What Hunting Animals Do? Probably the first man who ever kept sheep lost some to wolves, and cursed the wolves accordingly, passing on his opinions to his offspring so that wolves finally became ogres in fairy tales. In Europe one of the duties of feudal lords was to hunt wolves, and they did it so well that no wolves are left. In Alaska, agents of the the government are still killing wolves from airplanes, with the declared belief that it must be “good” for the “game” to do this.
No doubt part of this attitude stems from fear of the wolf, one of the few animals capable of attacking a man who does not hold a firearm. But our belief in the killing power of predators extends even to those that cannot hurt people. We tell preschool children that cats are necessary to “control” mice; while spiders are “good” because they eat “flies.” In western American states, comic cowboys have been shooting bald eagles from helicopters, giving that age-old excuse of the wolf-killer that the birds were taking their sheep.
Naturalists tend to frown on shooting wolves from airplanes or birds from helicopters, but they find it hard to escape from the underlying philosophy. Predators kill prey, but if they kill it all, they will themselves starve. On the other hand, they will obviously kill as much as they can get. There must be a “balance” between their efforts to kill and the efforts of the prey to escape, a balance that controls the numbers of both predators and prey.
We have learned that the supposed struggle between species is a decidedly muted affair that leads to peaceful coexistence; might not the struggle between predators and their prey be decisive in providing that general balance we see in nature? We are inclined to like this simple idea, but the truth is not so simple.
It is easy to think of a fierce hunting animal such as a tiger or a lion, or the even fiercer combination of wolves hunting together in a pack, as a fearsome scourge for their timid prey. The meek may escape by flight, but it is certain that the hunter must manage to fill its belly at regular intervals, or the big cats and wolves would not exist. We can easily think of their hunting as depredations, as shepherds have always thought of the activities of wolves.
And yet the few careful studies that we have of the last big cats and wolves tell a very different tale. Adolph Murie long ago watched the wolves on Mount McKinley, living for years in the wilderness, recording what the wolves did, and giving us our first impartial study of what big predators really do. A very important part of the wolves’ food supply was wild sheep, and Murie watched the wolves as they hunted. So here was the shepherd’s curse truly at work on sheep that were without the protection of a shepherd. And Murie, in his painstaking way, deciphered a very special record of what the wolves killed.
In the Arctic, before finally decomposing, bones lie about on the frozen ground for years, particularly the hardest parts such as the tops of skulls, and on Mount McKinley there were many whitening skulls of sheep. Murie collected all he found, 608 of them. His years of careful watching told him that the only important cause of death for a Mount McKinley sheep (other than by a human hunter who would take the head) was being killed and eaten by wolves.
So, these 608 skulls represented a large sample of the wolves’ victims. This would not be very informative, but Murie was able to tell the age of each sheep when it was killed by the wolves from growth-rings on the horns. There were only two age classes in the collection of skulls, the very old and the very young. Apparently, these were the only sheep the marauding wolf-packs caught, the infirm old and the feeble young.
Mount McKinley wolves did not kill sheep in the years of their prime; the skull collection showed this very clearly, and it was also quite consistent with Murie’s personal observations of the wolf pack at work. If a pack of hungry wolves is the terrible instrument for destruction described by folklore and fable, this is not what common sense would expect. The wolves did not kill sheep in their prime, which leads us inexorably to the conclusion that they could not. Apparently, natural selection has so fashioned sheep that they can outrun, outclimb, or outwit their formidable adversary.
More recently another pack of wolves has been watched at their hunting, this time on Isle Royale, an island forty miles long in Lake Superior. The only big game on the island that can feed the wolves through the winter are moose, and it is the powerful moose that the sixteen or so wolves of the Isle Royale pack hunt down through the winter snows.
The pack has an appetite that requires one moose every week. From the air David Mech watched to see how they got this moose, picking up the clear trail the wolves left through the deep snow in the early morning, then winging overhead as they went about their hunting. Sixty-nine times he followed them thus. Nine times he was up with the hunt all the way from the find to the check from the check to the view to the kill.
