The Company of Wolves (25 page)

In summers, when the wolves hide in the forest undergrowth, he would walk the game trails of Isle Royale, collecting moose bones to determine what the wolves were eating and how that related to moose-population cycles. He now has what must be the world’s largest collection of moose antlers, skulls, and assorted other bones, including bones collected by Adolph Murie on the island in the 1930s. The bones contain a coded history of the last sixty years of the island’s moose and, when arranged chronologically, tell of times of overbrowsing, and deformed bones and antler, and times of plenty, when moose were healthy and strong.

For years, the news from Isle Royale was that nature looked after itself, and smiled both on wolves and moose. Declared Allen in
The Wolves of Minong
, his detailed history of Isle Royale up to 1976, “These 18 years have been biologically productive.” But Allen warned, “Happy times do not last forever. The wolves probably have reached the maximum density they can tolerate, and they will be reduced.” And in the 1980s, the wolf population suddenly declined. In 1981 and 1982, fifty-two wolves died—some killed by other wolves, some by starvation, some, Peterson suspects, by canine parvovirus, an often-fatal disease carried by domestic dogs. By 1982, only fourteen wolves survived on the island. And in the ensuing years, there was no rebound. Pups were born, but few survived, and for every pup that lived, an adult died. After thirty years of watching the wolves increase, the researchers were stunned by this crash.

In 1988, the Park Service decided that the need to understand the collapse outweighed their desire to keep wolves free from human interference, and it allowed Peterson to begin using radio collars. These days, Peterson follows radio signals to find the wolves. From May through June, he tries to locate wolf kills in the woods. “We want to know about where the wolves are and if they’re alive,” says Peterson. “We’re mainly interested in whether they reproduce.”

He looks intensively for dens. If he finds one, Peterson insists on
being the first person to go in and howl and look at the rendezvous site. The most important research task is finding out whether the wolves are having pups, and, if they are, what is happening to them. Pups are afraid of airplanes, and hide from them so effectively that Peterson can’t make observations from the air. So he hikes in. “It’s the first time they’re seen, and I have to be out there,” he says. He is always careful not to get too familiar with the wolves. “We try to conceal the human form from wolves. Only rarely have we chased wolves off a kill to get a bone.” This may be overprudence, he allows: “I’d be surprised if wolves don’t know even that we’re in the plane. It could be they have a complete understanding of our whole operation.”

Twenty years ago, the Isle Royale wolves consumed every moment the researchers could spare. “In the 1970s, we were knee deep in wolves,” says Peterson. “There were up to three litters of pups going simultaneously. We had to find those pups on the ground without the aid of electronics, and get them to howl so we could count them.”

Now there are so few wolves that “it’s impossible to find them without radio collars. The packs are too small, and they don’t move around much.” Two wolves feed on a kill for five or six days, whereas a big pack would feed one or two days and move on. Besides, two wolves don’t leave many tracks, so they’re harder to find from the air.

“The activity hasn’t kept us very busy,” says Peterson, “because there’s nothing going on out there.”

What is happening to Isle Royale’s wolves? There seems little likelihood that humans are poaching the wolves in winter, when there are no humans on the island. Poachers would have to use airplanes, and, “If someone was doing that to wolves here,” says Peterson, “their behavior towards us in the airplane would change.” One winter in the 1970s, the wolves suddenly became afraid of the airplane. “It took them all year to get used to the plane,” says Peterson. Mech came up with an aerial photograph of a pack of fifteen wolves. Though the photographers represented it as having been taken in Minnesota, Mech knew of no such large packs in the area described by the photographer. The pack resembled one of Isle Royale’s. Apparently, someone had harassed the wolves in an airplane that winter, to hunt
or take pictures. But Peterson has seen no such shyness of airplanes since the population crash.

Before 1988, when no wolves were radio-collared, the researchers could not find and retrieve the carcass when a wolf died. Since 1988, only one dead wolf has been recovered for autopsy, and it provided no convincing explanations, so the researchers can only guess what is going on. Says Peterson, “It’s either disease or it’s food or it’s genetics.”

