Zebras and evolution

Please consider the images to be copyrighted and ask permission before using any of them. Thank you. DEClapp

This is a much delayed return trip to Africa. I spent many many years with at least one visit to Africa. I ended up with well over fifty safari outings and a lot of time crammed into an airplane. These were my favorite trips (even with the flights), my favorite ecosystems, my favorite animal assemblages, and my favorite people. It will be difficult not to spill all my stories in this first Africa post in a couple years. But I am going to pace myself and start off with maybe ten posts that deal with the grazers and browsers of this great continent. If you look back through the ontheroadwithdec posts it is back in 2018 when I last did a series on Africa and then in 2017 and all the years before that there are lots of African posts. In most of those posts there was a lot of predator imagery and gee whiz moments. But the great game parks of southern and east Africa are huge complex systems all functioning from the ground up. Or perhaps from the sun down. It is sunshine, water, elevation, soils, vegetation, microbes and fungi that provide the matrix for those predators to exist. The next level down from the predators are the masses of warthogs, antelope, gazelles, buffalo, zebra, giraffe, hippopotamus, rhinoceros, and elephant; the vegetation eaters – the great mass of vegans that roam the land and feed the lions.

So, I am going to do a series on those aforementioned mammals. Many are called ungulates which nowadays refers simply to a “hoofed” animal. In the earlier days the word ungulate referred to specific groups of hoofed animals but taxonomy has developed to the point where general terms are left behind and specific nomenclature has developed that is more accurate both in field use and now in genetic relationships as well. A bit of background is needed and then we will move right into some chatter about the striped horse of Africa.

There are lots of smaller animals that are usually preyed on and don’t usually predate. These animals include rodents, rabbits & hares, hyrax, elephants, and the various ungulates. There are predators that don’t get our (human) juices running; smaller animals like the bats, moles, shrews, monkeys, aardvark and pangolin. Each of those is in fact a hunter, a predator, but somehow we don’t get all excited about fly-eaters and termite-hunters. So for now we will leave those alone and in the wings waiting for their day to arrive.

There is one last bit of information needed as we look into the grazers and browsers of the African plains (grasslands for the most part) and that is how they are generally divided and classified. About 65,000,000 years ago mammals were sprung free from the dinosaur-dominated world when an asteroid crashed into our planet causing a great and nearly complete annihilation of life at that time. This was the end of the Age of Reptiles and the beginning of the earth and wildlife that we see today. Oh, there have been tens of millions of changes in the past 65,000,000 years but it was at the moment of that great collision that the door opened to life as we know it and the flighted dinosaurs (birds) and shrew-like mammals oozed out from under the diminishing reptilian shadows. The dinosaurs still exist as our feathered vertebrates, the birds; and those tiny mammals have taken over the air, land and sea as bats, gazelles, and whales; oh yes, and as humans, rats, chipmunks, and lemurs.

The common ancestor for all the horses and asses (donkeys) is seen in fossils about 4.5 million years ago; found (surprisingly) in Canada. They entered Eurasia about 3 million years ago (other references say as many as 11 million years ago) and into Africa about 2.3 MYA. The equines (horses) started to develop from a small animal with five toes. Over time the group has evolved to have only one toe on the ground. The many-toed equines and the single-toed group coexisted for millions of years. They were only 20 inches tall back in those post-asteroid millennia and slowly evolved in what is North America today and eventually spread back to Europe, Asia, and finally down into Africa. As the climate changed and the land dried out the more efficient single-toed horses were best suited and survived; the three-toed horses disappeared. There are three zebra types in Africa, all now in the same Genus; The Plains (Burchell’s), the Mountain, and the Grevy’s. There was a fourth, though perhaps it was just another form or population, called the Quagga that lived in southern Africa into the 1800’s.

Let’s look at some images….

