CHAPTER 5
During the initial years of the Yellowstone wolf reintroduction, while we were actively bringing in animals, the annual growth rate of the national park wolf population was roughly 40 to 50 percent. More than a few people heard those stats, did some fast figuring in their heads, and ran off to tell the world the sky was falling, that wolves would soon overtake us all. But such rates are similar to other places where wolf numbers have been severely clipped, often by 80 to 90 percent, through the use of government-sponsored control programs. (The major difference is that while wolf populations in other areas grew not just from reproduction but from wolves moving in from surrounding areas, Yellowstone had no would-be immigrants nearby. Here all the growth was based on reproduction.) Like a great many other animals, from beavers to coyotes, wolves tend to expand fastest when their numbers are well below the carrying capacity of the ecosystem. In simplest terms, animals able to react to new opportunities in their environment—in this case, enjoying plentiful food resources and relatively few competitors—often exhibit a rapid increase in number. For a time, wolf survival was high enough, about 80 percent for all age and sex classes, and mortality low enough that the population grew every year, settling in after the reintroduction phase to about 10 percent annually. The exceptions were 1999, when distemper hit the pups, as well as in 2005 and 2008, which can be described as the point when the park’s wolf population actually started leveling off.
The Yellowstone landscape those first animals stumbled into back in 1995 was surely the wolf version of paradise. In most areas where wolves live, after all, dispersing animals of breeding age leave their home territory only to encounter a world filled with other wolf packs—each one entrenched, not inclined to welcome strangers. Vacancies can be tough to come by, and more than a few end up being killed for trespassing where they don’t belong. In the early years at Yellowstone, though, adolescent animals had only to move next door to existing packs to find lands blissfully free of competition.
In order to put the movement and growth of Yellowstone’s wolf population into better perspective, it may help to note that here, as elsewhere, are found two different kinds of packs. The first, referred to as “simple,” is composed of a breeding pair along with pups. Complex packs, meanwhile, in addition to the current year’s pups also contain animals born in previous years—in Yellowstone, perhaps even four or five years before—thereby creating a multigenerational group. Whether a pack is simple or complex is the primary driving force behind how the group manages on a day-to-day basis. With simple packs, the fact that pups lack any basic skills for determining where to go, what prey to take, or even how to take it (not to mention their lousy fighting ability) means the alphas take care of just about everything. In complex packs, on the other hand, besides the pups there are always other “experts” around willing and able to help.
Most wolves in Yellowstone live in complex packs. In much of the rest of North America the opposite is true, likely because of human exploitation.1 In most of these other places, after all, wolves are hunted, often intensively, which leads to a constant breaking up of the family. New packs are always forming, and that keeps the structure simple. Thanks to protections offered here in Yellowstone, though, by the end of the first decade, seventeen of the nineteen wolf packs that had formed since 1995 were still around. Though this is still a speculative idea, such security may allow a kind of cultural inertia to settle in, whereby once a pack is formed it tends to stay in place by means of adults passing down their experiences to younger generations. True, hard times may cause the number of wolves in the group to dwindle. But a remnant pack will usually continue to survive, rebounding when conditions improve. In addition, world-renowned wolf researcher Rolf Peterson believes complex packs are also more common when the main prey is large, like moose or bison. The bigger and tougher the prey, his thinking goes, the more experience the pack needs to pull off a kill.
The story of a growing Yellowstone wolf population would prove to be about much more than young wolves simply hooking up with partners and breeding. Some of the greatest scientific findings of this project have come from watching how these animals made hay from an empty countryside overflowing with prey, often employing strategies that ended up shredding what we’d long thought of as so-called normal behaviors. For starters, for the first time in history we recorded pups only ten months old breeding in the wild. When female pup Number 16 was this age, for example, she ended up breeding with her stepfather, Number 8; several years later the shoe was on the other foot, when 16 bred with male pup Number 165 of the Leopold Pack.
