A recent study showed that the zebra stripes are not for crypsis, because those can only be distinguished by the predators from a determined distance. This means that the stripes do not blend with the environment and hide the zebra’s figure, so it can not successfully cover crypsis purposes.
The study, made by a team of researchers from Canada and the U.S, evaluated the hypothesis using digital images of zebras through species-specific spatial and colour filters to simulate their appearance for the zebra’s predators and zebras themselves. They also measured stripe widths and luminance contrast to estimate the maximum distances from which lions, hyaenas and zebras can resolve the stripes, according to the study.
Researchers found beyond 50 meters at daylight and 30 meters at twilight the zebra’s stripes are difficult to resolve for their predators. On moonless nights, when the carnivores hunt the most, the stripes are more difficult to resolve beyond 9 meters.
In open treeless habitats, where the zebras spend most of their time, they are clearly identified by the lion visual system as are similar-sized ungulates, this suggest that the stripes do not successfully confer crypsis by disrupting the zebra’s outline.
The stripes also confer a minor advantage in camouflage on wooden’s areas, but the effect is stronger in humans than in predators, and the carnivores can smell and hear them so it does not work at all. These makes any mechanist of camouflage highly ineffective so the researchers urge to find the purpose for the stripes somewhere else.
The team also considered the stripes for socializing purposes, but even though they can not effectively deny it, the analysis showed that zebras can likely discern stripes at greater distances that the carnivores that prey on them, but it does not mean that striping is driven by social necessity, as un-striped congeners are highly social and able to recognize individuals in the absence of striped pelage.
The camouflage hypothesis comes to rest after 120 years in the time of Charles Darwin, who dismissed the camouflage theory in a long-standing debate with Alfred Russel Wallace.
Source: Journal Plos One