White Rhinoceros – The Last Rung in My Big–Five Ladder

South Africa: 2007

For the past 45 minutes I’d crouched immobile behind a low thornbush on the edge of a 20–acre grass–covered meadow, watching five rhinos graze. Moving their enormous heads from side to side, they cut a swath through the field, ingesting an impressive amount of green groceries.

A slight wind was blowing in our direction; the quarry was completely unaware of our presence. When first spotted, they were approximately 70 yards off and had come no closer during their recent machinations. In the last three minutes, this situation changed. Two of the rhino, one with the largest horn, grazed in our direction moving from my left to right. The smaller one came to within 20 yards of us, while the larger was approximately 50 yards away.

 

For reasons known only to them, both rhino suddenly stopped not agitated, just frozen. The larger rhino was partially obscured by the closer. I held the dart gun on ‘ready.’ Carl had set the pressure for a distance of approximately 50 yards. Barry’s hands tightened on his .470 Krieghoff Classic double rifle just in case! Lady Luck smiled. After two to three minutes (it seemed a lot longer) the larger rhino walked forward, giving me an unobstructed view.

 

A moment of truth had arrived. I sighted the red dot on its right shoulder and squeezed the trigger. Following the whooshing sound as the dart flew, I could see the red tip impaled on the rhino’s shoulder. Startled by the sound, both rhino charged forward full speed luckily, not in our direction. They were joined by their companions and rapidly ran downhill. I breathed a sigh of relief and felt elated. Perhaps my final quest was over.

 

Six months prior this event, I had little interest in hunting a southern white rhinoceros. On two previous occasions I’d seen them in the wild and neither encounter had whetted my appetite to hunt these apparently docile behemoths. However, last fall I shot a very large male leopard in Namibia, and now had four of the African Big Five, all of record–book quality. I needed only a rhinoceros to complete SCI’s African Big Five Grand Slam.

 

The major impediment to my shooting a rhinoceros was the kill fee – at least $50,000… Out of the question. On the other hand, I could afford the substantially less cost of darting one of these ‘Pleistocene holdovers.’ Frank Cole of Cabela’s Outdoor Adventures arranged for me to hunt with Barry Burchell of Frontier Safaris. The hunt was to include darting a rhino, hunting caracal with Barry’s hounds, and introducing my daughter, Ruth Ann, to big–game hunting.

 

Accordingly, we arrived in Port Elizabeth in April after the obligatory 24–hour air travel. The facilities of the game ranch were very impressive. Approximately 50 miles inland from the Eastern Cape, the spectacular hilly terrain was sparsely covered with small bushes and short trees. The weather, early winter, was dry and the temperature ideal.

 

The first day, while getting over the jet lag, Ruth Ann practised shooting Barry’s Ruger Model 77 .270 calibre rifle. That afternoon she killed her first big–game trophy a very impressive Cape kudu bull.

 

The next morning, we drove 30 miles to the Lalibela Game Reserve through heavy fog and met PH Carl van Zyl, our primary guide. The veterinarian, a delightful individual, showed me the ins and outs of using his dart gun. This gun had a long, thin barrel and a red–dot sight. The maximum range was 50 yards. He made it very clear that, due to the parabolic trajectory of the dart, the precise distance to the quarry must to be known. (If the rhino was 20 yards away and the gun was set at 50 yards, the dart would go over its back. Conversely, if the rhino was 50 yards away and the gun was set at 20 yards, the dart would hit the dirt before reaching the rhino.) I practised several times, and managed to hit a small cardboard box.

 

We piled into a Land Cruiser and went hunting for rhino, first encountering a female rhino with a young calf. She didn’t seem too perturbed at our presence, but it was obvious she expected us to move on which we did. After about an hour, we found five grown rhinos in a grassy meadow and crawled slowly to the edge. One rhino had a trophy–quality large horn. Frankly, at that juncture, I could have borrowed Barry’s .470 Krieghoff and killed the rhino without further ado not a particularly challenging event, to say the least. However, since I was on a darting mission, the next 45 minutes were filled with excitement and anticipation as I sat still and waited…

 

After the rhinos had left the field, they soon disappeared from our view. Carl whistled for the crew to bring the vehicle and pick up Ruth Ann and the vet who’d hidden behind a tree about 75 yards behind us to watch the spectacle. All boarded, we followed the path made by the rhinos as they ran downhill into a ravine and spotted the darted rhino in thick bush – about 750 yards in all.