But that was just the beginning. More often than not, wolf packs have only one litter of pups each year—the offspring of the alpha male and female.2 (In this book, by the way, we still use alpha to describe the breeding pair, though in the scientific community that term is falling out of fashion.) Yet starting in 1996 and continuing for quite a few years, at least one pack in the park had more than one litter per season; indeed, in some years there were groups having three litters. By their nature wolves tend to avoid inbreeding—a fact vividly portrayed in the winter of 2002–2003, when the alpha male of the Druid Peak Pack tried to breed with his daughter, over the course of a single day making more than a half-dozen attempts to mount her, only to be met with a good hundred or so nips by the female. The following day this young female wandered away from her pack and almost immediately found a lone male nearby, one with whom she’d already bred a few days earlier—a Casanova wolf of sorts, who’d made something of an art out of slinking through other pack’s territories without getting caught. (This was Wolf 302, whom we’ve profiled on page 183.) Afterward she returned to her natal pack.3
Though not exactly common, this is the more typical way multiple litters happened in Yellowstone—a non-alpha female leaving the family for a short time to breed with males from other packs. Several times we’ve actually seen temporary clusters of ten or twelve wolves coming together to check each other out, some of which go on to breed with multiple partners. One February a wolf from the park’s interior traveled all the way to the northern range to join one of these gatherings, where he bred with a couple different females before returning to his home turf near Old Faithful. All that’s required for such trysts are females looking for the opportunity, along with nonterritorial males willing to risk trespassing in order to find partners in somebody else’s backyard. It’s been especially fascinating to discover that, by all appearances, females seem tolerant of these wandering males not just during breeding season but in other times of the year, as well. We’ve seen such travelers showing up at both den and rendezvous sites and be perfectly accepted—at least as long as none of the males of the pack is around. Should one of those males return, though, the intruder will waste no time packing it in and bolting away.4
These multiple litters probably occurred because of abundant food. It works like this: When food resources are merely adequate, or even limited, the dominant female in the pack engages in behaviors that actually suppress the estrus cycle of her adult female subordinates. On the other hand, when food is plentiful, such social tension is eased. The alpha no longer behaviorally restricts other females, and that means those subordinates start coming into their normal reproductive cycles. We believe the reason we see fewer multiple litters today than we once did is because after sixteen years, wolves have come into a kind of equilibrium with the food source. The enormous elk herd present at the beginning of the reintroduction has been whittled away by wolves and other predators, not to mention factors having to do with climate. In other words, we have a smaller, healthier elk herd than we did before. And that smaller herd has essentially trimmed the fat out of the wolf population. With less food available we expect to see more typical wolf breeding behavior, which means multiple breedings will be less common.
Once a young female is impregnated, she may return to her own group, only to move off alone when she’s about to give birth to find a den site of her own. Later, when the pups are slightly older, she may either bring them back to the pack’s main den and raise them there, or alternatively, try to tough it out alone through the summer. Wolf 103 is a good example of this latter behavior, having raised three pups alone with little help from other pack members—a decision that caused her no end of headaches, sometimes struggling even to fend off attacks by lowly coyotes.
More exceptional still in Yellowstone are cases where an alpha male breeds with other females in his pack not related by blood. We may have actually contributed to this sort of behavior by placing unrelated animals together in the acclimation pens. In such cases the alpha male, if so moved, could breed with several females, which is exactly what we saw happening in the Rose Creek, Chief Joseph, and Druid Packs. (Alpha females, by the way, have never been seen breeding with anyone but the alpha male.) All this said, it’s important to understand that, by and large, alpha pairs are monogamous. Even in those unusual cases where the alpha male ends up breeding with an animal other than the alpha female, his “pair bond” as scientists call it—the animal he tends to, is fiercely steadfast toward—remains always the alpha female. (A very good way to tell which wolves in a group are the alpha pair, though not entirely foolproof, is to watch for behavior called double scent marking. This involves one of the pair urinating, and then the other urinating in the exact same spot.) Should a mate die, though, and the surviving alpha maintains her position in the pack, she’ll readily take up with another wolf. Typically these new mates come from outside the pack, just as Number 21 of the Rose Creek Pack did in December of 1997, sensing the sudden vacancy in the Druids and moving right in. Likewise female Number 9 of Rose Creek had at least three mates in her life. This sometimes leads to situations where the breeding pair are of different ages.
