The differences between Minnesota and Isle Royale reflect the fact that not all wolf-prey systems are the same. Isle Royale has only wolves and moose. Sweden has only moose and humans. Gaspésie Provincial Park in Quebec has moose and bears. Bears, wolves, and humans alike prey on moose in Alaska’s Kenai National Wildlife Refuge. Wolves, bears, and lynx share Denali National Park with moose, caribou, and Dall’s sheep. Each system has its own wrinkles. Some, like Isle Royale, have good escape cover for prey. Cows with calves resort to small islets that fringe the island, where they are less likely to be attacked by wolves. Most wolf-prey systems once had human hunters to complicate the problem. There is still disagreement as to what role native Americans had in maintaining elk and sheep populations in Yellowstone National Park. The Kaibab Plateau deer herd may have been destined to overpopulate their range after the five hundred Indians that once hunted there were removed. The more complexity we find in these different systems, the harder it becomes to generalize from one to another.
The Minnesota deer herd’s decline still did not suggest to Mech that the old view was right, or that wolves were the ultimate cause of the deer decline. Comparing the ages of deer killed by wolves with the ages of deer killed by hunters, Mech found that the wolves were still taking the young and the old, the least fit members of the deer population. He was convinced that this was “compensatory” predation: the wolves were taking deer that would succumb anyway to disease or winter cold.
Mech believed that the evidence showed that reduced nutritional resources were the cause of the decline. There was less logging going on, and so the young aspen stands which came up right after logging, and in which deer browsed, were growing less common. The severe winters severely stressed the deer, and the deep snow hindered escape. With the deer so weak and slow, the wolves committed surplus killing—the killing of more deer than they could eat.
Mech believes that the effects of one hard winter might not be seen for years. He has described what he calls “the grandmother effect”: “If the grandmother is well during pregnancy, the grand-offspring stands a better chance of not being eaten by a wolf.” If a doe is stressed by hard winters, her offspring might have a weaker immune system or less intelligence, and if the offspring survives, its weakness may in turn affect the third generation. “These offspring might look perfectly healthy to any observers,” says Mech. “Chances are they’re a little lighter-weight. But laboratory studies on rats whose parents had been nutritionally stressed show they have fewer brain cells. They’re dumber; they can’t learn mazes well. Their immune systems aren’t as good.”
Mech’s contention about the victims of wolves is difficult to prove. He says: “Generally, when you come to a kill that a pack has made, there’s very little left. There may not be any bones. If we’re lucky, we have a jawbone, and that will give us some idea of age. If we get a leg bone, that will give us some idea of condition. But there’s a real flaw in the femur fat test. If the marrow is depleted, you can say this animal was close to dead anyway. But the converse is not true. If you find a fully fat leg bone, that doesn’t mean the animal was in good condition. It turns out that only 2 to 3 percent of the animal fat is in the bone marrow. If it’s fat, the deer could still have been down to its last 10 percent of fat. It doesn’t tell you whether the deer couldn’t see very well, or its IQ was way low.”
Others disagree with Mech’s contention that weather and food are the chief limiting factors. François Messier, of the University of Saskatchewan, looked over Mech’s data and declared that he could find no effects of snow on deer-population growth. He concluded that “in some situations wolf predation can prevent moose populations from increasing, even if environmental conditions and forage resources are suitable.” A. T. (Tom) Bergerud, of the University of Victoria in British Columbia, looking at moose-population figures in Pukaskwa National Park in Ontario, concluded, “Predation limited the increase of the moose population and may have caused a decline.”
Bergerud is in the forefront of Mech’s critics. At sixty-three, he has long straight hair, a white mustache, gold-rimmed glasses, and a faded denim jacket. He has a cracker-barrel informality, but it is laced with a tone of controlled anger.
“My Ph.D. is in caribou and lynx,” he says. “I went to Newfoundland in 1956, and I found these caribou with sores on their necks, and it was a major mortality factor. We all came out of school indoctrinated with Errington’s idea that predation was compensatory mortality and that predators take the weak and the sick. I lost almost ten years in Newfoundland trying to understand why these caribou were dying of sores on their necks. I was sitting around a campfire one night feeling, ‘I’m stumped. This is a wound. Somehow, something is going in there.’ At the campfire, a shepherd told me, ‘When lynx get my sheep, they always get ’em on the neck.’ We got the skull of a caribou, and there were four tooth holes that fit the bite of a lynx. It turned out that lynx have Pasturela multocida bacteria in their saliva. The lynx would attack the calves, and the mother would chase the lynx off, and the calves would die later. There’s a ten-year cycle in lynx and a ten-year cycle in caribou-calf crops. Lynx were definitely causing the decline.”
