Zebra stripes not for camouflage protection against predators

Canadian researchers have challenged the longstanding hypothesis of zebra striping being some type of camouflage protection against predators.

According to a study, stripes cannot be involved in allowing the zebras to blend in with the background of their environment or in making an outline of the zebra.

It is because the predators probably can hear or smell their zebra prey from the point from which they could see its stripes, the findings revealed.

"We 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," said Amanda Melin, an assistant professor at the University of Calgary in Canada.

Stripes that can be seen by humans are hard for zebra predators to distinguish beyond 50 metres in daylight or 30 metres at twilight, during which most predators hunt, the findings showed.

On moonless nights, the stripes are particularly difficult for all species to distinguish beyond nine metres, suggesting that the stripes do not provide camouflage in woodland areas, as theorised in earlier, the researchers elicited.

In open, treeless habitats, where zebras tend to spend most of their time, lions can see the outline of striped zebras just as easily as they could see similar-sized, prey with fairly solid-coloured hides, such as waterbuck, the study, published in the journal PLOS ONE, showed.

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 colour 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.