 

We gingerly approached the downed behemoth, but it became clear that the animal couldn’t move. Its respiration was shallow and rapid and its skin felt quite hot. The vet quickly began taking horn measurements, drawing blood samples, administering antibiotics, etc. The rest of the crew chopped down the nearby brush so that the rhino could be photographed. The dart was still in place; it had been driven in exactly perpendicular to the surface. This is important so that the sedating agent was injected directly into the muscle and not into the very thick skin.

 

After about 15 minutes, the dart was pulled out – we were ready to begin the final step. With all of us aboard, the vehicle was turned around and made ready to exit. The vet administered the antidote and hot–footed it back to the truck. The rhino seemed to shake itself somewhat and attempted to rise. We made a circle and returned higher up on the hill. By that time, approximately five minutes had elapsed. The rhino was up and walking around unsteadily, but headed in the direction of his departed buddies. Ten minutes later, we saw him grazing with the group as though nothing had happened.

 

Carl had told us that this was only the second rhino they’d darted, and that it had never been darted before. Also, they would not dart any animal more than once a year. He said that this darting episode had gone as smoothly as he’d experienced. (The next day, I received a certificate of the horn measurements for the SCI Record Book. A fibreglass replica of the horn using these measurements would be sent later.)

 

We drove back to Barry’s ranch. That afternoon, about 3 p.m., we rode in the high hills looking for smaller plains game. The scenery was absolutely spectacular, and we saw a number of different species. Just as the sun began to set, Barry decided to drive through an area of pines that looked much like Virginia spruce pine to look for a bushbuck with impressive horns.

 

Barry spotted the animal approximately 120 yards off. Ruth Ann put the rifle on the shooting sticks, but couldn’t see the bushbuck in spite of Barry’s directions. Finally, he said, “Do you see that brown rock?” She concurred. “Shoot the rock!” She did – and the bushbuck promptly fell.

 

We had an early start the next morning to hunt caracal. The hounds were turned out close to the lodge where two caracals had been seen crossing the road the day before. The handlers released the hounds and walked with them in a brush–covered valley while we remained on the crest of the hill watching their progress. After about 30 minutes, we heard the dogs strike. It soon became quite clear they’d jumped a predator. They ran in full cry for about 30 minutes, finally baying a caracal within about 300 yards of us. When we arrived at the tree, a large male clung to a branch that was densely covered by leaves. Although it was quite visible when I was close, from more than 10 feet away the cat was totally obscured by the foliage. This created a difficult situation because the rifle had a telescopic sight mounted close to the receiver. If I moved far enough away to see clearly through the telescope, the caracal was obscured by the leaves. At a short range, when the cat was visible, the scope couldn’t be focused. In desperation, I sighted down the left side of the barrel and guessed where the bullet should travel.

 

By sheer luck I killed the caracal. The cat fell out of the tree and was immediately retrieved by one of the handlers so that the hounds couldn’t tear the hide.

 

That afternoon, we drove to the edge of the Karoo dry–lands, approximately 75 miles north–west, where the terrain was flatter and the vegetation sparse – where Rush Ann completed her goal to acquire three antelope with her springbok. Barry told us that when springboks run a lot or are excited, the hairs on the back exude a particular odour much like cotton candy.

 

After a day of rest we began the tiring, boring long flight home. In the air, I relived the experience and mulled over the future. I’ve hunted four African countries and taken the Big Five. This safari clearly was not as high a level of excitement as I’d experienced before, but it certainly was far more of a challenge than killing the rhino would have been. I’m certain that our rhino was happier regarding the chosen alternative. In any case, I’ve now climbed the final rung in the African Big Five ladder.