The question of disease is hard to answer.

Each year, seventeen thousand people visit the park, and at least half of them are fishermen or others who come in their own boats. Although rules prohibit them, the boaters bring dogs, some of which may carry canine parvovirus or distemper. But none of the remaining wolves on the island have been found suffering from either disease, and with so few wolves surviving, researchers are unlikely to locate the remains of a victim of one of these diseases even if they are present.

Another possible cause of mortality is Lyme disease. A University of Wisconsin lab has held that moose ticks could carry the disease, but the claim is disputed by a University of Minnesota lab. As yet, there is no clear demonstration that either wild or captive wolves have come down with the disease. Explains Peterson, “The University of Wisconsin lab cultured moose ticks. Only one out of about three dozen cultured positive for Lyme disease. We do not have the deer tick, which is the common host for the disease, here. We don’t know whether the spirochete that causes Lyme disease is really here or not. Until wolves somewhere in the world come down with Lyme disease, I think there will continue to be a lot of skepticism.”

Peterson hopes the decline was caused by a scarcity of food. The moose population crashed in the 1970s, reaching a low of five to six hundred individuals in 1977, shortly before the wolf population crashed. In the 1980s, the moose population expanded again, hitting seventeen hundred in 1988, but the wolves did not recover with it. The moose population then dropped once more—not because of predation by wolves, but because of infestation by winter ticks. Moose are normally hosts to ticks. With mild winters, the ticks drop off the moose earlier in spring and go through their reproductive cycles earlier, because the soil, in which eggs develop, is not frozen.
That means more generations of ticks, and greater rates of infestation. The greater infestations weaken the moose by drawing more blood and by causing hair loss, which increases the moose’s heat loss in winter and places it under greater nutritional stress. Says Peterson, “In 1989, winter ticks were controlling moose.”

The moose survived the ticks, however, and their numbers increased once more. In 1992, numbering sixteen hundred, they were about to meet a more sinister adversary. “This year,” said Peterson, “it’s starvation. The numbers of moose are as high as we have ever seen here, but the forest is really in bad condition. On the west end of the island, there is a lot of balsam fir, the moose’s principal winter browse. But it has all been eaten away to heights moose can reach. Balsam fir only live about a century, and then they die. On the western end of the island, the old firs are starting to die, as they would naturally, but no new firs are coming up to replace them: moose have nipped the new growth in the bud. On the eastern side, there are regenerating trees, but the larger trees are browsed from the ground to the upper reach of a moose’s mouth. Moose calves are in poorer and poorer condition. They are generally small and more vulnerable to wolves.” There are fewer twins.

Most people predicted that, as the moose recovered from their earlier decline in the 1970s, wolf numbers would also increase, on the theory that more moose meant more food for wolves. But that hasn’t happened. Peterson’s theory is that the moose population is dominated by vigorous young adult moose that were born in the 1980s. Few moose between the ages of two and eight are taken by wolves. Numerically, more calves succumb to wolves, and most of the prey biomass comes from old moose. If food is the limiting factor, Peterson believes that as the present cohort of moose age, the wolf population will bounce back. “If we look at the number of old moose and the number of wolves in the past,” he says, “there’s a remarkable correlation, and that’s reasonable, because that’s what wolves eat. In the next few years, there’s going to be an amazing accumulation of old moose. If the wolves are food-regulated, they ought to turn it around.” By the end of 1993, however, the wolves hadn’t turned it around.

The third—and, some think, most likely—reason for the wolf decline is genetic. If the wolves don’t come out of the decline, the reason may be that they are too inbred to survive. Inbreeding is
potentially destructive to any species, because it increases the likelihood of expression of recessive and nonadaptive genes and because, continued for generations, it makes individuals more and more alike. Nature punishes uniformity—identical individuals are identically vulnerable to disease or changes in food resources or new competitors. Variation among individuals is a way of storing resources for use against such changes.