The Migration is a never ending year round event; following the rains and locating green grasses. The wildebeest (White-bearded Gnu), zebra, and many antelope move from the Maasai Mara in Kenya to the east and south over the Ngorongoro Highlands and down into the grasslands of the Serengeti well into Tanzania. Once on the Serengeti they drop their young and rebuild their bodies. They have found the rains and the green vegetation that they need. However the Serengeti grasses wear out and the rains stop and the herds are again forced to move; this time to the west and then north back into Kenya and up into the Mara grasslands. It is here that they can again stop for a few months and eat and mate. But again the rains stop and the need to move arises — this is the annual migration. The renowned anthropologist Mary Leaky always wrote of, and spoke of, the migration in capital letters; it was always The Migration, and she tried throughout her life to get out to the Ngorongoro Crater area each year to be awed and humbled by the moving streams of animals passing southward into the grasslands below.
When heading back north into Kenya there are two river crossings. These sites are not on most safari routes and I am afraid that the image above is pretty bad – it was a “film” shot that I have digitized; sorry. But it shows part of the greatest show on earth. The migration is mostly wildebeest and zebra. They are not one huge mass of two or three million animals but more like streams running parallel to each other head down into the sea of grass. Some groups may be only a few dozen and others may be a mile-long train of hundreds. Once they reach the grasslands there can be tens of thousands together, great beasts by the thousands all enjoying the new grasses they traveled so far to intercept.
Those river crossings are especially chaotic. Zebra travel as a family, or so the stallion would like to think. There is one stallion, a few females, and the young of that year. The male wants the group to stay together but there are hundreds and hundreds of family groups trying to get up the courage to enter the water. So like a good male he starts yelling – and like kids everywhere – he is often ignored. In a normal day of walking on a trail through the Serengeti the male can keep track of his gang pretty easily. But when they get to the river he loses control. Youngsters start to swim away toward Kenya, he calls them back and they sometimes turn and start swimming back into the hundreds of animals heading toward them. Families of zebra and hundreds of wildebeest are soon mixed up in the blender of the river crossing. Thousands of wildebeest and hundreds of zebra swim with passion and purpose to get to the other side, only vaguely aware that Nile Crocodiles have been waiting months for them to arrive. It is a noisy, dusty madhouse.
Once on land and stopped to eat they are immediately sought out by pesky flies. Though is seems that the black and white stripes may have evolved to keep tsetse flies at bay, they often stand as shown above and shake their manes and flash their tails to keep the insects moving. Always good to have a friend. The stripes have been explained many ways; to disrupt predators, to camouflage in the wooded savannah, or to help regulate body temperature but the most convincing research suggests that tsetse flies don’t like to land on a ruptive surface and so they generally keep away from zebras. I have been bitten by many a tsetse fly over the years and I think it only reasonable to evolve stripes to repel them; I would ooze DEET if only I could. The tsetse fly is the carrier of a parasite that can cause East African trypanosomiasis. Most flies do not carry the parasite but the bite is quite a painful nuisance. Tsetse flies are not very common and are rather specific to their chosen habitat. On most safaris the tourists will never see or feel a Tsetse Fly; but it is something to ask about each day as you start off into the bush.
The zebra stallion has to stay with his family group. The females can be stolen and the youngsters are, well, they are youngsters. This is a stallion standing over the body of one of his females as they were arriving onto the Serengeti near Naabi Hill and the Ndutu road. She is full with child and simply dropped dead as she was walking along. You never know about these things and conjecture is merely conjecture; perhaps something to do with her pregnancy, perhaps some bad food or water, or a genetic disorder, we don’t know. But the picture tells a tale. The male stayed for maybe five minutes but had to leave her and gather the others together. The rest of his family was moving along with the migratory wave and he would lose all and everything if he waited to long. He checked her and nuzzled a bit. He looked toward his receding family. He scattered the arriving vultures once or twice and then turned and followed the remaining mares and young into the grasslands. By the way, a White-backed Vulture, like this one, cannot open up a newly deceased zebra. The carrion-eating birds will eat the soft parts (eyes, tongue, lips, anus) and wait for hyenas, lions, or the passage of time to open the body.

