How wildebeest reshape the Serengeti during Africa’s Great Migration
Each spring, millions of wildebeest begin a 500-mile journey driven by rain, grass, and survival.
It’s the largest migration of big beasts on Earth.
As the spring drought begins to set in, millions of wildebeest, zebra, and gazelle prepare for a 500-mile round trip of nearly nonstop travel, following rain and carpets of greenery in the Serengeti. While the migration happens year-round, the spring is when the mass movement of so many iconic herbivores gets underway—from the southern part of Tanzania to Kenya’s Masai Mara to the north.
“All these species are part of a beautiful, shifting canvas fueled by pulses of rainfall and drought,” says National Geographic Explorer T. Michael Anderson. “It never fails to take my breath away.”
While dozens of species are involved in the great migration, the shaggy, horned wildebeest represents the central pulse of the movement.
Often with new calves in tow, the adult wildebeest huddle and trot together on an epic quest to mow down the freshest greens of the season. Ahead of them lies a journey shaped as much by instinct as uncertainty—where predators, drought, and shifting rivers ensure that no two crossings of the Serengeti are ever the same.
How Africa’s spring Great Migration starts
Survival is what drives the migration. The stark dry and wet seasons in the Serengeti determine where the nutritious plants the herbivores rely on will grow, and the herbivores effectively follow where plants are growing best.
Between January and April, wildebeest gather in the southern part of what’s now Serengeti National Park to give birth. The newborns have time to find their footing and keep up with the herd as the wildebeest fill up on vegetation before the annual dry season slows the growth of the huge amounts of plants the mammals rely on.
And there are a lot of mammals that rely on this vegetation. Half a million calves may be born in a year, while adult wildebeest in these herds number more than twice as many—altogether there's as many as 1.3 million of them. Meanwhile more than 200,000 zebra feed among the same grassland, along with over 400,000 Thompson’s gazelles. Nearly two million herbivorous animals, all feeding together. Until the food begins to run thin.
“Wildebeest would probably choose to stay in the Serengeti plains all year long because the grass is very high quality and energy rich,” Andersen says. “But they cannot because at the end of the rainy season grass growth slows and eventually stops,” he adds.
The ceased growth creates competition between the herbivorous mammals for each bite.
The wild horses feel the pressure of the competition first. An adult zebra weighs 500 pounds or more—about a hundred pounds more than an adult wildebeest, meaning they more food to fuel their bodies. In search of grasses not so heavily grazed by wildebeest, which outnumber them by more than five times, zebras start moving north first.
The wildebeest—having exhausted the best food in the southern Serengeti around this time—typically follow the northern path within less than four days. As the 1.3 million wildebeest set off, the Great Trek truly gets underway.
Wildebeest’s journey through the Serengeti
Wildebeest are not alone on their journey. Zebra and gazelles make the big round trip right alongside the wildebeest herds.
Zoologists have been puzzled by the recurring order of the Serengeti migration. “The mechanics of the migration have always baffled scientists because of the sheer size and magnitude of their movements,” Andersen says.
Some experts had previously proposed that zebra, wildebeest, and gazelles travel together for mutual protection from predators. The larger the herd, the smaller the chances any individual will be caught. And the more eyes watching out, the more likely the herbivores will spot a predator before the carnivore has a chance to leap out.
But when Andersen and colleagues analyzed migration camera-trap photos, wildebeest appeared alongside either species only about 5 percent of the time. Zebra and gazelle photos similarly showed an even lower overlap, each species largely keeping to themselves along the migration route. The three herbivore species were not clustering together to protect each other from carnivores but instead follow each other in a procession determined by the plants each species prefers to eat.
“Wildebeest mow the grass making high quality forbs, think dandelions or clover, easier to access,” Andersen says. That’s an advantage for the hundreds of thousands of gazelles that follow behind the wildebeest—which also benefit from the more nutritious grass that regrows in the wake of the wildebeest.
Fire is a far larger hazard than sharp-toothed predators for migrating wildebeests. Fires in dry years can put members of the herds at a higher risk for starvation, especially if spring fires destroy the year’s last vegetation and restoring rains are months away. Depending on the year, fire can turn vegetation to ash across areas as large as 200 square miles. Large fires also force herds of wildebeest and zebra to spend more energy trying to find enough food. If the land is too dry and fires occur in the months leading up to the migration, the entire process is disrupted as wildebeest’s necessary food source for the journey north is destroyed.
Most years, however, the vast herds readily follow the green carpet north. The herds don’t linger either. From their pushoff in April, the beasts keep hoofing it all through May, June, and early July.
By August, the herbivores reach the lush grasslands of Kenya’s Masai Mara National Reserve. The animals continue grazing there until the rains start to return across the Serengeti ecosystem in October, spurring new growth out of the dry ground. Wildebeest and their herbivorous neighbors turn around and follow the new growth south.
How to experience wildebeests Great Migration
The Serengeti Migration is an absolutely immense phenomenon that takes place between two countries. Nor do the animals follow a strict schedule. Rainfall, fire, and other conditions can change exactly when and where the mammals move. In 2014, for example, unexpectedly lush rains provided so much nourishment in the southern Serengeti a great deal of the wildebeest herd skipped the trip to munch on the refreshed plants where they already were.
Visiting the southern Serengeti, from December through May, will allow you to see the herbivore herds as they congregate, give birth, and prepare for the trip. The herds will then move to an area called the Western Corridor between May and July, flowing into the Serengeti Mara area along Kenya’s southern border before the herds begin moving south again in October. Due to the abundance of food during their journey south in the wet season, wildebeest stop in the middle of the Serengeti from November until the end of the year. As January comes back around, the zebra, wildebeest, and gazelle start gathering to the south again for the next big annual journey.
Serengeti National Park facilitates several ways to see what they call the Great Trek. The park hosts several hot air balloon launch sites that operate at different times of the year, as well as several lodges among its different regions that offer views of the herd as it moves through. And if you cannot visit Tanzania or Kenya yourself, live streams document parts of the wildebeest migration online.
