National Geographic - Great Migrations 2010

2010

Catch a glimpse of Christmas Island's stunning red crabs in their epic annual migration.

A National Geographic wildlife crew has captured the heroic mating ritual - and also the rare survival and return of more than a million tiny baby crabs.More information can be found at the Great Migrations website.

Transcript - Red crab marathon

Millions of generations have engineered these crabs for life on land, but their young must hatch in the ocean.

It's a brutal, month long migration, upto five 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, wherever and however they can.

For those who have made it this far, a more horrible fate awaits. Yellow crazy ants. Aliens accidentally introduced by cargo ships. Now, super-colonies of billions terrorise the migrating crabs. The ants attack, spraying acid into their mouths and eyes, blinding them, leaving them helpless. In the 1990s the crazy ants slashed the crab population by a third, from 80 million to 50 million.

Beyond the ants lies a dizzying descent. 40 feet, straight down to the beach. Now the males face the waters of their birth. They dip into the ocean to restore their bodies with salts and moisture.

Transcript - Crab dance

On Christmas Island, a different kind of homecoming preparation has begun. The males, though exhausted by their long pilgrimage, are readying snug burrows before the demanding females arrive, in search of nursery ready homes.

Having dipped in the ocean to renew themselves, the bright red would be mothers seek out the males. Once entwined, the tangle may last half an hour.

When she's ready, the female disengages and descends into her den. The male, duty done, begins the long trek back to the forest.

But for the female, the odyssey has just begun.

In darkness, she produces upto one hundred thousand glistening eggs and broods them for 12 or 13 days, waiting for the cue that drives her entire migration - the waning moon and the resulting mild tides.

Eggs stowed in abdominal sacs, the females make a clattering dash to the sea. Here, on the moonlit beaches of their own birth, they brace themselves at the waters edge and release their offspring, in an antic dance born of instinct and desperation.

Transcript - Millions of crab babies

Over the next three weeks, the red crab eggs will drift in the perilous nursery of the Indian Ocean and morph into larvae. Most years the larvae never make it home, swept away by ocean currents or devoured by fish.

But once or twice every decade, a confluence of mild weather and scarce predators gives birth to a moving miracle.

By the millions, they pour over the beaches of their birth like a living pink tide. They shed their larval casing, becoming air breathers and retrace their parents' torturous course guided only by instincts encoded deep in their DNA.

From this moment on, they are migrants, compelled to move no matter what.

The merciless yellow crazy ants take a terrible toll. But by sheer force of numbers and the inexorable will of their genes, they prevail.

Transcript - Moonlit crabs

This is the third night that we've been up all night, shooting crabs, so these guys are really tired. The crew, I bet the crabs are tired too.

This turns out to have been a huge spot, you know, the first time we came out here to shoot it never rained, it was the dry season the whole time which led to a really important part of the story but it wasn't what we had originally expected which happens all the time in this kind of film-making. But here we are in night three and there are still crabs - the whole island is going off on this spot and when the rains finally did come this whole beach has been going. This region of the island has just been flooded with crabs.

Alright, we have a picture. Beautiful. It is nice how that light is mimicking the feel of the moonlight. A bright moon I might add.

What we're trying to get is a close-up of the small legs they have inside the area where they store the eggs, that pushes out the eggs, to disperse them into the water.

And you'd think with all these crabs that it would be an easy shot to get, but it's actually really tough. You know, we're shooting at night, with a lot of light and shadow and you need the crab at a particular angle to really expose this really cool biological feature, so despite a lot of crabs it's really hard for Mark to find the perfect crab at the perfect angle with the perfect light.