U.S. Highway 89 links the hardscrabble mountain town of Gardiner, Montana, to the near-infinite natural wonders of Yellowstone National Park. At the park’s northern entrance, the road passes under the Roosevelt Arch, a rusticated triumphal archway whose stones bear the inscription, “For the Benefit and Enjoyment of the People.” The epigraph is an excerpt from The Act of Dedication, the piece of federal legislation that, in 1872, made Yellowstone the world’s first national park, preserving for posterity its more than two million awe-inspiring acres.
The drive from Gardiner out into Yellowstone’s Lamar Valley is long, but motorists are treated to an astounding array of roadside attractions. These include picturesque canyons, raging rivers, mountain ranges, and, famously, more than half of the world’s geothermic features. Along the way, visitors are likely to come face to face with all manner of diverse wildlife. Yellowstone is home to several hundred species of plants and animals. Bald eagles, grizzly bears, bighorn sheep, and colossal, sleepy-eyed bison are just a few of the more impressive “charismatic megafauna” likely to sidle up to your vehicle as you make your way across the park. But of all Yellowstone’s wild inhabitants, only one is particularly relevant to understanding why an epidemic of obesity is killing America’s dogs. That species is the gray wolf.
Wolves are indigenous to North America and packs once roamed the Northern Rockies in abundance. But the westward-ho expansion of settlers in the mid-nineteenth century funneled thousands of head of large, slow-moving, and valuable livestock smack into the middle of wolf territory. Wolves, impressive predators that they are, wreaked havoc on livestock populations. And they earned a reputation as the scourge of the cattleman’s herd: one part pesky vermin, one part bloodthirsty killer. A wide-ranging extermination campaign aimed at stamping out the gray wolf soon began in earnest. Hunters, trappers, cattlemen, and even public officials joined the cause. By any measure, they succeeded. In Montana alone, they killed as many as 100,000 wolves between the 1860s and the 1920s, and the gray wolf was thought to be completely extinct in the American West by 1926. It is often said that the last two wolves were shot and killed by Yellowstone park rangers.
That last bit has only recently become ironic, owing to a dramatic shift in public opinion about the relationship between government and wildlife that occurred amid the liberalism of the 1960s. Up until then, most Americans regarded wildlife as something that should be tolerated only to the extent that it served the needs and desires of man. If bison made for good eating, they should be eaten; if wolves threatened valuable livestock, they should be eradicated. And public officials such as park rangers should embody that ideology and effect policies aimed at furthering it. But the growth of the environmental movement allowed other philosophies to creep into the public consciousness, notably the idea that the actions of man should not jeopardize the outright survival of other species. That, although the eventual extinction of all species is inevitable—indeed, it has been estimated that more than 99.9% of all species that have ever walked the earth are now extinct—man should not cause other living beings to become extinct.
The idea caught on, and it reached something of a critical mass with the passage of The Endangered Species Act of 1973, a law that not only granted government the right to step in when it looks like a species is on the brink of being wiped out, but also to reestablish locally extinct species—to build vanished populations back up to what they once were.
Re-enter the wolf. By the beginning of the 1970s, the only wolves in the Lower Forty-Eight were a small band living in the very northern tip of Minnesota. But, thanks to the efforts of environmental organizations and a few dedicated individuals, the species was officially classified as endangered in 1974. A contentious battle to reintroduce wolves to the American West followed and, after much legal wrangling, a total of 66 wolves were finally reintroduced to two distinct Rocky Mountain locations—northern Idaho and Yellowstone National Park—in the mid-1990s. Today, less than two decades later, there are more than 1,600 wolves living in packs scattered widely across Montana, Wyoming, Idaho, Washington, Oregon, and California. The repopulation of wolves in the American West has been nothing short of a comprehensive success.
According to Abby Nelson, a biologist and wolf management specialist with Montana’s Department of Fish, Wildlife, and Parks, the primary reason for the wolf’s successful repopulation has been the species’ “extreme fecundity.” Wolves are genetically constructed to go forth and prosper in places like the greater Yellowstone area. They breed early and often, producing litters of five to ten pups every year, often for the better part of a decade. Additionally, about 10% of wolves will disperse from their packs upon reaching adulthood, leading to regular territorial expansion. And, as apex predators, they will succeed in just about any ecosystem they share with large numbers of suitable prey—something that the big herds of elk found throughout the Northern Rockies most certainly are.
