Firstly, lions, the predominant predator of zebras, do not have great colour vision. They have a higher density of rod cells in their eyes which help them to have better night vision than us, but as a result have a lower balance of cone cells, which predominantly aid in colour vision. The wavy black and white lines of a zebra therefore act as a sort of fatigue design, breaking up their outline and helping them to blend into the blowing grass or scrub around them that to a lion appears as a similar colour.
Added to this, there is a theory that the multiple mixtures of overlapping stripes of zebras as they stand together dazzles any potential predators. Imagine a zebra standing top to tail with other zebras, tails swishing, stripes overlapping, bodies crisscrossing. How exactly do you tell where one zebra starts and the other one ends and therefore how on earth do you plan your hunt? This may sound a little far fetched but there is one truly fantastic thing about zebras that you may never have noticed that does help to support this theory. This is the fact that the youngsters are born with legs the same length and therefore stomachs of the same height as the adults. The thinking that follows from this is that if a lion for example crouches down in the long grass and attempts to spot the weakest link by looking for the shorter body, it’s going to be a struggle. If the zebras stand or run together as a group, there is going to be a mess of stripes; how do you then tactically separate off and target one zebra if you can’t distinguish any of them as individuals?
This may get you thinking that zebras therefore all have identical stripe patterns but beautifully enough, this isn’t the case at all. Each zebra’s stripes not only differ from one zebra to another but even from one side of their body to the other. Some researchers believe that this is to help individuals to not only recognise each other in the group but it is also likely that the differences help to strengthen the group too. The broken and wavy lines act as a form of disruptive colouration, similar to the way in which the military use fatigue design in their uniforms. The more rigid and stringent the shape of something is in the bush, the more it stands out. Whereas the tumble of different length and shaped black and white lines, moving around and across each other can only add to the confusion, the dazzle.
Another completely different theory, which branches away from evading predators is that zebras have stripes for reasons of thermoregulation. The basic idea is that the black and white stripes heat up differently, causing an airflow between the two which produces a cooling effect. This is interesting to note as quite often you’ll find zebra grazing out in the open on hot summer days when other species are seeking shade. Some researchers even believe that the degree of striping on a zebra is closely linked to the typical temperatures of places where they are found. What they’ve noted is that thicker, bolder black and white striped zebras are more prevalent where “temperatures are consistently warm” and thinner, paler, incomplete stripes are found more commonly on species where temperatures tend to fluctuate and drop significantly during the winter months.
One of the things that is so fascinating about studying nature is that we can’t be sure about a lot of things and in this case we can only rely on healthy debate, theories and speculation. It’s interesting to explore the question but ultimately it doesn’t really matter why zebras have stripes; what matters is that it seems to work for them. Essentially for me, it reinforces the simple fact that a healthy mixture of differences in a group can be its greatest strength.
Contributed by Amy Attenborough