Far more buffalo can be grazed per acre than cattle, and wild buffalo roam again as the Great Plains become less habitable from the Ogallala aquifer depletion.
I found this book online and excerpted my favorite paragraphs.
Lott, Dale F. 2002. American Bison: A Natural History. University of California Press.
It’s hard to imagine—as you fly above mile after mile of corn, soybeans, and cattle feedlots or drive between them—but before East Africa became safari land, rich adventurers went on safari on the Great Plains. Buffalo Bill got his start in show business by laying on a safari for the Czarevitch of Russia—the Grand Duke Alexis. The Great Plains was a good choice. This vast, little—disturbed natural community covered a third of the United States—creating wonder, inviting adventure. Part of the appeal was the exotic indigenous people, but the main attraction was a sea of grass inhabited by an assemblage of animals mostly unknown elsewhere, and dominated by enormous herds of buffalo.
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In late July and early August, plumes of dust, rising with earth-warmed air from the brown grass and rolling rangeland, ascend into that bowl. The dust makers, a herd of bison on the National Bison Range, are going about their business—breeding;
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Most of the dust comes from wallows, shallow pits where the bison have torn away the sod with their horns and where the subsoil, dried by the sun and stirred by hooves and horns, turns to a flourlike dust. Some of the plumes start when threatening bulls paw and roll in these wallows; but most occur when fighting bulls plow the soil with their hooves, or when they slam their heads together and the shock explodes dust from their bodies. Now an old bull bellows. His back arches, his belly lifts, his neck extends, and a sound that seems equal parts lion’s roar and thunderclap booms across the grass. An eighteen-inch scar runs up his ribs. His horn tips, shattered in other battles, are blunted and worn. Fifty yards away his opponent, a six-year-old bull in his prime, bellows back, glances at the cow he is tending, then urinates into the dust of a wallow and rolls in it, slamming his 2,000 pounds sideways into the dust. It spurts from beneath him, filling the air around him like the burst of smoke a stage magician vanishes into. The prime bull emerges from this cloud, headed toward the old bull in a menacing walk. His forefeet stamp with each step, making the hair pantaloons on his legs dance and exploding little puffs of dust from his coat. As each front foot stamps, the bull snorts. His tail stands up like a living question mark. It’s an impressive display, and from where I sit, in an ancient jeep, an intimidating one. But the old bull is not intimidated. He too has wallowed and now advances, matching stamp with stamp, snort with snort. As they grow closer their bellows intensify; they seem to signify pure fury. Most such challenges seem to be elaborate tests of the opponent’s determination and end without a fight. Most fights involve a cautious locking of horns or hooking uppercuts or shoving head to head, ended when one animal signals submission and the winner lets him go. But this is not a test of determination and it’s a different kind of fight—one of those in which the bulls hurl themselves at each other, elongating their bulky bodies into animated battering rams as they launch themselves for the first blow. Their heads come together with a terrific shock. It ripples through their bodies in a visible wave. I once saw a bull somersaulted backward by such a charge: 2,000 pounds of bull flipped upside down like a lawn chair in a gust of wind. Both these bulls hold position after the first shock and dig in for a serious fight. They slam their heads together again. Clumps of hair the size of a fist are caught between their short, heavy, curved horns, then sheared off and tossed into the air. The animals circle, each trying to reach the other’s flank with a hooking horn. Both pivot around their forefeet with the speed of featherweight boxers, and each parries the other’s seeking horns with his own while their powerful necks absorb some of the force of the impact. Their hair absorbs some too. By the time a bull is six years old, a mat of hair several inches thick extends from the top of his head down across his forehead, thinning gradually until it stops just above his muzzle. His eyes peer from shallow wells, his ears flick out from deep recesses, and the space between his horns is completely filled with this luxuriant growth. Beneath this natural shock absorber, a thick layer of tough hide covers a rock-solid skull. Now the bulls lock horns and push hard, their hooves plowing soil as each tries to drive his opponent back. The old bull is pushed back and a little sideways, dust spurting from beneath his skidding feet. Suddenly a foot catches on a rock and he trips and falls onto his side. It is rare for a helpless bull to be attacked by the winner, but this time it happens. The younger bull strikes down and forward with his horns, slamming them into the old bull’s flank and hooking right and left. The curves of his horns make most of the contact and deliver bruising, possibly rib-breaking, but not fatal blows. Then the tip of one horn plunges through skin and muscles and into his opponent’s abdomen. Only one horn penetrates, and it penetrates only once, but the wound will be mortal.
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While physical prowess is an essential tool in managing a relationship between two males, it can’t be the only tool, and in fact it’s one of the least-often used. Much more frequently they use communication,
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A territorial animal can predict attack pretty successfully by knowing territorial boundaries. The territory owner usually challenges all competitors within a given space and keeps up the pressure with threats and attacks until they leave. But bull bison aren’t territorial. They are roamers, drifting singly or in small, temporary groups. Because they cannot use their location in space to predict whether or not another animal will attack them, they read the animals around them, detecting and responding to behavior that consistently precedes an attack.
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A bull doesn’t just walk toward his opponent: he stamps with each step, setting his foreleg pantaloons dancing, and grunting with each stamp. If forewarned is forearmed, why not attack first and give indication later? The reason, of course, is that it may not be necessary to attack at all.
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Fighting is an occasionally necessary grand spectacle, but the real biological drama lies in the complex, drawn—out, and frequently subtle ways in which most conflicts are settled by communication. Bulls do most of their communicating during the breeding season-the only time during the year that mature bulls and cows are together for any length of time. The bulls have been alone or in small, temporary groups. Now they join the cows, which have been living in larger groups with the calves and young bulls. The bulls seek out cows about to breed and stay with them (they “tend” them), keeping other bulls away by threatening and fighting. But threatening and fighting are also common between bulls that are not defending cows. Since receptive cows are the only scarce resource in the bull’s economy, this seems surprising at first: one wonders what the nontending bulls are fighting about. But a rival dominated now will probably give way later without a contest, saving a tending bull time and energy when he has none to spare. Not that the bull works it all out in this fashion. He simply has a powerful urge to dominate other bulls, and following this impulse works to his advantage. The drive to dominate is so powerful that it occasionally interferes with his real business and its ultimate function—bulls will sometimes leave a receptive cow to threaten a distant bull.