This fierce loyalty between alpha pairs reflects the fact that wolves evolved to be highly dependent on solid family units, or packs. These families, perhaps not unlike our own, benefit greatly from strong, consistent leadership—by being able to follow a male and female that, besides being strong and healthy, have an essential ability to make sound decisions about everything from hunting to defending territory.
The frequency with which multiple litters have occurred in Yellow-stone—perhaps 10 percent of all births have come about this way—may have something to do with the high population density of wolves on the northern range. In this part of the park, there’s simply more opportunity for it to happen, and so now and then it does—at least so long as prey is abundant. As mentioned earlier, in the year 2000 three females in the Druid Peak Pack produced twenty-one pups, twenty of which survived—catapulting the pack size to an amazing thirty-seven wolves, quite possibly the largest ever recorded. The only potentially bigger wolf pack was noted by wolf researcher Lu Carbyn in Wood Buffalo National Park in Alberta, Canada, when he spotted forty-two wolves together. In that region, though, in certain seasons wolves often follow migrating bison, collapsing their normal territoriality. Whether the group of wolves Lu saw was actually one pack or a mix of several is hard to say. (Today such a pack size would be unlikely, mostly because of the smaller, more vigorous elk herd now residing on the park’s northern range.)
Multiple litters have been recorded elsewhere, including Alaska and the Northwest Territories, yet in these other places too it seems definitely more the exception than the rule.5 Even when packs do have two or three litters, the survival of the second or third generally tends to be so poor that by fall the total number of pups is about what it would’ve been with only a single litter. Even in Yellowstone, out of approximately eighteen cases of wolf packs having more than one litter, we’ve recorded only one high-survivor event like the one we saw with Druid Peak in the year 2000—once again, a level of success that may be thanks to the abundant food supply. Indeed, between elk, bison, mule deer, and an occasional moose, the wolves of Yellowstone’s northern range probably have the highest known biomass of prey available anywhere in the world.6
When it comes to breeding behavior, these somewhat remarkable games of musical chairs have left us with a lot of unanswered questions. To learn more we’ve been leaning on not just direct observation and radio collars but also genetic techniques like DNA fingerprinting. Using blood taken during collaring operations, these genetic profiles allow us to not only study multiple females in the same pack but also basically genotype all the wolves we capture to see who their parents and other relatives are. In cases where we’re not able to actually catch a key wolf, but manage to see the spot where it defecates, we can collect feces and then genotype it using stray cells from the intestine. In 2005, for instance, we spent time tracking down just such a sample from what was then the new uncollared alpha male of the Druid Pack, nicknamed “New Black.” This work was conducted at Robert Wayne’s world-renowned lab at the University of California, Los Angeles.
In so many areas of wildlife science, the use of genetic tracking has opened up tremendous new opportunities for better understanding of animal health and behavior. In the northern Rockies, perhaps the most widely publicized use of the science had to do with wolves meeting key recovery criteria required to remove them from protection under the Endangered Species Act. Indeed, after the US Fish and Wildlife Service delisted wolves in the spring of 2008, a short time later they were placed back on protected status—part of a legal challenge in which the government was found to have not adequately established whether wolves were able to travel and breed between the three original recovery areas. This was a key requirement of the reintroduction, intended to make sure there continued to be healthy diversity in the gene pool. Thanks to genetic tracking, we’ve now been able to prove such mixing is actually happening.
Beyond all our current theories and speculations, there’s an enormous wild card that gets played out time and again in wolf society, and it has to do with personalities. Wolf Number 40 ruled the Druid Peak Pack with an iron fist, always the one in charge, while Number 7, alpha female of the Leopold Pack, seemed to manage her group by applying what was a far more gentle nature. Such character differences probably also determine which one of the alphas, male or female, ends up being the primary leader of the group. In the case of 40, she routinely initiated activity and generally led the group more often than did her mate. The personality card influences much of what wolves do and how they do it—from their willingness to suffer captivity, to the level of playfulness they exhibit, to whether they leave their natal pack to seek a life elsewhere. All in all wolves display a fantastic degree of individuality, which in turn makes nearly every theory we come up with subject to frequent and sudden second thoughts.
