CHAPTER 7
If we had to name the most important scientific aspect of Yellowstone wolf research, it would likely be the challenge of finding out what these animals mean to the functioning of the ecosystem as a whole. Wolves were of course part of the region long before Europeans arrived on the scene, which means most of the life here was well adapted to having them around. Yet the science we’ve conducted over the past decades has been on lands bereft of wolves. In that sense Yellowstone offers the best chance we’ve ever had to figure out the difference between a wilderness system with wolves versus one without them (a so-called time series experiment). And for those of us working as scientists, that’s an incredibly exciting thought. Naturally, central to this notion will be the wolves’ impact on elk. Not just directly, though, through killing for food, but indirectly from the fact that the mere presence of wolves changes both how elk are distributed as well as how they behave. And as those things change, it will inevitably lead to changes in the environment as a whole.
Wolves are often described by the term “apex carnivore,” which simply means that they sit on top of the food chain. (This food chain is also sometimes referred to as a food web. That name refers to the fact that if you map out all the connections that exist between organisms in a given ecosystem, you end up with a figure that looks much like a spider web.) In simplest terms the sun fuels the food chain through plants, which are then eaten by consumers like elk, bison, deer, etc. Those consumers, in turn, are eaten by wolves, cougars, and other carnivores, which are eventually themselves eaten by decomposers. In this way the energy from the sun can be said to cycle through the system. By sitting at the top of the food chain, wolves and certain other carnivores tend to have significant effects on the life around them. Those impacts can sometimes tumble down the entire chain all the way to the plant community—meaning the animal is affecting things indirectly, as well as directly—a phenomenon that lies at the heart of what scientists call a trophic cascade.
Though we’ve got several seminal pieces of research to lean on, proving the extent of a particular animal’s effect on the surrounding ecosystem is a hard thing to do, especially in big areas like Yellowstone, where interactions between wolves and prey and vegetation are remarkably tangled. Nonetheless, with the return of wolves it took little time before this national park became a crucible for such research, with competing teams of scientists vying with one another to be the first to document critical discoveries.
So far the focus of this work has been on the northern portion of the park—as noted earlier, a vital area for thousands of ungulates, including the northern Yellowstone elk herd. Because the large quantity of prey animals have made this region by far the busiest for wolf activity, if a trophic cascade is going to happen anywhere, this is the place. So far these studies have been looking at three woody species: cottonwood, aspen, and willow. While in truth these plants cover only about 2 percent of the northern range, scientists see those sites where they occur as biological hot spots, highly significant to a variety of animals. To put it simply, any recovery that gets going in these plant communities is going to affect lots of players.
A good example is the beaver. Biologist Dan Tyers reintroduced beavers adjacent to the park in the Gallatin National Forest shortly before we brought back wolves; since then those beavers have migrated downstream into the national park, able to settle in Yellowstone because of ongoing willow recovery. (While Dan’s reintroduction no doubt sped things up, this recovery probably would’ve happened anyway. Beavers have long occupied the Yellowstone River and would’ve surely migrated into the park as willow became available.) I’ve personally been involved in Yellowstone beaver surveys since 1996, when there was one beaver colony on the entire northern range of the national park. In 2003 there were nine colonies, and by 2011 that number had grown to ten or twelve, occupying sites in a range of locations including Slough Creek, Crystal Creek, and the Lamar Valley.
From what we know so far, willow recovery seems connected with wolf reintroduction, the rebound starting roughly two to three years after wolves were released. More impressive still, this resurgence began not when there were a mere four thousand elk in the northern herd, as there were in 1968, but when there were fourteen thousand. (The lower number in 1968 was due to ranger control actions, designed to reduce what was considered an overabundance of elk.) Admittedly, we have to be careful when making such associations—a kind of scientific shorthand known as correlational science—since in the end only actual experiments will prove the case. Those experiments are now ongoing, as is computer modeling, mostly done by outside researchers looking at everything from willow regeneration to seed production, from the effect of fire to the influence of beavers, elk, and moose.
