The Coolness of Zebra Stripes
By Candice Gaukel Andrews - 10. September 2019
We’re still learning about zebras and the reasons why they have their beautiful stripes. As the world continues to warm, we might be able to learn a lot from them.
Why zebras have stripes has been a matter for scientific debate for decades. A lot of theories have been put forth, such as they’ve evolved for camouflage, to confuse the vision of biting flies, to bewilder predators with “motion dazzle” or that they’re a means of identification among zebras themselves.
But now, new research postulates that zebra stripes may create air flows that provide the animals with a kind of natural air-conditioning system that helps them cool off in the heat of the African sun.
In living black-and-white
In a recent study, which was published on June 13, 2019 in the Journal of Natural History, the scientific publication of the British Natural History Museum, amateur naturalist and former biology technician Alison Cobb and her husband, zoologist Dr. Stephen Cobb, measured the temperature differences between the black stripes and the white stripes on two zebras living in their natural habitats in Kenya, Africa—something that hadn’t been tried before.
Unlike camouflage, which allows prey to blend into surroundings, “motion dazzle” masks movement, confusing predators about direction and speed.
The Cobbs had spent many years living in sub-Saharan Africa and were always amazed by how much time zebras spent grazing in the blazing heat of the day—for far more hours than the antelopes living in the same area. The Cobbs then moved to England; and without direct access to research animals, Alison enlisted the help of her three daughters, aged 8, 9 and 10. She made them wear rugby shirts on which she had sewed black-and-white stripes and encouraged her “experimental animals” to crawl around on their hands and knees in the sun.
Without looking, when Alison touched the different colored stripes on the girls’ backs, she could tell which ones were black and which were white just by how hot they were. But this made her wonder: if white stripes are cooler, why would zebras have the black ones at all?
By December 2003, the Cobbs were again living in Africa and got a chance to test some of their ideas about the question on a couple of captive zebras living on private ranches in Kenya. They measured the temperatures of adjacent black and white stripes on various parts of the zebras every 15 minutes, as well as taking ambient air temperatures near the animals. They also took similar measurements of a zebra hide wrapped around clothes in the shape of a horse left in the sun on the ranch.
Researchers noticed that zebras graze out in the sun and the heat for far more hours than other animals living in the same area.
Surprisingly, what they found was that the temperature of the black stripes and the white stripes differed greatly on the living animals and that the temperatures widened as the day heated up: the black stripes ended up being up to 27 degrees Fahrenheit hotter than the white stripes. That disparity, say the Cobbs, is enough to produce small convection currents (or air eddies) above the zebras’ skins that help to keep the animals cool by speeding up the evaporation of sweat.
The stripes on the inanimate hide had a similar difference between black and white stripes, but the highest temperatures of the black stripes could get up to another 27 degrees Fahrenheit hotter than the living animals’ coats. The living zebras’ black stripes got up to 132.8 degrees Fahrenheit, while the black stripes on the nonliving hide got up to a scorching 159.8 degrees Fahrenheit. In other words, the temperature didn’t stabilize throughout the day like it did in the living animals.
This indicates that there is an underlying mechanism to suppress heating in living zebras, and color is just one part of it. The Cobbs think they may know what another significant portion is.
Surprisingly, zebras are able to raise the hair in their black stripes straight up in the air while keeping the hair in their white stripes completely flat. Another caracteristic is the upstaning mane - unlike as in other horse-related species.
While conducting their research, the Cobbs also noted that the living zebras have an unexpected ability to raise the hair on their black stripes straight up in the air (like velvet) while the white ones remain flat. And they did so at some of the hottest times of the day.
The Cobbs think that this raising of the black hairs when it’s hottest and when the temperature between the black stripes and the white stripes is at its most variant assists with the transfer of heat from the skin to the hair surface, allowing air to flow out and water to evaporate more quickly. Conversely, when the stripes are at the same temperature in the early morning and there is no air movement, the raised black hairs could help trap the cooler air and keep it in.
There is evidence from other recent studies that backs up the idea that heat control may be key to why zebras have their striking coats. It has been demonstrated that the zebra stripes become remarkably more pronounced on animals living in the hottest climates, near the equator. Zebras are also smallest near the equator, providing a large surface area to volume ratio, which assists the animals’ ability to dissipate heat through evaporation.