Biography

 

Joseph C. Greenfield, Jr. is Professor of Medicine at Duke University. After stepping down as Chairman of the Department of Medicine, he hunted dangerous game on 12 safaris to four African. A number of these are chronicled in “Bwana Babu,” published in 2006 by Safari Press.

Last Chapter: Ninety Miles of Gravel

Cameroon: 2010

I went out the last morning of hunting and, except for a few baboons and some oribi that I never did spot, it was pretty quiet. By this time it was no great surprise to me.

 

René dug up some more roots and cut off some more bark to be made into manly medicine to keep his three wives back at the village happy. Occasionally he would set a fire in the long grass and if he and the tracker took too long, I would get up when I thought that we had rested long enough, make a few dorky dance moves… They always took the hint and away we would march. We did track one more roan that day, but again the beast was never spotted and eventually we started the long walk back to camp.

 

When I got back to camp I spotted my buddy Phill, and I swear that poor guy looked like 90 miles of gravel. He was about done. Sadly, around 10.00 a.m. that morning they’d come across the fresh spoor of a herd of buffalo heading into the mountains. With eight hours of daylight remaining, there was a chance to snatch victory out of the jaws of defeat. A buffalo bull is never to be despised and is certainly worth all the trouble and expense we had undergone to be there.

 

My great friend, totally worn out, declined to follow up the tracks and ended the hunt. I think that everyone involved was so disappointed. I sure in the hell was.

That evening we had the men come up one at a time and gave them each a tip and a brand–new panga. Cam Grieg had suggested the amounts for the tips, and mentioned that if more money were given, the guys would buy guns and/or ammunition and shoot game.  I should have packed some clothes/watches or something to augment the tips, but I really didn’t have any room in my suitcases. And money is always good.

 

When we broke camp early the next day, we had to make almost a seven–hour detour to the north to pay for the buffalo at the office that was in charge of such things. It was nice to see some new country along the way, and we were in no great hurry to get to town anyway, as the train left at 6.00 p.m. the following day. One always leaves a lot of extra time to allow for breakdowns in that country. Even the train was not beyond such things.

 

Daniel set us up in a $33–a–night motel back in Ngoundéré and we both quite liked the place. Phill had been craving a cold beer a few days earlier so when he went to his room to shower and rest for a while I sent the local cook/waitress out for two cold beers for my friend.

 

Later:

Me: Phill, I got the girl who works here to go out and get you a cold beer!
Phill: It had better not be Guinness!
Me: No! No! I saw the two bottles. They’re not Guinness.
Phill: Well, O.K. I’ll have a little. But what I really want is cold milk or iced tea.

 

That night the lady made us up some tasty but rather tough chicken and chips for supper. The meal for the two of us cost 8,000 Cameroon francs – about $16.00. I was happy with that but did wonder if they whacked the chicken as it was running a marathon race past the restaurant.

 

I really wanted to contact my wife, Margaret, after the satellite phone fiasco so Daniel and I walked down town about 7.00 p.m. As we left the gated compound we had to walk by about 10 or 12 men yelling at each other in the dark. We were about three feet from them as we walked by. A few big rigs were parked there and obviously the men were not happy about something. I probably should have taken a few flash pictures of the angry guys, but I have yet to descend into total stupidity.

 

I had no luck getting into the hotmail account, but I did try. We came back with Coke and watermelon and some oranges. All this pleased Ol’ Sir Phull.

 

The next morning Phill did his very best to get the cook to make him some fried eggs, over easy. He explained verbally, he drew pictures, he had a tracker there that could speak some English and had that guy explain it in French to the lady. And then he followed her into her tiny restaurant, grabbed an egg, pantomimed putting it in a frying pan that was sitting there… paused… pretended that he took the egg out of the pan onto a plate.

 

Twenty minutes later, my delicious ordered omelette was handed to me. Phill got a couple of eggs fried together, flipped over as an omelette and handed to him. He was not at all happy, as fried eggs are of utmost importance in his universe.

 

A day later he was wanted to order Coke and bitters from a lady in a bar in the last hotel we stayed at.  Wasn’t going to happen, and he quickly realized that when I pointed out the absurdity of the wish.

