Arctic Dreams, page 8
Both sexes grow slowly. Males reach maturity in size in their sixth or seventh year and females at five or six. According to Canadian zoologist Ben Hubert, muskoxen weights vary so much because, in the case of males, the animals are in a “positive nutritional state” (i.e., gaining weight) for only two months out of the year, July and August. He found them to be in a “neutral balance” for four months, and to be slowly losing weight the other six months, during rut in the fall and for much of the winter. Females gain weight during about five months of the year, and lose it in winter and during calving and lactation (the calves are nursed for about fifteen months).
The muskox’s unique, characteristic horns suggest a cape buffalo’s, but they curve down close to the cheeks before hooking out and up in a recurved point. The female’s horns are shorter and more slender. They also taper more sharply than the male’s and do not grow together, helmetlike, in a boss over the skull. The horns, which turn a darker brown with light tips in older animals, continue to grow slowly throughout an animal’s life. The female’s attain the finished line of the adult shape in about four years, the male’s in six. The horns are primarily defensive weapons, wielded against predators, but they also serve to uproot vegetation and in an important and complex way for social display and in fighting during the males’ rut.
The large eyes, which protrude from the skull to clear the thick pelt and permit a wider field of lateral vision, are superbly well adapted. A double retina serves to intensify images in the darkness and the low light of winter, and the pupil, a horizontal slit, can close completely to prevent snowblindness. (Traditional Eskimo snow goggles imitate this design.) The pupil is also heavily lined with corpora nigra, which shield the retina against glare from the sky above and from snow and ice on the ground.
For its size, the muskox is surprisingly nimble and surefooted. In part this is due to the shape and structure of its hooves, which are broadly round and sharp-edged with concave bottoms. A broad heel pad gives the animal excellent traction on rock and hard ground and on various snow surfaces. The front hooves, which are larger, are used in winter to break and paw through wind-slabbed snow and groundfast ice. The muskox also uses its chin for this purpose.
Muskoxen appear to have only two gaits, a walk and a gallop. The gallop is swift and energetic, in contrast to the slow, almost drifting walk. The animals can gallop for several miles without breaking stride, stop short in perfect balance, and run up steep talus slopes with remarkable speed, revelations of their mountain-climbing heritage. They have a curious habit of occasionally pausing to sit on their haunches when rising from a resting position, an action that gives them an air of being preoccupied with thought. Adults also roll over on their backs and loll, with their legs suspended in the air.
Adults maintain a generally stolid demeanor, even when calves cavort wildly among them or when arctic foxes scamper and feint back and forth through a herd. In summer, however, adults are just as apt to romp in creeks and rivers, which they seem to delight in splashing and whirling through. (An American archaeologist working on Banks Island told me about a herd of seventeen or eighteen he watched slide down a gravel hill into a creek on their rumps and then go bucking off like horses in various directions.) Moving water is a short-lived summer phenomenon, and Anne Gunn, a Scottish biologist, remembers watching newborn calves encountering it for the first time. “The calves were spell-bound. There were seven or eight of them, about two months old. They jostled each other at the edge, shocked to get their feet wet, then ran off into the herd, stomping and bucking to get away from it.” Young calves chase each other regularly through a grazing herd and play “king of the mountain,” perching their oddly tapirlike bodies on tussocks, their small feet pressed together like a mountain goat’s.
Muskoxen are unique among ruminants in the amount of body contact they make. Even when they are fleeing, they gallop away shoulder to shoulder, flank to flank. One of the most dazzling displays of this I ever witnessed occurred on Seward Peninsula when a herd of muskoxen spun around on a hill in confusion at the approach of a low-flying aircraft. They moved as a single animal, rising in a tight turn to change direction. The wild, synchronous sweep of their long skirts was like a dark wave of water climbing a sea cliff before falling back on itself. Long-term muskoxen researchers frequently comment on these synchronous aspects of their behavior, noting, for example, that a herd feeds and rests on a rough cycle of 150-minute periods, winter and summer.