Twice he saw the kill near where he could land his plane, came running at the pack waving his arms to drive the hungry wolves from their meal, and had a look at the carcass himself. Studying chewed-over remains of many more kills, he saw very clearly what happened when the wolf pack closed with a moose.
In the chase itself the wolves were superb. When they had once hit on the trail of a moose there was very little chance of the moose avoiding them as a fox so often avoids fox-hounds. Perhaps this is not surprising, for the trail of a moose running in thick snow would not need much trail-craft in the following, but most of the moose escaped with their lives all the same.
The wolf pack either gave up early or after a short skirmish with a moose that had turned and stood to confront its persecutors. Whenever a prime moose chose its place and stood to fight, the wolves gave up and went away. The moose they closed with and dragged down were always youngsters in their first two years of life, old senile moose, or the sick.
Both Mech’s observations of the hunting and his examination of the remains showed very clearly that the Isle Royale wolves never took prime moose. Like the Mount McKinley wolves, they took only the easy meat from the herd: the old, the young, and the sick.
It is easy to see why the wolves leave prime moose alone; they are too dangerous. There can be little doubt that if sixteen wolves really closed with any moose, they would overcome it, however strong and fit it might be. But some of the wolves would get hurt, and a hurt wolf can hunt no more. The natural selection sees to it that the strain of brave aggressiveness in wolves is purged from the wolf gene pool because such individuals would incur more than an average share of being fatally hurt and thus would leave fewer descendants.
The wolves that have survived the winnowing of natural selection are those that make do with the the prey they can kill without danger to themselves. Since packs of wolves habitually kill neither prime moose nor prime sheep (obviously for different reasons) our preconception that they might regulate the numbers of their prey is bound to develop doubts.
The wolves certainly have some effect on the populations of their victims because they kill some of the young, but this is much less than the depredations that folklore and intuition would lead us to expect. And for other big predators, which hunt alone, the difficulties of severely culling the numbers of their prey are even greater.
The American mountain lion, sometimes called a puma, a cougar, or even a catamount, is small as big cats go, but it is still a powerful animal and it is known to hunt white-tailed and mule deer. The accounts of mountain lions in popular mythology might make it seem as terrible a scourge to the “defenseless” deer as wolves were supposed to be to sheep, yet the reality is again very different.
We still have no good eyewitness accounts of much mountain-lion hunting, partly because the lions are secretive but also because our philosophy of killing them has made them nearly extinct over most of their old haunts. But there are some left in Idaho, and M. G. Homocker recently won a Ph.D. with some remarkable tracking and woodlore in the haunts of the mountain lions.
Homocker found that the Idaho mountain lions in winter are complete loners; each has a tract of wilderness through which it hunts alone. Tracks in the snow showed that this loneliness is from choice because a lion will turn away from the tracks or the presence of another. Even powerful males in their prime will turn aside from a weaker or younger animal. There is no social dominance in this, no expulsion of a weak animal from a superior’s preserves.
Homocker concluded that the lions habit of each keeping to itself had been preserved by natural selection because of the difficult task of hunting. The big cats could only kill deer if the deer were quite unsuspecting. Deer that were nervous because a marauding lion had been through the country were virtually unattackable by another.
Although there were plenty of deer in the wilderness, the mountain lions had to keep a very low profile, or they could not catch deer. This does not sound as if mountain lions kill easily or that they have much influence on the numbers of deer in a wild population.
The big cats are less than impersonal killing machines too. George Schaller relates the killing methods of tigers as they take tethered domestic buffaloes and his account does not suggest that killing is safe or easy for a tiger even with these advantages. The Tigers ran at their prey, half-climbed on their backs, wrestled them to the ground, then dodged the flailing hooves to seize the buffalo by the neck.
It always took several minutes for the buffalo to die. This was not at all the quick surgical operation of killing that nature-story accounts of the big cats would lead us to expect. If it has that much trouble with a tethered domestic buffalo, it is not improbable that a lurking tiger might normally let the formidable animals pass unmolested and look for something more out of sorts.
