January 19 – I Got Stripes

Today’s factismal: Zebras are black with white stripes.

Zebras are fun critters. They look like punk rock horses, they run like slalom skiers in a field of moguls, and they kick like a mule. But anyone who has ever seen a zebra will agree that the most interesting thing about zebras is their stripes. Based on studies of zebra embryos, we know that their body is black with white stripes because the black skin develops first on the embryos. But that is about all that we know for sure; we still don’t know why zebras have stripes.

Two zebras discussing if they are black with white stripes or white with black stripes (My camera)

Two zebras discussing if they are black with white stripes or white with black stripes
(My camera)

We know that having stripes has to give zebras some sort of an advantage or they wouldn’t have them. But what is it? Right now, there are five competing hypotheses. Some biologists think that the stripes act as a sort of bar code, helping one zebra know which zebra is which. And some think that the stripes serve as camouflage when the zebra is standing still. The vertical stripes blend in with the outlines of tall grass and trees, making it harder to see the zebra. Another group of biologists thinks that the stripes act as “dazzle camouflage”; when a group of zebras run, the moving stripes blend together and make it harder to pick out any single zebra for lunch. Still other biologists think that the stripes may act to keep flies away by confusing them. (See, camouflage isn’t all about lions.) And a fifth group has done some work showing that the stripes may act as a sort of air conditioner for zebras.

Zebras doing their camouflage bit (My camera)

Zebras doing their camouflage bit
(My camera)

But why would a zebra need an air conditioner? Because they aren’t very good at digesting their food, that’s why. Because zebras don’t do a good job of extracting nutrients from the grass that they eat, they have to eat a lot more grass which means that they spend a lot more time out in the hot sun chomping down on tough grasses. And that’s when a built-in air conditioner would be pretty handy. There is some support for the idea; a recent study has found that zebras in hotter areas have better-defined stripes. But that would also serve to hide the zebras from flies, which are more common in hotter, wetter regions. And there is similar support for each of the other ideas.

A zebra does its Steve Austin impression (My camera)

A zebra does its John Cena impression
(My camera)

So if we know what color a zebra’s stripes are but not why they have them, who knows what else might we learn by studying these animals? And the first way to study zebras (or any other mammal) is to know where they are. And that’s where you come in! MammalMap is looking for volunteers just like you to report where and when they see which mammals in Africa. Not in Africa? NO worries – you can still contribute by helping to identify the mammals that other folks have seen. To take part, herd on over to:
http://mammalmap.adu.org.za/

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