At the approach of a threatening animal, including men and their dogs, muskoxen begin to draw near to each other, sometimes quickly, and occasionally in response to the sudden bellow of a herd bull. (The herd bull is more often distinguished, however, by being the last to respond, and the first to relax, in these situations.) The animals may initially press together in a line abreast, with the herd bull toward the center and slightly forward, and younger bulls at the flanks. If the approaching animal changes direction, or if more than one animal is approaching, the muskoxen may back around into a rosette, rump to rump, with calves and yearlings wedged between adults.
This defensive formation is not always symmetrical, nor do muskoxen always take this position when challenged—sometimes they just run off. But in evolutionary terms it has been exceedingly effective against their major predator, the wolf. Bulls and cows rush out from this formation to make short, hooking charges with lowered heads. Wolves are only successful if they can get behind a charging animal and cut it off from the herd, or if they dash into a momentary opening and snatch a calf. Wolves are patient and opportunistic in these situations, or they wouldn’t still be around either.
This close-contact, defensive formation is found in no other species, and it is interesting to speculate about its origin. Some researchers have suggested that muskoxen prefer hilly country to open plains, noting that they often run to a hilltop before assuming their defensive formation. When caught out alone by wolves, a muskoxen will try to back itself into a snowbank or a landform of some sort, even backing slowly into a fast-moving river, to protect its hindquarters. In the defensive rosette, of course, each animal creates a back and a side wall for the others. This suggests that somewhere in their evolutionary history muskoxen lived a long while in open country, where they discovered a way to create, cooperatively, the spatial relief necessary to protect themselves.
Muskoxen herds change size and composition over the year. Summer groups tend to be small, from two to ten animals, while winter herds may consist of sixty or more animals. In summer, too, one is especially likely to see lone animals, almost always bulls, and single-sex herds—bulls or cows accompanied by younger animals and calves. As bulls come into rut the presence of a mature breeding bull within a herd may become apparent, though it is taking a step in the wrong direction to call such aggregations “bulls with their harems.” (Bulls are selecting themselves out as suitable male parents in their violent rutting encounters; what females are doing at this time is more obscure, but chances are they are not as passive in this drama as they appear.)3
The makeup of a particular herd, to take the extreme examples, can change frequently or remain stable for months on end. A large herd grazing in a sedge meadow may, after longer scrutiny, be seen actually to consist of multiple, discrete herds. Two herds may merge to become one; a day later three herds may emerge. Herds are neither disorganized nor rigidly organized. They are cohesive social arrangements existing in time. Biologists posit that they give some animals advantages in their feeding, breeding, and survival strategies, but they are not certain what these are.
Changes in the composition of muskox herds suggest that both individual animals and the aggregations themselves have “personalities.” Mixed herds do not always consist of retiring females and younger animals being led by domineering males. Cows as well as bulls influence herd movement and behavior, though the activity of herd bulls is frequently more evident. Herd leaders emerge not only at the approach of predators but whenever obstacles present themselves—a formidable river, a steep escarpment, or a crumbling cutbank. A knowledge of the other animals’ personalities, some actual experience with each other, may come into play in these situations and may be especially apparent in the creation of a defensive formation. Perhaps animals somewhat unknown to each other are the ones that panic, running off to leave calves and their mothers behind; while other groups, better known to each other, are the ones that move with efficient precision, the older animals butting and kicking momentarily confused or obstinate calves to the protective interior of the formation.
We are sometimes at a loss in trying to describe such events because we unthinkingly imagine the animals as instinctual. We are suspicious of motive and invention among them. The lesson of evolution with the muskox, an animal that has changed little in 2 million years, is that whether it is witty or dull in its deliberation, a significant number have consistently chosen correctly.
The muscular, restless behavior of rutting bulls is so charged with energy that humans experience nervous amusement as well as exhilaration in watching it. The same interactions—head-butting, horn display, charging—go on all year, but they increase in frequency and intensity during the rut. The bulls’ otherwise placid and presumably subtle relationships with each other take on a raw edge of intolerance.