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On a still day a bull’s bellow carries for miles. It’s a sort of roaring rumble, and if you can’t see the bull or don’t recognize the sound you may guess it’s a thunderstorm. If the competition presses, the bellowing becomes louder, and a quality that is hard to define but somehow easy to recognize—a quality of fury—begins to grow in it. Often one or both bulls will interrupt their bellowing to paw the ground or wallow.
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If the challenge does not end at the wallowing or bellowing stage, the bulls draw closer to each other and begin to posture. There seem to be two distinct postures. In the “head-on threat,” which is simply the posture and movement that precedes a charge, the bull moves toward his opponent with his head held slightly to one side. The more slowly the challengers are moving, the farther to the side their heads are held. When they approach nearly straight on, either one bull submits by turning away or they bang heads. But when they approach slowly with their heads well to one side, they often stop close to, but not quite touching, each other and “nod-threat.” Nod-threatening bulls stand close enough to reach one another; their bodies may form a single straight line or an angle of up to ninety degrees, but in either case they turn their heads aside. From this position they can attack suddenly by hooking a horn into the opponent’s head. The hook always starts when the head is close to the ground, the muzzle tucked back. But in the threat itself, the head-low, muzzle-back position is only a brief interruption of a head-high stance: the bulls’ heads drop in a matched movement, then swing back up again, still to one side. A hooking attack may start at the bottom of any one of the down swings, but the opponent never seems to be caught off guard. After a series of such nods one animal may suddenly submit, ending the clash. Nod-threatening takes place most often between bulls that are not tending cows, as does the “broadside threat.” A bull in this posture keeps himself broadside to his opponent with his head held a little higher than normal. Usually his back is arched and he is bellowing. If he moves, he does so slowly, in short, stiff steps that keep him broadside to his opponent. Often two bulls will threaten by standing parallel to each other just a few feet apart. Only rarely does this threat lead to a fight. The encounter may be long as threats go, lasting up to a minute or more, but one of the animals almost always submits.
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All bison submission signals are variations on a theme: the submitting bull turns away. Sometimes it’s a 180-degree turn followed by a galloping retreat. At other times it’s an abbreviated swing of the head and neck to one side. When it involves a go-degree turn, the submitting animal ends up in the same general position as one who is threatening broadside. But it’s easy to tell the difference. In submission the bull’s head is usually low, muzzle extended as if to graze—and sometimes he does graze—and the bull is silent. Whatever form the submission signal takes, it almost always stops the threats or attack immediately.
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How would a winning bull penalize himself by polishing off a loser? In fact, he would be deprived of two precious commodities: time and energy. The breeding season, when most conflicts take place, is limited, and time spent fighting, even a mop-up operation, is time lost from breeding. Fights to the finish would take even more energy, and that’s in shorter supply than you might imagine. When you see bulls in the middle of summer, in the midst of tall grass and warm sunshine, their good health and nutrition seem assured. But bison are northern animals, one of the most northern of the cattle family. They have adapted to a climate where food is scarce through long winter months. Bulls die during the winter if fall catches them without enough energy stored as body fat. As it is, the breeding season takes a lot of energy. Mature males lose an average of 200 pounds between June and October. If every fight were long and rough and ended in a cross-country chase, bison bulls, winners and losers alike, might well die before spring renewed the plains.
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The prolonged forewarnings, the reluctance to fight, and the generosity to losers are neither the last noble vestiges of chivalry in our time nor nature’s way of exhorting humans to live on a higher ethical plane. Rather, they are carefully balanced behavioral adjustments to the social and ecological circumstances in which the competition between bulls evolved.
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The older they get, the more likely they are to take the risks of combat in order to tend a breedable cow—not because older mature bulls are more likely to win than younger mature bulls, but because they have less to lose. Thereby hangs an intriguing budgeting issue, which might be titled “How to spend your life the way that buys the most descendants.” It’s an investment program in which your life is your capital and the return is your offspring’s offspring. For male bison, producing offspring usually involves conflict. Each such conflict puts their lives at risk. A bull bison’s optimal investment strategy weighs possible losses against possible gains and decides how much risk is prudent. He’s balancing making a killing against getting killed. Now, a male is not going to live forever, so an optimal strategy must be age sensitive. The younger he is, the more time and future opportunities he stands to lose if he dies. So he should invest cautiously when he’s young and has more to lose, but more and more boldly as he gets older and has less to lose. Bison behavior tracks this straightforward logic—the old bulls are the bold bulls.
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The way to a bull’s enthusiastic attendance is through his vomernasal organ, a sensory organ found in many mammals; it has an opening in the roof of the mouth. Cows’ urine is full of facts about how near ovulation is. The bull’s vomernasal organ seems specialized for an analysis of female urine chemistry that provides information on when a female will be ready to breed. But while bulls will joust seriously to get some female urine on their vomernasal organ, I’ve never noticed that females go out of their way to present it. However, I have many times seen bulls during the rut bring a resting cow to her feet by prodding her belly gently but firmly with a horn. The cows arise, with what I take to be resignation, and often urinate in a minute or two. The bull thrusts his muzzle into the stream of urine, then elevates his head, upper lip curled, tongue fluttering inside his mouth, his whole demeanor suggesting a gourmet’s appreciation of a fine wine. If he goes from lip-curling to tending, the chances are good that the cow will breed sometime that day.
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We call the several hours before the cow breeds pre-estrus, and bulls that test the urine of pre-estrous cows are likely to try to spend the next few hours with her. That’s not easy to do. Pre-estrous cows become restless—breaking away from a tending bull and running through the herd. A running cow attracts bulls, and a string of them are soon following her just as a tail follows its comet. When she stops they gather and quickly sort out who among the present company gets to stand by his cow. The cow’s best shot at having many grandchildren is to have sons that can claim a cow just as this bull claimed her. If we assume “like father, like son,” he is the best candidate in the immediate circle—but the cow may well make him prove it again with another run through the herd.
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the lower the tending bull’s rank, the more likely it was that the tended cow would run. In addition, cows that ran usually ended up with a bull that ranked higher than the one they ran from.