Cheetahs in Africa suffered a major population decline as human settlement expanded in the nineteenth and twentieth centuries. The reduced population is so inbred that it has less than a tenth of the genetic variety of humans or domestic cats; cheetah genetic resources have been compared to what one would find after ten to twenty generations of brother-sister matings. Immune systems within a species are normally diverse, but skin grafts from one cheetah to another are not rejected—an indication that they have identical, or nearly identical, immune systems. The consequences of such uniformity can be grim. In some zoos, 70 percent of cheetah cubs die without reaching maturity. When an epidemic of feline infectious peritonitis ran through a captive population in an Oregon wildlife park, it was hardly noticed in the lions, but it infected all the park’s forty-two cheetahs and proved fatal to twenty-five of them. Inbreeding usually reduces a species’ reproductive success, too. Abnormalities in sperm cells begin to proliferate. Studies have found 70 percent of cheetah sperm to be abnormally formed, compared with only 29 percent of domestic-cat sperm.

This danger is also faced by many other wildlife populations, as humankind cuts their habitat into small disconnected biological islands. Lions, for example, once occurred more or less continuously across Africa and Asia. By the end of the nineteenth century, the Asiatic lion had been hunted down to perhaps a last twenty-five individuals. All their descendants live in a small protected habitat in India, where no other lion genes enter their prides. Ngorongoro Crater in Tanzania has an isolated population of lions that was reduced to about fifteen individuals by a biting-fly infestation. They now number about 110 individuals, but the genetic consequences of the bottleneck are still with them: they have only a third of the genetic variety of the lions of Serengeti, a few miles away.

Both the Indian and Ngorongoro lions have high rates of abnormal
sperm and low testosterone concentrations. In the United States, black-footed ferrets have as little genetic variety as cheetahs and are known to be very susceptible to canine distemper. Bighorn sheep in the United States are thought to be much more prone to pneumonia and respiratory infections after population reductions.

Wolf reproductive strategies allow for a certain amount of inbreeding. Among wolf packs, as discussed earlier, typically only one pair reproduces, and those may be closely related individuals. Says Peterson, “In Kenai, Alaska, we had a grandfather and a granddaughter mate. They didn’t know they were related, but we did. They did fine. Their pups survived. And when the female died, the grandfather sired another litter with her sister.” In natural settings, such inbreeding does not go on for long. Eventually, the dominant wolves will cease to breed, and a disperser will come along to bring something fresh to the pack’s gene pool.

But there is a boundary around Isle Royale. The ice bridge crossed by a pair of wolves in 1948 does not form in most years, and to get to it wolves must cross a region now densely populated by humans. There has been no immigration of new breeding stock from the Canadian mainland since 1948, and the wolves on the island are therefore thought to all descend from a single pair. For thirty-two years, the Isle Royale wolves increased in number, spreading out into three or four packs to occupy different territories on the island. But all the while, they may have been losing genes. As a single pair breeds, it passes some genes on to one offspring, others to another. Different offspring carry different genes. And since not all offspring breed, some genes are lost.

Inbreeding can correct itself if new genes enter the population from the outside or if enough of the offspring breed to pass on most of the genes. “Here,” says Peterson, “we had probably two founders and never a large population. Here, given the number of breeders, we would estimate we would lose 15 percent of the genetic variability with every generation. Maybe what held this population together so long was that the original breeders lasted so long. The number of new breeders that came on line were kept to a minimum.” But by 1980, perhaps the loss of genes began to tell. “Certainly,” says Peterson, “the genetics are a problem.”

It’s not easy to confirm that inbreeding is the cause of the decline.
Says Peterson, “We could go one step further and look at male sperm. To do it would mean you’d have to do it during the breeding season. In February, you’d have to dart them from helicopters, and after that, these wolves would regard you differently forever. You get basically one crack at the animal. It would change the study techniques.” And even if the sperm samples showed no abnormalities, that would not eliminate the inbreeding hypothesis. “It may not be in the males,” says Peterson. “It may be in the females.” Perhaps they are miscarrying in their dens, or they are infertile. There are too many possibilities, and too few wolves with which to test them. Peterson says, “It’s premature to act on the basis of what we know about wolf genes right now.”