Migration

The annual wildebeest migration of herds in Kenya and Northern Tanzania is one of the world’s most spectacular wildlife events.
Often referred to as the ‘Greatest Show on Earth’, The Great Wildebeest Migration is a movement of approximately 1.5 million wildebeest and zebra throughout the Maasai Mara and Serengeti ecosystems.
Nowhere in the world is there a movement of animals as immense as the wildebeest migration.
The stage on which this show is set is loosely termed the Serengeti Ecosystem, about 40, 000 square kilometers pretty much defined by the dominant migration routes of the white bearded wildebeest (Connochaetes tuarinus mearnsi) and comprises parts of the Ngorongoro Conservation Area in the south; the Serengeti National Park and the adjacent Maswa Game Reserve and other ‘controlled’ areas in the centre, east and west; and the Maasai Mara National Reserve to the north. The principle players are the wildebeest, whose numbers appear to have settled at just under 1.5 million, with supporting roles from some 350,000 Thomson’s gazelle, 200,000 zebra and 12,000 eland. These are the main migrants and they cross the ranges of over a quarter of a million other resident herbivores and, of course, carnivores. The lions, hyenas, leopards, cheetahs and lesser predators await the annual coming of the migration with eager anticipation.
In reality there is no such single entity as ‘the migration’. The wildebeest are the migration – there is neither start nor finish to their endless search for food and water, as they circle the Serengeti- Mara ecosystem in a relentless sequence of life and death. ‘The only beginning is the moment of birth,’ notes acclaimed East African author and photographer Jonathan Scott, who has spent the better part of the last 30 years chronicling the events of the Serengeti and Maasai Mara. Similarly the only ending is death.
There is little predictability about the migration, and questions as to which is the best month to view it are likely to get different answers from different people. According to Scott, ‘You could spend a lifetime in the Serengeti-Mara waiting for the typical migration. The finer details of the herds’ movements are always different. It is a dynamic process which defies predictions: no two years are ever quite the same.’
Probably the most important element of the environment to its inhabitants is the weather and the cycle of four seasons per year undoubtedly has the defining influence on the migration. The seasons are reasonably defined: the ‘short dry season’ is typically December to February/March; the ‘long rains’ fall over a six week period from March through April and into May; and the ‘long dry season’ is from June to September, with the two-week ‘short rains’ falling any time from October into November. There are however, no guarantees about these dates.
This is a general description of the migration pattern. The exact timing of the Great Migration cannot be predicted, as it depends on each year’s rainy season and other variable factors. CAT Safaris cannot be held responsible for seasonal changes that cause the migration to vary from this description.

December to April: These months find wildebeest and zebra herds scattered across the plains of the southern Serengeti and the northern Ngorongoro Conservation Area in Tanzania. Calving season generally lasts from late January through mid-March, with the largest number of calves born within a two- to three-week span in February. Hundreds of thousands of wildebeest calves are born during this time. Predators in the area take advantage of the abundance of slower calves, and sightings of species such as lions, cheetahs and hyenas are plentiful at this time of year.

May to July: As the plains dry up in May at the end of the long rainy season, the herds begin to move westward and then northward in search of greener pastures. The scattered herds eventually gather to form columns up to 25 miles long as they begin their trek from the south to the western and northern Serengeti. Predators, which are territorial rather than migratory, hunt as the massive herds pass through their terrain. Mating season for wildebeests also occurs during this time, between late May and early June. As the herds of zebra and wildebeest make their way northward, they must cross the Grumeti River, where hungry crocodiles wait for those that stumble. The best time to see this migration in action in the western and northern Serengeti is in June and July.

July to November: As the plains of the western Serengeti dry out and the grasses are depleted, the migration must continue. Between July and mid-August, the wildebeest, zebras and gazelles leave the Serengeti and Tanzania, cross the Mara River with its own population of crocodiles, and head into Kenya’s Masai Mara, where lush green pastures await. A visit to the Masai Mara National Reserve when the migration arrives in August or September can make for an unforgettable experience due to the variety of species and the sheer number of animals. The herds scatter around the abundant grasslands of the Masai Mara until October or November, when the start of the short rainy season prompts them to begin their journey south, back to their breeding grounds in the Serengeti and Ngorongoro Conservation Area.

The Start of the Circle

Towards the end of the short dry season, around March, the short-grass plains of the southernmost Serengeti begin to dry out and the wildebeest begin (or continue) their journey, heading towards the western woodlands.

