What’s black and white all over and runs like the wind if it senses a lion?
Of course you know that answer to that one, but have you ever paused to wonder why a zebra has black and white stripes?
This is a common question from people out on safari because the purpose of the stripes is just not that obvious. We usually expect colours and patterns on the fur of wild animals to be related to improving their chances of camouflaging themselves.
We understand a lion’s tawny hues might help it fade into brownish/green grasslands. Many antelope sport shades of brown to help them remain hidden in the veldt (savannah) or bushes.
The legendary author, Rudyard Kipling offers an interesting explanation for the assorted patterns on the skins of African animals. He describes the journey of a mixed band of creatures:
They scuttled for days and days and days till they came to a great forest, ‘sclusively full of trees and bushes and stripy, speckly, patchy-blatchy shadows, and there they hid: and after another long time, what with standing half in the shade and half out of it, and what with the slippery-slidy shadows of the trees falling on them, the Giraffe grew blotchy, and the Zebra grew stripy, and the Eland and the Koodoo grew darker, with little wavy grey lines on their backs like bark on a tree trunk; and so, though you could hear them and smell them, you could very seldom see them, and then only when you knew precisely where to look. – Rudyard Kipling, from ‘How the Leopard Got His Spots’.
If you ask your safari guide about the zebras’ stripes he will probably respond confidently as if he were revealing some secret mystery. He’s been expecting this question, and he has an answer. In fact, he doesn’t know. There are a few theories bouncing around wildlife and academic circles, but none of them has been convincingly proven.
Quite honestly, some of these theories sound a little bizarre to me. Check out these theories below and let’s hear your take.
The first explanation I heard from a safari guide was that when zebras are tightly packed in a herd, their dazzling stripes confuse predators and make it difficult to identify a single prey. I’m sure you’ve seen pictures of tightly packed zig-zag lines that create optical illusions making the viewer believe that the picture is moving.
I find that explanation hard to believe as I’ve seen lions hunting zebras in real life and in many wildlife videos and never did the lion look bedazzled. Of course, often lions don’t catch their intended prey but there are many reasons why that could happen.
A second attempted explanation suggests that stripes provide good camouflage in grass or among trees even though their contrasting colours stand out because lions and other predators are colour blind. I find this explanation even less plausible because when zebras sense predators in their immediate vicinity, they do not hide or try to blend in with “the slippery-slidy shadows of trees”. They run like crazy. Zebras are good runners and they are strong on their feet. They don’t get knocked over easily and a predator has to work really hard or be lucky to bring down an adult zebra.
A third theory for why zebras are striped argues that the alternating black white stripes somehow manage to keep the equine cool in hot African conditions. Alison and Stephen Cobb, two scientists working in Kenya, measured temperatures on the black and white stripes of two zebras and a zebra hide and found that the black stripes were consistently 12-15 degrees hotter than the white stripes. You can read their paper here.
The sharp temperature difference between the stripes, they argued, created ‘chaotic air movement’ above the zebras’ fur. That air turbulence above the stripes helped remove heat from the animals’ skin.
The Cobbs may have something there. It is plausible that the black and white stripes have different temperatures, but personally I find it hard to imagine little weather systems cooling zebras off. It just sounds too weird.
I also have a problem with this experiment because of the tiny sample size – two ‘live’ zebras and a hide? This can’t be serious.
They conclude that, “the primary function of the stripes may be thermoregulation and a secondary benefit, fly-deterrence”.
This last observation is interesting because it proposes that stripes help keep flies away. The notion is not new – it has been muddling around since the 1930s – but it returned to centre-stage recently when a group of biologists at the University of California Davis published a new study.
Popular articles were widely published in mainstream media based on the work of the nine biologists who wrote up the academic paper. Many experts and field guides now confirm this theory as fact: horse-flies are less likely to bite zebras because of their stripes.
The scientists observed that flies are more likely to land on horses than on zebras and the probable reason for this observation is that zebras have stripes. To make it more interesting, they put striped coats on the horses and found that fewer flies landed on them than if they were wearing plain coloured coats.
The biologists admitted that they did not know why fewer flies landed on striped equines but they speculated that the stripes might somehow dazzle the little insects.
Personally, I am cautious about taking these conclusions too seriously for two reasons:
1. Once again, the sample size was small – only three zebras and nine horses
2. The experiments were conducted in the United Kingdom where it is possible that English horse-flies behave differently to African horse-flies.
There are of course other theories about why zebras have stripes, but so far, none sound convincing. We just have to accept that for now, we don’t know. It’s possible that one day we might find out – it is not unknowable – but until then, I will just admire them for their photographic beauty.
Links:
Zebras are posers - Real safari Newsletter
Maryland zebras no longer on the loose - Real Safari Newsletter
Why Zebra has Stripes - Tinga Tinga tales on YouTube - for children
Requiem for a zebra foal - Real Safari Newsletter