population began to grow again. In 1979, 1,200 nests were counted in California, a remarkable comeback.
Marine mammals of the U.S. Pacific coast include four species of pinnipeds - members of the seal group. They are elephant seals, harbor seals, Steller sea lions and California sea lions.
South of the United States and northern Mexico, the character of the land and its wildlife changes. Desert, chaparral, and plains give way to tropical forest. In places rainfall exceeds 500 cm (200 in) annually, and a mild average temperature of 27°C (81°F) prevails.
As in most rain forests, primates dominate. In America they consist of dozens of species of monkeys and marmosets. New World monkeys are only distantly related to those of the Old World. Many species have prehensile tails, a feaure lacking in the Old World monkeys. This "fifth hand" is especially well developed in the spider monkey.
Not all of the rain forest's primates have prehensile tails. Marmosets of the forests of Panama and the Amazon basin lack it. And the uakari has a mere stub of a tail, making it the only short-tailed New World monkey.
South America is home to approximately 40 percent of the world's birds, and most of them live in its rain forest. Two groups of rain forest birds are among the most colorful in the world - the hummingbirds and parrots.
Known as "living jewels," hummingbirds are found only in the New World, where they live from southern Alaska to Tierra del Fuego. However, they are primarily tropical birds. There are 319 known species which range in size from the world's smallest bird, the 57 mm (2 1/2 in) long Cuban bee hummer, to the giant hummingbird of the high Andes, measuring 216 mm (8 1/2 in) in length.
A second group of colorful rain forest birds, the parrots, are distributed worldwide in the tropics and on all lands in the southern hemisphere excepting the southern tip of Africa and some of the more remote Pacific islands. In the New World,they reach northward into southern Arizona and New Mexico, where they are represented by occasional visits of the endangered thick-billed parrot.
The only parrot native to the United States is now extinct. In the early 19th century, the Carolina parakeet ranged from North Dakota and central New York south to eastern Texas and Florida. It was especially abundant in the Mississippi River bottoms and along the Atlantic seaboard The little bird was slaughtered for sport and to control its depredations on fruit crops The last one was sighted m the Florida Everglades m the early 1920 s
In addition to its wealth of birds, the South Amen can rain forest is the home of a wide variety of other animals The world s slowest mammal, the sloth which spends long periods hanging upside down from tree branches, is a forest dweller So are opossums, anteaters, poisonous frogs, jaguars, tapirs, and several snakes, among them the anaconda, the world s largest An anaconda can measure more than 9 m (30 ft) in length Its prev includes the world s largest rodent, the hog sized capybara, and the caiman, South America s counterpart of the alligator
To the west, the rain forest terminates at the Andes, the mountain ranges stretching the length of South America The highest point m the western hemi sphere, 7,000 m (22,834 ft) tall Mt Aconcagua, is m the Andes
America s smallest deer, the pudu, and one of the world s largest flying birds, the Andean condor, live in these mountains Probably the best known of Andean animals are the guanacos, vicunas, llamas, and alpacas, New World relatives of camels, which are found at high elevations. Llamas have been domesticated as beasts of burden since pre-Columbian times; vicunas and alpacas are prized for their high-quality wool.
The cold water off South America's west coast is rich with plankton, a link in a food chain which reaches up through fish and ends with the millions of sea birds living on the South American coast and nearby islands. Among them, the guanay cormorant breeds in enormous numbers. Cormorant rookeries are not particularly pleasant places for humans. They reek of drop-pings, dead birds and regurgitated food, and there are flies everywhere. The droppings, called guano, make a superb fertilizer and are harvested commercially in Peru and Chile.
South America's grassland is called the pampas. Although similar to the Great Plains of North America, the pampas never was home to the vast herds of wild animals which once roamed North America.
One of the world's large, nonflying birds, the common rhea, lives on the pampas. It was once hunted by gauchos on horseback for its tail plumes, which were used as dusters. A second species, Darwin's rhea, roams the Andean foothills from Peru to Bolivia and south to the Straits of Magellan. It is an endangered species.
The pampas' predators include foxes, skunks, rattlesnakes, hawks, and one which is found only in South America, the rare maned wolf. This mammal looks more like a fox than like a wolf. It is solitary, nocturnal, and wide-ranging. It hunts small mammals, birds, and reptiles and also eats fruits and other plant material.