Count of the wildebeest in Serengeti ecosystem

Each year, enormous herds of wildebeest and zebra move thousands of kilometres across the Serengeti-Mara. These herds have a pivotal role in maintaining the ecosystem.

Serengeti Count
It would be impossible to count large numbers of individual animals without an airplane. (Photo: Felix Borner)

Serengeti, Tanzania 11 June 2015 by Bryna Griffin


From April 30 to May 2, 2015, Frankfurt Zoological Society (FZS) and the Tanzania Wildlife Research Institute (TAWIRI), in partnership with Tanzania National Parks Authority (TANAPA) and a number of collaborative researchers, completed a count of the wildebeest Serengeti ecosystem. The count, which normally happens every two to three years, is essential to document and monitor what is often called “the great migration.”  This is the 21st count since 1957.


Each year, enormous herds of wildebeest and zebra move thousands of kilometres across the Serengeti-Mara ecosystem. Numerous predators depend on these herds and follow them closely as they move. In fact, these herds have a pivotal role in maintaining ecosystem, from supporting other biodiversity to impacting the growth grass and frequency of fires. This remarkable phenomenon is a flagship for Serengeti, an important part of what makes this region so unique. Therefore, it is critical that we monitor the health of the wildebeest herds as a way to understand the health of the entire ecosystem.


The timing for the count depends on the wildebeest themselves. They must be disbursed in a very specific way: evenly spaced and not hidden by trees so that we can easily see the majority of the individuals by air.  This normally happens only for a few weeks each year on the short grass plains in eastern Serengeti National Park, Ngorongoro Conservation Area and Loliondo Game Controlled Area.


In addition, although the herds normally follow a general clockwise pattern across the ecosystem, the rains are not always on time and the wildebeest often zigzag back and forth in order to find the best grass, sometimes traveling hundreds of extra kilometres. While we can assume very generally when they may reach the short grass plains, it is nearly impossible to predict exactly which days the wildebeest will be both in the right place and in the necessary distribution for counting.

So how do we make it happen?

This year, with some irregular rainfall, the wildebeest seemed to be moving erratically across the landscape in search of green grass. We worried that they would never be in the right place, and so nearly decided to postpone until next year. However, suddenly they seemed to be converging. After discussion with our partners and colleagues from TAWIRI, TANAPA, and a number of research projects, we decided to begin reconnaissance flights over the plains.  We watched, we waited, and watched some more.

Finally, it appeared that the wildebeest were distributed adequately for the count to happen.  For the next few days, the count team flew hundreds of kilometres of carefully plotted transects over the herds. These transects were designed for statistical accuracy, and photos were taken from the plane using strict protocol. Thankfully the weather held out and the herds stayed put long enough to have their group portrait taken!

Now the next phase of work begins. Each of these photos must be collated and analysed. The wildebeest must be counted and the statistical models run. This part of the count is not as glamorous as flying low over the plains looking for the herds, but it is just as critical to get right. We expect this work to take some time and will require the collaboration and consultation of several partners working together.