How the Great Migration Works: Rain, Grass and the Wildebeest Loop Explained

How the Great Migration works comes down to a simple chain: rain grows fresh grass, grass pulls the herds, and the herds pull the predators. Travellers often picture one column marching to a timetable, then plan a trip around a date and are surprised when the animals are somewhere else. This page settles the mechanism. It explains why about 1.3 to 1.5 million wildebeest keep moving, what route they follow, who travels with them and what that means for choosing a region and a window. For the wider picture, start with our Great Migration safari guide.

Facts checked 12 October 2026. Fees, schedules and herd positions change, so we confirm them again when we quote.

How the Great Migration works: a loop, not a line

The Great Migration is a clockwise loop through the Serengeti–Mara ecosystem, which Tanzania and Kenya share. The loop is about 800 to 1,000 km around and it has no real start or finish. The herds pass through the same sequence of regions each year, and rain decides the pace.

Two protected areas hold most of the ground. Serengeti National Park covers about 14,763 km² and was listed as a UNESCO World Heritage Site in 1981. The Maasai Mara National Reserve, which many travellers search for as the Masai Mara, covers about 1,510 km², with private conservancies beside it. In a typical year the herds spend about nine months in Tanzania and roughly July to October in Kenya.

Rain grows the fresh short grass, and the herds follow the grass. Because rain does not keep to dates, any stage of the loop can run two to four weeks early or late.

Why do wildebeest migrate? Rain, grass and minerals

Wildebeest migrate because the rain that grows their food falls in different places at different times of year. A herd that stayed in one spot would soon be standing where the rain has already passed. Three forces explain the movement.

1. Rain and fresh grass. Rain brings up fresh short grass, and the herds drift towards wherever it has recently fallen.
2. Minerals in the south. The southern plains sit on volcanic ash that is rich in phosphorus and calcium. Pregnant and nursing females need those minerals, so the herds return to this short-grass country for the calving months. The detail of that season sits in our guide to the wildebeest calving season.
3. Safety in numbers. A very large herd gives each animal better odds against lions, hyenas and cheetahs. The calves are born together in the south, most of them within a window of two to three weeks.

The route repeats each year, but the dates depend on where the rain falls.

Who migrates: wildebeest, zebra, gazelle and the followers

Three grazers make up the migration, and a ring of predators follows them. Wildebeest are the largest group and give the event its name, but they do not travel alone.

Grazing succession: zebra, then wildebeest, then gazelle

The order in which the three species work through a patch of grass is called grazing succession: zebra first, wildebeest next, gazelle after. It is why zebra and gazelle travel with the wildebeest: all three belong to one feeding sequence.

The predators that follow

Lions are the most visible followers, and the Serengeti's lions form one of the largest populations in Africa. Spotted hyenas and cheetahs hunt the same plains, with cheetahs favouring the open southern country and hyena clans following the calving herds. Leopards work the riverine trees, and Nile crocodiles wait in the rivers the herds must cross.

A second, smaller wildebeest population

Kenya has its own wildebeest as well. The smaller Loita herds live on the Loita Plains and arrive in the Maasai Mara from the east around the same time as the Serengeti herds, in about July. That population has declined because of fencing, farming and settlement.

The wildebeest migration route: the Great Migration cycle in five stages

The Great Migration cycle has five stages in a typical year, and together they make up the wildebeest migration route. Each summary below is short on purpose. The linked guide holds the detail, and our Great Migration by month page shows the weeks. Remember that the herds can run two to four weeks early or late.

Stage 1: the southern plains, December to March

The herds gather on the short-grass plains around Ndutu, Kakesio, Lake Masek, Naabi Hill and Gol Kopjes, with the Ngorongoro Conservation Area edge on the southern side. Most calving falls between late January and March, with a February peak, and the first calves can arrive in the last days of December. Cheetahs and lions hunt in open country, with hyena clans trailing the herds. The southern Serengeti migration guide covers where to base yourself.

Stage 2: central Serengeti, April and May

April is the wettest month, and the herds leave the southern plains for the north-west through Moru Kopjes and the Seronera area. Some camps close and the parks are quiet. In May the rains ease, the rut (the mating season) begins with males grunting and chasing, and the herds in central Serengeti push west. Late in the month the first groups reach the Grumeti River.

Stage 3: the Western Corridor, late May to early July

The Western Corridor, around Kirawira and the Grumeti River, hosts the Grumeti crossings, which usually run from late May to early July, with June the most reliable month. In late June part of the herd moves north through Ikorongo and Lobo. Our guide to Grumeti River crossings explains how they differ from the Mara.

