DC_Amazing Earth_5of9_Ice Age Survivors
Transcript
00:00At the dawn of the Ice Age, large mammals roamed the Earth in vast numbers.
00:11They enjoyed an abundant food supply and a world without boundaries.
00:17But by the end of the Ice Age, only 10,000 years ago, many great mammals had died out.
00:30The woolly mammoth, the dire wolf, the saber-toothed cat, and others disappeared as a result of severe
00:38climatic changes that engulfed the planet. And yet other animals persevered.
00:44Today, they go on in dwindling numbers as the last of the Ice Age survivors.
00:53Throughout the past two and a half million years, the Earth has been gripped by several
01:10periods of extreme cold. During the most recent, which ended only 6,000
01:17years before the rise of the Egyptian civilization, about a third of the Earth's
01:21surface was covered in ice. We call this the Ice Age.
01:29The Ice Age was the result of a combination of factors. The Earth's
01:34elliptical orbit had reached its farthest point from the Sun, an occurrence
01:39which happens about every 100,000 years.
01:43The added distance prevented the Sun's warming rays from melting the snow in
01:48summer. Snow began to accumulate, and over centuries, glaciers began to form.
01:58When they became big enough, they started to move.
02:09The enormous ice sheets that descended upon Canada and the northern United
02:13States are thought to have been as much as two miles thick. As they moved, they
02:19forced animals to move further and further south to survive. New York City
02:26would have been almost completely buried in ice.
02:34Most of North America's large mammals adapted to the extreme conditions, but
02:39they still face severe challenges in their struggle to survive. Horses of the
02:46Ice Age shared most of the same characteristics as today's horses.
02:54They digest their food in a way that enables them to live on relatively low
02:58quality food, like grass, which has few nutrients.
03:09But they must eat large quantities to maintain their strength, and in winter,
03:13grass can be hard to find.
03:29At the end of the Ice Age, when the glaciers retreated and the climate
03:32changed, the native horses of North America vanished from the continent. But
03:38horses survived in Europe, and these in America today are their descendants,
03:41brought by the Spaniards during the colonization of the New World.
03:48They now carry the lineage of the great herds of wild horses that once roamed
03:53this land.
04:09Bison are among North America's most rugged and enduring large mammals. During
04:16the Ice Age, they adopted long hair for insulation against the bitter cold, but
04:24even today, many die each winter.
04:31Here in places like Yellowstone National Park, bison endure as they have for
04:36millions of years. During the Ice Age, there were several species of bison, one
04:45of which had horns that measured 7 feet from tip to tip, and weighed almost 2,200
04:51pounds. The horn is thought to have been ornamental, and today's bison horns are
04:59less impressive, at about one and a half feet across. But today's bison have
05:06maintained most of their bulk, a feature which has its advantages.
05:14Large animals have a greater density that enables them to retain heat better
05:18than smaller animals. Another element of bison success is their ability to find
05:27food in winter. A massive head makes a good plow for burrowing under the snow,
05:39and once uncovered, grassy patches are closely guarded.
05:46Bison originated in Eurasia, and were among the last animals to cross into
05:57North America over the Bering Land Bridge that once linked Siberia and
06:01Alaska. Their success here was remarkable, at one time numbering 40 to 60 million.
06:16Rivers create their own microclimate. The flowing water can often be warmer
06:22than the air, allowing grass to grow along its mossy banks.
06:30Though bison survived the Ice Age, millions were killed during the 19th
06:35century expansion into the American West.
06:40The descendants of those who survived are but a mere fraction of the millions
06:46that once roamed this land.
07:02The ancestry of dogs can be traced back in North America more than 30 million
07:07years. One of the most enduring and recognizable members of the dog family
07:13is the coyote. Today's coyotes appear much the same as they did during the
07:20Ice Age, and have changed little over time.
07:31For the most part, they are opportunists, relying on small prey and carry on when
07:36available.