 

As a change of pace, we ordered fish and chips for lunch and were given a complete little fish on a plate. I’m happy to say that it was delicious. After that, our ride to the train depot showed up, and we grabbed our gear and drove away. Phill forgot to pay, I didn’t. I left my motel key in the room; Phill handed his to Daniel later that night a few hours into the train ride.

 

We did the long train ride, and again we had chicken for our evening meal. Hard to know how they kill them as they’re tough old birds. But tasty.

 

We told Daniel we were willing to pay more money for a hotel room as Phill was craving air–conditioning. As so often happened on this trip Daniel listened carefully, agreed totally, and then took us back to the old hotel where nothing worked including the air–conditioning.

 

It wasn’t all bad – Phill finally got his fried eggs the next morning. The waiter not only could speak English, but also knew enough not to bring the change back after the meal, so Phill ended up giving the chap about a four–dollar tip.

 

On the trip downtown I had the pleasure of watching a traffic cop in a traffic circle go nuts! Some dude in a car had offended him and he was shouting at the fellow, and then started kicking the front of his car, then kicked down on his hood denting it. From there he went around to the side of the rapidly depreciating automobile and started kicking in the side! Suddenly, from out of nowhere came the only jeep that I was to see in Cameroon. It was driven by another cop who rammed the car head on!

 

Later we drove by the poor shell–shocked fellow. He was having a very bad day. I think that he was in the wrong lane, but since most drivers in that city drive like they’re insane, I’m not exactly sure what set off the copper.

 

After a shopping trip that was mostly a fiasco, we spent the last six hours in Cameroon in Daniel’s house watching music videos. The Cameroon chicks sure like to shake their booty…

 

Pascal, our driver, did not show up to take us to the airport. Daniel got on the phone and yelled for a while. He then drove us to the main road and waited. Once again he got on his cell phone and did some more yelling.

 

Eventually, Pascal showed up with his little boy. He got behind the wheel and started shouting at Daniel as he drove. Daniel was now silent. Pascal next phoned some lady and hollered at her.

The airport was about 10 miles away and we had five hours to get there. Pascal tried to do it in five minutes. About eight miles into the trip, and after just missing another head–on collision, I saw Phill putting on his seatbelt. My nerves might have been getting a bit frayed about then as I snarled at him, “Are you nuts? Now you’re putting on your seat belt?”

 

My big consolation in all this was that if I got killed in a head–on, Pascal was not going to be getting any tip from me! On that I was adamant.

 

At the airport we got our guns cleared for take–off … a nice lady wanted elephant meat but we had shot no jumbo. Daniel gave the official a bribe when all the paperwork was done.

 

Later, we went through security and the lady cop hit me for 5,000 francs. She pointed at her breast and said, “Pour moi.” I gave her the nasty bribe and, now that I think about it, being a man (and all men being pigs), if she’d taken off her blouse, I might have given her 10,000 francs and there would have been no hard feelings…

 

Phill was taken for 3,000 francs. He was sent to the same lady with the person doing the sending saying, “An American. They will take him.” Or some such comment of what was about to happen.

 

On the long flight to Zurich, Phill finally got his milk that he had wanted for so long.

 

It was warm.

Biography

 

Richard Powell is an average–looking, middle–aged (if he lives to be in his 120s) redneck from Alberta, Canada. The chap with the silver Fu Manchu moustache writes hunting books of assorted misadventures in Africa, and in North and South America. His tenth book, “Obsession” will be published this year.

The Common Zebra is an Uncommon Mammal

The Common Zebra is an uncommon mammal Richard D Estes, PhD, explores the evolutionary rationale behind this most intriguing paradox.

 

If you have ever tried to sex and age the Common or Plains Zebra, you will know it is hard work. Eagle-eyed driver-guides will tell you that the stallions have brighter, more contrasting stripes, but I find that method unreliable. Wildlife researchers and managers tasked with telling the sexes apart can also pick out mature stallions from their more robust build, especially as reflected in their necks, which are thicker than those of mares. And it helps to know that herd stallions usually bring up the rear of a family unit. But the most reliable way to ID the sex of both adults and young is from a full rear view. 