How do they know which way to go? There are at least two possible answers, according to behaviorist and ecologist Harvey Croze, co-author of The Great Migration. The wildebeest’s journey is dictated primarily by their response to the weather; they follow the rains and the growth of new grass. And, although there is no scientific proof that this is true, it seems that they, and other animals, react to lightning and thunderstorms in the distance. ‘It would be surprising if even the wildebeest could overlook such prominent portents of change,’ writes Croze.

But it is probably instinctive knowledge, etched into their DNA by hundreds of thousands of years of natural selection, that is the major reason why these ‘clowns of the plains’ know in which direction they must travel. Over the millennia, those wildebeest that went the ‘wrong’ way would have died (of thirst and starvation) long before they could reproduce, so the wildebeest that lived to produce the future generations were the ones that went the ‘right’ way.

From the plains around Olduvai the herds head west towards the trio of small lakes, Ndutu, Masek and Lagarja. At this time their biggest need is usually to find water, and these more westerly areas can provide it. Still feeding and fattening on the nutritious short grass the herds scatter widely across the plains, shifting on a whim in response to factors beyond our knowledge. On any given day they’ll be spread out in their thousands across the expansive plains west of Ndutu, the next they’ll be gone. By now the first downpours of the long rains will be falling, and the wildebeest will canter across the plains towards the distant thunderstorms, frequently returning a day or two later if the promise did not match the reality.

The Birthing

For want of a better place in which to ‘start’ the migration, we’ll begin in January and February, when the wildebeest cows drop their young in a synchronized birthing that sees some 300,000 to 400,000 calves born within two to three weeks of one another, eight and a half months after the rut. The birthing occurs on the short-grass plains that, at the southernmost extent of the wildebeests’ range, spread over the lower northern slopes of the Ngorongoro Crater highlands and are scattered around Olduvai Gorge. Here, at the ‘cradle of mankind’ many notable fossil finds have been discovered, including some that show that wildebeest have grazed the Serengeti almost unchanged for over a million years.
The annual period of birthing provides a feast for predators. Driving across the plains, one can count literally hundreds of hyenas and dozens of lions scattered about. It may seem that the wildebeest are doing the predators a favor by dropping their young all at the same time, but in fact a surfeit of wildebeest veal in very short period results in the predators’ becoming satiated and unable to consume as much as they would if the calving happened over a longer time span. The predators thus have only a limited impact on the population of newborn calves; any calves born outside the peak are far more likely to perish.
To watch any birth is amazing but watching the wildebeest birthing verges on the incredible. A newborn wildebeest gains co-ordination faster than any other ungulates and is usually on its feet two to three minutes after birth. It can run with the herd at the age of five minutes and is able to outrun a lioness soon thereafter. Notwithstanding this, many do die within their first year, from predation (although research indicates only about one percent die this way), malnutrition, fatigue or disease. Many calves get separated from their mothers when the herds panic (which happens frequently) or cross rivers or lakes in their path. The calves then wander for days looking for mum, bleating and bawling incessantly. On rare occasions they may be lucky to find her, but no wildebeest cow will adopt a strange calf, even if she has lost her own and is lactating at the time. As it weakens, a lost calf becomes an easy victim for any watching predator, from jackal up to hyena and lion.

The Rut

As the rains set in, the herds head north-west past the granite outcrops of the Simba and Morukoppies and into the woodlands of the hilly country west of Seronera towards Lake Victoria. This is the time of the annual rut, with half a million cows mated in less than a month as the herds consolidate in the woodlands and on the plains of the Serengeti’s Western Corridor. The peak of the rut seems heavily influences by the state of the moon, with the full moon in May/June being a good bet for anyone seeking the most action.

Seemingly vicious fighting between dominant or territorial males takes place during the rut, though there is generally little actual violence or serious injury. And in spite of these energetic duels, the males have little say over their choice of mates, for it is the females who do the actual choosing.

The Crossing

From the western Serengeti the herds head north, following the rains (or their effects) into Kenya and the Maasai Mara Game Reserve. On their trek the wildebeests’ path is cut several times by rivers: in the Serengeti by the Mbalangeti and the Grumeti, and in Kenya by the Mara. For most of the year these rivers are relatively placid, but they can become violent torrents in response to rainfall in their catchments areas, and then they present major obstacles to the progress of the wildebeest.

The rivers and indeed the few isolated lakes in the south of the Serengeti, are terrifying to the wildebeest firstly because of the animals’ fear of the water itself and the creatures it may hide, and secondly because water generally means vegetation, and thickets that may conceal predators. Yet the wildebeest have an inherent instinct to trek in a certain direction at any cost – despite their terror. The lakes in the south – Ndutu, Masek and Lagarja – for example, are little more than a few kilometers long, and could easily be walked around. But natural selection steps in once more: the wildebeest that crossed the lakes in previous generations survived to breed, so the waters pose no fear to their progeny; those that did not make it gave no further input to the gene pool.