The zebra of the southern countries (South Africa, Botswana, Zimbabwe, Zambia, Angola, and Namibia) are a bit different. Climate change during the past few thousand years has isolated populations of all sorts of animals and zebra are no different. The habitat and climate of East Africa requires a great migration where the habitats in southern Africa do not. Oh, the animals move according to the weather and the loss of food sources but they do not move in the great waves that we see in east Africa. They are on different land, different soil, with different plants, and have had to accommodate different pressures. Thus they look a bit different and behave differently as well. This is simply survival of the most fit, the best adapted to the current habitat, and the tendency for a population to look different over time.

The zebras shown in the first images were all Plains Zebra; or Common Zebra or Burchell’s Zebra. They are rather sharply marked with black and white stripes. As you move south the animals become a bit more hazy with a dusky gray “shadow” stripe often showing in between the black stripes. The zebra above is from South Africa and is rather typical of zebra in the southern part of Africa. Most of the open grassland habitat is found in Kenya and Tanzania where the sharply black and white zebra live and the southern animals have habitat that is a bit more wooded. Perhaps this has something to do with their tendency toward shadow striping.
The shadow stripes are more obvious on the rump as you can see in this animal. This habitat is also rather typical of that found in the southern african country’s of South Africa, Botswana, Zambia, Zimbabwe, and parts of Namibia. The dry rugged portion of Namibia has another zebra type called the Mountain Zebra
Youngsters are born in December-March in the Serengeti as the herds arrive in the southern part of the migratory route, but in southern Africa there is much less of a migration and youngsters are born throughout the year. The gestation for all zebra is about 380 days or a year and a few weeks. The young will stay with the family unit for about one year and then go off and join a “herd”. As they mature they will form their own family units.They will live to be thirty years or more in the wild. But many don’t.
Many of the safari destinations are national parks. Many of the national parks manage water to move wildlife around and to keep naturally wet areas from being over used. A water hole offers photographic opportunities and you can find animals at water holes most any time of day. Grazing animals get moisture from the grasses they eat but almost all large animals will use a water hole at some time each day.
This zebra could be from the northern population as it has sharply black and white stripes, but it also has a modest shadow stripe. It is from the northern population. The bird on the zebra’s back is a kind of specialized starling called an oxpecker; a Red-billed Oxpecker in this case. This species, and its Yellow-billed cousin, make a living by cleaning the larger animals of the plains. They will travel in smallish groups, family groups most likely, and stay with the big mammals day after day. They will pick ticks, and lice and flies from the ears and noses of Cape Buffalo, giraffes, zebra, and most antelope and gazelles. They will find ticks and insect larvae in the “legpits” of the big herbivores. They will also peel and eat scabs from the skin of these animals and return the next day to get the newer scab as well. There is a starling called Fischer’s Starling that travels in more starling-like tight flocks that is also a predator of the insects that bother big mammals.
This is another older image take north of the equator in Kenya. North of the equator doesn’t seem like much of geographical designation but in east Africas there is quite a real meaning to the phrase. There are Reticulated Giraffe, Gerenuk, and Grevy’s Zebra north of the equator but not south of it. It’s a wonder. Anyway, this old image is of a fine, and finely striped, Grevy’s Zebra. It is a northern animal of east Africa, and one at great risk for reasons I will explain in the future . The legs are well marked and the belly is white. As I said there will be more later of these “north of the equator” animals.
Lastly a rather hot and hazy image of the Hartmann’s Zebra, one of the Mountain Zebras. This is a species (most taxonomists think it’s a species) that is found in arid, high rugged locations in South Africa, Angola, and mostly in Namibia. They are in mountains that get moisture from the ocean and thus provide water year round. But it is not water from rainfall for the most part. These animals are more solidly built than the Common Zebra and the three or four very broad and bold rump stripes are a definitive marker. As there are no other zebras in the habitat these animals utilize, identification can be done by geography. If you are in a very remote part of western Namibia or southwestern Angola in hot and arid region with some elevation and you see a zebra – bingo, it’s a Hartmann’s Mountain Zebra. There is still a tiny population of the Cape Mountain Zebra in South Africa, but a very small population and for the most part not really wild.

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