Montana FWP is a state agency, and Abby’s job involves much overseeing of the conflicts that have inevitably arisen as repopulated wolves have spread into areas previously dominated by Montana ranchers and their grazing livestock. But another (smaller) part of her job is to partner with the Yellowstone Association to take people like me out into the field and inside the fascinating world of wild wolves. To help the public understand what makes this thriving, prosperous species tick.
And so, on a chilly, overcast morning in early October, Abby and I found ourselves making the long drive from Gardiner to the Lamar Valley, a hotbed of Yellowstone’s wolf activity. I’d come to Montana because I hoped that she and her colleagues could help me with a question, one whose answer might go a long way toward explaining why so many of America’s dogs are dying from an epidemic of obesity: how come wolves don’t get fat?
When it comes to obesity, dogs and wolves have managed to arrange themselves into a remarkable kind of “natural experiment,” the results of which provide a conceptual framework that may well explain why so many of our dogs are obese. In one sense—in their respective capacities to become obese—dogs and wolves are strikingly similar. Indeed, on the whole, the two species possess genes that are so similar as to blur the line between one and the other. But in another sense—in the frequency with which members of the two species actually become obese—they could hardly be more different. On the one hand, according to APOP and others, the majority of modern-day domestic dogs are either overweight or obese. On the other, effectively zero wolves are. Thus, in a fundamental sense, understanding why America’s dogs are dying from an epidemic of obesity can only begin by identifying the ways in which they no longer live like their wolf brethren have for thousands of generations.
So just how similar are the two species? A study published in 2014 in the journal PLoS Genetics reports that the genetic divergence between dogs and wolves occurred only about 14,000 years ago. That may sound like a long time, but in evolutionary terms it is only a heartbeat. By contrast, the genetic divergence between humans and our closest living genetic cousins, the chimpanzees, probably occurred some 13 million years ago—making it about a thousand times more distant than the dog-wolf split. To think of it another way, consider that if you were to take the 60 million years or so that have transpired since canine species first appeared on the evolutionary map, then condense that period into 180 days (about half a year), the split between wolves and dogs would occur only about an hour before midnight on the final day.
Because dogs and wolves diverged from their common ancestor so recently, there has been little time for genetic differences to arise between the two. In total, they share some 98% or more of their mitochondrial DNA. The overlap is so significant, in fact, that the two can be, and in many corners of the world are, successfully interbred.
Interbreeding between species is a truly rare biological phenomenon. Even when two animals are taxonomic first-cousins, it’s not an enterprise that tends to work out very well for those involved, as the idea of a human being mating with a chimpanzee might suggest to you. In fact, the word “species” is usually defined as a group of individual organisms that can successfully breed with one another. So, by definition, members of different species shouldn’t be able to breed with one another at all. Nevertheless, and despite the fact that most states affirmatively prohibit the breeding of dog-wolf hybrids, current estimates of their population in the United States range from 300,000 to more than a million.
Of course, one needn’t be a geneticist to see just how physically similar dogs and wolves are. Notwithstanding the array of diverse forms that human tinkering has produced in the modern-day domestic dog, the two species sure look an awful lot alike: the same strong, muscular hindquarters, the same sharp, serrated teeth, the big, attentive ears, the long muzzles, the padded paws, the swinging tails, the forward-facing eyes. The French use the expression l’heure entre chien et loup (“the hour between dog and wolf”) to refer to dusk, a time of day when the fading light makes it all but impossible to differentiate one species from the other. It’s not hard to see why.
None of which is to say that there aren’t genetic differences between dogs and wolves. The two are, after all, different species. Recently, geneticists have used genome-sequencing technology to identify and map out the few major differences that separate one from the other. And it turns out that most of the differences concern brain function. This is not an altogether unexpected finding, as these between-the-ears differences manifest as some remarkably different behavioral tendencies. Notably, as anyone reading these words surely knows, dogs form close emotional bonds with their humans. Bonds which make them do cute things like jump into bed with us in the morning, wait by the door when we leave for work, and turn wiggly, spastic circles when we come home.