With the beaver have come beaver ponds—rich, vibrant oases providing habitat for insects, fish, amphibians, reptiles, small mammals, birds, even moose. Likewise the area immediately surrounding beaver ponds and streams, known as riparian zones, are home for a number of plants and animals unable to exist anywhere else. Research in similar environments at other natural areas—one south of Yellowstone in Grand Teton National Park, as well as in Canada’s Banff National Park—offers strong evidence of the connections between riparian zones and various songbirds, including yellow and Wilson’s warblers.1
Any amateur naturalist walking into the northern range with an eye to what’s going on with willow would in no time at all figure out that the recovery isn’t uniform. That’s more evidence still that wolves are involved. After all, if willow growth were the result of a landscape-based effect—something, say, related to climate change—we’d expect to see it everywhere. But the spottiness of the recovery is possibly because it’s happening in those places where elk have learned they’re at higher risk of being killed by wolves; once aware of this, the elk simply don’t spend their time in such locations, or not nearly as much as they used to. And it’s in exactly those areas that willow is coming back.
Recent research by David Cooper and Tom Hobbs at Colorado State University suggests that, at least in the case of willow production, the increase is probably due to a combination of lower elk numbers and changed elk browsing behavior, both of which have been altered by wolves, as well as the basic availability of water. On one hand, while wolves helped bring about the release of willow growth—either by trimming elk numbers or causing them to move—such positive effects are generally being seen only in those willow stands that also have adequate water supplies. At the same time, the converse seems to also be true: If there are too many elk in one place, overbrowsing the willow, it really doesn’t matter how much water the plants have—they just don’t do well.
In short, if there’s overwhelming pressure from browsing elk, then the characteristics of the site don’t much matter. Reduce that pressure, though, which wolves have done, and site characteristics start to come into play. In Yellowstone, in those places where elk browsing has been lightened and the site is good (again, this mostly refers to plentiful water), woody vegetation is booming.
Not that the wolf is the only piece of the willow puzzle. Work by Dr. Dan Tyers has shown that the number of moose declined significantly following the massive fire season of 1988, primarily due to a loss of critical forest-based winter habitat. (In those places not burned in the 1988 fires, there are today just as many moose as there were before.)2 Given how much moose eat, fewer moose certainly couldn’t hurt the cause of willow regeneration. Yet if these animals were a primary factor, why didn’t the recovery begin earlier, closer to the time when moose populations plummeted after the fires? Furthermore, we don’t yet understand if willow is being helped simply because of fewer moose or also because moose, like elk, are changing their behavior in the face of wolf packs.
Plenty of attention is also being given to cottonwood and aspen, both of which were declining on the northern range. So far cottonwood recruitment seems to be on the increase since wolf reintroduction. At the same time, researcher Eric Larsen at the University of Wisconsin, Stevens Point, who’s had aspen study plots in the park since 1987, has noted that 30 to 40 percent of his plots are thriving.3 Again, much as with willow, those aspen stands that are doing well tend to be those growing on favorable sites, which in large part means adequate water. Meanwhile Douglas Frank of Syracuse University in New York has said he’s beginning to see a wolf effect on park grasses. On so-called high-risk sites—areas with poor visibility, where it would be hard to spot an oncoming wolf—grass production increased. These results are only preliminary, but they’re yet another part of trophic cascade research worth watching.
Still another kind of trophic cascade playing out in Yellowstone stems from all the carcasses wolves are leaving behind. Even if a pack is big enough to eat nearly all of the prey animal they kill, there’ll always be morsels left behind for other scavengers. (To a degree we can actually correlate the size of wolf packs to how big their major food source is. Wolves that kill deer, for example, live in packs of five to seven, while elk-killing packs typically range from eight to twelve. Moose- and bison-killing packs will often be fifteen-plus animals strong.) Thus far we’ve observed no less than twelve different species using prey killed by wolves, including ravens, magpies, bald and golden eagles, and coyotes.4 Biologist John Varley has dubbed this phenomenon “food for the masses.” “In all the planning, all the studies,” says Varley, “the one thing we totally underestimated was how many other mouths the wolves would feed. Beetles and flies and mountain bluebirds—I mean this is incredible.”
