How the Migration Works

by Leigh Kemp, 20 March 2008

An infinite line of headstrong wildebeest moves relentlessly through the trees in the direction of the already mottled plains.

Africa's great migration has begun ... or has it?

Around us another vast herd grazes peacefully on fresh shoots, apparently in no hurry to leave the delectable greenery behind.

"Some of these have been here since May,” our guide informs us.

"So they didn't migrate?”

"No, these ones stayed behind.”

And therein lies the confusion that is the great migration: nature continually throws curveballs at our knowledge of how things work.

In the past it was understood that the herds gathered and gave birth on the southern plains of the Serengeti before moving north into the Masai Mara.

After grazing there for a time, they would return south with the rains. But apparently it's not quite that simple.

Which Route to Greener Grass?

It's true that the wildebeest give birth on the southern plains before heading north, but that's where the certainty ends. Precisely when the migration will begin and which route the animals will follow is anything but set in stone.

Early rain may interrupt the grazers' departure, or late rains in the north may cause a delay, as will local showers en route. But why talk about delays and departures when nature controls the rhythm of life here?

The migration has happened each year for thousands of years, sometimes earlier in the year, sometimes later, but never delayed. It happens precisely as nature dictates.

Rain controls where the herds will be at a particular time with the animals moving according to where the rain has fallen. Rain provides the animals with essential surface water across the migration route.

If rain hasn't fallen somewhere the herds will avoid that area and herds will often split in response to rainfall consistency.

How Many Gnus?

The numbers of wildebeest in the Serengeti/Mara ecosystem have fluctuated greatly over the past 50 years - when serious studies were first undertaken.

A father and son research team, the Grzimeks, began their aerial research in the late 1950s when they estimated that there were 90 000 wildebeest.

These comparatively low numbers were largely caused by the rinderpest virus that continued to survive in the animals' systems after the epidemic of the late 1800s.

Rinderpest was wiped out of the east African herds in the 1960s (although new evidence suggests possible re-infection) and today approximately 1.2 million wildebeest live on the plains.

Some biologists believe this number to be the ideal capacity for the wildebeest herd.

Serengeti in November

On a recent trip to the Serengeti in late November, I was expecting to catch the first wildebeest arriving on the southern plains.

Having read reports before I left on the trip, I learned that the herds had left the Masai Mara on their march south and, figuring that the southern Serengeti plains would be green from the first rains, I naively believed that we would come across the herds there.

I was surprised at what we found - the southern Serengeti plains were a dustbowl. No rain had fallen.

And where were the wildebeest if they had left the Masai Mara some weeks back? I was to find out over the next few days.

The herds were in the northern Serengeti along the Grumeti River, gathering and waiting for the push south - waiting for the ancient call.

It's a known fact that animals can sense rain and in the case of the wildebeest the call from the southern plains hadn't happened as the rain had stayed away.

Rain had fallen in the north and the grass was green, albeit in short supply due to the extended period the herds had spent there.

The migration is one of the world's most dramatic spectacles, totally deserving of the tag 'Greatest Show on Earth', and for those who have been privileged to experience it, it will always be a highlight.

Readers' Comments:

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