In his definitive documentary on the migration, The Year of the Wildebeest, filmmaker Alan Root describes how he watched a crossing at Lake Lagarja, where, once the main body of the herd had crossed cows that had become separated from their calves turned back to look for them re-entering the water and swimming back. On reaching the other side, still not reunited with their offspring, they turned back once again. This to and fro went on for seven days, until eventually the numbers of arriving wildebeest built up again and the stragglers were forced to move on with the main body of the herd. Thousands of wildebeest died in the lake that year. While such tragedies may appear to be a disaster for the wildebeest, the deaths only represent a mere handful of the hundreds of thousands of calves born each year. Without a degree of natural mortality, the wildebeest population could spiral out of control.

Wildebeest arrive at the Mara River in their tens of thousands, and gather waiting to cross. For days their numbers can be building up and anticipation grows but many times, for no apparent reason, they turn and wander away from the water’s edge. Eventually the wildebeest will choose a crossing point, something that can vary from year to year and cannot be predicted with any accuracy. Usually the chosen point will be a fairly placid stretch of water without too much predator-concealing vegetation in the far side, although occasionally they will choose seemingly suicidal places and drown in their hundreds. Perhaps, once again, this is because crossing places are genetically imprinted in the minds of the animals.

Some fords do attract larger numbers of animals than others though, probably because they’re visible from a greater distance and the arriving herds are able to see others of their kind either in the process of crossing the river or grazing on the lush grass on the far side.

Closing the Circle

By late October, when the first of the short rains are falling on the Serengeti’s short-grass plains, filling seasonal waterholes and bringing new flushes of growth, the wildebeest start heading south again. The herds trek down through the eastern woodlands of the Serengeti, some 90 per cent of the cows’ heavy with the new season’s young. Tightly grouped as they pass through the wooded country the wildebeest scatter and spread out again once they reach the open plains.

Migration Facts

  • The Serengeti ecosystem covers 10,000 square miles.
  • The roughly triangular route the migrants follow is about 300 miles from start to finish, as the crow flies. The trip can be considerably longer depending on which way the wildebeest wander.
  • Any given year, depending on the rain and other conditions, the Serengeti migratory wildebeest number between 1.2 and 1.5 million animals.
  • Wildebeest are also known as Gnus (pronounced “news”).
  • The wildebeest are joined on their journey by up to 200,000 Burchelli’s zebras.
  • A wildebeest consumes 3200 pounds of food in a year and a zebra consumes 4800 pounds.
  • A lion eats 7200 pounds of its neighbors each year, a leopard eats 3200 pounds, a cheetah eats 4015, and the cold-blooded crocodile eats just 1600 pounds of food each year.
  • An elephant consumes 69,000 pounds of food each year
  • An American consumes 1950 pounds a food per year.
  • As many as 500,000 wildebeest are born each February.
  • Three percent of the wildebeest that begin the journey each year do not survive to finish it.
  • A lucky wildebeest can live as long as 20 years.

Southern Serengeti

The Serengeti-Mara ecosystem upon which the wildebeest trod consists of two eco-regions key to the migration – the Southern Acacia-Commiphora Bush lands and the Serengeti Volcanic Grasslands. The Southern Acacia-Commiphora Bush lands cover 88,000 square miles of territory, stretching from southwestern Kenya along the eastern edges of Lake Victoria and south to central Tanzania. The Serengeti Volcanic Grasslands cut through the southern parts of this larger eco-region and across the plain to the south and east.

For the wildebeest, it all begins on the Serengeti Volcanic Grasslands. The combination of fine volcanic soil and the cycles of wet and dry promotes the growth of the wildebeests’ preferred forage. After the Short Rains of November and December, short grasses sprout for a brief time over the ashy volcanic soil. These grasses are at their richest in the southeastern corner of Serengeti National Park where it adjoins the Ngorongoro Crater Conservation area. This is where the calving takes place and where the herd fattens up for the year’s march.

The Ngorongoro Crater played a significant role in the creation of the short grass plains. The crater is what remains of a massive prehistoric volcano. Millennia of ash fall from that volcano, and from others in the region, some of which are still active, generated soil conditions suitable only for the hardiest grasses and shrubs. The short wet seasons and frequent droughts lead to brief growing seasons. By early spring, the landscape is reduced to dry brown stubble, too dry to support wildebeest and zebras, who depart the Serengeti Volcanic Grasslands for the Southern Acacia-Commiphoria Bush lands to the north and west.