Biologist Dan Stahler and noted raven expert Bernd Heinrich have been spending time watching ravens following wolves, the birds knowing full well that if they stick around long enough they’re going to get a meal. In virtually every case, ravens are at a wolf-kill site as soon as the prey animal falls. As Heinrich once told me, ravens have a hard time pecking the eye out of a dead squirrel, let alone opening up a seven-hundred-pound dead elk. Here they can have the wolves do it for them. In one remarkable scene, some 135 ravens were seen on two adjacent kills. (The average wolf kill attracts twenty-nine ravens.) As part of ongoing research, Stahler and Heinrich compared the birds’ reliance on wolf-killed carcasses to situations where meat was supplied artificially. Basically the two men hiked around placing on open ground the legs from elk carcasses. The ravens didn’t bite. Some would fly over and do a double-take, but in the end they just kept going. On wolf kills, though, the birds started feeding immediately. Stahler and Heinrich’s conclusion, based on a solid understanding of the raven’s habits, was that these birds are extremely cautious about approaching unknown food sources. While feasts being offered by humans are suspect, meals made courtesy of wolves or other predators are comfortable, well-charted territory.5
Magpies too are eager to take their own turn at wolf kills, sometimes being the first to a carcass, though never by much. So too will eagles eventually come, as well as both black bears and grizzlies—at least when they’re not asleep in their dens. For all their power, grizzlies lack the speed and agility needed to regularly take adult elk on their own. Yet as noted earlier, a grizzly can usually command a wolf kill at his pleasure, in the process gaining food that may prove critical to his survival. In Pelican Valley, one of the densest grizzly bear areas in the park, virtually every kill the wolves make is stolen by grizzlies. It’s not a matter of if the bears will come calling after a kill, but when. In one case in the Pelican Valley a bear biologist observed twelve grizzlies and four wolves on a wolf-killed elk. On several occasions I’ve seen four to six bears descending on a wolf kill, and in one extreme case, watched dumbfounded as a large grizzly on a wolf-killed elk fended off twenty-four wolves. Time after time individual wolves mustered the courage to approach the kill, only to be met head-on with an angry charge. Afterward the bear always returned to lie on the dead elk, determined to protect every morsel.
For the most part wolves are to bears what mosquitoes might be to the rest of us—pesky annoyances. Wolves dart in and out with abandon, even sit on their haunches six or eight feet away from the bear, looking calm, knowing full well the bruin lacks the quickness to ever catch them. Several times I’ve seen a bear lurch and swipe at a wolf harassing him, but a wolf can leap out of harm’s way in the blink of an eye. If wolves encounter a bear on neutral ground, with no kill around, they may—though not always—hassle it in a halfhearted manner and be on their way. The intensity of the interaction increases if a food source is involved. The harassment reaches the highest level only if the bears wander near the wolves’ dens or rendezvous sites, where pups are vulnerable. At those times several wolves will dart in and out all at once, clearly more antagonistic, as often as not biting the bear on the butt every chance they get. Even with this sort of insult the bears usually don’t bother going after the wolves, knowing it’s a hopeless cause. More often than not they seem to simply grow weary and finally amble away. (Grizzly cubs, though, are more vulnerable; so far we’ve been able to document three of them having been killed by wolves. Because of this, mother bears are less inclined to challenge wolves for carcasses.)
