The wildebeest migration in the Serengeti is the most documented, most photographed, and most visited wildlife event on earth. Yet despite this coverage, a surprising number of travelers arrive at the Serengeti with fundamental misunderstandings about how the migration works, where it is at any given time, and what they can realistically expect to see. This complete guide to the Serengeti wildebeest migration cuts through the mythology and gives you the facts: the numbers, the route, the drivers, the predators, and the practical information you need to plan a migration safari that matches your expectations.
The Numbers: Scale of the Great Migration
The Great Migration involves approximately 1.5 million wildebeest (also called gnu), 200,000 plains zebra, and 500,000 Thomson’s gazelle. These figures are estimates based on periodic aerial surveys and they represent one of the largest concentrations of large mammals anywhere on earth. The total biomass of the Serengeti-Mara ecosystem during migration season exceeds that of virtually any other terrestrial ecosystem, and the ecological impact of 1.5 million large grazing animals moving through a landscape creates soil disturbance, nutrient cycling, and vegetation dynamics that sustain thousands of other species from insects to eagles.
The wildebeest themselves are extraordinary animals when examined closely. An adult wildebeest weighs between 150 and 250 kilograms. They are members of the antelope family, despite their somewhat buffalo-like appearance. They can run at speeds up to 80 kilometres per hour for short distances and are remarkably tough and resilient animals. Despite this toughness, the migration kills approximately 250,000 wildebeest per year through predation, river crossings, exhaustion, and disease. The same 250,000 are replaced by calves born during the February calving season, creating the population stability that has sustained the migration for tens of thousands of years.
Why Do Wildebeest Migrate?
The wildebeest do not migrate because of instinct embedded over evolutionary time alone. They migrate because they are following food. Specifically, they follow the growth of short, nutritious grass that appears in different parts of the Serengeti-Mara ecosystem at different times of year in response to rainfall. The short grass plains of the southern Serengeti, fertilized by volcanic ash from the Ngorongoro highlands, produce the most nutritious grass on the plains, particularly during and immediately after the short rains of November to January. This is why the wildebeest spend January and February there, despite the predator pressure of calving season: the nutritional quality of the southern grass is worth the risk.
As the southern grass is grazed down and the long rains bring fresh growth further north, the wildebeest follow. The medium-height grass of the central Serengeti sustains them through March and April. The tall grass of the western corridor draws them west and north in May. By July the Mara River stands between them and the fresh grass of the Masai Mara to the north, and the crossings happen because the nutritional pull of the grass beyond the river exceeds the fear of the water and the crocodiles within it. This simple equation, grass nutrition vs. predation risk, drives one of the most complex and beautiful natural phenomena on the planet.
The Annual Cycle in Detail
January to March: Southern Serengeti and Ndutu. The calving season produces 500,000 calves in the space of a few weeks. Predators converge from across the ecosystem. The short grass plains are covered in wildebeest for hundreds of square kilometres. The calves that survive their first week have a reasonable chance of completing at least one full migration circuit before they succumb to predation, disease, or age.
April to May: Central Serengeti and Western Corridor. The long rains push the herds northward. Columns of wildebeest stretch for kilometres through the central Serengeti. The western corridor’s Grumeti River provides the first major crossing obstacle of the northward journey. The crocodiles of the Grumeti, among the largest in Africa, take their annual toll as the herds push through.
June to July: Northern Serengeti. The leading edge of the migration reaches the Mara River. The first tentative crossings occur in late June or early July. The scale of the herd arrival in the north, with millions of animals converging on a relatively small river crossing area, creates an ecological intensity that has few parallels anywhere on earth.
July to October: Northern Serengeti and Masai Mara. The main crossing season. The herds shuttle between the Tanzanian and Kenyan sides of the border, crossing the Mara River repeatedly in both directions in response to the availability of grass and the pressure of other herds. Individual animals may make the crossing many times during their time in the north. The river crossings can occur at multiple points along the Mara River and the frequency varies enormously from day to day and year to year.
October to December: Returning South. The short rains arrive in the south, bringing fresh grass to the short grass plains. The herds turn southward, moving through the central Serengeti in large columns and reaching the southern plains and Ndutu area by November and December. By late December, the cycle is preparing to begin again as the first calves of the new season appear on the short grass plains.
The Predators of the Migration
The migration sustains an extraordinary predator community across the Serengeti-Mara ecosystem. The sheer volume of prey that moves through each zone at each time of year means that every predator from the Nile crocodile to the spotted hyena to the black-backed jackal is calibrated to exploit the migration’s bounty at the right moment.
Lions are the most conspicuous beneficiaries. Serengeti lion prides shift their territories and activity patterns in response to migration timing, following the herds as prey availability shifts across the landscape. The lion prides of the northern Serengeti gorge in July through October, while the central and southern prides benefit most from the calving season abundance of January and February.
Spotted hyena clans in the Serengeti have the largest territories of any hyena population studied, reflecting the fact that they must follow the migration to maintain access to adequate prey. Hyenas are actually more efficient predators of wildebeest than lions, taking approximately as many animals through direct hunting as through scavenging, contrary to their popular reputation as pure scavengers.
The Nile crocodiles of both the Mara and Grumeti rivers are the migration’s most specialized predators. Individual large crocodiles in these rivers are estimated to survive entirely or primarily on the annual migration harvest, spending the months between crossings in a state of reduced metabolic activity that allows them to sustain themselves until the next annual abundance arrives.
Is the Great Migration Guaranteed?
No single event within the migration is ever guaranteed. The river crossings, which are the most dramatic and most sought-after event, can be avoided by the herds for days at a time as they mill along the bank and decide not to cross. Some years see many crossings in a short period; others are frustratingly quiet. The calving season is more predictable: if you are in the right area in February, you will see calves and predator action. The migration’s annual circuit is reliable in its broad outline; the specific events within it are never certain.
This uncertainty is itself part of what makes the migration experience compelling. Unlike a theme park attraction, the Serengeti migration does not perform on schedule. It performs on nature’s schedule, and positioning yourself correctly with a knowledgeable guide and sufficient time in the right area is the only reliable strategy for maximizing what you see.
