Zebras: white with black stripes, or the other way 'round?

Old question, familiar conundrum: Are zebras white with black stripes, or black with white stripes?
It’s not an entirely frivolous question, as the question of what makes animals the colours they are, and why, remains one that vexes field biologists and nature photographers alike.
That was thrown into sharp relief once again this past week in a Washington Post piece headed, Why are pandas black and white?
Again, it’s not a frivolous question. Bears, after all, tend to be monochromatic, whether grizzly, polar bear or the clue-is-in-the-name black bear and brown bear. Why is the panda different? Is the panda even a bear? The answer is similar, but not identical, to why the African plains zebra, which inhabits very different terrain from the Chinese panda, is also black and white.

©Getty Images/BBC

©Getty Images/BBC

Biologists with the University of California at Davis and California State University (Long Beach) published a paper in the nature journal Behavioral Ecology earlier this week that suggests panda colourationis for both camouflage and communication.
That mirrors similar findings with zebras.
Field studies in Africa have determined that while zebras might not seem to blend into yellow grasslands with their black and white stripes, predators have a hard time distinguishing one zebra from another when they’re pressed together in a herd.
Lions hunt mainly by sight, which is why they tend to pick off strays lagging behind the herd, rather than singling out an individual in the middle of a herd for special attention.

©Africa Wildlife

©Africa Wildlife

Along similar lines, a newborn zebra will recognize its mother by its stripe pattern; that’s why an infant, separated from its mother, may have a hard time finding her again in a large herd.
That can be a problem for infant zebras, because unlike many other mammals, female zebras will not attend to others’ young.
The panda study made similar findings, though with some marked differences.
The biologists studied pandas’ ears, eye patches, limbs and white bodies for clues as to their behaviour.
Tim Caro, a biologist with the University of California Davis’ Wildlife, Fish and Conservation Biology department, wrote that panda colouration has been a long-standing debate because virtually no other mammal, other than the zebra, has the same combination of colours, which makes analogies difficult.
The biologists reached their conclusions by combing through hundreds of photographs of 40 types of bears, in a bid to identify and isolate fur colour over different parts of the body — back, legs, ears and head. They then divided animals’ faces into separate, independent areas.
Animals that grow winter coats were found to have significantly lighter fur in cold-weather climes.
That’s key, because forest shade and snow appears to have played the major role in influencing the panda’s coat.

©Mohd Rasfan/AFP

©Mohd Rasfan/AFP

Unlike North American and Russian bears, pandas do not sleep through the winter, because there is little nutritional value in bamboo, the pandas’ primary dietary source. A steady diet of bamboo is insufficient to give them the fat reserves needed to hibernate through a long winter. That means they’re forced to forage for winter food in treed areas that change suddenly from light snow to dark forest shade.
As for that overarching question, asked on virtually every safari by every safari-goer — are zebras are white with black stripes, or the other way round — scientific consensus favours the latter.
We humans find this hard to believe at first because we tend to perceive shapes and colours as being against a white backdrop. A child draws on white paper, for example. We write in black ink, on a light surface.

©Science Now

©Science Now

There’s more scientific, evolutionary proof as to why zebras are, at their core, dark-coloured animals with light markings. The plains zebra (Equus quagga) evolved from the African wild ass (Equus africanus), which was coloured a solid brown, as with most horses and donkeys.
Zebras have white or grey stomachs — another reason we tend to think of them as having a white base with black stripes— but many darker coloured mammals have light or even white-coloured underbellies, including predators like lions and leopards that prey on zebras.
Black is the predominant pigmentation in the zebra’s coat; white contains very little pigmentation.

It’s believed white stripes may have evolved as a way to shield the zebra’s skin base against the harsh African sun, as suggested by the fact that zebras from more temperate, high-altitude regions, such as the Hartmann’s zebra (Equus zebra hartmannae) and mountain zebra (Equus zebra), tend to be darker than their savannah cousins. Darker pigmentation in zebras shows itself as thin white stripes and larger, fatter black stripes. Not all zebras are alike, in other words, just as pandas are unlike other bears.

It’s believed white stripes may have evolved as a way to shield the zebra’s skin base against the harsh African sun, as suggested by the fact that zebras from more temperate, high-altitude regions, such as the Hartmann’s zebra (Equus zebra hartmannae) and mountain zebra (Equus zebra), tend to be darker than their savannah cousins.
Darker pigmentation in zebras shows itself as thin white stripes and larger, fatter black stripes.
Not all zebras are alike, in other words, just as pandas are unlike other bears.