英语听力：自然百科 大迁徙 Great Migrations—2

What on earth could drive this headlong rush to slaughter? Only earth herself with her insistent clocks. This story begins in the Great Rift Valley, where the continent is tearing itself apart and being reborn. The plains in the shadow of the rift, t

英语听力：自然百科 大迁徙 Great Migrations—3

Apprentice killers wait for their taste of the chase. But they're about to learn that hell has no fury like a zebra protecting her foal. Older cheetahs know the value of patience. Soon, the herd will move on. Hungry eyes turn to one of the last-born

英语听力：自然百科 大迁徙 Great Migrations—4

Only the fit and the lucky will inherit the relay race of their lives. It is a race that is increasingly endangered like many of the world's great migrations. Climate change disrupts weather patterns and exploding human populations encroach on their

英语听力：自然百科 大迁徙 Great Migrations—5

It's a brutal, month-long migration, up to 5 miles, an ultra-marathon for a crab. The cruel sun makes its appearance, threatening them with dehydration. And they face a gauntlet of roads, crisscrossing the island. They stop only to nourish themselves

英语听力：自然百科 大迁徙 Great Migrations—6

Ravenous triggerfish seize the luckless, an unceremonious end to an epic quest. For the surviving males, the odyssey has just begun. The females will arrive within days, urged on by celestial forces demanding they reach the males and the sea in time.

英语听力：自然百科 大迁徙 Great Migrations—7

Then the brilliant masses take to the wing, heading to a place they've never been. Their only map, imprinted on their genes. A mysterious interplay of sun on eyes and antennae, an uncanny sense of magnetic north guides the way. It will take five mont

英语听力：自然百科 大迁徙 Great Migrations—8

For the delicate monarch, it may as well be a trip to the moon. And yet somehow they do it, their tiny bodies attuned to a seasonal sundial and resonating to the invisible signature of the earth's core--its magnetic field. Around the planet, animals,

英语听力：自然百科 大迁徙 Great Migrations—9

Females travel in family groups, sometimes leading their young on yearly wanderings of up to 20,000 miles. Each day, they gather to reaffirm their bonds. They seem to crave physical contact. Finally, the mothers disperse to feed in shifts. They leave

英语听力：自然百科 大迁徙 Great Migrations—10

A quarter of a million wildebeest will die in their yearly odyssey. In the sun burnt Serengeti, hunger keeps the wildebeests thundering northward, following the rain. A collective intelligence keeps the herd on track, neighbor leading neighbor, along

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—1

They are driven to move, to move and to multiply. Possessed by the /insatiable need to breed, they will journey to brutal African battle fields, and grow on South Atlantic shores. For the sake of their young, they will blacken the skies, and terroriz

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—2

And for Johnny rook, the wait is over. Because some of the world's greatest wanderers are heading his way. They've been traveling the globe for months, even years. Only one thing can bring their wanderings to a halt, none of them can give birth at se

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—3

From tip to tip, its wings stand eight feet. This superb blighter can soar almost e* 24 hours a day. Waiting in this bustling, the troublous of hundreds of thousands of birds, her mate shores up the nest from last year's breeding. And after seven lon

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—4

An egg tumbled from the nest is fair game for Johnny rook. He'll soon have his own clamoring brood to look after. On another stretch of beach, the shoreline quakes with desperate battles to dominate. The stakes are unimaginably high. Only a privilege

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—5

Blood runs freely from slashed noses and necks. They even fight dirty, going for the eyes. The loser's breeding chances for now are ground into the sand. But this beachmaster's triumph is just the beginning of his troubles. Ahead lie dozens of fights

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—6

Parenting on the move is all about sacrifice. And in the forests of northeastern Australia, another great journey spurred by parental dedication is about to begin. On translucent tawny wings, a little red flying fox flaps homeward after a night of in

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—7

But they can't migrate to greener pastures until the last of the youngsters has been winged. So mother has become stingy and edgy. Readying for the migration ahead, she tongues oily secretions over every bit of her flight equipment. A bat's wings are

英语听力：自然百科 大迁徙之繁衍生息 Need to Breed—8

In the war-racked country of Sudan, lies Boma National Park, the largest intact savanna in East Africa. Mile upon mile of what looks like pristine wilderness unfolds. But much of this is an empty paradise. During the Sudan's decades of ruinous civil

英语听力：自然百科 海洋天堂大堡礁:堡礁内外—17

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英语听力：自然百科 海洋天堂大堡礁:堡礁内外—16

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英语听力：自然百科 海洋天堂大堡礁:堡礁内外—15

But that pales into insignificance, when compared to the daily vertical migration of these mircoscopic animals called zooplankton. At sunset, all of these tiny creatures swin upwards, and under cover of darkness, they grease on floating algae close t