There probably isn’t one, single reason that zebras have evolved stripes. But what we do know is that stripes become remarkably more pronounced on zebras living in the hottest climates, near the equator.
But Gabor Horvath, a researcher at Eotvos Lorand University in Budapest, Hungary, who has studied zebra stripes, does not believe that thermoregulation is the primary function of zebra stripes. He thinks that if the main function of zebra stripes were cooling by air eddies, then only the nearly horizontal areas on the zebras’ backs should be striped. And Tim Caro, a wildlife biologist at the University of California, Davis, said that he doesn’t think the the Cobbs’ study advances our understanding of the principal evolutionary drivers of these stripe patterns in the animals. His research and that of others indicates that the stripes could deter insects from landing.
At the same time, though, Caro is open to the idea that the stripes have thermal consequences for zebras. He, Horvath and the Cobbs all agree that likely there isn’t only one, single reason zebras have evolved stripes.
What is unequivocal from the results of this new study is that zebras are far more complex and beautiful than we previously imagined. And as global temperatures continue to rise, there is a lot more to learn about them—and from them, perhaps, in order to keep our own cool.
Candice Gaukel Andrews
A multiple award-winning author and writer specializing in nature-travel topics and environmental issues, Candice has traveled around the world, from the Arctic Circle to Antarctica, and from New Zealand to Scotland's far northern, remote regions. Her assignments have been equally diverse, from covering Alaska’s Yukon Quest dogsled race to writing a history of the Galapagos Islands to describing and photographing the national snow-sculpting competition in her home state of Wisconsin. In addition to being a five-time book author, Candice's work has also appeared in several national and international publications, such as "The Huffington Post" and "Outside Magazine Online." To read her web columns and see samples of her nature photography, visit her website at www.candiceandrews.com and like her Nature Traveler Facebook page at www.facebook.com/naturetraveler.
Grevy’s zebra; The Quiet Wonder
Published by ecolife on
Did you know a zebra’s stripe patterns are as unique as a fingerprint!
Imagine in ten or twenty years from now, in a museum, there stands a perfectly preserved beauty. It looks like the common picture of a zebra, but with distinct differences. It is tall with a long narrow neck that supports a long narrow head with a distinct mane. The body is all covered up in distinct black and white thin stripes all the way to its ears. The stripes are not only narrow, but are also closely set and run across the back except their belly and base of the tail.
Ever seen or heard of it? Most of us have not. This, of course is the Grevy’s zebra, a profound and unique member of the zebra family.
The reason why this majestic creature might be frozen in a museum in the years to come is due to its rapid decline in numbers over the years. It is now listed among the endangered species list on the World conservation Union (IUCN). In the 1970s, their numbers were estimated to be 15,000 and currently they have been reduced to only 2500.
The grevy’s zebra stands tall at 1.3 – 1.6 meters, the male ranges in weight between 350 – 450 kilograms and females slightly less, between 350 – 400 kilograms.
The mating period for the grevy’s is in the rainy season between August and October and the gestation period is about 350 – 400 days. A grevy’s young one is called a foal. The foals hang around their mothers for up to three years and suckle for up to three months without drinking water.
In the wild the grevy’s zebra can live up to 20 years under right conditions and in captivity they can go up to 40 years.
Fact: within the first hour of birth a foul can follow any moving zebra and therefore within the first hour of birth, females tend to be very protective of their new born. This is so as to prevent any other females from adopting the new foal as it’s on.
What we see in most of our national parks and reserves and what is most common are the plain zebras. The grevy’s zebra are rarer, found mostly in the northern part of Kenya. In the early years, 1970s, these zebras were found across the horn of Africa region; Somalia, Djibouti, Eritrea, Ethiopia and Kenya. As at now, these rare gems are only found in Northern Kenya and Southern Ethiopia, with Kenya boasting of larger numbers.
A number of factors have contributed to their worrying reduction in numbers.
Habitat loss is the primary cause of the decline over the years. Since the early years, human population has been on the rise continuously. With this comes more demand on environmental resources. In the northern part of Kenya, the communities are majorly pastoralists who keep large number of cattle for their sustenance. This increase in number of cattle greatly affected the grevy’s traditional range areas.