It is probably generally true that large vertebrate predators go about their killing cautiously. Whether it is a lion or tiger stalking a game herd on the plains, or wolves running down their quarry through a northern winter, the predator always faces the reality that it must kill again and again if it is to survive. Fifty-two desperate encounters a year would be likely to result in hereditary oblivion.
Neither big cats nor pack-hunting canines have the firepower to pull off fifty-two safe butchering’s a year if they attack the fit and the strong. They avoid desperate encounters, unless extreme hunger drives them. Usually, they feed by culling the old, the sick, and the young.
There is no doubt that all these big fierce predators have some effect on the numbers of their prey because they kill the young. But they cannot usually kill a very large proportion of the young because the number of predators is relatively small. The young typically make their appearance at only one time of the year, and the predators must live the rest of it too. The numbers of big cats and wolves that a herbivore mother must look out for in the spring is mercifully low because it will be the number that has been kept alive through the winter by the supply of old and sick animals.
It thus seems very likely that the larger and fiercer predators are not nearly so important in regulating the numbers of animals in nature as common sense suggests. They are really to be looked upon as scavengers without the patience to wait for their meat to die. They cheat the bacteria who would have got the bodies otherwise.
Two rather pleasing thoughts come from this discovery. One is that the lives of big game animals are lived in a large measure of freedom from the awful world of tooth and claw that we can conjure up by a careless reading of Darwin. Not only do these animals live in that peaceful coexistence with their neighbors, which the mathematical ecologists discovered, but they also may live with less fear of being killed than we had supposed, except as a sort of euthanasia.
The second pleasing thought is that those who like to shoot big game themselves no longer have a pretext for killing off the wolves and cats before they start on the deer. But if the firepower of a big cat is insufficient to devastate a herd of game, the firepower of the smaller predators may be truly awful. A spider or a wasp is a deadly efficient engine of destruction.
Perhaps most of the species of hymenopteran insect that we loosely call wasps are in the business of hunting caterpillars and grubs of other insects, piercing them and laying their eggs under the skin, letting the maggots feed and grow on the living flesh of their victims, and eventually flying away from the empty carcass as mature wasps themselves.
Although the victim thus takes longer to die, the crucial predatory act is the initial attack by the female wasp on the caterpillar, and in this encounter the caterpillar stands no chance. When a wasp strikes, it is not like a tiger striking a buffalo; the issue is never in doubt; the chance of the wasps being wounded is zero. The same must be true when a web-spider closes with a fly struggling in it meshes.
It must also be true when a spider-hunting hornet plunges like a dive-bomber, with its armor-plated body and its poison-loaded stinger, on a spider, sighted in the open. It must also be true when a tiger-beetle pounces, when a praying mantis reaches out with its dreadful arms, and when a large carnivorous diving beetle finds a small tadpole.
In all these, the only hopes for the hunted are to escape detection or timely flight. We might expect, therefore, that small predators can have more potent effects on their prey than do large predators. That these small predators can truly be devastating has been shown by the success stories of entomologists when they have ridded farmlands of an agricultural pest by introducing a suitable natural enemy, so-called biological control.
Celebrated among these successes is that of the Californians who rode the orange groves of the little, white, flightless insect called the cottony- cushion scale, which had appeared in plague-like proportions in the 1880s, threatening to destroy the entire citrus industry. The cottony-cushion scale was an Australian insect that must have come to California by the sea in a cargo of fruit, so a Californian entomologist went to Australia to look for enemies of the scale.
He had wasps in mind, and he found some, but they turned out to be ineffective. Then he found an Australian ladybird beetle called the vedalia. A little red ladybird with black spots like those common in Europe and North America. He sent to California a total of 129 live vedalias.
In January the few vedalias were put on an orange tree heavily infested with the cottony-cushion scales and the tree were covered with a muslin tent. By April the tented orange tree was free from scales but rich in ladybirds, and they opened the tent to let the beetles out. By July the whole orchard of 75 trees was free from the pest. The news spread, and planters journeyed far to collect the precious beetles for their own estates. Within a year the whole of southern California was rid of the plague of cotton scales.
