The stripes don’t help the zebra blend with the background
(Mirror Daily, United States) – When looking through a predator’s eyes, a zebra’s stripes are useless for camouflage against the woodland or grassland backdrop of their native regions. It appears that the debate has not been settled, but one theory has been eliminated.
Researchers from the University of Calgary and the University of California Davis have managed to debunk a popular notion. For decades, starting with Charles Darwin around 120 years ago, it was believed that the iconic black and white stripes of a zebra were used for camouflage. In fact, earlier beliefs noted the black stripes mimicking tree trunks, with the white serving as a way to appear as lines of light across the tress.
And yet, it seems it’s not so.
According to lead author of the study, Amanda Melin, from the University of Calgary, the long-standing belief was that crypsis, or camouflage, was the main purpose of the stripes. However, the professor of biological anthropology stated that previous theories have been built on human eyesight. It skewed the results, considering a natural predator of zebras would have a very different view.
To test out the hypothesis, the team of researchers carried out an experiment on a series of images snapped in Tanzania. Using spatial and color filters, they were able to simulate how the zebras would be seen through the eyes of lions or hyenas, who are their main threats. That way, they would be able to understand just how useful the black and white stripes were against dangerous predators.
The team of researchers also measured luminance to ascertain at what distance the patterns became indiscernible in daylight, twilight, and moonless nights. As it turns out, at any distance over 164 feet (50 meters) during the day and 98 feet (30 meters) during twilight, the stripes became difficult to see by predators. That is the peak hunting time for lions and hyenas. At that distance though, they can no longer tell between the black and white lines.
During nighttime, the stripes were impossible to notice at distances over 29 feet (9 meters). At those lengths though, predators would not even need to see them anymore, as they had likely already heard or smelled the zebras. Thus, the black and white stripes are of no use in regards to blending into the background. Their outlines were as visible as any other potential prey, such as a waterbuck or impala.
What the study does is eliminate one theory, but that leaves the question open. What do the black and white stripes truly do then? They don’t do much to help them blend with their surroundings, and other experts have ruled out a social purpose behind them. The theories now remain that they might be used to confuse predators during an attack, repel biting flies, or used to control their body heat.
The study, according to the researchers, thus denies the debates sparked by Charles Darwin himself.
Image source: flickr.com