It's called the "great migration," an endless march of life, and death and rebirth for millions of animals. When you see it, you might agree this is one of the greatest shows on Earth. We thought you should see it now, because there's no guarantee that it'll be around forever.
There was a time when epic migrations were common, when millions of buffalo in North America were on the move, for example. But today, to see what that must have been like, you have to travel to East Africa.
There, in late summer, more than a million wildebeest cross the volcanic plain of the Maasai Mara in Kenya, pushing through one of the most awe-inspiring wildlife habitats on Earth. Nearly everything Africa has to offer can all be found in one place - zebras, giraffes, elephants, lions, crocodiles and more.
The dry season is moving the herds, concentrating them where there is still grass and water. It's a march of 350 miles, up from the Serengeti National Park in Tanzania to the Maasai Mara National Reserve in Kenya and back again.
American scientist Robin Reid was hooked the very first time she saw it as a student.
She's on the faculty at Colorado State University and has spent decades studying the animals and the Maasai people who share the land with the Mara migration.
"We don't have migrations anymore this large. So, this is the only one that stands by itself that is this large," Reid explained to 60 Minutes correspondent Scott Pelley. "Now, if you're talking about butterflies or you're talking about birds, you're talking about, you know, smaller animals, absolutely. You easily get up into these kinds of numbers. But as far as big animals that are walking long distance, this is the one."
According to Reid, it's the largest great migration of this size on Earth.
"Wildebeest" is Dutch and Afrikaans for "wild beast," which may refer more to its appearance than any ferocity. It's a relative of the antelope but it's unlike anything you've ever seen.
"They call lions regal, and elephants majestic. I wonder what you'd call a wildebeest?" Pelley asked.
"I think they look insane," Reid replied, laughing. "Their horns are kind of, you know, this way and that. And then they have these big shoulders. And why in the heck is that? And they're a funny color. You know, they're not pretty. And they've got a long tail. You know, they're put together in pieces."
"Well, somebody once said it looks like an animal that's made out of spare parts," Pelley remarked.
"And that's very apt," Reid agreed.