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Tending pairs are unveiled as the movement of a grazing herd leaves them behind. Study a pair and you will see the cow grazing a bit, looking fretfully toward the increasingly distant herd. A big bull stands beside her, moving to block her when she sets off after the departing herd. He moves like a basketball player staying between a dribbling point guard and the goal. Sometimes she allows him to hold her in place, but “allows” is the operative word. His moves to block her are quick and graceful, but she is still quicker and more graceful. If she stays it’s because she has chosen—or at least settled for—him, not because he has chosen her. She may head straight for another tending bull. When Jerry Wolff compared the ranks of the bulls left to those approached, he found the cows were usually approaching a higher ranking bull. That’s one of the forms of choice a cow has, and it makes sense for her to be as choosy as she can manage to be.
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We don’t yet know what cues besides age the cow may use in making her choice. Could all that bellowing make a difference as to which bull is standing beside her when she stops running? Could it work like some birdsongs or frog croaks—a clue to the female about who might be a better mate? The bulls don’t seem to be sending a signal—they appear only to bellow to other bulls. They seldom bellow unless they already have a cow, are trying to displace a bull that has one, or are in the midst of a dominance contest.
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However important bellows may be to a resistant cow, her priorities and behavior change as ovulation approaches. The time of choosing is a period of conflict between the cow and the many courting bulls. The more competitors, the better for her but the worse for him. His earlier behavior minimized the number, hers maximized it. But now their interests coincide, and they must cooperate and collaborate. Often the cow redirects the relationship. Her physiology is changing fast, altering her behavior along with it. Now, instead of breaking into a gallop every time the bull is distracted by a challenger, she follows him, and when he has disposed of the distraction she stands close, perhaps even positions herself in front of him. If he continues to glower round at the competition instead of mounting her, she may announce her readiness to breed by licking him or by sticking a horn in his ribs and prying upward—extracting from the bull a grunt, a tuft of hair, and more attention. She may even mount him, and when he begins to mount her she
squirts forward like a stepped-on bar of wet soap, but plants her feet and moves her tail to one side. Even so he may half mount, then drop off several times before he catches on and copulates. Bison sex does not involve a lingering mingling of mucous membranes. He clamps his forelegs around her ribs and penetrates with a lunge. The bull almost always ejaculates within five seconds of intromission (I timed it from movies of the event). His last pelvic thrust is driven home by a contraction of his abdominal muscles so strong that it jerks his hind feet forward and completely clear of the ground, making the 1,100-pound cow’s hindquarters suddenly support an extra ton of buffalo. Brief though the encounter is, it’s usually enough for the cow. She staggers under his weight, not infrequently limps for a while afterward, and four times out of five rejects further attempts by this or any other bull to mount her again for the coming twelve months.
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In a well-nourished herd, 85 to 90% of the mature cows will bear a calf in the spring. Breeding season moves at a spanking pace. I’ve seen half the cows breed in the peak four days.
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While breeding, bulls lose 10 to 15 percent of their body weight—mostly fat they will dearly miss in the coming winter. But the potential rewards are also enormous. The winning bulls win big. One year I saw one bull breed five cows while others bred none—one-third of the bulls sired two-thirds of the coming spring’s calves. Over three years Jerry Wolff saw one bull breed sixteen cows, while another never bred. The biologists Joel Berger and Carol Cunningham followed a herd for four years and saw one bull breed twenty-eight times while others never bred.
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more and more of the bulls drift away to concentrate on providing their complicated digestive system with the fodder it will convert to fat to carry them through the winter. Their interactions change from constant confrontation to nearly invariable tolerance or passive avoidance. They’re not looking for any trouble, and, in the two months following the rut, they come to look a lot less like trouble. The magnificent, menacing mass of hair on their forehead and between their horns, the flowing beard, and the dancing pantaloons that gave advancing bulls such presence are gone. Much of the hair between their horns was barbered away—caught between rubbing horns and sheared off during fights. But the rest of that hair, the beard and the pantaloons, simply falls out after the rut ends and before winter starts. Only mature bulls molt this way, not cows and not even young bulls. Perhaps the hair loss is triggered by the stress of the rut—and perhaps instead, or in addition, it de-escalates the tension between the bulls: each benefits by looking less big-male threatening
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Storing and using fat is somewhat inefficient. Converting digested food to fat uses some of the food’s energy, and converting it back to usable energy requires still more. But what the process lacks in efficiency it makes up in reliability. It makes it possible to survive lean times like the hard winters that always lie ahead
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dominance relationships between the cows are no laughing matter. While there’s very little violence, there’s lots more subtle action. Alan counted aggressive interactions and saw two per cow—hour, ranging from a subordinate withdrawing to a dominant swinging her horns or lunging. The cows are under social pressure, expressed in the physical and social distance between neighbors. As is so often true of participants in relationships, they want to be close, but not too close. The closer a cow’s neighbors, the less the danger from wolves but the more the competition—for food, wallows, and water. Being close takes a lot of fine—tuning. Every step brings you closer or takes you farther away from several others, all of whom are also fine—tuning the distance they are from you. Physically, a buffalo cow just plods across ground and through air. But socially, it’s as though the air between each two cows were contained in transparent bags that compress and expand as each animal moves closer to or farther from a neighbor. The pressure inside the bags depends on the relationship between a cow and each of her neighbors; and since the relationship is not symmetrical, the pressure of the “same” bag is different for each of the cows. The dominant member of a pair may feel a little pressure when stepping toward her neighbor, while the subordinate may feel intense pressure when stepping toward the dominant, and not move as far. In addition, the cows can vary that stable, baseline pressure. A deferential head duck by the subordinate decreases the pressure for both; a threatening head swing by the dominant raises the pressure for the subordinate. The cows aren’t seeking an absence of pressure. If they can’t feel any there they find somebody. And up to an optimal point, the more pressures they can feel the better. Being a dominant member of a group has high potential payoff.
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In Yellowstone Park, subordinates searched more and harvested less than dominants. Feast and famine were regular visitors to the Great Plains, with wet weather in some years and drought in others. In drought years every mouthful became precious to a cow eating to store enough fat to trigger ovulation and to carry a growing fetus through a hard winter. Dominance would have a big payoff in those years. And dominance would pay off any time that the snow was deep. Foraging bison sweep the snow from the grass by swinging their heads from side to side and using their muzzles as plows. They clear little craters in the snow and eat the grass at the bottom. At least, they eat that grass unless and until a dominant makes them move on and takes over that patch. A dominant will eat everything it clears and some that it doesn’t clear. A subordinate will eat only part of what it clears. That difference can be really big at crucial times. All other things being equal, the dominants will get fatter and the subordinates will get leaner. So the cows are interacting constantly, dominants and subordinates in a careful dance of distance; and being the dominant is worthwhile.