The meat wolves leave behind becomes especially important to bears in autumn, when they’re driven to put on as much fat as they can before the big sleep. For decades there’ve been only a few really good sources of food for bears in this season, one of which is the nut crop of the whitebark pine. But whitebark pine stands are declining throughout Yellowstone, victims of blister rust and pine bark beetles, both of which seem to be exacerbated by the changing climate. The other problem is that these trees produce nuts only sporadically. One season may offer a bumper crop, only to have next year’s harvest be a total bust. We now have reason to believe that in those lean years especially bears are turning to wolf kills. In fact the highest number of grizzlies ever seen on wolf kills—not just in the Pelican Valley, but throughout the park—was during a fall when the nut crop completely failed. Lastly, so too are these carcasses important to bears at the end of winter, when they emerge from dens ravenously hungry.
While grizzlies have the luxury of approaching wolf kills with impunity, not so with the coyotes who come calling. When much of your normal diet consists of mice and ground squirrels, the sight of several hundred pounds of elk meat must be awfully hard to resist. Yet coyotes have to exercise tremendous caution, given that wolves frequently kill them at both den sites and on carcasses—so many, in fact, that it took little time before the coyote population on the northern range had declined by half. Yet according to a theory developed by coyote researchers Bob Crabtree and Jenny Sheldon, in recent years coyotes have been doing pretty well, having made certain “social adjustments.” In particular, they’ve abandoned living in wolf like packs, which they were doing back in 1995, returning to a more classic coyote structure composed of a single adult pair with pups; that change has in turn reduced their vulnerability to wolves.
It’s unlikely wolves will eliminate coyotes altogether, as they did on Isle Royale, but this smaller canine will probably never again have the place in the ecosystem that it did prior to the wolves’ return. This in itself may not be a bad thing, given that prior to the wolf reintroduction Yellowstone supported one of the densest coyote populations in all of North America.
Coyote-wolf interactions provide yet another great example of the fact that you can’t pull on one strand in the web of life without it being felt someplace else. Some researchers think red foxes, which are commonly preyed on by coyotes, will make a strong comeback in the years to come. Likewise coyotes are major predators of pronghorn antelope fawns, taking them in that period before they’re old enough to run with such blazing speed—when the only strategy is for their mothers to hide them. Working in conjunction with pronghorn researcher John Byers from the University of Idaho, we’ve found that the areas with the highest pronghorn fawn survival rate are located near wolf dens. Wolves rarely prey on pronghorn fawns, apparently having better things to do than spend their time hunting up their hiding places. And for their part coyotes wisely avoid wolf dens like the plague. Loss of coyotes could also lead to an increased availability of rodents, since these make up the canine’s primary food source. If rodents increase, it might bode well for other animals that like to eat them, including hawks and owls. Though right now it’s impossible to say, we may one day discover that along with all the other changes wolves have ignited, they may also be indirectly responsible for an increase in raptors. This coyote-rodent connection has been documented around wolf dens in nearby Grand Teton National Park by researcher Brian Miller, though more testing needs to be done.
Some people who aren’t particularly fond of wolves have made the comment that even without them the scavenger community was doing just fine, what with hunters being counted on to shoot elk and deer every fall. But there are big differences between the remains of hunters and those provided by wolves. For starters, wolves leave carcasses lying around at all times of the year, across nearly the entire landscape.6 Human-related leftovers such as gut piles, on the other hand, occur only in fall, and at clumped locations. Still other people have suggested that there’s plenty of food being left by other scavengers, in particular the cougar—a predator that’s actually a more efficient killer than a wolf. (On average one wolf kills an elk about every fifteen days, while a cougar takes one every week.)7 But cougars are solitary hunters, and as such have evolved to cover their kills in order to make them less available. I saw this play out vividly one day from a place called Hell-roaring Overlook, where a cougar and a pack of six wolves had each killed an elk, roughly a half-mile apart. The wolves had eaten and were bedded down sleeping, ignoring the ravens and magpies swarming around their kill. The cougar, meanwhile, was frantic in the face of these interlopers, diving and dashing in a desperate attempt to chase them away.
