Big mammal migration in Botswana too

In Botswana, tens of thousands of zebras roam and with them hundreds of buffaloes and deer. These migrated from the flooded areas of the Okavango estuary to areas north of the Okavango Delta where there are large wetlands - the Makgadikgadi wetlands, which after a rainy season turn into fertile pastures.

Many have heard of the Great Migration, and the lucky ones have even seen it. The Great Migration takes place between the Serengeti Plains in Tanzania and the Masai Mara in Kenya. About 2 million wildebeest and zebras take part in it, moving over about 1500 km depending on the seasons, the rain and the growth of grass that is used as pasture.

Migration also occurs in the south of the Black Continent, albeit in small numbers and over a small area, but no less interesting. In Botswana, tens of thousands of zebras roam and with them hundreds of buffaloes and deer. These migrated from the flooded areas of the Okavango estuary to areas north of the Okavango Delta where there are large wetlands - the Makgadikgadi wetlands, which after a rainy season turn into fertile pastures.

In September there are seasonal rains that grow grass in the Makgadikgadi plains. As a structured response, the herds of zebras turn north and begin a journey of more than 500 km. In April, rainwater that fell in the mountains in Angola flows in the Okavango River and the river water floods the large alluvial fan that turns into a green and rich oasis - the Okavango Fan. The water and the greenery attract the herds from the far north and they migrate south, and this is how the annual migration takes place over a distance of more than a thousand km.

As with the wildebeest migration in East Africa, so also in Botswana the question arose as to what drives the migration and how do the zebras know where to go?
As in East Africa, researchers assumed that the "smell of rain", the sounds of thunder and the sight of lightning could be an impetus for the start of the northward migration. When the voices and sights arrive at the same time as the vegetable dries up in Okongo, the picture is clear. But the question remains: how is the migration route determined? This question became acute because of the "cattle fence".

Following trade agreements between Botswana and European countries and because the Europeans are afraid of cattle diseases, especially the foot-and-mouth disease, a huge fence was erected in Botswana that crossed the country from east to west for hundreds of kilometers. The fence was erected with the idea that buffaloes spread the disease and to prevent buffalo herds from reaching areas where cattle herds graze. The foot and mouth epidemic has stopped. The traditional migration also stopped.

The fence was erected in 1968 and in the first years hundreds of animals died that came to the fence and were looking for the migration route. After two decades the zebras and the other herbivores "learned" that there is no crossing and the number of animals that tried to continue their migration and were stopped and died along the fence decreased to a few.

In 2004, under pressure from green bodies, the fence was lowered in the areas where the migration took place in the past, and see it's a miracle - about two years after the opening of the route, the zebras started migrating along the "old" route. The question arises, how did the zebras know that there are meadows 500 km to the north? How did they know the route to the fresh pasture? The lifespan of a zebra is about 12 years. That is, from the establishment of the fence until its removal, about three generations have passed and the transfer of information between the individuals from old to young is not possible.

As in other places in the world, so also in Botswana - migration routes of large animals, in this case zebras, are weak points where the migrants may be harmed. That is why it is important to understand the drive for migration and learn how to allow its continued existence despite the human presence.

Although the migration is an annual event (which is renewed) the researchers who follow the event have only general information. It is not clear when the migration will begin, what the route will be and why one route is preferred over another. A team led by Peter Beck from the Pieter Beck Research Institute, Woods Hole Research Center studied the migration in order to understand what was happening. The research was published in: Journal of Geophysical Research - Biogeosciences.

The researchers' assumption was that the zebras "rediscovered" the migration routes by "exploratory walks". With the help of the American space agency NASA, the researchers examined rain and vegetation data and found that "when enough rain has fallen there is clear green growth", and according to Beck "the distant rain and the dry vegetation where they are cause the herds to start moving".

But it turns out that when the rains are not strong enough (to grow vegetables) the herds stop and retrace their steps, according to the researchers such cases are rare. It also turns out that when the rainy season continues for a longer period than usual, the herds will stay and not go south.

This behavior - adaptation to the climatic events in the environment - led the researchers to wonder how global warming will affect the zebra herds in Botswana in particular and migratory herds in general. According to Beck, the research examined the possibility that weather systems would affect animals that depend on seasonal changes.

The question of whether the animals will "learn" and adapt their behavior to the extent that is sufficient to cope with the changes is important in everything related to the conservation and preservation of wild animals. The research is good and interesting and may even be useful to the conservationists, but about the questions: How did the zebras know how to find the migration routes and how did they know how to get to the seasonal pastures? We have not yet received an answer.