07:51But as during the Ice Age, when there's large game around, they form loosely
07:55organized hunting packs.
08:07Feeding order is determined through displays of dominance and submission.
08:23The alpha male of the group usually eats first, but because coyote packs are
08:29loosely organized, other members will try for anything they can get.
08:36Predators like the coyote help to maintain balance in the natural world.
08:54Each death permits the survival of another animal.
09:06Rivals often attempt to take over a kill, so this pack must constantly be on guard.
09:30Though this advance seems aggressive, it is actually a submissive posture,
09:35recognizable by the arched back and tail held between the legs.
09:42He sizes up his chances before taking any overt action.
09:55Today, as it was 10,000 years ago, the coyote's staple diet is mice.
10:02Blanketed with snow, mice can be hard to catch, but sensitive ears detect even the
10:10slightest movement.
10:32Opportunities for food are few and far between in winter, and anything that
11:01moves is investigated.
11:11But these otters have their escape routes carefully planned,
11:14and the coyote can do little to catch them.
11:31Though the hardships of the ice age are past, the endless search for prey continues,
11:57often ending in frustration.
12:27North American elk migrated here in great numbers during the ice age.
12:52They are descendants of a Eurasian lineage that at one time included a giant elk with antlers
12:56that spanned over 10 feet.
13:12After the ice age, when warming climates caused other large herbivores to die out,
13:17elk expanded their range in North America, and at one point numbered over 10 million,
13:21a population second only to the great bison herds.
13:37During the summer, males are mainly solitary, but in winter they maintain bachelor groups.
13:46In order to attract cows and defeat rival bulls, an elk must become large and powerful.
14:07The elk's antlers reflect this, and are used as weapons to establish dominance.
14:16Though the antlers can cause severe damage, males rarely kill each other,
14:39as a fight to the death would expend more energy than it would be worth.
15:02Using their hooves to dig beneath a layer of snow, elk feed mainly on grass, shoots,
15:07twigs, and leaves. The ability to dig for food in this way was a benefit
15:16during the brutal winters of the ice age.
15:30Elk also feed in riverbeds, where the warm water supports an aquatic pasture.
15:42But this bull must remain constantly on the lookout for his age-old nemesis,
16:02the wolf and the grizzly bear.
16:13Females stay together throughout the year.
16:20As with all herd animals, the group provides security,
16:23since there are more eyes, ears, and noses to detect a stalking predator.
16:33In a nearby clearing, a young calf has become trapped in quicksand.
16:48It is a scene that has been played throughout history,
16:51and one which has provided us with our richest source of fossil remains.
17:03When predators like this coyote approach, they too can become trapped.
17:33Fossils obtained from scenarios like this have allowed us to reconstruct a remarkably
17:37detailed portrait of North America during the ice age.
17:42But there are many unanswered questions.
17:49What we do know is that about 10,000 years ago,
17:52global temperatures suddenly began to rise.
17:58As the earth grew warmer, open prairies turned to forests,
18:02and plants that were once plentiful suddenly disappeared.
18:10Animals that relied on these plants were, in many cases, unable to adjust to the changes.
18:18At around the same time, the first human hunters arrived in North America.
18:24With many species like the woolly mammoth already weakened by environmental changes,
18:28it didn't take much for human hunters to finish them off.
18:36North America would never again sustain such a diverse and plentiful mammal population.
18:54The plains of Africa.
18:56The vast diversity of animals here is a living reminder of the world
19:00as it was before the ice age extinctions.
19:10Africa's geographical position protected most of its animals from the arctic cold,
19:14permitting huge herds to migrate across its limitless terrain.
19:19Today, Africa is still the home of the world's most magnificent herds of large mammals.
19:37Elephants are the largest land mammal in the world.
19:41During the ice age, they enjoyed the boundless resources Africa provided.
19:49Although they managed to survive the climatic changes at the end of the ice age,
19:53some of their distant relatives were less fortunate.