 

The female’s vulva forms a broad band of black skin between the buttocks. Males also have bare black skin extending down from the anus, but this extends only a short way and is of a more triangular shape. The difference is not always clear, however – you really need an under-tail good look. But why is this scrutiny necessary? Why not just check out the male’s external genitalia? Because these are hard to see, that’s why. Seen from the rear, the testes blend in with the broad black stripe running along the belly midline, and the hind legs obscure the penile sheath except in a three-quarter view looking from front to back.

 

The difficulty of telling males and females apart begs the question: why is the Common Zebra the hardest of all plains game to sex and to age (with the possible exception of the oryx)? Such species contradict Darwin’s theory of sexual selection (Darwin 1871), according to which zebra stallions should look very different from mares. The theory holds that, in polygynous mating systems, in which some males can monopolize mating with more than one female at the expense of other males, male sexual competition (coupled with female preference) will lead to increased size and conspicuous display organs – that is to say, pronounced sexual dimorphism.

 

The Plains Zebra has an unusual (in mammals) harem social/mating system, shared by the Mountain Zebra and the horse, where stallions own harems numbering as many as five or six mares, captured one by one in fierce competition. Mare-less stallions associate in all-male (bachelor) groups.

 

Clearly then, the Common Zebra is an exception to Darwin’s theory. How come? I was confronted with the same paradox in my studies of antelopes. The wildebeest, subject of my PhD dissertation and later research, also displays minimal sexual dimorphism despite being highly polygynous. Females even have a faux penile tuft that makes it harder to determine gender. When I am recording the sex and age of a long line of passing gnus, I rely on differences in the horns, which are thicker and wider in the males. The same applies to the related topi and blesbok. In the oryx, however, females have horns as long as or longer than the males’ horns, and sport identical, highly conspicuous colouring and markings. Even the penile sheath is inconspicuous.

 

It took me decades to come up with a plausible explanation. The first clue emerged when I made a survey of the social and mating systems of the 72 species of African Bovidae, comprising antelopes, sheep and goats, and the buffalo, for a symposium on the behaviour of hoofed mammals (Estes 1974). It turned out that nearly all the herd forming (i.e. sociable) species with minimal sexual dimorphism live for at least part of the year in aggregations that include adults of both sexes. There had to be some kind of counter-selection, I reasoned, against development of conspicuous male secondary characters in species that live in sexually integrated groups.

 

Conversely, species with pronounced sexual dimorphism (such as impala, sable, Grant’s gazelle and kob) tend to remain segregated according to sex and age except for breeding. In territorial species, only males with exclusive territories succeed in breeding. The small über-class of breeding males enforces separation of bachelor males from females and young. Non-territorial bovids – notably kudu, nyala, eland, cattle, goats and sheep – are still more sexually dimorphic, and are also the most segregated. Male sexual competition is more rigorous in such dominance-hierarchy breeding systems, causing males to keep growing long after females mature, while at the same time developing the most extreme gender differences in size and display organs.

 

What is the source of selection that counters male peer competition for conspicuous secondary characters? Broadening the scope of the inquiry to other classes of vertebrates, we find that the sexes are virtually indistinguishable in schools of many fish species and in many birds that live in flocks. Pigeons, geese, and swans come to mind – “Birds of a feather flock together,” as the saying goes. It is clear that in such societies natural selection would weed out individuals that fail to fit the mold; ones that are different are likely to be peripheral to the school or flock and are most likely to be picked off by predators. An outstanding characteristic of these schools and flocks is the wonderful coordination of all the members; they wheel and turn simultaneously as though responding to an unseen conductor.

 

Could any of this information help explain the case of the zebra? I think it can:

    A. Minimal sexual dimorphism correlates with living in mixed groups. The closer the resemblance between the sexes, the more integrated and coordinated are group movements.
    B. Obvious sexual dimorphism correlates with sexual segregation. Males and females live in largely separate societies except for breeding males that, intolerant of potential rivals, are the enforcers of segregation.