Ever since, he has sought to show that predators can be the chief factor holding down prey populations. He put radio collars on caribou so that when they died he could find the carcasses and judge what had killed them. “The first thing we found was, the calves were being killed by bears and wolves,” he says. Comparing estimates of moose populations in areas with and without wolves, he concluded, “Moose populations in North America appear to be limited by predation.” Bergerud performed statistical analyses of moose and caribou populations in various areas where there were government-operated wolf-control programs in British Columbia, Alaska, and the Yukon. In lectures, he displays graphs depicting moose and caribou populations before and after a number of these hunts. Except where bears were responsible for most of the ungulate predation in the first place, he concludes that the moose and caribou populations increased after wolf controls. That, he believes, is proof that wolves had been limiting them all along. In one Alaska study, he judged that, during the year of the hardest winter, biologists found no starved caribou. He dismissed Mech’s hypothesis that a hard winter may dispose calves to predation generations later as vague and impossible to prove.
Bergerud believes that biologists who view wolf predation as compensatory are misled by Isle Royale. Says Bergerud, “Isle Royale really griped me. It’s in all the textbooks as a classical example. Isle Royale is really an abnormality, an artifact. The artifact is that there is no ingress of wolves.” Anywhere else, he says, when there is a plentiful food supply, wolves come in from other areas.
The idea that predators do not regulate prey has come under increasing attack in Alaska and Canada. In the 1970s, biologists there were concerned about a continuing decline among caribou, and their seeming inability to rebound when habitat conditions seemed capable of supporting more of them. Theoretically, as prey populations decline, predators find less to eat and also decline, until eventually the prey population recovers. Mech’s study in Minnesota showed that, as the deer population declined, the wolf population decreased by one-third. Mech believed that, as predation relaxed, the deer herd would recover. In Alaska, game officials thought they saw something different happening. Says David Kelleyhouse, director of the Alaska Department of Fish and Game’s Division of Wildlife, “It was a prevalent notion in the 1950s and ’60s that predation had a rapid feedback effect. If the prey went down, the predators would go down immediately. But that was wrong. They lag.”
When the moose and caribou populations have declined to such a low density, says Kelleyhouse, the wolf population is still high, and the wolves no longer bypass the healthy animals to attack the weak. They are forced to hunt healthy moose and caribou, and they prove perfectly capable of killing them. “It’s strictly additive mortality,” says Kelleyhouse. “It’s not compensatory any more.” Kelleyhouse says he has seen e
vidence of this: “I have seen a big male wolf keep diving in on this cow moose and repeatedly getting kicked. She was a perfectly healthy cow. We shot the wolf and autopsied him. He had a broken jaw and broken ribs. Broken bones all over.”
In some circumstances, as one prey population declines, wolves will switch to alternate prey. In interior Alaska, when caribou decline, wolves might switch to moose. Wolf numbers might then remain high while the caribou continue to decline, and thus, Alaskan officials believe, keep caribou or moose at unnaturally low numbers. And because many people have come to Alaska for the hunting, low moose and caribou numbers become political issues.
Bowing to hunter pressure, and backed by biologists convinced that moose and caribou declines were due to growing wolf populations, the Alaska Department of Fish and Game began killing wolves. Between 1976 and 1982, government hunters went out in helicopters and shot more than 70 percent of the wolves in certain areas. In the years following the control efforts, moose populations increased in some of the areas. William Gasaway, Kelleyhouse, and other Alaska Department of Fish and Game biologists reasoned that, if the wolves had been merely killing the weak and the sick, the weak and the sick would go on dying after the wolves had been removed. They concluded that, since the prey populations increased, the wolves must have been the limiting force. Similar hunts were initiated in the Yukon, and moose and caribou populations increased there as well. Wrote Gasaway, “Increasing evidence suggests predation by wolves and one or two species of bear is the primary factor limiting moose at densities well below carrying capacity [the maximum number of moose the habitat can support].” Declared Alaska Department of Fish and Game biologist Robert Boertje, “In the 1960s, we didn’t think predation had much effect on prey numbers. Now we’ve gone pretty much full-circle. Where wolves are regulated, moose density is much higher, and harvest by hunters is much higher. Moose will occur in low density in Alaska unless wolf and bear populations are manipulated.”
Others say that Bergerud’s studies and those of the Alaska Department of Fish and Game are inconclusive, that they don’t show that weather, disease, or changes in food resources or other factors didn’t predispose the moose and caribou to wolf predation. Rolf Peterson criticized one study for using different census techniques on prey populations from year to year, for not taking into account differences in vegetation, and for using overly broad indicators of snowfall. Wolf controls in Alaska were not followed with long-term research to see whether prey populations remained high after the predators recovered. Moreover, since sport and subsistence hunting continued during and after the controls, the effect of human hunters clouded the picture. So far, the studies show only that one can, over the short term, increase the number of moose or caribou available for hunters by shooting wolves.
Bergerud claims victory. “Most pro-wolf people still want to make the argument that wolves are doing nice things out there, keeping us healthy,” he says. “The argument is really over. I don’t think many front-line biologists are saying wolves don’t have an impact.”
