It has long been thought a zebra’s distinctive black and white striping serves as camouflage from predators, but a new study finds that is not the case.
Writing in the journal PLOS ONE, researchers from the University of California Davis and the University of Calgary say they calculated how a zebra’s stripes would appear to lions, spotted hyenas and other zebras when viewed in varying levels of light.
"The most longstanding hypothesis for zebra striping is crypsis, or camouflaging, but until now the question has always been framed through human eyes," said the study's lead author Amanda Melin, an assistant professor of biological anthropology at the University of Calgary, Canada.
They found that the stripes “cannot be involved in allowing the zebras to blend in with the background of their environment or in breaking up the outline of the zebra” because at the distance a predator would be able to see the stripes, they would likely already have heard or smelled the zebra.
The researchers noted that at further than 50 meters in daylight or 30 meters at twilight, a zebra’s stripes are easily seen by humans, but not so for would-be predators. On a moonless night, the researchers said the stripes were hard to see by predators and humans, even from just 9 meters away.
This, researchers said, means that the idea that a zebra’s stripes mimicked tree trunks and shafts of light, did not make sense.
Furthermore, in the open, where zebras are most commonly found, the stripes do not “disrupt the outline” of the zebra. Lions, researchers said, could see the the outline of zebras just as they could a solid-colored animal.
"The results from this new study provide no support at all for the idea that the zebra's stripes provide some type of anti-predator camouflaging effect,"said Tim Caro, a UC Davis professor of wildlife biology. "Instead, we reject this long-standing hypothesis that was debated by Charles Darwin and Alfred Russell Wallace."
Another theory about the stripes, that they better allow zebra’s to see one another was also discredited by the research. While zebra’s can see the stripes over a further distance than its predators, other animals related to zebras can also see each other despite not being striped.
While not conclusive, the researchers say one reason for the stripes might be to deter biting flies, a common zebra pest.