WILDLIFE & ECOLOGY

Why are there so many wildebeest in Mara?

Sara Gastaldi, Safari Guide & Designer, Italy

21 August 2020

When you’re having game drives through hundreds of thousands of wildebeest you may wonder why there are so many of them and ask yourself why not zebra, impala, topi, hartbeest or one of the other antelopes?

This subject has been discussed very well by the ecologist Dr. Colin. In fact he says there are things that shape or influence the environment, and the environment then shapes the species in it. It’s a two-way interaction that influence what happens. For example when there is predation on plants they evolve defense mechanisms like thorns or chemicals.

So, what is there in Masai Mara that promotes massive herds of wildebeest?

The answer is simple: Climate and soils

Wildebeests (Connochaetes taurinus) – Mara North Cons. – 2018

Photo by Emanuele Trabucco

The entire Mara-Serengeti ecosystem always has drinking water and nutritious grass somewhere at all times of the year. But why wildebeest are the most numerous? Why not zebra, gazzelles, eland  etc.?

The answer again is simple and interesting: Wildebeest are special.

Wildebeest belong to a subfamily of bovidae called Alcelaphinae. This means they are closely related and if you wish to know how close, you will be shocked! They are about 4 million year old cousins.

All of them are ruminants, which means they have four-part stomachs, which allows them to chew food more than once in order to digest cellulose. Rumination is a very efficient way of taking out nutrients from plants but each species have its own efficiency and Coke’s hartebeest are actually the most efficient of the Alcelaphinae subfamily. So why isn’t it Coke’s hartebeest?

Let’s start by looking at the mouth structure of wildebeest

The mouth of wildebeest is perfect for eating grass which is 3 cm high, right when it has the highest levels of protein.

Another thing wildebeest do is to eat the parts of the grass which are more nutritious, like fresh shoots the leaves. Topi and Coke’s hartebeest choose more stems and leaf sheaths than wildebeest, zebra survive on almost only stems. But the quantity of grass stems are much higher than grass leaves, therefore we’d rather expect zebra populations to be in the millions. But they aren’t! What really happens here is that zebras suffer very high losses of young, because predators keep zebra numbers down.

Spotted hyena (Crocuta crocuta) with wildebeest carcasse – 2019

Photo by Sara Gastaldi

So now you would ask to me: why aren’t wildebeest populations kept low by predators too?

The answer is: Rumination and sinchronized reproduction

80% of wildebeest calves are born withing the space of 3 weeks in February, every year. We are talking about 250,000 wildebeest calves; 500 per hour! This is an anti-predation strategy: extreme synchronous breeding overcomes predator’s ability to limit wildebeest numbers.

Calves are most vulnerable when they are very young but at a certain age they become vulnerable as the adult wildebeest. There is a limit to how many calves predators can prey every day. That is why by all having their babies at the same time, more calves have the possibility to survive and to reach the adult age. Kongoni, topi, zebra etc. don’t have synchronized breeding.

A newborn wildebeest, placenta still clearly visible – 2020

Photo by Sara Gastaldi

As I wrote earlier, wildebeest are ruminants and they spend about 8 hours a day grazing. This means they have 16 hours left to look for predators. Zebra on the other hand, spend 15 hours a day grazing so they only have 9 hours left to look for predators. This is because they are hind-gut fermentators, having only one stomach. In response to a less efficient digestion, zebra have infact to eat more.

Now, we’ve clarified the benefit of a four-chambered stomach and synchronized breeding.

Short grass plains in south-east part of the ecosystem (Tanzania) are also the best place for the females to get the nutrients they need to lactate, but they are also a fantastic place to spot predators, because there are no trees to obstruct the view; this  helps to reduce the number of calves killed too. This area in south-east Serengeti in Tanzania are also less populated by predators, precisely because there is no cover where to hide.

Lastly, calves are born precocial with a very strong imprinting instinct. The mother and calf will know soon how to recognize each other by smell and the calf can stand after few minutes. It also tends to run on the hidden side of the female so that it would be difficult for predators to see it. The effect will be again the reduction of predation.

In short, the Mara-Serengeti unique climate and soils offer the perfect conditions to enable wildebeest to live in such large migratory herds because of their unique biology and adaptation. 

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