Bergerud is partly right. Says Peterson, “Nobody would argue wolves aren’t important in the regulation of prey. The scientific viewpoint that predation was just a compensatory thing, that they just killed the weak and the sick, has pretty much been tossed aside.” But the argument is far from over. Now biologists contend over how predation, weather, food resources, and other factors relate to one another. If wolves do regulate a caribou population, for how long do they do so? A year? Two years? Or more than that? How do logging, hard winters, dry summers, or the activities of other predators relate to the effects of wolves?
The answers to these questions—and the lack of answers—lie at the heart of nearly everything we do about wolves. If wolves limit moose and caribou, for example, should we manipulate wolf populations to boost caribou populations that are alarmingly low in parts of Canada and Alaska? Previous experience shows that we can, at least temporarily, increase some caribou populations by killing wolves. But what are the long-term consequences of such programs?
Theoretically, as prey increase, predators increase, until at some point the two reach a point of equilibrium, with predators just numerous enough to keep the prey population steady. Barring environmental changes, the number of predator and prey could remain the same for centuries. Most biologists believe there is only one such point of equilibrium. But a theory advanced by A. R. E. Sinclair, of the University of British Columbia, and Gordon Haber, an independent researcher in Alaska, proposes that there may be multiple equilibria. Thus, wolves may hold moose or caribou populations at low densities. Or the prey population may increase until there are a lot of healthy breeding adults and more than enough young and old to feed the predators. At this higher population of prey, predators are limited by other factors, such as the availability of adequate denning sites, and the inability to live in very large packs. They fight with one another. They invade one another’s territories. In the stress that follows, fertility rates fall. The high prey population and the self-regulated predator population may persist indefinitely.
A study in Australia removed foxes and feral cats from an area to see whether afterward, when predators repopulated the area, they would again reduce the rabbit population. The study found that the rabbits increased to higher densities, but when the foxes returned, the rabbit population did not drop back to its earlier low density. The researchers concluded that this demonstrated the existence of multiple equilibria. If multiple equilibria exist in wolf-caribou systems, a wildlife agency might undertake one wolf-control operation and ever after allow nature to manage the system.
Wolf biologists today argue heatedly over the existence of multiple equilibria, but as yet there has been no direct test of the theory with wolves. A test could come out of a wolf-control program begun in the Yukon in 1993. The Aishihik caribou herd in the southwestern Yukon began to decline in the early 1980s. Between 1980 and 1990, the population plummeted from fourteen hundred to seven hundred individuals. Meanwhile, moose populations dropped to the lowest density recorded anywhere in boreal forests. The local native peoples, who depend upon moose and caribou for subsistence, urged the government to do something. It is not clear why the moose and caribou declined. Neither subsistence nor sport hunters appear to have exerted much pressure on the caribou population. “There is some evidence that the population was being limited by wolf predation,” says Robert Hayes of the Yukon Fish and Wildlife Branch. But researchers fear that putting radio collars on caribou calves, to verify that wolves are taking them, might make them more conspicuous and therefore more vulnerable to predators.
Instead, in 1993 the Yukon Fish and Wildlife Branch began to control wolves in the area. After removing 75 to 85 percent of the wolves, it planned to prohibit hunting and to monitor the moose, caribou, and wolf populations for several years, to see whether there is a higher density of prey that would support both wolves and hunters with no future need for wolf controls.
A lot rests on the outcome of the debate over multiple equilibria. If there is only one point of equilibrium—if wolves normally regulate prey at low densities—then wildlife managers will feel they must choose between hunters, who pay their salaries, and wolves, who don’t. If there are multiple equilibria, then it may be possible in the future to manage the herds for humans and wolves without shooting wolves.
We have come a long way from the view that wolves are simply a curse on the gentler forms of life, but we haven’t yet arrived at our destination. What we have found is that predation is far more complex, far more varied, far more difficult to understand than we ever thought it would be.
Even if we can encompass all this complexity, it seems to me unlikely that we will ever really understand predation, for its greatest complication lies not in the woods of Minnesota or the mountains of Alaska but in our own minds. We will always have difficulty separating what killing means to wolves from what killing means to humans. And we may never agree upon what killing means to humans.
Swaney meant to make them feel that they stood pale and trembling outside the elemental relationships of life, and that they were immoral because they could not connect act with spirit. It was a fairly delicious act of red man’s revenge.
That line between object and feeling often daunts us. During the Gulf War of 1991, for example, Americans sat in front of their television sets, gripped by the sleek precision of smart bombs which carried their own televised point of view as they dropped from the wings of jet aircraft, slid in great whistling arcs over the desert landscape, fell with eye-widening speed toward a looming bunker below, slipped soundlessly through an airshaft, and exploded inside, committing their own concussive suicide in the process. As we watched, we seemed to become machines. The war was, to our hearts and eyes, bloodless. Though one hundred thousand Iraqis died, we never saw a body, and we had no feeling whatsoever for their death or any individual suffering. Killing became an abstraction.
The Company of Wolves Page 10