Today was my “longest, hardest” day and always among its best. After ten hours we’d seen so much that the exhaustion wasn’t from the bumps but the sights.

Lots of people go to Olduvai Gorge when leaving Ngorongoro Crater, just as we did. And a few of them then continue to the site where Zinj was found, and fewer still continue as we did to the mysterious Shifting Sands.

I won’t give away the secret as to why these seven large hills walk themselves across the grassland plains, sometimes 20 meters a year, sometimes 200 meters. And we were further surprised by the arrival of some legitimate Maasai warriors who bumbed some water off us.

But very, very few people then know how to continue off the tracks altogether into the southern grassland plains between Olduvai and the Lemuta Kopjes. Two weeks ago the plain was filled with wildebeest. Today it was nearly wildebeest empty, because it had dried out.

But there were still literally tens of thousands of Thompson’s Gazelle. These beautiful plains creatures don’t migrate; they don’t have to. They eat the roots of the grass, and they rarely drink after suckling and then it’s usually for salt, not water.

But the unexpected twist to the day game when our lone two vehicles on the plane were intercepted by a white Toyota sedan car!

It was a German couple trying to drive themselves, and they were understandably lost. I was beside myself with anger and worry. The last thing East African tourism needs is a reported lost of two casual tourists.

They were using a map that was about 40 years out of date and large enough to direct them to Morocco, in other words, useless. They had come from a cheap camp in the northern Serengeti and wanted to go to Lake Natron.

They had missed their turn three hours before. We explained all this to them and told them the safest thing to do was to continue in the direction they were heading, since that was only two hours from Ngorongoro, and they were at least 6 hours from where they wanted to go.

But now, the woman driver said, they didn’t want to “go back” to Ngorongoro. After some questioning, it seemed they were reluctant to spend the extra $100 in fees it would cost them to reenter the Conservation Area.

I offered to give them the $100. As I said the last thing I want is for some tourists to hit the headlines as having been lost in the Serengeti.

But she refused, and there was nothing we could do. They turned around and headed back to where they’d come from, and we continued on our journey onto the Lemuta Kopjes for lunch.

And right after lunch we intercepted the herds. It meant they had shifted about ten miles west of where I had seen them two weeks ago.

Understandably, people think the “great migration” is some strictly defined circle of movement, but of course it isn’t. Although wildebeest can’t stand still and will act like they’re moving all the time, if the grass is good, there’s no reason they need to move.

And the grass was phenomenally good. Today the migration is mostly in a rectangle, 40 x 20km that begins just west of the Lemuta Kopje and angles southwest to the Kusini Plains at Hidden Valley. I’d dare say that probably half or more of the 3 million animals currently composing the wildebeest, including young and zebra, are in this rectangle.

It is a sight to behold. And for the first time in nearly 12 years, Hidden Valley is once again open to us, the rhinos that were reintroduced here considered totally acclimated.

So we gingerly slid the cruisers into the valley to watch a large female cheetah stalk Grant’s gazelle. To no avail, as is the case with the majority of hunting attempts, but still a wonderful drama.

We set our elaborate breakfast, the best in all of Tanzania prepared by Ndutu Lodge, off the edge of the herds to avoid some flies. But even as we were eating, the herds started to envelope us.

We headed back to the lodge about six hours after we began, stopping to watch a magnificently beautiful and very full lioness grudgingly lift herself and her belly out of the grass to look quizzically at a line of wildebeest passing her bye.

She was just too full to hunt but too young to go back to sleep!

There is no natural spectacle on earth as great as this. I’ve been so fortunate that it has continued and prospered even during my forty years of guiding. I just hope that it will be so for the generations to come!

Yes, we saw hundreds if not thousands of the world’s largest mammal and hundreds of its largest antelope, the eland, and dozens of its smallest, the dik-dik.

Yes, we saw Africa’s smallest owl, the pearl-spotted owlet; a mating dance of Africa’s largest owls, the Verreaux Eagle Owl; and the rare and funny crepuscular marsh owl hopping among the thick grass.

Yes, we saw nearly 50 lion and several kills, and yes, we watched a male cheetah stalk, run, kill and eat a baby wildebeest.

We saw a really weird white rupell’s (Nubian) vulture (which I’ve never seen before since the bird is always black) and at least a dozen bat-eared fox, steenbok, reedbok and even oribi. Waterbuck, impala, buffalo, grants gazelle, oodles of ostrich and we were inundated with erupting termite mounds after a heavy rain.

But what I’ll remember is the great migration.

The “great migration” is a much misused term, and I admit to being one of the most egregious users. Many tens of thousands of kinds of animals migrate, and each migration is different.

Some animal migrations like with most birds are precise and predictable, year after year. Many more, as with the great wildebeest migration, are triggered by available food sources and much less precise.

In the case of the great migration through the Serengeti ecosystem, 1½ million white-bearded gnu (wildebeest) constantly move in search of better grasslands. But sometimes I think they just move because that’s how they’re hard-wired.

I’ve often seen tens of thousands of wilde leave a beautiful area of new grass with no earthly reason why or linger among the dust when the horizon is filled with rain.

Each year’s wilde migration is different. Roughly clockwise, roughly beginning in the southern Serengeti with the birth of new wilde, they’re joined by more than a half million zebra in a year’s trek north and back south again, following the better grasslands which bloom with the rains that slowly recede into Lake Victoria.

The entire first half of the year in Tanzania is the bountiful rainy season that draws them to the southern grassland plains of the Serengeti. There the young ones feast on nutrient grasses, growing strong enough for a raced migration north when the rains stop.

But where exactly in this 2000 sq. mile southern plains area the millions of wilde and zebra are at any given moment is impossible to predict.

They could be scattered in groups of twenty thousand in twenty different places. They could be spread out, 100 to the mile, when the grazing is at its optimum.

Or, as with us this year, they could be concentrated. I think the entire two million plus animals are right now concentrated in an area hardly 20 miles long by about ten miles wide in the south eastern Serengeti.

We found them the moment we turned into Olduvai having left the crater, and we were among them as we traveled more than 50 miles up and around and back to Lake Ndutu. Until we reached the main Serengeti road, we were driving off-road completely, seeing the entire day a single other vehicle, but millions of animals.

And we were never not surrounded from horizon to horizon by the animals.

It was a migration to be remembered. It was provided by a good measure of luck and a lot of common sense about when the right time and right place to be is. We played the averages, and this time was bingo.

Having lunch about 2000 feet above the grassland plains we could see about 30 miles in all directions. And there it was, mother earth’s greatest wildlife spectacle on earth.