From: Pat Bailey, UC Davis
Published January 25, 2016 07:02 AM

Zebra stripe camouflage hypothesis debated

If you’ve always thought of a zebra’s stripes as offering some type of camouflaging protection against predators, it’s time to think again, suggest scientists at the University of Calgary and UC Davis.

Findings from their study will be published Friday, Jan. 22, in the journal PLOS ONE.

“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.

“We, instead, carried out a series of calculations through which we were able to estimate the distances at which lions and spotted hyenas, as well as zebras, can see zebra stripes under daylight, twilight, or during a moonless night.

Melin conducted the study with Tim Caro, a UC Davis professor of wildlife biology. In earlier studies, Caro and other colleagues have provided evidence suggesting that the zebra’s stripes provide an evolutionary advantage by discouraging biting flies, which are natural pests of zebras.

In the new study, Melin, Caro and colleagues Donald Kline and Chihiro Hiramatsu found that 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 point at which predators can see zebras stripes, they probably already have heard or smelled their zebra prey.

“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,” Caro said. “Instead, we reject this long-standing hypothesis that was debated by Charles Darwin and Alfred Russell Wallace.”

New findings

To test the hypothesis that stripes camouflage the zebras against the backdrop of their natural environment, the researchers passed digital images taken in the field in Tanzania through spatial and color filters that simulated how the zebras would appear to their main predators — lions and spotted hyenas — as well as to other zebras.

They also measured the stripes’ widths and light contrast, or luminance, in order to estimate the maximum distance from which lions, spotted hyenas and zebras could detect stripes, using information about these animals’ visual capabilities.

Continue reading at UC Davis. 

Zebra image via Shutterstock.

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