19:59In the late 1800s and early 1900s,
20:03elephants were the largest land mammals in the world.
20:07Their distant relatives were less fortunate.
20:11Mammoths migrated throughout the world,
20:13but when the glaciers retreated and their food supply disappeared, so did the mammoths.
20:21Like the mammoths, today's elephants travel in large herds over enormous tracts of land.
20:31They require huge amounts of food,
20:33quantities that today's shrinking habitat can barely supply.
20:53Grasses, shrubs, and the bark from trees make up most of their diet.
20:57They chew their food with huge, block-like teeth that regrow as they wear down.
21:17In order to reach and manipulate food, elephants evolved trunks.
21:27Though powerful enough to lift a whole tree, the trunk is also acutely sensitive to smell and touch.
21:43Stripping bark from trees and shrubs enables elephants to utilize a food source other animals can neither reach nor digest.
21:57In order to reach and manipulate food, elephants evolved trunks.
22:01Though powerful enough to lift a whole tree, the trunk is also acutely sensitive to smell and touch.
22:27As they did during the Ice Age, elephants travel great distances in search of water sources,
22:37capable of supplying each elephant with up to 20 gallons a day.
22:45Often following the same paths over time, elephant roads are carved through even the densest vegetation.
22:57Female elephants live in groups of two or three sisters and their infants.
23:07Mothers carry their young for 22 months and closely defend them through childhood.
23:28Elephants' skin is highly sensitive, so they bathe frequently, followed by a powdering with dust to prevent parasites and disease.
23:42Today's African lions retain the basic characteristics of their extinct relatives.
23:50But a tight social structure sets them apart from many of today's other cat species.
23:57Copulation serves a dual purpose as it also bonds members of the pride.
24:21Ovulation is induced by the act of mating and pairs may copulate up to 30 times a day.
24:27The male dismounts quickly since females sometimes become aggressive toward their partners.
24:57Litters average three or four cubs and enjoy a long period of parental care.
25:27Support comes from all the females in the group, lending a nursery-like atmosphere to the pride.
25:47Communal suckling is rare among mammals.
25:50Lions are one of the few whose females will actually nurse offspring other than their own.
25:58Lions have the largest brains and are the most social of all cats.
26:02Two traits that today, as they did during the Ice Age, contribute immensely to their survival.
26:09Females do most of the hunting and will teach their young at an early age.
26:14The wild lions are the most active in the wild,
26:16but they are also the most vulnerable to predators.
26:26The wild lions are the most active in the wild,
26:29but they are also the most vulnerable to predators.
26:32Camouflage and stealth are the keys to a successful hunt.
27:02In this video, we're going to show you how to use camouflage and stealth to your advantage.
27:07Camouflage and stealth are the keys to a successful hunt.
27:32Lions succeed in the hunt only once in every five tries.
27:49But through trial and error, this mother will train her cubs as quickly as possible so they can begin to fend for themselves.
28:02In isolated areas of the African plains, an animal endures today whose prehistoric appearance evokes the past.
28:25Like elephants and hippos, rhinos were far more abundant during the Ice Age.
28:46Millions of years ago, a rhino lived who was as slender and fast as a horse.
28:54Though today's are not quite as agile, they can still make an impressive charge when threatened.
29:04The name rhinoceros derives from the horn on the snout.
29:11Unlike bison and elk, whose horns have a bony core, the rhino's horns are made of tightly matted hair.
29:22Rhinos have poor vision and are unable to detect a moving object more than 100 feet away.
29:29Their eyes are placed on either side of the head, so in order to see forward, they must look with one eye and then the other.
29:40This trait, combined with their relatively small brain, causes them to be easily startled and has given them a reputation for unprovoked aggression.
29:52On average, rhinos live about 45 years, with females first giving birth at the age of six or seven.
30:00A single birth is the norm, and babies are relatively small, weighing only about 100 pounds, compared to the mother's 5,000.
