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.
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
biomes.
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
which can exist between predator and prey. This owl hunts hares and
lemmings. When these mammals are plentiful, female owls lay clutches of
seven to ten eggs. When the food supply drops, only one to three eggs are
laid.
Lemmings are among the most plentiful animals of the far north. These
tiny rodents, found throughout the Arctic, are characterized by wide
fluctuations in population. When vegetation is plentiful, the lemmings'
numbers skyrocket. This population density seems to trigger a drive to
migrate. Hordes of lemmings move out. Nothing deters them — swamps,
forests, lakes, rivers. Eventually some reach the sea, which seems just one
more obstacle. They plunge in, swim out, and drown.
Each summer the far north comes alive with the millions of birds which
have migrated from the south to mate, build nests and raise their young.
Waterfowl make up the majority of these migrants. Shore birds, pelagic
birds, geese and ducks abound in the short Arctic summer. Some have come
thousands of miles. The champion migrant is the Arctic tern, which flies •
16,000 km (10,000 mi) from the Antarctic, and in autumn flies back again.
When the birds leave the Arctic at the end of summer, they follow
ancient flyways south. One of the flyways follows the Pacific coastline
from Alaska to California. Small ponds and estuaries along the coast
resound to the gabbling of hundreds of ducks.
The southern edge of North America's tundra borders on the taiga. Here
wildlife tends to stay on the forest's edge, in meadows, along streams, on
lakes and in old burns. Grass, sedges, and willows grow most profusely in
these openings.
The lakes of Wood Buffalo Park in Canada's taiga are the summer
nesting sites of the whooping crane, the rarest of all cranes and the
object of a decades-long conservation effort. In 1949 there were only 21
left out of a population which once ranged from the East Coast to the Rocky
Mountains. With complete protection, the population rose to 109 birds by
1979. Eighty-three lived in the wilderness; the others were captives.
Twice a year the wild birds migrate a hazardous 4,000 km (2,500 mi)
from their nesting grounds in Wood Buffalo Park to the Aransas Wildlife
Refuge on the Texas coast. The possibility of a major storm or devastating
disease striking this flock is a threat which makes biologists shudder. One
of the basic rules in the management of an endangered species is to spread
the risk. A daring experiment was undertaken with the whooping cranes. Eggs
were removed from nests in Wood Buffalo Park for artificial incubation and
placement under setting sandhill cranes, a related, more plentiful species.
The artificially incubated eggs are hatching and producing birds that are
raised in captivity. Several whooping cranes have been hatched and are
being raised by their foster parent sandhills in Idaho. If the experiment
succeeds, a new flock of whooping cranes will have been produced, one which
migrates a much smaller distance, over a different route, than the original
group. A fringe benefit of taking eggs is that it stimulates the female
bird to continue laying, thus generating more than the usual number of
clutches per year. The most common grazing animal of the American
coniferous and deciduous forests is the white-tailed deer. In the far West,
it is replaced by the mule deer. There are actually more deer now in North
America than when Europeans first arrived, because of the clearing of
forest land, plus game management.
Bears once occurred throughout the forests of America north of Mexico.
The world's largest is a brown bear, the Alaskan or Kodiak. The grizzly,
also a brown bear, has been known to launch unprovoked attacks against
humans.
American black bears are quite common in much of their range —
practically all the wooded areas of North America north of central Mexico.
