“Why do zebra have stripes?”
This is certainly a topic that has been covered numerous times, not only on the Londolozi blog but by most guests that come on safari here too. So, why revisit it? Well, with new research comes new information and with that comes different opinions or some scientific evidence to back up previous theories. James Tyrrell did open the table to this topic: “any thoughts on the matter?”
Many theories have been suggested from camouflage, confusion tactics, to deterring flies but the theory that has the most scientific backup is thermoregulation. Animals have evolved (and continue to do so) for millennia and the underlying reason for this is to better cope with the environment that they live in. Zebras are grazers, meaning they feed on grass, and therefore they favour open savannah as opposed to thicker woodier areas. Open savannah goes hand-in-hand with less shade and more exposure to the blistering African heat.
Now I’m not saying that zebras are not plagued by biting flies and that there may be evolutionary changes to cope with this, perhaps the involuntary twitching of their skin has evolved millennia ago for this very reason. What I’m saying is that surely the most important aspect for an animal spending the majority of their time in the sun is to ensure that they do not overheat.
An amateur naturalist, Alison Cobb, spent many years with her husband, zoologist Stephen Cobb, living in sub-Saharan Africa and devoted a significant amount of time to researching zebras. Stephen had a student that worked with zebras who reported the ability to calm them down by brushing them with a long-handled broom. This prompted Alison to ask for permission to try and tame a zebra at the Animal Orphanage in Nairobi, which would aid her in collecting research data. She attempted to brush the zebra daily in the hopes the zebra would become accustomed to her and comfortable with her presence. What Alison realized, apart from the fact that the zebra enjoyed the brushing, was that the zebra was able to erect the black stripes of her coat. Through previous research she had already determined that the black stripes of the zebra would, on any given day, heat up to between 12 – 15 degrees Celsius higher in comparison to the white stripes. Whereas a lifeless zebra hide draped over a clothes horse would increase to more than 16 degrees Celsius. So what function was the raised hair playing?
Zebra are part of the Equidae family of which a characteristic is the ability to sweat. Think of a racehorse galloping down the home stretch covered in sweat. The sweat, however, is different from humans’ sweat; it’s frothy. Equines produce a protein called latherin enabling the production of this frothy sweat. The raised black hair allows this sweat to be spread all the way to the tips of the hair. This increases the surface area and lowers the surface tension so that evaporation is more effective over the black stripes of their coat in the heat of the day.
Furthermore, the temperature gradient between the black and white stripes creates small-scale convection air currents just above the skin. This, in my opinion, is a twofold adaptation. Firstly, with increased airflow over the sweat, evaporation is increased. Secondly, which backs up the fly deterrent theory, is that flies find it more difficult to land on an animal with stripes but not due to their inability to spot a landing on a striped surface but rather due to the mildly turbulent air just above the skin of the zebra.
To dismiss any of the previously mentioned theories would be futile but why should we write off the fact that zebras have evolved to adapt for all of these different reasons? The fact that we can still go out on game drive and sit and discuss the different reasons for animals having the adaptations they do is what keeps me, and I’m sure many of you, coming back time and time again.