This pretty ladybird, the vedalia, has proved itself to be a far more deadly predator than any wolf or tiger. It searches with diligence and kills with utter certainty. It processes the calories from the bodies of its victims into its own babies with such dispatch that the next generation is ready to carry on the killing in just twenty-six days. As we have seen, this ferocious attack can exterminate the prey in an entire country within a season. But what can the ladybirds do then?
Only part of the success of the vedalias was due to their deadliness and mobility; the rest came about because they were given a concentrated target. In the wild Australian home of both the vedalia and the scales, there were no citrus orchards, and the food base of both must have been scattered trees in the forest. Life in a colony of cottony-cushion scales on an isolated forest tree might well go on for generations before a flying beetle found the colony to begin its killing.
And life for vedalia beetles who must hunt them would involve sending out the next generation in pioneering searches for new and distant trees bearing colonies of their food. The scales escaped their enemies by living scattered across the land, and their ladybird hunters got their livelihood by arduous and unremitting searches.
After the first slaughter in California it seems that something like the ancestral Australian the pattern was established between the vedalia beetles and their prey. In later years the infestation was gone, but if you looked hard enough you could find a colony of scales somewhere in the orchards, but they were so few they were no longer a nuisance.
Chance had let a few escapes the attack of the vedalias and they served to found new colonies after the scourge of beetles had passed them by. Each colony would live until a wandering beetle found it when it would be rapidly wiped out. But meanwhile, another colony started up somewhere else. Life for both vedalias and scales became a game of hiding and seek across the spaces of California.
It is likely that games of hiding and seek between predators and prey run on indefinitely for many small species of animals. The outcome is a consequence of devastating killing power, and it can be expected on common-sense grounds as well as predicted by formal mathematics. Scientists make equations that show the numbers of prey growing in the classic geometric way, but which are cut back by the attacks of predators.
In this formal scheme each attack results in a kill, as it will for small animals, and each predator turns its victims into more predators after a suitable time lag for the business of reproduction. The result is a model that predicts the absolute wiping out of the prey as the predator numbers build-up, perhaps after some oscillations. This is what we see in nature.
Locally the prey is wiped out as the model of efficient hunting says it must be, but the game has been started all over again somewhere else by refugees from the first game. The result is a scattered population of prey animals living many generations in security, but occasionally faced with local annihilation. This pattern results even when the game is started on so uniform aboard as was provided by the ranks of citrus trees in the equable Californian climate, but in nature there are many other forces at work to frustrate the hunters.
The plant food of the prey is itself scattered, there are various physical barriers to both search and escape, and the fluctuating seasons, to say nothing of vagaries of the weather, influence the outcome.
In places of seasonal climate both predator and prey must endure a hostile time, perhaps a winter through which they must persist in some quiescent state, as seeds, eggs, or dormant adults. It often happens that only small numbers survive this lean time. With every growing season, therefore, a new game starts, and this game has some of the qualities of a race.
The few prey animals that have got through the winter set about the business of reproduction, probably helped by the lush spring growth of their food plants. But the predators will find little to eat and will not be able to produce many young until later in the summer when the population of its prey will have built up. The predators may not have time to build up devastating populations before the coming of the next winter clears the game board once more for a fresh start.
The lives of small predators and their prey are thus different in fundamental ways from the lives of large animals. Large predators live alongside and within sight of their prey, like a pride of lions lying in the sun as the herds of African game wander by them. This is essential because the weapons of the big hunters are not good enough for the safe pursuit of indiscriminate slaughter.
But this peaceful coexistence is not possible for small predators and their prey, so they must live scattered, the one fleeing and hiding, the other searching and destroying. Moreover, the large animals live through many different seasons, which lets them smooth out the effects of weather. Short-lived insects and their kind pass through several generations a year so that they meet the different seasons with different generations.
The numbers of predators and prey can be differently hit by such adversities as winter. This means that the effective power of the predators is often nullified by the further scattering or reduction of populations. Large predators and prey persist in harmony which owes much to a certain lack of weaponry. Small predators and prey coexist, if not in harmony then in relative safety, because the very deadliness of the weapons combines with chance and their short lives to keep the antagonists scattered and apart.
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