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2-year-olds dominated 1-year-olds, and 3-year-olds dominated 2-year-olds; through age eight, all older cows dominated all younger ones. When they were young, of course, the older cows were also bigger than the younger cows. But by the time they were 3 years old that was no longer so, for they’d reached their full size. Yet 3-year-olds, even when bigger, didn’t dominate 6-year-olds.
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it’s typical of a dominance system that the dominant individuals launch a steady stream of preemptive bullyings—sort of like those “Don’t even think about it” admonitions.
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on Catalina only about 30% annually were giving birth. We captured 7 cows in a corral, determined their weight and age, and then hung radio transmitters around their necks and watched them. In a corral the cows had a strict dominance hierarchy. That hierarchy correlated perfectly with body weight: every cow dominated every lighter cow and was subordinate to every heavier one. Weight was all that mattered—age was irrelevant. Dominant cows ate better than subordinate, going through the oat hay in the feed troughs to get the grain that fell from the shattered heads and leaving the straw for the less dominant who were waiting their turn. After a few days of watching, we turned the cows back to the Range and followed them for four years. They went their separate ways, and we only rarely saw them together again. The more dominant they were in that corral for those few days, the more calves they had. The heaviest, most dominant cows calved every year; the lightest, most subordinate not at all. That is a huge difference. Natural selection is nothing more than some individuals rearing more offspring than others.
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On the National Bison Range calves are born in April and May—spring
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Within a minute or two, as soon as his mother has freed him from the membrane that surrounded him in the womb, he begins a frantic—seeming struggle to get to his feet. He gets halfway up several times, and falls forward, backward, and sideways. I think, “Take it easy, little one, rest a minute. There’s no rush!” But the brain that has guided calves to adulthood for thousands of generations knows better. The calf hasn’t got a minute to spare. Wolves may arrive any moment. A late winter storm could drop six inches of snow tonight, and winter is certain to return in a few months. Winter and wolves. These ancient forces selected which among calves past would bear or sire another generation. And so they have shaped this calf—bones, brains, and behavior. To survive them the calf must grow: bigger, faster, fatter. So much growing to do, in so little time.
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Adult bison spend a good part of their day ruminating; it’s an essential part of their digestion. But bison calves don’t ruminate for the first three months.
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The calf needs to stay close to its mother, and to nurse. Evolution not only made nursing a necessity but set up a positive feedback loop. Nursing releases oxytocin, so the more the calf nurses the more mother loves it; and the more she loves it the more she allows it to nurse.
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A bison calf’s first priority is to get to its feet and walk. By the stopwatch I kept time with as I watched a dozen births, that takes all of seven or eight minutes. An hour—old calf can scamper pretty well.
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The bouncing baby bison doesn’t bounce aimlessly. It bounces toward something big and close. Mom is big and close and the ball usually bounces her way. But sometimes it fixes its eye on some other bison that passes by and rushes after it. Then mother chases both down and retrieves her young. A calf a few months old that loses its mother will attach itself to anything large and moving. An orphan calf followed Captain Meriwether Lewis all one afternoon as he walked west beside the Missouri River.
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Many animals that move in herds or flocks have a call that signals with much the same effect of a human crying out, “I’m here; where are you?”
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You hear their call occasionally while the animals are grazing, more frequently as a group of cows and calves walk along as they’re going somewhere—say to water. You hear a lot of grunting when a herd has just stampeded, separating cows and calves. Mothers and calves grunt to each other across a post stampede herd and track the right—sounding voice they hear to a reunion. The grunts that are so alike to our ears are different enough to theirs to convey identity—like a familiar voice saying hello when answering your phone call. But like someone responding to an on—the—phone hello, the hearer sometimes gets it wrong. I’ve several times seen a cow and a calf exchange grunts across a herd, make their way through it and come together, noses extended, only to fail the gold standard—the sniff test.
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To measure the life span of a relationship, you must record first its birth, then its death. It’s easy to say when a cow—calf relationship begins, but harder to say when it is over. So we rely on proximity—inferring that the closer the bodies, the closer the relationship.
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mothers must choose where to give birth. She and the calf need some way to ensure that each develops a relationship with the right other individual—smells the right smell, hears the right voice. For though they have been intensely connected physiologically—sharing one body and one blood supply—socially they are complete strangers. They must create the relationship quickly and surely, before the precocious calf becomes so mobile that it mingles with others that look and sound very like it. Cows can make sure of that privacy by being alone when they give birth. On Catalina Island most cows gave birth in solitude, usually among bushes, scrub oak, ceanothus, or coast live oak trees. There they were hard to see. They had both privacy and shelter from prying eyes—they had cover. But on the National Bison Range most cows stayed in their herd to give birth. There were exceptions to both rules, but the general patterns showed a striking distinction between the two places. This difference must have a cause, and my reasoning centers around the trade—offs between privacy and predation. Wolves hunt mostly by sight. If wolves are your worry, then being out of their sight is best. If there are bushes or trees you can hide among them. But if the tallest plants are ankle—high grasses, the only thing big enough to hide behind is another bison—or better still, a bunch of bison. On the National Bison Range I was watching cows give birth on a grassland; on Catalina Island they were giving birth in a coastal scrub community.
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Selection has prepared a pregnant mother to prepare for another calf. Part of that preparation takes the form of ceasing to invest in her current calf so she can rebuild herself to deliver a healthy calf in just nine months. Thus the best deal for the cow is to invest less in this calf so she can invest more in the calf to come. She’s equally related to both, and to her calves that may come even further in the future. That’s not the best deal for the current calf. Mother’s new calf is unlikely to be closer than a half sibling—sharing one—fourth of its genes. All things considered, its best deal is for mother to continue to invest in it no matter the cost to its future half siblings. The result is a classic conflict of genetic interest. Pregnancy is crunch time. Now the cow has one calf at her udder and one in her womb. Her resources—her energy and her body’s tissues-are finite, and she must divide them between her two calves. Wendy’s pregnant cows’ behavior toward the one at their udder changed sharply, unlike the behavior of the mothers that didn’t get pregnant. Through the next three months (until the calf was six months old), pregnant mothers were more than twice as aggressive toward their calves when they nursed and attempted to nurse. From six months on, the differences were even more dramatic.