30:12Though rhinos have survived for millions of years, they are now under grave threat from man.
30:20Today, the five living species of rhinos survive in dwindling numbers, but their long-term fate remains in question.
30:51Millions of years ago, hippos lived in forests and were much smaller than today's three-ton average.
31:01But as forests gradually gave way to open plains, hippos moved out of the forest and into the water.
31:12By the time of the Ice Age, hippos had already acquired their unique skin structure.
31:20Because their skin dehydrates quickly, they spend most of the day in water, leaving only at night to feed in the grassy meadows nearby.
31:30They are slightly denser than water and can easily walk on the bottom of riverbeds for up to five minutes at a time.
31:39Their reliance on water is part of a trade-off from their past.
31:45When they moved from the forests to the lakes, they gained access to a greater food supply.
31:51But in so doing, they lost their sweat glands and are now forever tied to the water.
32:09Today's hippos are fully adapted to aquatic life, with eyes, ears, and nostrils placed on top of the head.
32:19By barely breaking the surface, they know everything about their surroundings.
32:27As their Ice Age ancestors did, dominant bulls maintain exclusive mating rights in their territories and defend them rigorously.
32:43Their razor-sharp lower canines are up to 20 inches long and can inflict severe damage.
32:53As evening approaches, groups begin to come ashore for feeding.
32:59They'll walk along their regular trails to their favorite pastures and may not return until morning.
33:07In a nearby lake, ancient predators defend their nests.
33:13Crocodile evolution spans more than 200 million years, qualifying them among the most enduring animals on the planet.
33:23During the dinosaur era, the population of crocodiles grew exponentially.
33:32During the dinosaur era, the largest known crocodile was over 35 feet long, with a six-foot head and razor-sharp teeth.
33:50Today's crocs average about 16 feet, but they still possess many of the same traits as their predecessors.
33:59As they did here during the Ice Age, female crocs come ashore to lay their eggs.
34:07After about three months, the female uncovers the nest, allowing the eggs to hatch.
34:14To ensure their safety, she gently picks up each hatchling with her teeth and holds them in the pouch of her mouth.
34:34It was once believed that mothers ate their young, and it still seems a precarious situation for the youngster.
34:44The youngster, however, does not want to give up.
35:00Carrying as many newborn and unhatched eggs as she can, she makes her way back to the water.
35:13Here she will release the hatchlings, and then gently crack open the remaining eggs by swishing them from side to side in her mouth.
35:44She releases the hatchlings, and then goes back to the water.
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36:20Just as they have done through countless generations,
36:22the remaining hatchlings on shore
36:24make their way down to the water's edge.
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36:44They do so just in time,
36:46as the nest is now under attack by an army of ants.
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37:18There are many other perils for young crocs
37:20and their mothers to face.
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37:26A nest must be defended with vigilance
37:28if its eggs are going to survive.
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37:35But today, as during the Ice Age,
37:37it is estimated that only 2% of all crocodile young
37:41make it to adulthood.
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38:16The first few weeks of life are full of risk,
38:18and the young stand the best chance of surviving
38:21by staying close to mom.
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38:51Leopards are among the most solitary
38:53and secretive members of the cat family.
38:56As they did during the Ice Age,
38:58they use camouflage and speed to ambush their prey.
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39:53This one decides to wait for a better opportunity.
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40:01Leopards maintain territories of up to 20 square miles.
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40:09Because territories often overlap,
40:12they must be diligent about marking their turf.
40:35Leopards have adapted to a wider variety of habitats
40:38than any other wild cat.
40:50They spend much of their time in trees.
40:58Trees provide a good perch from which to search for prey
41:01or stage an ambush.
41:09And after a kill, trees make a good place to store prey
41:13out of the reach of scavengers.
41:19Adult males average about 130 pounds
41:22and can take down animals several times their own size.
