Nov. 17, 2006 -- More than 1 million wildebeests, half a million gazelles, and 200,000 zebras constantly on the move -- they're all in search of fresh grass and water.
Welcome to the Serengeti and the Masai Mara plains in the heart of East Africa -- the seventh New Wonder of the World.
Covering about 10,000 square miles of land teeming with life, the Serengeti is home not only to some of the most diverse wildlife on this planet, but the start and finish line for one of the world's last great migrations.
"Good Morning America's" expert panel had a spirited debate about the merits of a moveable, natural wonder of the world.
"It's one of the great wonders in terms of animal migrations," said oceanographer and panelist Sylvia Earle. "It's just over the top."
In the end, the uniqueness of the area and the preservation it provides to so many species living in harmony landed it on our list.
"Serengeti-Mara ecosystems [are] considered to be perhaps the last of the ecosystems … in which … human impact is less than 5 percent," said professor Karim Hirji, former director of the Serengeti Wildlife Research Center.
Year-round, wildebeests, zebras and gazelles roam, pushing ever forward in a clockwise rotation covering the Serengeti in Tanzania and Masai Mara in Kenya, along the way encountering friends and foes alike.
"There's high drama almost the whole time," said tour guide David Bromham. "If they're not birthing 300,000 calves in the 3½-week period, they're leaping into rivers for 20 [feet] up."
Wildebeests may have been making the trek for millions of years, coping with disease, drought and predators.
"It would be astonishing and wondrous to watch the migrations go by," said Neil deGrasse Tyson, a panelist and astrophysicist.
Those lucky enough to travel here see wild animals in their purest state.
Wildebeests Key to Circle of Life
On the East African plains, you'll see lions, elephants, giraffes, and lots of wildebeests.
Guide Gerald Selempo told "Good Morning America's Weekend Edition" anchor Kate Snow that the locals had a nickname for them.
"They call them 'the clowns,' because when you look at a wildebeest he looks like he was made up of the leftovers of all the other animals," Selempo said. "They have like a head of a buffalo, have tail of a horse. They have legs of an antelope. They just don't look very balanced."
But the wildebeests do bring balance to this fragile ecosystem, made up of the Serengeti and the Masai Mara. They are the heart and soul of the Great Migration -- the key to survival on the vast plains.
"Without the migration, it's harder to conceive Serengeti-Mara being what it is today," Hirji said. "Everything else survives within that migration -- the predators and so on the vegetation."
The journey is quite literally the circle of life. It happens year-round, a 700-mile trek, finely tuned to the region's rainy seasons. The herds follow the rain.
"They just move and hopefully wherever they are going they can get as much grass and as much water as possible," Selempo said.
After spending the late summer and early fall in the north, here in the Masai Mara, dry land and lack of food forces the herds south to the Serengeti, which is lush with new grass.
There's even a pattern to the way they eat. First, the zebras come.
"The zebra seems to be eating the top grass," Selempo said. "The wildebeests go for the middle and then the herd beasts. … Like the gazelles, go for the lowest part."
It's not always easygoing. With the circle of life, comes the promise of death. Lions, cheetahs and leopards look forward to the herds' arrival. Wildebeests are easy prey for a big cat, and once the predators are done, the vultures move in to clear away the leftovers.
Sometimes the migrating beasts seal their own fate. One group of wildebeests starts out going south, but are then distracted when they sense rain to the north. The result can be crossing a river filled with unfriendly crocodiles. It happens over and over again.
"They'll have to crisscross their river several times, sometimes 10, 20 times, depending on which direction they are going," Selempo said.
But the miracle of the Great Migration is that the animals mysteriously always find their way.
No one knows exactly how far back the migration dates, perhaps millions of years. But one change in the environment here can trigger enormous consequences.
In the early 1900s, a savage disease cut through Africa, and drastically reduced the herds from 2 million to just a few hundred thousand.
Then, a devastating drought in the 1990s decimated the population even further.
"If the climate changes drastically, then this whole equilibrium, this whole tune up, this whole finely tuned movement is going to be thrown out of phase," Hirji said.
The wildebeest population is stable again and is more than a million strong.
In the late winter and early spring, the herds move to their version of a maternity ward -- the nutrient-rich south. It's the only place on the migration route where wildebeests can successfully have babies. And they do; 300,000 calves are born in just three weeks.
Those new babies join their parents, the zebras, and other migratory animals making the turn north and following the rains again, a never-ending circle reminding us of the wonder of life.
To learn more, visit the David Sheldrick Wildlife Trust's Web site.