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the calf isn’t just pushed away, it also walks away-choosing to spend more and more time with age-mates and getting more and more of its nutrition from the grasses it grazes. Sons become mere acquaintances first, but daughters eventually do too, when they have their first calf, if not before. Each is pursuing the path that will maximize the number of its genes in the next generation. They have moved on.
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Harvey Wallbanger, a flesh—and—blood buffalo, regularly showed his heels to racehorses in the 440-yard dash. Harvey’s triumph would not have surprised the Sioux, Crow, Black—feet, Comanches, and Cheyennes who hunted buffalo from horseback for nearly two centuries. While most of their horses could overtake one buffalo, only a few could overtake several buffalo in one chase. A buffalo’s skinny rump and long front legs give it a long—enduring stride—a good match for a coursing predator like the wolf. It is an animal faster than, well, some speeding racehorses, and able to leap tall road cuts at a single bound.
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Management installed some cattle guards on the National Bison range. They were working fine for buffalo cows and calves, but not very well for bulls. Bulls were getting past them somehow, and one day I saw how. A bull walked calmly up the road to a cattle guard, stood placidly on one side of it, then hopped—no other word would really describe it—across, landing on all four feet on the other side. This hop had to be long enough to deposit his hind feet on the far side of the cattle guard, so he cleared the width of the cattle guard plus the distance from his front feet to his rear feet, say another six feet, for a total of fourteen feet. A very impressive standing broad jump. Well, at least I was impressed. If the bull was impressed, it didn’t show. He stood where he had landed for a quiet moment, then, with an air of “been here, done this,” cropped a mouthful of grass from the side of the road and walked on—patiently and efficiently.
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National Bison Range personnel countered the buffalo hop strategy by placing 2 cattle guards end to end. Now a bull would have to hop 16 plus 6 feet; and so far as I know, none ever did. But buffalo bulldom had not exhausted the arrows in its quiver. One day in breeding season I pulled my ancient Jeep to the side of the road, just after passing through one of these amplified cattle guards, and sat looking at the herd ahead of me. From behind came a distinct pinging, as though someone were tapping something metal with a piece of wood. A bull’s image filled most of my rearview mirror. He was in the middle of the cattle guard, placing his feet delicately, cautiously, one at a time but still confidently, so they were centered on the narrow bars of the cattle guard as he walked across with all the poise, and a good bit of the daring, of a man on a tightrope. I would not have been any more astonished if he had also been singing “Tiptoe through the Tulips” in a friendly falsetto. When he reached solid ground he walked past me and joined the herd, leaving me to ponder the demonstration of footwork finesse I had just witnessed and somehow make it fit with the demonstrations of brute power I had also seen. For while buffalo leaps and sprints are spectacular, walking is the athletic talent that brings the animals to food and water day after day. Bison are roamers. Even in the confined spaces where they live today, they will travel ten or twelve miles overnight. On the Great Plains they may have traveled hundreds of miles from season to season—perhaps searching for a better place to spend the winter, or for a location with fewer human beings. They surely gained something from each step of those journeys, but (and here is where a physical feat is required) to be profitable each had to gain them enough to offset its costs. And the cost is high; bulls weigh about a ton. When a vehicle that size is fueled with blades of grass, every blade has to count. So the athletic challenge becomes like one of those competitions to see how far a vehicle can travel on a gallon of gas. It’s all about efficiency—getting the most out of every drop of gas or blade of grass. Why is it that an animal that runs so fast walks so slow? It’s all about energy. Buffalo, and just about everything else that walks, set a pace that matches the natural period of the pendulum constituted by its leg. A buffalo’s leg, like yours and mine, swings forward and back as the animal walks, so it’s a pendulum.
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At its natural period pace a buffalo, or any other 4-footed beast, can recover 35 to 50% of the energy put into each stride. But when it comes to walking, two legs are better. Bipedal striders (creatures like ostriches and us) recover more, maybe as much as 70% of each stride’s energy just by walking naturally.
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Harvey Wallbanger didn’t walk away from those racehorses. Both parties were galloping flat out for a quarter of a mile, and both could gallop—a little more slowly, to be sure—for miles and miles, as most hoofed animals can. How do they get the energy? By conserving it. This illustrates not the pendulum effect, since the bison’s legs are moving much faster than their natural period, but more a pogo stick effect. As their feet land, they store the force of gravity in tendons and ligaments threaded the long way around the joints in their legs. When their legs flex with gravity, those ligaments and tendons stretch like the spring on a screen door, and that energy is recovered as the leg straightens for the next step.
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Sheep can recover about 30% of their running energy this way, and camels may recover 50%. Buffalo fall somewhere in that range. We humans don’t have the feet for this feat. Bison are always on their toes: that joint about a third of the way up their leg isn’t a backward knee but the heel of their foot, and the tendon from their real knee to their toes is long and stretchy.
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A bull has to twist and turn—quickly enough to protect his own flanks, quickly enough to get a horn into his opponent’s flank. Selection is intense. Bulls are wounded every breeding season, and in most years 5 or 6 percent of the mature bulls in any population die of their wounds. So the bulls are built to be quick in battle. To protect their body with their head, they need to pivot around their front feet. They have a great form for that function: much of their weight is centered over their front legs—their diminutive rear end is balanced in part by their massive head and neck. And the weight of their head is partly suspended from a point above their shoulders.
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There, rays of bone a foot long (called vertebral processes) project up from their vertebrae and anchor a tendon that attaches to the rear of the skull. This efficiently supports the transfer of their head’s weight to their front feet, on which they pirouette on the sod like a hockey player on ice.
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many plants produce tannin, which does nothing for the plant but makes it difficult for the animal that eats it to digest proteins. Many plant eaters, including humans, have evolved a countermeasure—our saliva contains a molecule that binds with tannin and neutralizes it. The astringent taste of the neutralized tannin gives a sip of red wine its special flavor.