Wolves, perhaps the quintessential “wild animals,” are not usually so inclined. Teaching a wolf—even one raised from puppyhood as a pampered Park Avenue house pet—to do things like cuddle in bed and perform parlor tricks is not likely to be an enjoyable or rewarding experience, either for trainer or trainee.
Still, on the whole, dogs and wolves are about as genetically similar as two distinct species can be. But those nearly identical genes have managed to produce two species that are, in one particularly glaring way, near-polar opposites of one another.
Weight problems aren’t exactly common among wolves. Rolf Peterson, a professor at Michigan Technological University who studies wild gray wolves at Isle Royale National Park, once put it to me this way: “I’d say there is no evidence of obese wolves in the wild.”
Abby Nelson, who spends her professional life tracking wolves in the Yellowstone area, speaks in similarly unequivocal terms: “I have never observed a wild wolf even approaching obesity.”
Wild wolves simply don’t become fat. It just doesn’t happen.
Importantly, this is not to say that they don’t have any fat whatsoever in their bodies. In fact, they carry it in most of the same places as dogs do—packed between the internal organs, layered in deposits underneath the skin, interfused with bone marrow. Way down at the molecular level, their various types of fat tissues look just like the stuff we find in our dogs too.
Wild wolves just don’t pack it on the way our dogs do. The most definitive scientific analysis of the body composition of wild wolves involved a study of 38 Alaskan wolves living in an environment where the food supply was so abundant as to be, according to the study’s authors, “unlimited.” The researchers found that the animals tended to maintain average body fat percentage (BFP) levels of around 3.5% in the summer and 7% in the fall. Not a single one of them ever maintained a BFP of more than 10%. This despite the fact that the animals lived in the chilly Alaskan wilderness, where a warm layer of subcutaneous body fat is a rather useful thing to have in one’s body, and despite the fact that their feast-or-famine lifestyle meant that they usually lived off their stored body fat for several days in between meals. Another recent study shows that even captive wolves tend to maintain BFPs of only about 10% when fully fed, even with their roaming space drastically curtailed and their meals regulated.
The body compositions of other wild canine species have been studied too. During the summer months, when additional body fat isn’t necessary to protect against harsh winter conditions, arctic foxes have been shown to maintain BFP levels of about 7%. Coyotes tend to stay at about 10%. And Australian red foxes at only 3% or 4%.
In fact, when it comes to modern-day canine species, there is really only one whose typical body composition stands out from the others: the domestic dog. Despite regular trips to the vet and specialized weight-loss foods and caring human guardians, about half the dogs in America today are so fat that it is as if they are smoking a pack of cigarettes a day. More specifically, extrapolating from data gathered by Dr. Ernie Ward and APOP, more than half of the dogs in the United States today have a BFP higher than 30%. By weight, about a third of the tissue in the average American dog is probably body fat. This means that the typical American dog has perhaps 800% as much fat in its body as the typical Alaskan wolf and is just about as fat as a garden-variety blue whale (average BFP of 35%). In a great many cases, our dogs are even fatter than that. They are, quite literally, fatter than whales.
To understand how this truly absurd reality has come to be, our first task must be to understand the basic features of the lives our dogs so recently left behind. To understand why our dogs are dying from an epidemic of obesity, we must first understand what it’s like to live like a wolf.
Yellowstone presently is home to about 60 adult wolves and 35 pups. They have divided themselves into ten packs, each including somewhere between two and 15 adolescents and full-fledged adults. Breeding females typically birth their pups in the spring and the Junction Butte pack had added five of them to its ranks not long before my October visit. They joined the four yearlings who survived from last year’s breeding season, along with the pack’s two leaders (the “alphas,” in the formal language of wolf social dynamics), a six-year-old female and a large, three-year-old black male.
It was cold and blustery in the pre-dawn darkness as Abby and I ventured into the lesser darkness of the Lamar Valley, a kind of natural paradise found squarely in the middle of the Junction Butte pack’s territory. A fresh elk kill had been reported on the eastern edge of the valley and Abby was hopeful that the pack would be feeding upon it sometime around dawn.