David Gray, a Canadian muskox biologist who observed bulls’ behavior closely for a number of years in the Polar Bear Pass region of Bathurst Island, was the first to fully describe these male encounters, using the categories that follow (from least to most intense).
First is the (usually) passive displacement of one bull by another at a feeding spot. As one bull approaches, the other simply moves on, often to displace another animal. A bull might raise its head to regard another bull, ordinarily a sign of attentiveness or alarm as well as a mild threat display (or, to be perfectly candid, a sign he is only urinating). A more serious threat display, one unique to muskoxen, is lowering the head to rub one or the other of two pear-shaped glands below the eye on the inside of a foreleg. This is often done with great vigor, suggesting a “whetting of the horns.” More agitation still is expressed by an animal raking the ground with the tips of his horns, or escalating his irritation to head tilting. In head tilting, bulls move toward each other with averted eyes, leading with a shoulder and a prominent display of the horn boss. In doing so alone, one bull appears to be circling sideways around the other animal; when two bulls are head tilting simultaneously, they are said to be “parallel walking.”
The most serious confrontations are actual head butts and charges, which vary in their intensity. Two bulls may place their horn bosses together and push mild-manneredly at each other for a few moments—or push off their forequarters with driving strength and quick, ferocious thrusts of the head. A loss of advantage here opens an animal to sideways, jabbing hooks with the horns, or goring. When two bulls engage each other like this—head tilting, parallel walking, butting and charging—their movements become stylized. They select flat terrain for these meetings, heightening the aura of ritual. The usual deliberate walking gait becomes stiff-legged, slow, and exaggerated. A charge is preceded by side-to-side head swinging and a backing away from each other, as though the air between them had suddenly expanded. They charge from 20 to 30 feet apart, furious head-to-head crashes that can knock one animal back on its haunches or carry both animals up on their hind legs. The sound of their meeting is like the fracturing of sea ice.
Bulls may charge each other repeatedly. When they back away, bristling with energy, the image is primordial. The mane is erect. The neck is swollen, exaggerating the size of the forequarters. Their eyes, their long guard hairs, glisten with light. Should a wind be blowing and tatters of underfur be whipping about their flanks in streamers, their appearance is apocalyptic, savage with intent. The encounters are sometimes fatal.
Mating is a less violent affair. The males, again in the human view, seem fulsome in their attentions to receptive females. They approach them repeatedly, overwrought and obsequious, sniffing the vaginal opening, drawing close along the female’s flanks and resting a chin on her buttocks, nosing her neck, sometimes scraping her flanks with a foreleg. Bulls also engage in a mating display of sorts by twisting their heads over to look up at a female. And they bellow. David Gray describes the sound as “similar to the roar of a caged African lion.”
Mating occurs when a female, repeatedly tested in these ways, remains stationary. The bull, rising on his hind legs, mounts her. The act lasts but a moment.
Mating takes place from mid-August to mid-September. Calves are born 240 to 250 days later, in mid-April to mid-May. Like most prey species, muskox calves are born precocious, able to stand up almost immediately and very soon able to run. Mid-April is still winter, but as long as they do not get wet, calves seem to survive very well. They are well insulated and born with ample adipose (brown) fat reserves from which they can draw heat. They spend much of their first few days resting and nursing. Their mothers call after them softly. In cool weather they take advantage of their mother’s body as a shield, curling between her legs to sleep while she turns her back to the wind.
Herds are stationary during calving, which might go on for a month: but they rarely travel far at any time. Their summer ranges, where succulent sedges and other forbs emerge in June, and their winter ranges, where sun-cured grasses are exposed by winds, are often within only a few miles of each other. The infrequency of large-scale movement underscores a salient aspect of muskox ecology: only a relatively few, widely scattered feeding areas in this severe arctic environment will support muskoxen.