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Grass hasn’t evolved tannin, but it stores most of its carbohydrates as cellulose, and until the cellulose has been digested the carbohydrates are not available. In turn, most of the Great Plains’ big animals—bison, antelope, deer, and elk—counter cellulose with rumination, which turns grass into gas: figurative gas, as fuel to run their physical systems, and literal gas, as methane. Digesting anything is a strictly chemical matter of subjecting it to an enzyme that breaks certain molecular bonds, simple enough if you have the right enzyme. Put the food in your digestive tract, secrete the enzyme. Neither you nor I can secrete an enzyme that can digest cellulose. As a matter of fact, bison don’t secrete such an enzyme either, but they rely on a method as good and in some ways better: they enlist colonies of bacteria.
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A third of mature bulls have at least one rib that has been broken and has healed.
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WALLOWING. All bison wallow several times a day in summer, filling their hair with dust. The dust probably discourages insects and may reduce the bison’s body temperature.
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Bison cool their bodies by evaporating water from their lungs. On hot summer days they need a lot of water. On Catalina Island, cows go to water twice a day, drinking four to six gallons at a time. Bulls there drink once a day in the summer.
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WILD BULL RESISTING ROUNDUP The bull pictured is reacting to men trying to move him through a corral on the National Bison Range during the annual roundup. Handling wild bison is difficult, dangerous, and expensive. Domestication will select for more tractable—hence less wild—animals. This bull’s behavior will be tolerated in this publicly owned herd, but a rancher would be compelled to shoot him. Some buffalo, usually castrated males, have been trained to carry a rider or pull a cart. They remain dangerous.
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Bison are better suited to western grasslands than are cattle, requiring less care and doing less damage. More than 95 percent of bison in North America are privately owned and live on ranches. There selective breeding will produce a domesticated form of bison with little wildness left.
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fermentation bacteria have waste products, which include alcohol. It’s a sobering fact that 12 or 13 percent of a bottle of Dom Perignon Champagne is bacteria pee.
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For the bison a percentage of bacteria waste products that high would be a calamity, because it would mean that the bacteria were themselves using the energy their enzymes were releasing. Here we come to one of those built—in conflicts of interest that are part of nearly all relationships. Up to the point of converting cellulose to usable carbos and fatty acids, bison and bacteria have the same goals and collaborate. But now each has its own uses for the energy the enzymes have released—now they compete. It has to be a restrained competition, because both would starve if either were to get all the energy. Yet within the rumen, subtly different lines of bacteria must be striving to win a bigger share of the goodies. The bacteria—on—bacteria competition takes place in a friendly environment—the bison’s rumen—so the bison, being the environment as well as collaborator and competitor, has leverage that makes up for its slower evolutionary rate.
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Bison don’t limit their bacteria’s food, but they severely limit their oxygen and their time. Some bacteria—anaerobic bacteria—can function without oxygen, but they function slowly. In time they would use up the energy they have released from the grass, so bison don’t give them time. They move the grass on out of the rumen after two or three days, pushing the partially digested food, and some of the bacteria that digested it to that point, further on. In the stomach, their own enzymes finish the job on the plants and digest some of the helpful bacteria as well. Timing is everything in this matter, and the ruminants have the timing down so well that they get about 90% of the energy for themselves. The mechanics of rumination are a bit inelegant. The ruminant assists the process by chewing its food after swallowing it—the bison brings up fist—sized wads of partially digested grass (cuds) from its rumen and chews them while lying at rest. If Buffalo Bill and the Czarevitch had sat in their saddles and contemplated a resting bison they’d have seen this; bison spend hours every day doing it. Although cud chewing—ruminating—gives them a faraway—focused, meditative, serene sort of look, it isn’t an elegant activity. But as an adaptation, rumination is elegance itself.
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The immediate products of bison digestion are heat, energy, and tissue maintenance for the digesters’ bodies. The final end products of bison digestion are buffalo calves and buffalo chips.
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Analyzing parasites is the most straightforward part of this study—just look and count. Figuring out what bison are eating is also straightforward, though rather more time—consuming. The cell walls of plants are pretty distinctive and pretty tough. You pick through the chips and locate cell walls. You compare the cell walls to the cell walls of plants from your reference collection—representatives of each plant that grows where the bison are feeding. The reference collection is needed to set some boundaries on your search for matches. And that’s it. You can find out how many of the plants in its habitat a bison feeds on and, by comparing the percentage appearing in the chips with the percentage in the field, estimate which plants the bison favors.
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Why aren’t all buffalo white? White is a good summer color. It reflects the sun’s heat, and that heat is a fact of life for bison. They evolved in the grasslands, where summer sunshine is plentiful and shade is nonexistent; bison spend most of the long summer days absorbing the sun’s heat into their dark coats. White is also a good winter color. Some rabbits turn white in the winter to blend with the snow, and so do some of the weasels that stalk them. Wolves hunt bison all winter long. Wouldn’t blending with the background be a good idea?
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But not only are white buffalo rare, they don’t seem to do well.
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Bison seldom if ever die of heat, but they often die of cold. The dark coat that makes the sun a nuisance in summer may be a lifesaver in winter. Bison evolved in really terrible winters; and even now, especially severe winters kill many of the old and the young. The sun is low and the days are short, but every calorie of heat absorbed from the sun is a calorie the bison does not have to manufacture from the scarce forage—forage that must be won by sweeping the snow from each bite with that heavy head—or drawn from its precious cache of calories in the form of stored fat. Like deer and elk, bison cut their energy output by losing their appetite. They eat less and produce less heat—and not just because food is scarcer in winter. Even when they can have all they want from full feeding troughs in an experimenter’s corral, they eat 30 percent less food and produce 30 percent less heat in February and March than in April and May.
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A buffalo robe was a possession prized by humans dwelling on the North American plains. It can keep you warm in a terrible storm. Cattle have replaced the buffalo, but there isn’t much point in bundling up in a cattle robe. The buffalo robe’s superiority is quite straightforward—a square inch of buffalo skin has ten times as many hairs growing from it as a square inch of cow skin. The difference, when temperatures and fat stores are low, is the difference between life and death. But when summer arrives there is a price to pay. The North American plains are a place of extreme heat as well as extreme cold. It’s a bit like jumping from the deep freeze to the frying pan, and the challenge in summer is keeping cool. The first thing the bison do is shed their winter coats. The long, twisted, almost woolly hair of winter molts, and from the front shoulder back a sleek coat of short hair is revealed. It insulates only a little, allowing the nearly ceaseless wind of North America’s grassland to blow away body heat. That surely helps; but still, the sun is hot, their dark hair absorbs its heat, and they also produce heat as they ferment their food and move around. If they couldn’t get rid of the heat they generate and the heat they accumulate, they would soon be walking pot roasts.