The wolves’ strategy is basically to out-eat the birds—make a kill and then try to consume it right then and there. Though not proven, some researchers speculate that the reason wolves live in packs in the first place is just for this reason, to out-eat scavengers.8 Generally speaking, in Yellowstone it takes about ten wolves to consume most of a carcass, leaving behind only small pieces of meat.9 Above ten wolves and some animals in the pack aren’t going to get enough to eat; below ten, and scavengers will consume the leftovers. But being alone, cougars simply can’t eat the whole kill in one sitting, instead staying on it for days, maybe even a week. In those times when the animal isn’t actually eating, the carcass stays buried, keeping others from getting to it. By all indications the strategy works. Observation has shown very little use of a prey animal killed by a cougar other than by the cat that killed it.10
So far all we’ve talked about are vertebrate scavengers. But once all the aforementioned animals have had their turn—and several others not mentioned—the invertebrates take over, especially beetles. And what the beetles don’t get leaches into the soil in the form of nutrients—so many nutrients, in fact, that a study on the Konza Prairie Reserve in Kansas found that carcasses contributed more nutrients to the soil than did either feces or urine.11 While this hasn’t been tested enough to be universally accepted, it seems likely that the kills wolves leave on the landscape are a solid source of nutrients for the functioning of the system. All of this simply because wolves killed an elk. In that sense the death isn’t merely an end, but a beginning. The diversity wolves help support means a healthier, more resilient system. “If we have all the parts of this ecosystem,” says John Varley, “then, as Aldo Leopold said, it should function better. To the extent we’re able to know, the wolf has restored the prehistoric and historic biodiversity of Yellowstone. And in all the Lower 48 states, this is the only little scrap of land where that claim can be made.” Indeed, if we’re to take seriously the longstanding policy of the National Park Service to restore natural conditions, it would be hard to imagine a better way to achieve it than through the restoration of the wolf.
Over the past several years, perhaps the biggest mental challenge for those of us involved with this project has been grappling with claims that wolves are wholly responsible for declines in the northern Yellowstone elk herd, which now stands at roughly five thousand animals—down from almost twenty thousand in the early 1990s. Adding fuel to the fire was scientific research from 2002 documenting drops in the survival rate of elk calves—known as the “recruitment rate”—a trend suggesting that elk numbers may at least in the short term stay lower than they were a decade ago.12 But historically we’ve always seen great fluctuations in elk numbers in Yellowstone—even when no wolves were present. What’s more, population monitoring suggests the decline of the northern elk herd began well before wolves hit the ground.13
It’s not that wolves don’t play a role in such fluctuations, because they clearly do. But they’re just one part of the story, along with factors like drought, harsh winters, and human hunting. As discussed, seven out of eight elk herds in Yellowstone leave the national park every winter, at which point most are fair game for hunters. But beyond all that, there’s something strange about this sudden panic over a declining elk herd. For more than three decades, from 1932 to 1968, elk were regularly hunted by park rangers in order to protect the resource from overgrazing and overbrowsing; with the end of those artificial control actions, along with the discovery of new wintering areas north of the park, by 1992 the population had swelled to a staggering twenty thousand animals. Those high numbers spurred great criticism from both the public as well as some segments of the scientific community, who worried that too many elk were damaging the ecosystem. In part as a reaction to those concerns, in 1995 and 1996 Montana Fish, Wildlife and Parks increased the number of cow permits given to elk hunters—a move expressly intended to initiate population declines. How amazing, then, that within just a few years—for no other reason than that wolves are now in the picture—the debate switched from having too many elk in the ecosystem to having too few.
In addition to wolves coming back to this landscape, in the past fifteen years other major predators have been on the increase. The population of grizzly bears—a major consumer of elk calves—is considerably higher now than it was in the early 1980s, as is the number of cougars, which again have a significantly better per capita kill rate than do wolves. In all today there are six major elk predators in greater Yellowstone, forming a multi-carnivore system that will continue to exert a strong influence on their prey.