Researchers speculate that migration to a new area may occur as a result of the rut, when a single male forces other mature males to leave the area and these bulls depart with a few cows to establish a herd of their own. One theory about how whole herds locate new range to move to is that solitary bulls, wandering great distances in summer, find areas of suitable, year-round forage, then return to a herd in the vicinity of the one they left. Come fall, they lead the herd across sparsely vegetated range (including sea ice) to the new pasture. Pheromones (biochemical substances an animal produces and which its olfactory system can later detect) might make such movements possible. Bulls scent-mark by dribbling their urine on grasses and other elevated spots, especially during the rut. They also mark tussocks with secretions from their preorbital glands. These scent posts very likely play a role in mating but may also be important in regulating the spatial arrangement of muskoxen in a given landscape. Over time, such scent-making might well prevent over-grazing in those areas where muskoxen thrive, by “forcing” animals to spread out.
How muskoxen navigate over their native landscapes in darkness and snow, how they conceive of the space around them, is unknown.
Muskoxen maintain a constant body temperature of about 101°F, no matter what the air temperature. Because they routinely endure extremes of –40°F for prolonged periods of time, conditions that would drive polar bears and perhaps even arctic fox to shelter, the ability to maintain a constant temperature is striking. The heat they depend upon is generated by normal cell metabolism and the burning of stored fats and by other complex biochemical processes connected with nutrition. Their thick coats provide such excellent insulation that little of this heat escapes, the reason why snow that accumulates on their backs in a storm doesn’t melt.
Ecologists are reasonably certain that arctic animals do not increase their basal rate of metabolism until the temperature reaches a certain critical level, different for each animal but around –50°F. (Birds are an exception.) The climate, in other words, does not force arctic animals to eat more. Heat retention, not increased heat production, is an animal’s principal defense against cold. In 1847 Karl Bergmann suggested that since heat production is a three-dimensional process (heat radiates in all directions) and heat loss is a two-dimensional phenomenon (it occurs only at the surface of the skin), it would stand to reason that animals living in cold environments would evolve larger body sizes, with a greater ratio of mass (heat production) to surface (heat loss).
Bergmann’s Rule, as it is called, is a somewhat archaic concept, as is a companion, Allen’s Rule, set out in 1877. Allen believed that in cold environments there is a tendency toward the evolution of shorter extremities—ears, limbs, tails, and snouts. Both rules have a firm empirical basis in spite of many exceptions. What makes them archaic is that other adaptations for heat retention are comparatively more effective. The insulation provided by hair and underfur, exceptional in the case of the arctic fox and the muskox, is one source of warmth in severe cold. Polar bears are heavily insulated with fat, and den up in the worst weather. Other animals, particularly birds, warm cold venous blood from exposed extremities by running it through a coil of warm arterial blood before it reaches the body core. Animals also use differential heating (arctic fox, for example, can reduce the temperature of their footpads to near 32°F), and changes in the electrical conductivity of their nervous systems to stay warm. No single one of these adaptations, however, is effective by itself; and physiological and biochemical research continues to reveal a more complicated picture of how arctic animals function in severe cold (e.g., how they control the loss of water from their bodies, or replenish what they do lose).
Muskoxen and other animals also conserve heat in winter by a conspicuous economy of action. In very cold weather, when any movement at all requires the burning of limited fat reserves, animals will just stand still for long periods of time, so long that someone has suggested the term “standing hibernation.” When muskoxen do travel in cold weather, they move in single file through any appreciable accumulation of snow, stepping carefully in the track cleared by the animal ahead of them. During blizzards they might even bed down for several days. (An explorer in Greenland once terrified himself by seeking refuge from a storm in the lee of what he first took to be mounds of snow-covered earth. They were muskoxen, and they began to stand up as he walked over them.) Alwin Pederson believed that in the severest storms muskoxen choose an open area where the wind blows in a single direction and form a wedge into it, the herd bull at the apex, calves and yearlings to the rear. David Gray, for one, doubts that this occurs. He once observed a herd of muskoxen in a storm with 24-knot winds, blowing snow, and a temperature of –27°F (wind chill about –90°F). The animals “continued to feed in the usual manner or remained lying down” with their backs and sides to the wind.4