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Bison don’t sweat, but they breathe, and lots of animals, again including humans, lose heat by evaporating water in their lungs.
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Evaporative cooling works well, but it has one major cost. You have to go through a lot of water in order that a lot of water can go through you. That internal supply must be replenished regularly. Surely the bison can do something to reduce the number of trips to water. Of course they could find some shade, but they don’t seem much inclined to. It’s astonishingly common to see them lying in the hot sun only twenty feet from dense shade.
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Bison wallow in the summer, especially during the middle of the day. Wallowing puts soil into and onto their coat. They can work so much nice, dry, powdery soil into their coat that as they walk away from the wallow it cascades down, jarred loose by each step. Like most old-timey bison watchers, I have always thought they were wallowing to make their hair a lousy place for lice and other parasites. I still think that’s likely, but wallowing may also lower their heat load. Elephants have a heat problem much like bison have, and we know that a good coat of dirt is one of their solutions.
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There was a witness, the dead bull himself, and though he was silenced 36,000 years ago, he has testified through the forensic skills of the paleontologist Dale Guthrie. He is not one of the anonymous dead; he has a name: Blue Babe. He is here to tell his story because after the lions killed him and made a meal of his hump, a mud slide buried him. The mud froze, and the mud and Blue Babe remained frozen until a gold miner washed away the mud and revealed the mummy one July day in 1979. Copper precipitation had given Blue Babe’s hide a blue tint and his hump had gone to fill the lions’ stomachs, but the rest of him was remarkably well preserved. The tooth and claw marks in his hide were still so clear that Dale could take an American lion’s skull, place its canine teeth on the marks left by the killer’s canines, and see a perfect match. Even the flesh was so well preserved that when the corpse had yielded all its secrets Dale and his colleagues made an acceptable stew with a bit of the meat.
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Blue Babe was a Bison prisons—at least two phylogenetic steps back from today’s Bison bison. He was very like his ancestors that came to North America from Siberia. It wasn’t a long journey. When the route was dry, bison could have walked from Siberia to Alaska in three or four days.
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Bison branched off from the primitive cow family line—Leptobos—about a million years ago. The first bison were small-bodied, small-horned, fast-moving residents of forest edges and meadows. Gradually the bison line became northern specialists, able to live where other cattle couldn’t. They also became open grassland specialists.
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A question springs to mind. Was there enough grass in North America to feed 100 million bison? Or, as an ecologist would put it, “What was the carrying capacity of the whole area bison lived in?” In still other words, what’s the biggest population the continent’s bison habitat could have supported? That won’t tell us how many were there—it just sets an upper limit;
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In 1972 the zoologist Tom McHugh determined carrying capacity by starting with the total area of the central grasslands, 1,250,000 square miles, then took “a range manager’s” approach to keeping livestock numbers within carrying capacity. Using existing formulas developed for cattle, McHugh calculated conservatively to take dry years into account. He assumed that carrying capacity varied from 1 buffalo per 10 acres in the tall grass prairie just west of the Mississippi to 1 per 45 acres in the short-grass prairie just east of the Rocky Mountains. He got an overall average of 25 acres per buffalo, or 26 buffalo per square mile. That gives the Great Plains a carrying capacity of 32 million bison. McHugh deducted 4 million for competing grazers—pronghorn, elk, and prairie dogs—and added 2 million for bison living elsewhere, for a final estimate of a maximum of 30 million buffalo on the continent in primitive times.
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Mary Meagher, a Park Service biologist who has studied Yellowstone’s bison for more than 40 years, has seen several winters kill 20% of the population. A bison population can have much bigger busts than booms. In fact, no bison population has ever grown faster than 20 percent a year even when it had zero predation and negligible winter kills.
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About all we can confidently say is that primitive America’s bison population was probably less than 30 million—perhaps, on average, 3 to 6 million less.
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GRASSLAND ECOLOGY From southern Alberta to central Texas, from the Rocky Mountains to the Mississippi River, a sea of grass covered the middle of North America—the area called the Great Plains covered 15 percent of the entire continent. The bulk of primitive America’s bison population lived there. Plants conform to a simple general rule: where the clouds bring more water as rain and snow than the sun and wind can evaporate in an average year, trees grow. Grass grows where there is at least half as much precipitation as the sun and wind can evaporate. If there is so little precipitation or so much evaporation that grass can’t grow, you are standing in a desert. In a temperate climate like that of the American Prairie, a very rough rule of thumb is that more than ten but less than forty inches of precipitation per year makes for a grassland. But while fourteen inches might be plenty in northern Montana, it might be too little in southern Texas. The American Prairie is doubly rooted in the Rocky Mountains. The rise of the Rockies created a rain shadow favoring grassland over forest, and the soils the grasses grow in came largely from the Rockies. About half the original mass of today’s Rocky Mountains has eroded. Water, often in the form of ice, did most of the eroding, and moving water carried many of the eroded particles east as far as the looth meridian of longitude. The looth meridian lies just east of Pierre, South Dakota, and hits Dodge City, Kansas, almost dead center—about halfway across the central plains. But there was another great conveyor belt at work too: moving air—the prairie winds. Loess is wind-borne silt. The prevailing westerlies carried loess to and beyond the Mississippi. Nebraska and Kansas were almost completely covered by a thin layer (less than five feet deep) of loess. Take away plant cover and roots, stir the loess, and it’s ready to ― 82 ― move again. What wind brings, the wind can take away. It was loess that the westerlies carried from the Midwest’s dust bowl to the Atlantic in the 19303. The central grassland’s native plants, along with dirt dwellers such as earthworms, modified those materials into fertile soil. But not always the same soil. Hudson Bay and the Gulf of Mexico are at sea level. The western edge of the American Prairie, just east of the foot of the Rocky Mountains, is nearly a mile high, and, located in the Rocky Mountains’ rain shadow, pretty dry. Every mile downslope, to the east, it’s lower, wetter, and warmer and the soil is darker—from brown in the west through chestnut to black at the eastern edge of the prairie. Ecologists divide the American Prairie into three regions, each named for its predominant grass. Other things being equal, the closer to the Rockies a given location is, the less rain it receives and the shorter its grass. At the foot of the Rockies—say Denver, Colorado, or Billings, Montana—you’re at the western edge of the short-grass prairie. Travel east to Kansas’s western border, and you’ll find the short-grass prairie blending with the mixed-grass prairie. It’s a blurred and shifting border, not at all precise, but nevertheless important. The mixed-grass prairie attracted more bison than either of the other two. It covered all but the eastern edge of the north-south tier of states starting with North Dakota and extending through South Dakota, Nebraska, Kansas, and Oklahoma and into central Texas. The tall grass prairie lies between the mixed-grass prairie and the Mississippi. During a long drought—say eight to ten years—the short-grass prairie moves east as its dry-adapted plants outcompete the taller, thirstier tall grass prairie plants. When the rain returns, the mixed-grass boundary region shifts west again. Dividing the central grasslands into sections can make each seem small. It helps to remember that the short-grass prairie alone is about the size of western Europe. The American Prairie’s grasses are deeply and broadly rooted in the soil: established for the long run. They’re perennials—their root systems are designed not for months but for decades. Only 10 percent of growth is above ground in leaves and seeds; 90 percent of growth is in the roots, and each plant sends about three-fourths of its carbon below ground into its roots. With so much energy stored below ground, the plant can persist ― 83 ― through years-long droughts. In the wettest grassland, eight-foot-tall grasses such as Indian grass and big bluestem spread their hundreds of roots as far as six feet down into the deep black soil to tap the moisture accumulated there in past years. In the west, blue grama and buffalo grass send up stalks about ten inches tall and fill the soil below and beside them with roots outfitted with tiny hairs that absorb water from the upper thirty inches of soil, thereby capturing the moisture from even small storms.
