SANParks.org Forums

Many wildlife guides confidently state that temperature differences between the black and white stripes on a zebra set up convection currents that help to control its body temperature.

Does anyone know where this comes from ? - an internet search of the scientific literature does not provide any sources at all.

Or is it a modern version of a just so story ?

Peter Apps

Hi Peter!

I can remember reading about that on the science part of the BBC site, a study had indeed gotten results that pointed in that direction. I just spent half an hour looking for it, but can't seem to find the right keywords.
I may actually have posted it under the Zebra topic in Mammals here...

Sorry if I am ignorant, but why do a zebra require such sophisticated cooling while the wildebeest and buffalo grazing next to him are much darker in color without such space-age cooling technology ?

Hello, Peter!
I don't know, but an interesting bumshot I posted under "quizzes" a while back shows a clear difference in the consistency of the black and white hairs, shown up by more mud sticking to the black ones...interesting!

Maybe the black ones are indeed hotter?

Can remember that bummer, priceless!
Maybe there are some truth to this statement

Welcome to the forums Peter

Is your forum name your real name as well? If so I would have thought you might be able to tell us more about it than we could

I once read a paper outlining a number of theories related to the evolutionary fitness benefits of the zebra coat. The main theories they looked at were that the coat evolved as a predatory avoidance characteristic, making the zebra look bigger, as well as the fact that stripes blend in with tall grass. Also along these lines is the idea that moving stripes dazzle predators and that the colouration and patterning are hard to pick out in poor light.

The next major theory looks at the evolutionary development along the lines of social benefits ITO group bonding as a marker for grooming and as a means to identify individuals in the group.

Then comes the idea of thermoregulation which is basically the question you have asked, but unfortunately from an evolutionary and therefore fitness point of view this theory has little merit.

Then lastly my favourite theory. Where the coat is believed to have evolved as a means of protection from tsetse flies.This theory has quite allot of evidence to support it and makes logical sense too. Waage showed experimentally that there was a significant difference between the number of flies attracted to solid colours and those attracted to striped patterns (horizontal).

All of the theories have their advantages and disadvantages and I would list them but a bit short of time. If anyone has access to the paper the reference is:

Ruxton, G.D. 2002. The possible fitness benefits of striped coat colouration for zebra. Mammal Review 32(4):237-244.

In 'Beat about the bush - mammals' Carnaby states that research has shown more capillaries under the black stripes and this is thought to be to do with dissipating heat. Probably where the guides get the information from. (see page 229)

Hello, ej!

Maybe the capillaries developed there to counter the added heat, rather than the other way around? Presumably blood heat-loss would be directed to cooler areas?

Interesting point!

Hi RP!

I think I also read somewhere the theory about temperature gradients and micro-breezes too, but cannot remember where.

Some of the theories scientists come up with really amuse me - they can never just accept that some things maybe just are like that! And some are just totally contradictory too......try the white marks round eyes to make it easier to collect light and focus....vs the dark marks on a cheetah's face to reduce glare!!!!

Thank you all.

I am who my forum name says, but like you I cannot find any original reference to proper scientific work on this micro-convection story. This rather strengthens my suspicion that it is a plausible hypothesis that seems eminently reasonable and has some corroborating evidence of a kind; the different distribution of blood under the black and white areas, but which has never been rigorously tested. It has the allure of sophisticated science about it, and is more convincing than telling a client that nobody really knows why zebras have stripes. Before long it becomes a sort of accepted wisdom and before you know it is being repeated on TV and all over the internet, and when it appears in a book - well it must be true, I read it in a book !

For what it is worth, the explanation that I find most convincing is that contrasting black and white stripes allow zebras to see one another under conditions of poor visibility, thus allowing them to stay closely bunched when fleeing from predators at night in clouds of dust. Zebras are the only species that have this particular anti-predator behaviour, and the only species with black and white stripes.

If anyone does find the original reference, please post the citation.

Thanks again Peter

Well, some other species also have stripes, tigers being the obvious example, but probably just camouflage...

The other herbivore that comes to mind is the rare okapi, which has similar attempted stripes along its buttocks, but is related to giraffe!

Kudu and nyala also have stripes!


Curiouser and curiouser!

Hi Peter

I wasn't aware of this at all, until I read an article about it in a copy of Africa Geographic about research being done into biomimicry and how this can benefit the human world.
But now I cannot find that article for you.

But ye it did pertain to the view that the Zebra strips were a possible cooling system for the Zebra in that the darker stripes allowed the animal to dump heat from these dark stripes.

Sorry its a bit vague without the article I read

Seems its been dispelled already

http://www.bio.davidson.edu/people/veca ... tripes.htm

Thanks, and welcome down here, Ross!

Here's an excerpt from the link:

Thermoregulation

The thermoregulatory hypothesis’ basis is that the black and white stripes work together to keep the animal cooler than if it was solid colored (Ruxton 2002). Through experiments, it was seen that there was no difference in the temperature of striped objects as solid colored objects (Ruxton 2002). Although the theory of black and white stripes as a cooling mechanism has been dispelled, it is interesting to note that zebras have a stripes of fat that coincide with the black stripes that seem to function as heat absorbers (Elzenga 1992). As Ruxton believes that thermoregulation is the least plausible explanation for striping and said, “If black and white stripes were an effective method of dissipating heat from structures, then I think that thermal engineers would know about it” (2002).

The rest makes fascinating reading too!

Thanks again.

So, it is fair to summarize that there is no hard evidence that zebra stripes are a cooling mechanism. The differential fat distribution and blood supply suggest that they could serve that role (and these biological features were not covered by the simple comparison of striped and plain solid objects), but micro-convection will be disrupted by even the tinient of breezes, and so if there is a significant difference in heat exchange between black and white stripes it is probably due to radiation rather than convection. It is important to stress though that nobody has ever taken any measurements of heat flow and body temperature that support the thermoregulation theory. Or, if they have taken the measurements, for some reason they have not published them.

It is time for this myth to die. The next time you hear a wildlife guide spouting off about it, or see it in a magazine or on the web, please ask them where they got the information. And put them right, in the nicest possible way of course.

Peter