Stage 4: northern Serengeti and the Mara, July to October

The herds reach Kogatende and Lamai in July, and the first Mara River crossings often come that month. In August and September the herds spread across the northern Serengeti and the Maasai Mara and cross the river again and again, in both directions, on no fixed day. The best odds fall from mid-August to mid-September, and a crossing is never guaranteed on any given day. Read our northern Serengeti migration guide for the Tanzanian side and Mara River crossing points for how a crossing works.

Stage 5: back south, late October to December

In October the herds start drifting south. Crossings still occur, often southbound, and the first short rains can arrive late in the month. In November the short rains set in and the herds stream south along the eastern side through Lobo and eastern Serengeti towards the centre, with a few crossings still possible early in the month. By December they are on or near the southern plains and the loop begins again. See Great Migration in November and Great Migration in December for those weeks.

How far do wildebeest travel? The loop in kilometres

The loop is about 800 to 1,000 km, and that is the best single answer to how far do wildebeest travel in a year. It is a measure of scale, not an odometer reading. The herds do not walk it in a straight line. They gather at river banks, mill, retreat and sometimes wait for days, and in the north they cross the Mara in both directions repeatedly. The distance any one animal actually walks is therefore not the same as the length of the loop.

Three more numbers help to put the movement in proportion.

• The herds spend about nine months of a typical year in Tanzania and roughly three to four months, from July to October, in Kenya.
• Serengeti National Park, at about 14,763 km², is nearly ten times the size of the Maasai Mara National Reserve at about 1,510 km², which fits the herds spending most of the year in Tanzania.
• A single river crossing can last from a few minutes to over an hour, and the herd may need days of gathering before it commits.

For the park itself, including its regions and gates, see our Serengeti National Park guide.

How the herds recovered: rinderpest and the growth of the population

The herds you see today are a recovered population. Rinderpest vaccination in the 1960s let the wildebeest recover. The population grew from about 250,000 to over a million by the late 1970s, and today it stands at about 1.3 to 1.5 million.

The herd size has changed over time, and the smaller Loita herds in Kenya show what can happen when land is fenced, farmed and settled. The Serengeti–Mara loop works because there is still open land for it to turn.

How the Great Migration works in practice: what to take into your plan

The main lesson of the mechanism is that herds follow rain, so you should plan for a region and a window, not a date. These points follow directly.

• Choose the stage you most want to see first, then the region it belongs to, then a window wide enough to allow for the herds running early or late.
• Build flexibility into the plan, not just the dates. We recommend at least four nights in the main migration area. On a longer trip a split stay, such as three nights at Kogatende and three in a Mara conservancy, lets you follow the herds if they are early or late.
• Book early for the stage you want. Camps close to crossing points and calving zones sell out first, and our guide to how far ahead to book sets out the windows.
• Decide the country after the stage. Our comparison of Serengeti vs Masai Mara migration helps with that choice, and where to stay in the Masai Mara covers the Kenyan side.

Our guide to how to plan a Great Migration safari turns these rules into a step-by-step method.

A trip built around the loop

Ten days on the Tanzania Grand Migration Explorer, from US$7,200 per person, covers Ndutu and the southern Serengeti, the centre, the north and the Mara River, flying between Ndutu, Seronera and Kogatende. It is timed either for calving (late December to March) or for crossings (late June to September). It suits travellers who want to see more than one region of the herds' range.

Three misunderstandings about how the Great Migration works

The herds arrive on a fixed date

They do not. The herds follow rain, and rain runs early or late by two to four weeks. A date in a brochure describes a typical year, not a promise.

The migration is a river crossing

The crossings are one stage of five, and the Mara River is only one of the rivers involved. If you came for the full story of the year, the calving months and the Western Corridor are part of the story too.

It is one herd, and it happens in Kenya

The migration is made up of herds, not a single column, and they spend about nine months of a typical year in Tanzania. Kenya sees the Serengeti herds for roughly July to October, joined by the smaller Loita population. Calling it a Kenyan event misses most of the loop.

Where to go next after learning how the Great Migration works

1. Pick the stage that matters most to you: calving, the Western Corridor, the Mara River or the quieter shoulder weeks.
2. Read the guide for that stage, linked in the five-stage section above, and note the typical window.
3. Send us your dates, party size and nationality, so we can match a region and check fees and visa rules.
4. Ask for a quote. That is the point at which we confirm herd positions, camp availability and prices, and each itinerary page shows its terms.

If you want to see every package built around the herds, open the full Great Migration safari guide and go to the packages section.

Keep reading: related Great Migration guides

For the whole picture, see our Great Migration safari guide. If you are ready to price a trip, Tanzania Grand Migration Explorer starts from US$7,200 per person.