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For each buffalo the shift in weather meant hunger, less chance of reproducing, more chance of dying. For the bison as a whole it meant a shrinking population. But the dry years were what kept the prairie a grassland. If every year were wet, trees would grow, grass would go,
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their bad luck was an inescapable part of the boom-and-bust cycle of all temperate grasslands. And it’s the bust part of that cycle that made sure the minerals from their bones nourished a grassland covered with living bison and not a woodland haunted by their ghosts. The wind-rippled grassland whose surface undulates from horizon to horizon strongly evokes a sea, but it’s a sea that can catch fire. Grass burns all in an instant. A dry stem glows red and turns to curling ash while you are still drawing a breath. When a wind pushes it, a prairie fire runs fast. The American Prairie has always burned.
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For millions of years lightning caused combustion, but people began to burn the prairie several thousand years ago—often with buffalo in mind. Sometimes they used the flames to herd the bison, driving them to a place for easier and safer killing by people on foot. Sometimes they burned the grass so that new growth would attract bison to a more convenient killing place. Growth-stimulating fires were set in the spring when new growth would quickly replace the old. In the fall, new growth was up to six months away. Bison deserted the bare ground created by a fall fire until spring, and the people who hunted that ground faced starvation.
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In tall grass prairie, where mature grasses and their litter intercept 99% of the sun’s rays before they reach the ground, fire creates a moment when a short plant’s leaves can nourish their roots. The plant community that rises from the ashes is richer in species and more complex. The grasses surge back from their roots—the soil two inches down would not have been warmed even two degrees Fahrenheit by the fire—but the new leaves are different from those whose ashes they rise through. Enough nitrogen is carried away in the smoke so that the new growth has a higher ratio of carbon to nitrogen. That makes it poorer forage than was the now-burned grass when it was newly growing, but better forage than the mature plants that burned. Fire decreases production in the short-grass prairies, where water limits growth. But in the tall grasses, where the failure of radiation to reach the soil limits growth, fire increases production. Fire interacts with grazing. In the mixed-grass prairie, little bluestem presents grazers with an in-your-face defense—stiff tillers (stalks) that the grazer must push through to get to the green leaves. Fire removes the tillers, and bison, which avoid tillered little bluestem, graze the new-growing little bluestem as readily as other grasses. The fire that consumed little bluestem’s defenses thus helped little bluestem’s competitors through the mechanism of bison grazing. The grasslands are as much creatures of the grazers as the grazers are creatures of the grasslands. Other, smaller, grazers also played a role. Grasshoppers, for example, were always present, and occasionally a tidal wave of Rocky Mountain locusts would roll east with the westerly wind, eating every blade of grass in a swath a hundred miles wide and hundreds of miles long. And below the surface nematodes, nibbling at the roots, ate more grass than everything else put together. Still, in their heyday, bison were big on the plains—big enough to be called a keystone species. Grassland has a reciprocal relationship with bison, though the reciprocity is somewhat roundabout. Bison aren’t very picky, but given the choice they will choose grass over forbs (i.e., herbs other than grass). That small preference makes a big difference to the grassland. In the tall grass prairie, grazing bison keep the dominant tall grasses such as big bluestem and Indian grass short enough so other species can also grow. Consequently there are more plants representing more species where bison graze. Grasses resist being eaten. The tall grasses outgrow the grazers. In a few weeks they become tough, unpalatable, and protein poor. In the West, where there isn’t enough water to outgrow the grazers, buffalo grass employs the opposite strategy. It grows too short to be grazed easily, keeping its leaves low and tucking them back and down where they’re hard to reach. Grazing costs the grazed grasses much of their leaf structure—the photosynthetic, energy-producing part of the plant—and the plants react. They boost the photosynthesis of the remaining and replacement leaves to compensate. In the short term this strategy makes up for the lost tissue. In the long term there’s no free photosynthesis: the grasses boost their short-term output by dipping into their capital of stored nitrogen, and as that gets drawn down they’re less and less able to compensate. They need about two years’ rest to recharge their carbohydrate and nitrogen batteries from a big draw-down. Bison affect species composition in two ways. First, they wander. When they had the whole prairie to wander over, particular patches of grass probably had two-year rests fairly regularly, especially as bison choose areas where grasses are growing most vigorously. When the tall grass canopy is grazed off, the sunlight reaches the earth and the shorter plants do better. There are fewer individuals of more species after grazing—just as after fire. But grazing-stimulated growth in the western short grasses tends to eclipse smaller plants. Grazed short-grass prairie has more individuals of fewer species. Second, bison don’t just take away. They give something back—fertilizer. From a prairie plant