How might these findings apply to Plains- Zebra society? In zebra aggregations, you have herds of bachelor stallions interspersed with families of females and young, each guarded by a stallion. Herd stallions interact with one another and with bachelors, yet rarely fight; most encounters take the form of the greeting ceremony. This is really a test of fitness, whereby a herd stallion serves notice that he is the owner of a group of females and young. An illustration of the greeting ceremony adorns the cover of my book, The Safari Companion (Estes 1999).

 

The respect of a stallion’s right of ownership is remarkable; it is comparable with the respect of the property rights of territorial males. In both systems, males have made a huge effort to win mating rights, and are prepared to defend those rights against all comers.

 

Probably the harem system of the Plains and Mountain Zebra and the horse evolved from a territorial system, which persists in other extant members of the family: the wild asses and Grevy’s Zebra. My colleague, Hans Klingel, who carried out his seminal study of Plains Zebra socio-ecology at the same time as I was studying the Ngorongoro wildebeest (1967; in press), believes that early equids such as the ‘dawn horse’ Eohippus defended resource territories like solitary antelopes (e.g. did-dik, oribi, blue duiker).

 

By exchanging ownership of real estate for ownership of females, the Plains Zebra and the horse gained the freedom to lead a nomadic existence, whether in separate herds or in aggregations of many units. This very unusual social and mating system largely explains why the Plains Zebra is – and why the undomesticated horse was – among the most numerous and successful of hoofed mammals.

 

As a consequence of the gentleman’s agreement about ownership of mares, males compete mainly over fillies. Now we’re talking about serious fights. Beginning in their second year (indeed, as early as 18 months), females come into heat for as many as five days every month. They advertise their condition by frequent urination and a conspicuous posture with hind legs straddled and tail slightly raised. Reacting to this come-on, stallions converge from far and wide, each hell bent on adding a filly to his own harem. They fight with the father, who behaves as though his mares were up for grabs, and with one another. Battles lasting for hours and whole days test the mettle and endurance of the contestants . Eventually a stallion succeeds in abducting the filly, which – after a trial period perhaps lasting weeks – is accepted into the company of mares already in the seraglio.

 

Adult mares display the estrous posture only immediately before copulation, ensuring that other stallions are not attracted and the family is left in peace. When approached by a stallion, and during copulation, young and adult mares assume a facial expression that Germans call Rossigskeitgesicht – a splendid term with the mundane English translation “mare-in-heat face”. This display also signals submission.

 

Unfortunately for the stallion that abducted her, however, the filly comes into estrus again a month later. The battle royal begins all over again and he may well lose her to another stallion. And she keeps coming into heat without becoming pregnant for up to a year. When she is finally in foal, the filly settles down for good in the sire’s harem.

 

The resemblance between male and female Plains Zebras is close enough that, in a band containing family and bachelor groups, it is behaviour, rather than looks, that makes the stallions stand out. The herding (Fig. 5) and greeting behaviour of herd stallions and the horsing around often seen in bachelor herds are a give-away. Call me crazy, but I see a parallel between zebras and pigeons (which I kept as a child). Like zebras, male pigeons are a bit more robust than females, but you cannot pick them out in a flock until the males start courting and fighting.

 

Alert readers may at this stage be saying to themselves: “This is all very well, maybe even interesting, but the real question – how did this masking of male secondary characters came about – remains unanswered.” Point taken… My attempt to account for this looks at the zebra’s presumed ancestral social organization and draws on my explanation of minimal sexual dimorphism in wildebeest, oryx, and the like. Both may be considered highly speculative. Indeed, the theory I advanced, in Estes (1991), to account for the condition in bovids is not widely known and has even been discounted – at least by some colleagues of mine who have read the paper.

 

I proposed that male sexual competition comes in two forms with opposite effects: the familiar peer competition that Darwin recognized, and a much less familiar kind called despotic competition that he didn’t. Peer competition, involving males of the same age and development stage, promotes sexual dimorphism. Despotic competition involves aggression by older and bigger males against younger, weaker males. Competition of the latter kind leads to the eviction of adolescent males from female herds when they develop secondary characters that reveal their gender and trigger the aggression of breeding males. Following eviction, the sex ratio, which remains roughly equal as long as both sexes stay in their natal herd and home range, becomes skewed due to higher male mortality rates.

