Science News

How the zebra got its stripes

Fri, 14th Aug 2015

James Farr

The effectiveness of 'dazzle patterns' as a camouflage technique has been called into question by new research.Zebra storm

These patterns are made up of highly contrasting stripes, usually black and white, and so are quite unlike  the muted blends we associate with camouflage..

Even if an animal blends in well with its background, as soon as it starts to move it becomes very easy to spot. As such, animals that like to move around a lot sometimes use a different method altogether.

Rather than making themselves difficult to spot, it was thought that animals such as zebras employed dazzle patterns to try and confuse predators by making it difficult to judge how fast and in what direction they are moving. Furthermore, it has been suggested that this effect is particularly effective when animals move in groups as telling where one zebra ends and another begins could be much harder.

The famous 'dazzle-ships' of World War I were inspired by such patterns, but, until recently, the effectiveness of the designs had never been scientifically tested.

In an attempt to clarify the situation, Anna Hughes and her team from the University of Cambridge investigated whether the patterns have the intended effect, potentially answering the age-old question 'Why does the Zebra have stripes?'.

Anna designed a touch-screen computer game which involved 'catching' shapes of various different patterns as they moved across the screen.

Writing in Frontiers in Zoology, the scientists found that, when participants only had one shape to catch, the success rates for striped and plain shapes were very similar. However, when several shapes were being targeted at once, the striped shapes were actually easier to catch.

This was a very unexpected result, suggesting that confusing predators may not have caused the evolutionary development of the stripes.

However, it is important to remember that any test is always limited, and the authors urge caution in interpreting the results.

"Humans are not the natural predator of zebra," Anna reminds us, "Lions and other predators do have different visual systems, so it could be that this is partly an artifact of how we set up the game". Similarly, lions donít catch zebras by just clicking a mouse!

Indeed, it is perfectly possible that zebrasí stripes serve a different purpose altogether.

One theory is that the high-contrast pattern is designed to ward off insects such as mosquitos, which could transmit diseases like malaria. Another suggests that the different absorption properties of the black and the white areas are designed to encourage airflow over the zebras, acting as a cooling mechanism of sorts.

Most likely of all, is that the stripes serve several purposes at once, combining a number of different effects, all of which aid the zebras in some way.

As Anna says, "it's probably not necessarily just one explanation but maybe several different things that have come together to create really quite unique patterning in this animal."



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