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41:34Between hunts, trees offer safety,
41:37allowing this leopard to doze in the late afternoon sun.
41:42Between hunts, trees offer safety,
41:45allowing this leopard to doze in the late afternoon sun.
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42:16In a nearby patch of open savanna,
42:19a pack of African wild dogs huddles around their young.
42:26They bear some unusual traits for mammals
42:29that have endured almost unchanged
42:31since long before the Ice Age.
42:41Instead of the females raising the young,
42:43it is the male dogs that take the lead in child-rearing.
42:51Accordingly, males in the pack
42:53outnumber the females by two to one.
43:07Pups are born blind in their den
43:09and don't emerge until they're about three weeks old.
43:19Of course, fathers can't do everything,
43:21and this mom must endure the demands
43:23of a litter full of hungry pups.
43:26It is usually only the dominant male and female that breed,
43:30and if another female in the pack were to produce a litter,
43:33it is likely this alpha female would kill the pups
43:37and possibly even the mother.
43:45In the early morning hours of the day,
43:47it is possible that the male dogs
43:49will be the first to arrive in the pack.
43:55The mother decides that the pups have had enough,
43:58as she sees other duties calling.
44:00The mother decides that the pups have had enough,
44:03as she sees other duties calling.
44:06The mother decides that the pups have had enough,
44:09as she sees other duties calling.
44:23Through the ages,
44:25the male dogs have become the first to arrive in the pack.
44:35Through the ages, wild dogs have perfected the art of pack hunting
44:38and can bring down animals five times their size.
44:48They run at speeds up to 35 miles per hour,
44:51but like wolves, it is their team effort
44:53that makes them so successful.
45:05They run at speeds up to 35 miles per hour,
45:08but like wolves, it is their team effort
45:10that makes them so successful.
45:35They run at speeds up to 35 miles per hour,
45:38but like wolves, it is their team effort
45:40that makes them so successful.
46:06The pups are usually allowed to eat first.
46:09The pups are usually allowed to eat first.
46:16The pups are usually allowed to eat first.
46:21Wild dogs are exclusively meat-eaters
46:23and have short, powerful jaws
46:25with an impressive array of shearing teeth.
46:35But they do not kill haphazardly.
46:41Each hunt preserves the balance of life on the African plains.
46:50After the dogs have had their fill,
46:52the vultures arrive to finish off the carcass.
47:05Nothing is left to waste in the wild
47:07as meals are few and far between.
47:16Hyenas are one of the few animals that can digest bone
47:19and thus fill a niche in the food chain
47:21that ensures nothing will be left behind.
47:35These pups are just beginning to learn the hunting skills
47:38These pups are just beginning to learn the hunting skills
47:40and take this opportunity to practice the chase.
47:42and take this opportunity to practice the chase.
47:45These pups are just beginning to learn the hunting skills
47:48These pups are just beginning to learn the hunting skills
47:50and take this opportunity to practice the chase.
48:14Soon they'll be responsible for the pack's survival,
48:17but today they enjoy the carefree pleasures of youth.
48:33As evening approaches, the adults create a perimeter around the den
48:37where they will post guard through the night.
48:44As evening approaches, the adults create a perimeter around the den
48:46where they will post guard through the night.
48:58Much as their ancestors have for millions of years,
49:01these adults have invested heavily in their pups.
49:08But as with all the animals that survived the ice age,
49:11their future remains uncertain.
49:15Although they don't know it now,
49:19the struggles these pups will face over disappearing land
49:22and dwindling supplies of food
49:24may ultimately lead to a struggle for their species' survival.
49:37Today, 10,000 years after the ice age,
49:40the Earth's climate continues to warm.
49:44Animals that lived through the ice age now face a far tougher test
49:48in the struggle for depleted resources in space.
49:55And now it is man, rather than nature,
49:58that determines who will survive.
50:13Transcribed by ESO, translated by —
50:43Transcribed by ESO, translated by —