Competition for food; as stated, the pastoral communities have seen an increase in the number of cattle reared over the years. This has also resulted in overgrazing and its negative effects such as erosion, further putting a strain on the pasture available for the grevy’s zebra. They primarily eat grass and times leaves, spending 60% of their time grazing and this time increases when the pasture is less.
Declining water; although the grevy’s zebra can go up to five days without water, the female however needs water on a daily basis, during the lactating period. As it has been witnessed over the years, water sources have been on the decline due to climate change, pollution, overdrawing and exclusion. Climate change has resulted in very little rainfall and further spread of heat and dry conditions. This has in turn resulted in drying up of the water holes and water points. The Ewaso Ngiro river basin is a very important water source for the grevy’s zebra. Due to over extraction upstream for irrigation purposes, the volume of water has greatly decreased.
Culture; Some cultures believe in the medicinal value of the grevy’s meat and fat. In order to get this, the zebras have to be hunted and killed. Another negative cultural effect is just simply the disregard of their importance. This plays out when the community members chase away the zebras from the water sources.
Poaching and predation; Over the years, the grevy’s zebras have been massively hunted and killed (poached) for their beautiful and uniquely stripped skin. This has been greatly demanded by the fashion industry and market.
Other inevitable factors have also been diseases and infestation. Sometimes cattle can transmit diseases like anthrax to the zebras.
Biodiversity and Intrinsic value: The fact that the grevy’s zebras exist makes them of great importance and a national treasure to the country. This warrants their protection and right to survive. They are only found in two countries on earth and Kenya boasts of having the largest numbers. Laikipia County has the most population; however they can also be found in Marsabit, Meru, Isiolo and of course Samburu areas. they therefore contribute to the biodiversity of these areas.
Economic contribution: since the zebra is a tourist attraction, it therefore contributes to the over 12 percent of the country’s Gross Domestic Product (GDP) .Apart from the national contribution, tourism also contributes greatly to local economies. This is through the associated businesses such curio shops, sale of traditional beads and other shops and establishments that local communities engage in.
Research and academic purposes: Kenya being among the two countries with the population places us at a special position to support research opportunities and academia from across the world. This is an avenue to involve school children in conservation at an early age.
Way forward and Successes
As Wangari Maathai one stated “I’m very conscious of the fact that one can’t do it alone. It is team work. When you do it alone you run the risk that when you are no longer there nobody else will do it” this is the reason why a multi-collaborative approach is important.
All is not lost however; the situation is not entirely doom and gloom. Recent efforts to improve on the grevy’s population have borne fruits and numbers have reported increased from 2350 in 2016 to 2812 currently. This is according to the recent KWS Grevy’s Zebra Conservation and Research Conference.
There have been efforts from local and national government, conservancies, international and local organizations to ensure the survival of these zebras.
There have been efforts to ensure a steady number of the zebras and their success has been mainly attributed to the full involvement of the local communities in every step and effort. The locals are the ones who directly interact with nature and therefore have the best understanding of what works and what is needed. They are the first conservation experts.
Top among the efforts is land use planning within communities. This simply entails dividing grazing lands and rotation of the livestock. It is a method that has in time resulted in positive results. It gives time for the degraded land to regrow new grass and additionally, the cattle droppings also serve as manure.
Another range of efforts have been the conservancies and reserves. 90 percent of the current grevy’s zebra populations are in protected areas such as the Lewa conservancy. This is a better way to monitor the populations and ensure their well-being and survival.
Awareness campaigns within communities and general public also helps in bringing about conversation around the topic. This has been through directly involving communities in monitoring the zebra well-being and reporting any concerning case. Another way has been through the use of mainstream media to create general public awareness on the plight of the zebras as well as efforts and how one can help.
So what can you do?
Participate in the initiatives such as the most recent Great Grevy’s Rally, an opportunity to learn, create awareness and support the programs. Visit the conservancies and learn more about these rare animals first hand and practically.
The Grevy’ s Zebra in its own right and uniqueness serves to bring a balance that we shouldn’t wait to find out about it when there is only one remaining.