Another significant factor influencing elk populations is weather and climate. One example is the calamitous winter of 1988—89, following the catastrophic fires of the previous summer, which burned some 36 percent of the national park. (The 1988 fires, by the way, were an enormous event here in Yellowstone. Hundreds of thousands of acres burned. Smoke poured into the sky, making the normally clear, brilliant days of late summer dark and murky and full of soot. For a time, at least, what had been cool, shaded stands of living conifers were changed into a patchwork of blackened trunks rising out of knee-high, nutrient-rich grasses and forbs. Yet nature reclaimed the world lost in that season in remarkably short order. Except for the age of the timber—and therefore the density, since young trees grow more compactly than do old ones—in most places today you’ll find the very same plant communities as before the burn. So far as we can tell, in the grand scheme of things the fires had little effect on the business of being a wolf.)
Even more significant was the winter of 1996—97, in Yellowstone one of the most severe of the entire twentieth century. Heavy snows in November and December made it tough for elk and other ungulates to move around and find forage. Then around New Year’s, typically a very cold time, it started raining, followed soon afterward by temperatures plummeting to well below zero. The heavy snow, then rain, then extreme cold turned the snowpack to concrete, sealing off grasses under a hard shell of ice—a catastrophic situation for ungulates. Before long both elk and bison began leaving the park in huge numbers, with thousands of elk dying along the way. Nor would many of their calves make it through the winter. Meanwhile fleeing bison were being rigorously monitored—part of an agreement with the state of Montana to prohibit them from leaving the park, due to fears of spreading a disease known as brucellosis to the region’s cattle. Out of a population of four thousand bison, some fourteen hundred died that winter, eleven hundred of them shot at the park boundary.
As for the wolves, in late winter of 1997 it seemed they couldn’t kill enough elk. Indeed, this was the only year we’ve documented so-called surplus killing, which refers to wolves taking more than they can immediately eat. Even so, as we continued to watch those carcasses over the next few weeks, many of which did in fact still have meat on them, we saw wolves returning to feed a second and even third time. In truth some reports of surplus killing stem from people surprising wolves on a kill and thus driving them away, then being incredulous about how little they consumed. Despite a sordid mythology that paints wolves as bloodthirsty killing machines, in the vast majority of cases a wolf taking everything he can means just plain getting enough to keep going. For every hunt that leads to a kill, a pack endures many times that number of failed attempts; in Yellowstone proper, only one out of every five attempts is successful.
As critical to declining elk numbers as the winter of 1996—97 was, possibly more consequential was the record drought that followed—one that by some indications was as bad or worse than the dust bowl of the 1930s. At first the milder winters with less snowfall actually helped ungulates. The low snowpack made travel easier, thereby allowing greater access to forage. But over time low precipitation—especially during summer, when both the quality and quantity of grass are set for the rest of the year—is a major stress factor.14 Had such conditions lasted only a year or two, the system would’ve adjusted. Most soils do tend to store moisture, after all, besides which many grasses are remarkably resistant to drought. But we’re talking six years of it—one of the longest known dry spells on record.
Current computer analyses suggest that given the recent severe drought, significant declines in the northern range elk herd would’ve occurred even had wolves never been reintroduced. Research by the wolf project suggests that wolf predation has been compensatory, which basically means prey animals killed by one cause—in this case, wolves—would’ve died anyway because of being severely stressed by other factors. Another way of saying it is that a wolf taking one animal means another will survive. Had drought not occurred, on the other hand, wolf predation on elk may well have been additive mortality, meaning that each elk killed probably would have lived had wolves not killed it. (Some other research models, though, indicate that most wolf predation has been additive.15) While predicting the cycling of elk populations is a terribly complex task, there seems little doubt that if all the above-mentioned factors occur simultaneously—from weather and climate stresses (including severe winters coming back-to-back), to liberal hunting policies, to high levels of predation—elk may well decline to even lower levels than they are now. Yet by all indications, a drought of the magnitude seen over the past six years may trump everything else, becoming the most important life factor not just for elk but for virtually every other plant and animal in the ecosystem.