When to Visit: The migratory herds begin to return to the region in January. Calving usually occurs in February, however predicting this event with precision is difficult, one made more difficult by its brevity. In the span of two to three weeks, wildebeest cows will give birth to several hundred thousand calves. While the local predators will take plenty, they cannot take enough to threaten the survival of the herds themselves. The sheer multitude of calves virtually guarantees that tens of thousands will live to adulthood.

Western Corridor

Despite the importance of the Volcanic Grasslands to the life cycle of the wildebeest, the herds spend most of their lives in the Southern Acacia-Commiphora Bush lands. This is due, of course, to the patterns of rainfall and drought. It’s also due to the immensity of the eco-region. The eco-region stretches from the southwestern Serengeti, along the eastern shore of Lake Victoria and north well into Kenya where it meets another eco-region – the Northern Acacia-Commiphora Bush lands.

The Bush lands would be a lot bushier if not for the activities of elephants and the people who live on its periphery. Elephants and other browsers limit the growth of trees and shrubs. In fact, the acacia takes its familiar umbrella shape because of the grazing of giraffes. Fires – some occurring naturally, many set by pastoral livestock herders to promote new growth – further restrict the growth of larger plants.
When to Visit: The herds depart the southeastern Serengeti in April and continue to filter through the area until late June. Rutting takes place in the Western Corridor, usually in May. Males mark and defend territory from one another. When a female enters a bull’s territory, he courts her by following her. If she’s interested, she’ll stop. If not, she’ll lie down, or continue moving on to the next territory.

Mara Triangle

The Maasai Mara Reserve marks the northern terminus of the migration, but the wildebeest are not the only visitors. Wildebeest and zebras and antelopes arrive from much closer rangelands, all drawn to the Mara Triangle’s rich grasslands and abundant water. Rhinos, white and black are found in drier, bushier areas of the park. Hippos and crocodiles wade and lurk in the reserves’ trio of rivers – the Mara, the Talek, and the Sand.

The Mara River begins as a trickle in the Mau Forest a few hundred miles to the north and eventually drains into Lake Victoria. In the Mara Reserve, as the river flows under the Oloololo Escarpment, it feeds the Olpunyata Swamp and the neighboring grasslands. This region, southwest of the river, bounded by the escarpment to the west and the Tanzanian border to the south, is the “Mara Triangle” and offers, perhaps, the best opportunities for game viewing in all of East Africa. It is in this triangle that the wildebeest usually congregate at the end of their march.
As the river continues through the reserve, it is joined first by the Talek in the center of the reserve, and then by the Sand, just across the border in Tanzania. As the herds move through the reserve and back and forth between the Mara and the Serengeti, they will cross and re-cross these rivers dozens of times.
When to Visit: Wildlife is abundant throughout the year in the Mara. The migratory herds begin to arrive in August. They will remain in the region through October. By November they will have begun the long trek back to the volcanic grasslands in the south.

Eastern Serengeti

After the rains of October and November have irrigated the Southern Volcanic Grasslands, the herds return south via the most direct route, which is more or less along the border of the Serengeti and Ngorongoro Reserves. Hundreds of wildebeest form up into long narrow columns and filter through the landscape of low hills and scattered woodlands, much as they did through the Western Corridor six months previously. Scores of such columns wind through the region.
Although the grasses along the route have ripened following the rains, the herds do not tarry. They are bound for the richer short grasses in the south.

When to Visit: The migrants stream through the region throughout November and December. By January they will have arrived in the southern corner of Serengeti/Ngorongoro, where the journey began.

Migration threats

Just as many of earth’s natural places, the migration faces threats from encroaching human populations. The complex of reserves and conservation areas that make up most of the ecosystem – Serengeti National Park, Maasai Mara Reserve, Ngorongoro Conservation Area and associated wildlife corridors and buffer zones – is 10,000 square miles, roughly the same size as state of Massachusetts. However during droughts the protected area is not large enough to accommodate the herds as they move into the settlements. In all times the protected area is too large for the growing number of people who live within its boundaries. Farmers and ranchers are constantly putting up fences, which restrict the animal movement. Poacher illegally hunts as many as 160,000 migratory herbivores annually. Arrests for illegal hunting in the Western Corridor mirror the arrival of the migration. What is true for lions is true for bush meat hunters; predators linked to the land must wait for the prey that is linked to the migration.