Because of their famously private nature, tracking wolves is a difficult business. Fortunately, many of the Yellowstone wolves wear radio-transmitting collars, devices that help the biologists with the Yellowstone Wolf Project keep track of the animals. It’s something that they do phenomenally well—these packs are some of the most closely watched wolves on the planet and all the reams of data that have been gathered over the past two decades have been packaged into dozens of published studies, papers that have cast new light on all manner of wolf behavior and ecology. Yellowstone’s wolves are particularly appropriate subjects for scientific study because their habitat is a national park, a place whose wildness is preserved by federal mandate. So, for research biologists and writers alike, Yellowstone is perhaps the best place in the country to see what the “natural” life of a wolf really looks like.
Abby and I spent the morning in the Lamar, tracing maps and peering through high-powered scopes. But we didn’t have much luck. We drove around the park for the better part of two hours, until the sky had turned a pale shade of blue. But the wolves evaded us. Abby is a remarkably cheerful and patient person, but frustration looked to be creeping into her eyes.
“We should find Rick,” she said.
Rick is Richard McIntyre, a man who is legendary among wolf buffs. A woman back at Yellowstone Association headquarters had referred to him gushingly as “the Pied Piper of Yellowstone Wolf-Watching.” When Rick first came to Yellowstone he wasn’t affiliated with the Park Service. To hear him tell it, he just wanted to study wolves all on his own. But after learning of his superhuman dedication to the task of meticulously gathering data on wild wolves, the Park Service recruited him.
In any profession, it’s rare to find an individual who achieves the level of total commitment that Rick brings to his professional life. He gets up before dawn seven days a week and allegedly hasn’t taken a vacation or otherwise missed a single day of wolf-watching in over eight years. He recently notched his 3,000th consecutive day in the field. He lives primarily in his car, driving around the park eating blueberry Nutri-Grain bars and using telemetry technology to track wolves. He uses a high-powered, single-barrel scope to locate them high up in the pine forests and a Dictaphone to record observational data. At the end of each day, his data—what the wolves are eating, where they are going, what they are doing—is added to the massive database maintained and analyzed by the Yellowstone Wolf Project. He also makes time to give talks to park visitors, enriching their experiences with his encyclopedic knowledge and wealth of wolf anecdotes.
We caught up with him at the Tower Ranger Station in the mid-morning, the sun now bright overhead. He is a trim man with a precise and delicate manner. A shock of brown hair and boyish features belie the age otherwise suggested by his considerable experience. He stood in the parking lot, encircled by wolf-loving park visitors, giving them an oral history of wolves in Yellowstone. We listened as he told them about the Junction Butte pack, describing its lineage all the way back to the original wolves brought to the park from Alberta in the mid-1990s. He then told them about 21, a wolf whom he called the “undisputed heavyweight champ” of Yellowstone. 21 was a legendary alpha male whose physical attributes were so off-the-charts that he was comparable to a once-in-a-generation athletic talent like Michael Jordan. He weighed more than 130 pounds and dominated his territory like no other wolf in the park’s history.
When the history lesson was finished, we made our way back out to the Lamar. Abby and I followed Rick as he drove slowly along, then pulled his car off to the shoulder, darted across the road, set his scope on a tripod, and peered out across the valley. We stayed quiet as he whispered notes into his Dictaphone. He looked at us and shook his head. Abby grimaced and we headed back to the cars. The pattern repeated itself a few more times and the day stretched on.
In the afternoon Abby and I set off on our own, exiting the park and heading for the Montana backcountry. We followed a dirt logging road up into the woods, through the remnants of a tiny, archaic town and past the ruins of abandoned mines. I thought that perhaps our luck had changed when, shortly after leaving the car, we came upon a set of frighteningly large, clawed animal tracks. We stopped and examined them, but Abby concluded that they were made by a bear, not a wolf. We went on, Abby looking intrepid with a can of bear spray in her grip. I tried to take heart from her bravery—even as I panicked at the sound of every snapping twig and my eyes nervously searched the enveloping woods for signs of a charging grizzly.
We walked the hills of the Montana backcountry until the Gallatin Range purpled and the setting sun filled the big sky with shades of orange. Abby worked her radio antenna. I kept my fingers crossed. But it was not to be; I went to bed that night having yet to see my first wild wolf in the fur.