Zebras are masters of confusion. Their collective noun is ‘a dazzle’, which is fitting since their bodies and behaviour have been surprising scientists for centuries.
Let’s start with their sassy stripes, which have been the subject of scientific debate since the time of Darwin. They were originally assumed to be a form of camouflage to protect these equine grazers against big predators. Others hypothesized that the pattern, which varies amongst individuals much like a thumb print, acts as a means of identity signalling. Some even considered the black and white stripes a form of wearable air conditioner to protect their owner against the fierce equatorial sun.
It transpires that the zebras’ stripes evolved to confuse flies, not scientists. A team of British scientists dressed horses in zebra print to deduce how the unique monochrome pattern dazzled the insects, prevented them from making a controlled landing. The high contrast between black and white most likely creates a disorienting illusion of movement, and tricks the fly’s low-resolution vision. The lively pattern stops the zebra being bitten and protects them from the deadly diseases carried by biting flies.
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The zebra’s social structure has proved equally confusing. Plains zebra (Equus quagga) inhabit the savannahs of east and southern Africa, where they live in groups comprising a single male with 2-5 females and their young. Described as a harem, it was assumed the stallion led group movements and the females were only bonded to the male, not each other. Yet recent work by Princeton University ecologists has exposed the flaws in this patriarchal assumption.
First, it transpires that females are the leaders of zebra society. The female that dictates group movement isn’t the head of some hard-won hierarchy or even the oldest, as one might expect. It is instead a democratic decision: the leader is generally the female that’s nursing a foal. This makes sense. Lactation requires additional energy and water, and this drives her motivation to seek out fresh supplies. The others follow.
This fluid egalitarian system is possible thanks to the zebra’s communication skills. Notably the head-bob – a visual signal that encourages one zebra to follow another’s movement. Much like a hand gesture might work for humans to direct other humans, the head-bob is a way to focus joint attention and initiate group movement.
In addition to signalling a change of movement, the head-bob also encourages females to engage in affiliative behaviours, such as nuzzling or side-by-side grazing, noses touching. These cosy social behaviours might not seem unusual, but they are. The females in these groups are unrelated and would be expected to behave competitively. Instead, researchers discovered that females forge surprisingly strong and lasting bonds.
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This sisterhood of zebra friends evolved to protect their foals – not from predators, but from infanticidal stallions.
When a fresh stallion takes over a group, he wants to mate with the females, but if they are nursing, they will be unreceptive. Killing the foal would force the female into early oestrus – a tactic employed by lions and some alpha male primates.
Female coalitions could offer protection, but had not been witnessed in the wild until recently. A female zebra was documented risking her life by stepping in to protect her friend’s newborn foal. She sandwiched herself between the foal and the stallion and repeatedly kicked his head to prevent an attack. The rarity of such attacks suggests that in this particular battle of the sexes, the females and their besties are winning.
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