It’s easy to be excited about the benefits that a top predator like the wolf brings to the Yellowstone landscape. The simple fact that wolves prey on elk has been a key factor in creating a very different-looking national park. Willow, as we’ve discussed elsewhere, has in many places returned with bells on. And that has in turn provided habitat for everything from yellow warblers to colonies of beaver. Still, it’s important to note that such benefits aren’t being realized, nor are they likely to be, on most of the lands outside Yellowstone. This is because the positive effects we’ve seen here are the result of wolves having achieved what ecologists refer to as “natural density.” (A good way to think of natural density is the number of wolves that can be supported by the “biomass” of the landscape—or more plainly, the number of deer and elk available for them to eat. Another, perhaps better term would be “ecologically effective density.”) Outside Yellowstone wolves rarely achieve ecologically effective density because they’re continually being killed, either due to livestock-related conflicts or from people hunting or poaching them. It’s not that wolves don’t have positive impacts elsewhere, including possibly being a check on the spread of dangerous diseases in deer and elk, such as brucellosis and chronic wasting disease. But the transformation of landscapes into places that function close to their full potential is going to be seen mostly in Yellowstone. (As we mentioned earlier, in part due to their much smaller size, Glacier and Grand Teton National Parks don’t have a single wolf pack residing entirely within their borders. In Yellowstone, on the other hand, roughly 80 percent of the wolves are able to make a year-round living entirely, or almost entirely, within the borders of the park.)
On first glance there may seem to be a contradiction in all this. Despite the ongoing uproar by some who claim that wolves are wiping out elk, with less than a handful of exceptions (one of them being the northern border of Yellowstone) hunter harvests of elk in Wyoming, Montana, and Idaho game districts, while variable, have been generally robust. Yet how could that be, when we’ve just made the point that elk populations in Yellowstone have diminished since wolves returned—the same reduction that seems to be driving the rebound of willow, cottonwood, and aspen? As it turns out, elk harvests have declined significantly in less than a handful of places, all of them being where multiple predators are present—in particular, grizzly bears, wolves, and cougars. In those parts of the northern Rockies where such multiple predator conditions don’t apply—and that’s the majority of the region—elk harvests are for the most part solid. (Curiously the Jackson elk herd, long popular with hunters, proves that even the “multiple predator factor” has shades of gray. As of 2010 the Jackson elk herd was close to twelve thousand animals, roughly seven hundred animals more than what the Wyoming Game and Fish Department considered ideal.) While it’s true that high ungulate populations can overharvest the food supply, especially in drought periods, thereby leading to greater mortality from all causes, the animals that make it through are left to enjoy greater abundance. That, in turn, eventually leads to an increased survival rate in calves. This isn’t to say that with a fully restored suite of predators elk will be as plentiful as they were before. But changing the dynamics of the ecosystem by bringing back its top predator doesn’t diminish the ability of that system to persevere. Generally speaking, the idea that elk would disappear in the face of wolves being back in the landscape flies in the face of the two species having coexisted in relatively stable fashion throughout the northern Rockies for thousands of years.
Portrait of a WolfNUMBER 7
One of the most noteworthy events marshaled by those first wolves released in 1995 was the formation of the Leopold Pack, created by a pairing between Number 2 of the Crystal Creek wolves and Number 7 of the Rose Creek group. This would prove to be the first naturally forming wolf pack in what we now call Yellowstone’s New Wolf Era; as a way of commemorating the event, we named the group after Aldo Leopold, the brilliant scientist who first recommended wolf reintroduction to Yellowstone in 1944. Leopold, considered by many the father of modern-day wildlife management, was even wiser than many give him credit for, fostering the notion that predators had value long before it was a popular idea even among biologists. “A thing is right,” Leopold claimed in his classic work, A Sand County Almanac, “when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.”