Portrait of a WolfNUMBER 5
Summer of 2000. Veteran radio tracking pilot Roger Stradley and I are hanging in the sky some five hundred feet above the wilds of central Yellowstone, drifting over a ghostly sweep of charred tree trunks from the 1988 fires. It’s July, the season when wolves move their pups to rendezvous sites, when elk and their young are climbing across grassy swales and through broken forests, heading for higher elevations. In the past sixteen years Roger and I have spent well over two thousand hours together in this tiny Piper Super Cub, scanning the ground first in 1995 for three wolf packs, then six packs by 1997, and by 2005, fifteen. This time is different. Today we’re looking hard for one wolf in particular—a kind of celebrity of the reintroduction, a matriarch who spent five years as alpha female of the Crystal Creek Pack. Number 5 was the very first wolf to actually arrive in Yellowstone in 1995, huddled in a metal crate and carried into an acclimation pen with the whole world watching, surrounded by Secretary of Interior Bruce Babbitt, the late director of the US Fish and Wildlife Service Mollie Beattie, wolf project director Mike Phillips, and then-superintendent of Yellowstone Michael Finley. There she’d spend the next ten weeks, walking to freedom in the third week of March. On the last couple tracking flights, we haven’t been able to find her. We’re determined to uncover what happened.
Wolf Number 5, along with females 9 and 14, were in many ways the centerpiece of Yellowstone wolf recovery. They were the original alpha females, the lead animals of the wolf world—responsible not just for denning and giving birth but also for making daily decisions about establishing territory and hunting for food. But for Number 5, life hadn’t been easy. One year after leaving the acclimation pen, she gave birth to a litter of pups, all of which were likely killed in a fight with those ruffians of greater Yellowstone, the Druid Peak Pack—a brawl that also brought the death of her mate, Number 4. Her pack all but destroyed, she herself severely injured, 5 hobbled out of the Lamar Valley with a single young male in tow, moving south toward the lush grasslands of the Pelican Valley. With this move, though it was made under difficult circumstances, she would take the steps that would later allow her to establish the first pack in central Yellowstone; that, in turn, provided a springboard for other packs to begin forming in this part of the park. She and the other wolves that in time gathered around her would become among the first of the bison hunters—chased and kicked and generally sent packing by the bison time and again, until at last they got it right.
Through years of weekly tracking flights, we’d managed to locate Number 5 nearly every time: watching as she led pack mates along the edges of the lodgepole forest in search of elk, going head-to-head with moose on the banks of Pelican Creek, or even tangling—sometimes for hours at a time—with the nearly invincible bison. Yet as of late she’d been showing her age, looking ever more gray. There’d also appeared a black line under one eye, ever more pronounced, almost like the bags a person might get from not sleeping enough. Over the past winter we noticed her sometimes lagging behind her pack mates, struggling through the deep snow. We last made visual contact with her in January of the preceding winter, on her home ground in the Pelican Valley. As we flew over she looked up at us, just as she had so many times before. But this time it was a different look. Her eyes seemed changed, as if something had gone out of them. Where her gaze before seemed defiant, almost like she was daring us to try something, suddenly she seemed worried at our approach, as though the plane might do something terrible to her.
Finding her proves fairly easy. I spot her lying on her side on the ground below, her beautiful, ivory-colored coat looking stark against the black husk of a burned log. As we circle I notice she looks big, full in body—a good sign that at least she hasn’t starved. We keep turning and turning, trying to get her to move, watching for a lift of the head, a twitch of a leg. While steady circling in the plane almost always produces some sort of movement in a wolf, we get nothing. I make a mental note of the spot, but on our next overflight a week later, she’s gone. We continue to search actively for weeks, then more sporadically for months after that. Years later I’ll catch myself scanning for her radio collar frequency, hoping to hear that comforting beep indicating a live animal. A few times I’ll even think I hear it, but sadly these turn out to be “ghost” beeps—a common occurrence when one radio tracks so much, spending thousands of hours listening to static through headphones. One time I’ll tell Roger about it, ask him to listen, but he won’t be able to pick it up. Not that he’ll come out and tell me that, mind you—just simply fail to acknowledge it. Out of respect, I suppose, knowing all too well how much I want to hear it.