 

Accordingly, natural selection should favour a suppression of male secondary characters until the stage is reached when the benefits of leaving (to join bachelor herds and engage in peer competition) outweigh the costs of skulking in female herds. Considering that the fittest males pass on their genes to far more offspring than females can (large antelopes produce only one calf a year for say eight to ten years), mothers should do whatever they can to promote survival of their sons. The same holds true for zebras and horses, which have a 12- month gestation and can produce only one foal a year.

 

In my obscure 1991 paper, I proposed that female bovids get around the problem of keeping their sons with them, while at the same time allowing them to develop the weapons essential for peer competition, by themselves growing horns and copying other male secondary characters.

 

When horns of similar size and shape are present in both sexes, they cease to be badges of gender. Ditto markings, beards, manes, and other traits evolved by males to advertise their gender. While I know that females with horns use their horns as weapons, I maintain that natural and sexual selection for keeping males with females until they are prepared to join male society is stronger than selection for horns as weapons in females. There is not much evidence, after all, to suggest that horned females are subject to lower predation rates than hornless ones.

 

My theory would explain how it happened that oryx males and females are more alike than, say, wildebeest or topi. These desert species roam widely and exist at very low population densities. Evicted subadult males would be unlikely to find a separate bachelor herd they could join. Consequently, the costs of leaving are greatly outweighed by the benefits of staying. So oryx herds include bachelor males intermixed with females. The alpha male treats them all the same as long as they behave the same: that is, submissively. Female-mimicry of male horns and other markings originally reserved for males to the adult stage might explain how this unusual transformation of an originally territorial mating system came about.

 

Enough said already about bovids, however. This article is supposed to be about a hoofed mammal from an altogether different order: an odd-toed, not an even-toed ungulate. What gave rise to the selection pressure that would account for look-alike male and female Plains Zebras?

 

I cannot even use the argument that the risk of being evicted from the herd is the source of counter-selection, because male offspring are not evicted. In the harem system, selection favours stallions that take a paternal interest in their offspring by allowing them to stay on in the natal family.

 

Eventually, at between two and three years of age, they leave of their own accord and join a bachelor herd, where they remain until mature and ready to start their own harems at five years or so.

 

If the zebra’s ancestors were territorial, then that might explain how it all started. The benefits of staying with the mother in a female herd would select for sons that avoid eviction by territorial stallions through continuing to look like females. Regardless of how the harem system might have come about, minimal sexual dimorphism would facilitate association in aggregations with minimal strife and become what socio-biologists call an evolutionarily stable strategy (ESS).

 

I want to make just one final point: Grevy’s Zebra was once widely distributed in Africa. It is now an endangered relict species that the Plains Zebra has replaced everywhere except in the most arid parts of its former range. The same may be said of the wild asses. This is proof (I would argue) that the nomadic harem system of the Plains Zebra and the horse is superior to the territorial society of the Grevy’s Zebra and the wild asses. Although the explanation I have offered for the Plains Zebra’s lack of sexual dimorphism is pure speculation and is unprovable, I hope that I have made the case that toning down gender differences by reducing male aggressiveness helps Plains Zebras to live together in relative peace.

References: Darwin, C R 1871. The Descent of Man and Selection in Relation to Sex. Appletonn New York.

Estes, R D 1974. Social organization of the African Bovidae. Proceedings of an International Symposium on the Behavior of Ungulates and its Relation to Management. IUCN Special Publication (New Series) No. 24, Morges, Switzerland, pp. 166- 205.

Estes, R D 1991, The significance of horns and other male secondary sexual characters in female bovids. Applied Animal Behavior Science 29: 403-51.

Estes, R D 1999, The Safari Companion. Chelsea Green, White River Junction, VT.

Klingel, H 1967,. Soziale Organisation und Verhalten freilbender Steppenzebras (Equus quagga). Zeitschrift für Tierpsychologie 27: pp. 580-624

Klingel, H (in press). Equus quagga (in) Kingdon, J S and Hoffmann, M: The Mammals of Africa Vol. 5: Equids

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