Number 7 had left her mother and stepfather, Number 9 and 10, almost immediately after being released from the acclimation pen. For the next ten months she traveled as a lone wolf, making her own kills, thriving. Then on Blacktail Deer Plateau she paired with Number 2, who’d split from his own pack only a month before. That match created tremendous excitement not just among those of us working the wolf project, but among park staff as a whole. On first sighting them, I snapped a photograph—a lousy one, it turned out, mostly due to the uncontrollable excitement I was feeling at the time. (For all the thrill, this pairing did cause some concern given that we’d just built an acclimation pen on Blacktail to hold two wolves, Numbers 35 and 36, which at that point were ready for release. With 2 and 7 having settled the area naturally, we had to find another place for these other animals, finally letting them go in the Lone Star Geyser Basin.) The pairing of 2 and 7 marked nothing less than the beginning of wolves expanding successfully on their own. Even better, their choice of homes on Blacktail Deer Plateau was a great location for observing, allowing us to easily record their comings and goings.
In their first year together the Leopold wolves had three pups. Amazingly, Number 7 was out killing elk only days before giving birth—a significant feat, though one that wouldn’t have been necessary had she been in a larger pack with helpers at her side. The pair chose to excavate a den on Blacktail Deer Plateau at a site we still call the den forest, but used it only one year before moving to another location. This second den site was used for many years; even in 2003, the first year Number 7 was no longer the breeding female of the pack, the new alpha female continued to use this den—a great example of how tradition plays out in wolf culture.
During their stint as alpha wolves, Numbers 7 and 2 would produce seven litters totaling thirty-four pups, at least twenty-nine of which managed to survive past the age of one. Two of those offspring went on to form the nearby Swan Lake Pack, as well as the Cougar Creek Pack. Yet another pup grew up to become a key member of the Rose Creek Pack, meaning that he dispersed back to his mother’s group of origin. Through much of 2004 the territorial boundaries of the Leopold wolves were among the least changing of any in the Yellowstone ecosystem. They never left Yellowstone National Park (from 1995 to 2003 only four packs could make that claim), and their pack size was extremely stable, fluctuating over six years between eleven and thirteen members. While in that same era the alphas of other packs were producing multiple litters, 2 and 7 faithfully bred only with each other, with no breeding activity outside the alpha pair. Curiously, after these two wolves died, the size of the pack swelled to nineteen members, then twenty-four by late 2004—by far the largest ever recorded for the group. Just as the Rose Creek wolves rose to prominence with twenty-four animals on the northern range in 1998, followed by the Druid Peak Pack at thirty-seven members in 2001, the Leopold wolves may well be the next power pack of the region.
Despite their phenomenal run as alphas, the end for these founding members of Leopold came somewhat abruptly. In May 2002, Number 7 was killed by the neighboring Geode Creek wolves, a new group forming after the breakup of the massive thirty-seven-member Druid Peak Pack. When we found her carcass, it was evident that not only had she given birth to a litter of pups that year—at the time of her death they were about a month old—but that she was still nursing, being several weeks from completing her weaning. Yet thanks to the communal, family-driven nature of wolves, other females from the pack were quick to come onboard and care for the pups—not nursing them, since these other adults wouldn’t have been lactating, but still providing food. All eight survived. As for 7’s partner, Number 2, after losing his dominant status in the pack he died in much the same fashion as did his mate, on the last day of 2002, falling at the jaws of the Geode wolves.
To signify this changing of the guard, we began referring to this group as Leopold II. They continued to use the same territory, frequenting the same haunts the original pack established back in 1996. In truth we expected this pack to thrive in this stable, spacious territory for many years. Much to our surprise, though, by 2008 the Leopold Pack had crumbled and disappeared. The alpha male had been killed by other wolves, and the alpha female may have been, as well. In 2008 every single pup—twenty-five of them, in three litters—were killed by distemper. And if all that wasn’t enough, several of the remaining wolves became infested with mange, a disorder caused by mites attaching themselves to an animal’s fur or skin, causing lesions and fur loss. Indeed, we had the sorry experience of watching one of the surviving members of Leopold wandering off on his own, nearly hairless.