Реферат на тему:
THE ANIMALS OF THE AMERICAS
North and South America comprise the only continuous land mass that
reaches from the north to south polar regions, a distance of more than
14,500 km (9,000 mi). The combined area of the two continents is 41.4
million sq km (16 million sq mi), in which are found all terrestrial
The two continents have been joined for the past two or three million
years. Earlier South America was an island, set apart from the northern
land mass for at least 60 million years. This gave time for animal
species unique to the continent to evolve. After the Isthmus of Panama
emerged, there was an interchange of animals between North and South
America, much as that experienced by Eurasia and America during the Ice
Ages. One of the animals found in both Eurasia and America is the polar
bear. Its habitat is along the entire Arctic coast. It has even been
sighted hunting seals on ice floes hundreds of miles at sea. The polar
bear's heavy coat insulates it from the icy water and air. Thick hair
growing between its toes keep it from slipping on the ice. The thick,
white pelt made the animal a prized trophy and reduced its population.
The bear is now protected throughout its range.
The musk ox, resident of the far north, also has had to be protected
from excessive hunting. At one time it came very close to extinction. A
member of the cow family, the musk ox has adapted to the bitter cold by
developing a heavy, shaggy coat consisting of two parts — a coarse outer
covering of long guard hairs and a soft inner coat so dense that neither
cold nor moisture can penetrate.
Musk oxen form a defensive ring when threatened. Adults stand along the
perimeter, heads and horns pointing out, and the calves cluster together
inside. This defensive posture works well against the ox's chief enemy,
wolves, but is of little avail when high-powered rifles are the enemy.
Wolves prey on many species in the north — musk ox, caribou, moose,
deer, hares, and even rodents. These carnivores are among the most
maligned of all animals, victims of false myths and legends and
systematic programs of extermination. They are accused of attacking
humans and destroying entire herds of domestic animals. But their
depredations of livestock are less severe than often claimed. And
unprovoked attacks by healthy wolves in North America on humans are
unknown. Those recorded from Europe's Middle Ages are thought to have
been made by rabid animals or hybrids.
The world will be a far lonelier place if the last wolf dies. As
biologist Ernest P. Walker wrote in his book, Mammals of the World, "The
howl of the wolf and coyote, which to some people is of more enduring
significance than superhighways and skyscrapers, should always remain a
part of our heritage."
Some Arctic wolves remain snow white year round, an adoption to their
environment. Three other predators of the far north— the snowy owl,
Arctic fox, and weasel— are white at least part of the year.
The life cycle of the snowy owl demonstrates the close relationship
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