{"id":2235,"date":"2019-05-30T12:01:25","date_gmt":"2019-05-30T12:01:25","guid":{"rendered":"https:\/\/blogs.mathworks.com\/headlines\/?p=2235"},"modified":"2019-05-30T12:01:25","modified_gmt":"2019-05-30T12:01:25","slug":"image-processing-helps-solve-the-age-old-mystery-of-why-do-zebras-have-stripes","status":"publish","type":"post","link":"https:\/\/blogs.mathworks.com\/headlines\/2019\/05\/30\/image-processing-helps-solve-the-age-old-mystery-of-why-do-zebras-have-stripes\/","title":{"rendered":"Image processing helps solve the age-old mystery of \u201cWhy do zebras have stripes?\u201d"},"content":{"rendered":"

Why are zebras striped? The hypotheses are many and varied. Do the stripes work as camouflage, temperature regulation, or a barcode so that individuals are distinguishable in a herd?<\/p>\n

The most popular theory by far, dating all the way back to the 1870s and Charles Darwin\u2019s theory of natural selection, was that the zebra stripes acted as a form of camouflage against predators such as lions. Last year, scientists tested<\/a> \u2013 and disproved- the theory that the stripes created a microclimate on the animals’ fur and helped them stay cool. It turns out that neither of these explanations is accurate.<\/p>\n

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Image Credit: Frans Lanting\/National Geographic Creative<\/p><\/div><\/p>\n

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In his book Zebra Stripes<\/em><\/a>, Professor Tim Caro, University of California Davis, describes a decade of testing the various hypotheses of the purpose of zebras\u2019 stripes. He observes that striping is most intense where biting flies, or tabanids, are abundant. Knowing zebras\u2019 susceptibility to biting flies and vulnerability to the diseases that flies carry\u2014Caro concludes that black-and-white stripes are an adaptation to avoid biting flies and the diseases that they carry which are often fatal to zebras.<\/p>\n

A horse dressed as a zebra<\/h2>\n

In a paper recently published in PLOS One<\/a>, Professor Caro and a team from the University of Exeter, Aeres University, and the University of Bristol showed that the zebras\u2019 stripes were a mechanism to thwart the biting flies. To test this\u00a0hypothesis the researches filmed horse flies trying to land on zebras, horses, and horses dressed in zebra print. They then used image processing techniques to analyze the flight patterns and percentage of successful \u201clandings\u201d of the tabanids that were hoping to feast on the animals.<\/p>\n

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Image Credit: Tim Caro\/UC Davis<\/p><\/div><\/p>\n

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The researchers collected video recordings of zebras and horses from a fixed distance. From these videos, the length of time that tabanids remained on animals\u2019 coats, the general locations of the landings, and whether the tabanid left voluntarily or was forced off by the animal was recorded.\u00a0The flight trajectories of tabanids in the vicinity of horses and zebras were extracted from the video recordings by marking their position every 0.02s using MATLAB<\/a>. The use of custom-written zoom tools ensured that fly location could be digitized to the nearest pixel, resulting in accurate and repeatable tracks.<\/p>\n

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The tabanids\u2019 flight paths are shown in red at 0.1-second intervals. Blue stars indicate points of contact (landings). Image Credit: Tim Caro\/UC Davis, PLOS One.<\/p><\/div><\/p>\n

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While the team did not see a significant difference in the rates at which the flies circled near the horses and zebras, they did see a meaningful decline in the actual landings on the zebras. To ensure this wasn\u2019t due to the different odor of the zebras, the team then dressed horses in zebra print and videotaped the tabanids\u2019 behavior. Again, the zebra stripes worked. The new data showed there were measurably fewer landings on the horses dressed as zebras than on the horses that weren\u2019t wearing zebra print. The one exception was the horses\u2019 heads, which weren\u2019t covered in the zebra print cloth.<\/p>\n

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The mean of tabanids touching the cloth(a) and landing on the horses (b) by color and print of their covering. Section (c) shows that tabanid landings on the horses\u2019 uncovered heads were more similar. Image Credit: Caro et al, PLOS One.<\/p><\/div><\/p>\n

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As the study reported, \u201cAn important finding made here supported this idea that stripes do not thwart approach from a distance. There was no significant difference in rates of landings on horses\u2019 naked heads … This suggests that stripes had little effect at a distance but, once close up, stripes prevented landings, with flies turning their attention to the naked head instead.\u201d<\/p>\n

The flies can\u2019t zero-in on the striped animals<\/h2>\n

The study did not pinpoint a reason the flies bounced off the zebras or horses wearing zebra print, but Caro points to a couple of possibilities.<\/p>\n

\u201cCaro said that they might treat the black stripes like a pair of trees, try to fly between them, and end up colliding with the white stripes. Alternatively, the stripes might mess with their optic flow\u2014their sense of objects moving across their visual field,\u201d stated Ed Yong for The Atlantic<\/a><\/em>.<\/p>\n

\u201cI think that the key is that the stripes\u2019 thickness and orientation [are] not consistent, either within a stripe or across them,\u201d Paloma Gonzalez-Bellido of the University of Minnesota, who studies insect vision. \u201cThis is probably what makes it difficult for the flies to control their landing.\u201d<\/p>\n

Either way, it\u2019s good to know there\u2019s a way to avoid biting flies. As the New York Times<\/a> <\/em>concluded, \u201cIf you spend time around horses or flies, you might want to invest in some zebra print.\u201d<\/p>\n

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Why are zebras striped? The hypotheses are many and varied. Do the stripes work as camouflage, temperature regulation, or a barcode so that individuals are distinguishable in a herd?
\nThe most popular… read more >><\/a><\/p>\n","protected":false},"author":138,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/posts\/2235"}],"collection":[{"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/users\/138"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/comments?post=2235"}],"version-history":[{"count":2,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/posts\/2235\/revisions"}],"predecessor-version":[{"id":2241,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/posts\/2235\/revisions\/2241"}],"wp:attachment":[{"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/media?parent=2235"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/categories?post=2235"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.mathworks.com\/headlines\/wp-json\/wp\/v2\/tags?post=2235"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}