Do you know | Why do zebra have stripes | learnwithsuhaas

#learnwithsuhaas #learnwithme #facts Reference:: https://earthsky.org/earth/why-zebra-has-stripes/ Zebras are famous for their contrasting black and white stripes – but until very recently no one really knew why they sport their unusual striped pattern. It’s a question that’s been discussed as far back as 150 years ago by great Victorian biologists like Charles Darwin and Alfred Russel Wallace Since then many ideas have been put on the table but only in the last few years have there been serious attempts to test them. These ideas fall into four main categories: Zebras are striped to evade capture by predators, zebras are striped for social reasons, zebras are striped to keep cool, or they have stripes to avoid attack by biting flies. What’s the advantage of zebra stripes? Could stripes help zebras avoid becoming a predator’s meal? There are many problems with this idea. Field experiments show that zebras stand out to the human eye when they’re among trees or in grassland even when illumination is poor – they appear far from camouflaged. And when fleeing from danger, zebras do not behave in ways to maximize any confusion possibly caused by striping, making hypothetical ideas about dazzling predators untenable. Worse still for this idea, the eyesight of lions and spotted hyenas is much weaker than ours; these predators can only resolve stripes when zebras are very close up, at a distance when they can likely hear or smell the prey anyway. So stripes are unlikely to be of much use in anti-predator defense. Most damaging, zebras are a preferred prey item for lions – in study after study across Africa, lions kill them more than might be expected from their numerical abundance. So stripes cannot be a very effective anti-predator defense against this important carnivore. So much for the evading-predators hypothesis. What about the idea that stripes help zebras engage with members of their own species? Every zebra has a unique pattern of striping. Could it be useful in individual recognition? This possibility seems highly unlikely given that uniformly colored domestic horses can recognize other individuals by sight and sound. Striped members of the horse family do not groom each other – a form of social bonding – more than unstriped equid species either. And very unusual unstriped individual zebras are not shunned by group members, and they breed successfully. What about some kind of defense against the hot African sun? Given that black stripes might be expected to absorb radiation and white stripes reflect it, one idea proposed that stripes set up convection currents along the animal’s back, thereby cooling it. It is important to remember that flies have much poorer vision than people. We found that zebras and horses received a similar number of approaches from horseflies, probably attracted by their smell – but zebras experienced far fewer landings. Around horses, flies hover, spiral and turn before touching down again and again. In contrast, around zebras flies either flew right past them or made a single quick landing and flew off again. Frame-by-frame analyses of our videos showed that flies slowly decelerated as they approached brown or black horses before making a controlled landing. But they failed to decelerate as they approached zebras. Instead they would fly straight past or literally bump into the animal and bounce off. When we placed black coats or white coats or striped coats on the same horse so as to control for any differences in animal behavior or smell, again flies did not land on the stripes. But there was no difference in landing rates on the horse’s naked head, showing that stripes exert their effect close up but do not impede fly approaches at a distance. And it showed us that striped horse coats, currently sold by two companies, really do work. When the researchers put various colored cloth coats on horses, the zebra-patterned coat led to a drastic drop in how many flies they saw landing on a horse's covered body. Below, the vertical axis measures the average number of fly landings observed per half hour. But horses wearing the zebra-striped coat had about the same number of flies land on their uncovered heads as those in solid white or black coats. Flies seem to stay away from stripes, but stripes at a distance don't protect the horses.

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