No Longer Top Dog
Studies of coyotes in Yellowstone National Park show that wolf reintroduction is changing the canine social hierarchy
- Roger Di Silvestro
- Oct 01, 1996
Biologist Bob Crabtree and several of his colleagues expected nothing out of the ordinary that June day in 1995. As usual, the researchers were perched at vantage points above the Lamar River Valley in the northeast corner of Yellowstone National Park. As always, the river's clear, cold waters ran in lazy curves through rich meadows flanked by tree-crowned ridges. Elk, bison, deer and pronghorn grazed as expected among the tall grasses. The animals that held the biologists' attention--a group of four coyotes that Crabtree had dubbed the Norris Peak Pack after a local landmark--were where they should be, with their pups at a den on one of the ridges.
But then something occurred that no one had seen in the park in recent memory, if ever. A pack of five wolves moved across the valley floor and caught sight or smell of the coyotes. The wolves immediately moved toward the ridge and the den. The coyotes, bound to the spot by attachment to their young, yelped and howled as the wolves drew near. While their caterwauling might have discouraged the advance of other coyotes, the wolves did not break stride. When they reached the den, they attacked. Outweighed perhaps three to one, the coyotes fought a losing battle for 15 minutes, then fled. The wolves tried to dig out the coyote den. That evening the biologist found a dead pup at the den site.
The incident answered one question that had been preying on Crabtree's mind since the U.S. Fish and Wildlife Service had released 14 gray wolves from Alberta into the park the previous March: Would the wolves kill park coyotes? With that answered, he could go on to other matters: "Coyotes will survive wolf reintroduction," he says, "but the question is, how? Will the coyote's social structure change? Will wolves affect what coyotes prey upon? And how deeply will coyotes decline?"
The extirpation of Yellowstone wolves is an artifact of the earliest era of modern wildlife management. In 1872, Congress made Yellowstone the world's first national park. Before the decade was out, administrators were trying to kill off park predators on the assumption that wiping out wolves, coyotes, cougars and bobcats would protect hoofed animals. The fact that elk, deer, bison and moose had thrived under a full ecological complement of predators seems to have eluded the policy makers.
The control effort continued into the 1930s, but Yellowstone's wolves had been wiped out during the previous decade. All other park predators survived. Now, under an endangered-species recovery plan, the federal government is reintroducing wolves to the park in an effort to restore natural balances. For Crabtree, his coyotes and the Yellowstone ecosystem, the reintroduction signals an ecological revolution that will reverberate through the lives of the many species with which the wolves will coexist, including coyotes, elk, grizzlies and even, Crabtree's studies suggest, rodents.
Crabtree made his first professional visit to Yellowstone National Park in 1974, when he worked as a busboy at Old Faithful Inn. That was also the year he saw his first coyote and got hooked on the animals. "I've always liked dogs," he says, "and after I saw my first coyotes, I knew that was the species I wanted to study."
Crabtree was only a high-school student then, but his interest in animals already went back many years. Born in Astoria, Oregon, he moved to Moscow, Idaho, when he was five. His father had died when he was young, but in Moscow, a university town, he met three biologists who became, he says, "surrogate fathers" and sparked his interest in wildlife research. By the sixth grade, Crabtree knew he wanted to be a biologist. He published his first scientific paper while still an undergraduate. In 1985, he started a four-year study of coyotes at the Hanford Nuclear Reservation in southwestern Washington. There he honed the skills that would serve him at Yellowstone, where, in 1989, he began a long-term coyote study at the invitation of the National Park Service.
Photo By George Harrison
Coyote in Glacier National Park
Yellowstone was the ideal place for his work because park coyotes are virtually undisturbed by human activities. This is a rare find in the United States, where the federal Animal Damage Control program has killed tens of thousands of the animals every year for decades. "When a wildlife population is under that kind of pressure, its social and biological character breaks down," says Crabtree.
The coyote is a smallish, predominately brown canine native to Mexico and the western United States and Canada. Though subject to the same control efforts that killed off almost all of the nation's wolves, the coyote during the past century has expanded its range into Alaska, Central America and eastern North America as far as Nova Scotia. This success was a result of the coyote's adaptability. While gray wolves specialize in hunting large hoofed animals, coyotes are generalists that feed on everything from elk to mice and don't turn up their noses at refuse, eating out of garbage cans in urban settings such as New York City and Los Angeles. Crabtree estimates that insects make up 5 to 10 percent of the coyote diet in Yellowstone.
Crabtree's studies are done under the auspices of Yellowstone Ecosystem Studies (YES), a research group that Crabtree founded in 1993. He raises funds through YES, then links graduate students and other scientists with research projects. He also accepts untrained volunteers, who make a donation to YES and work under professional guidance. Crabtree and his colleagues have tallied about 450 coyotes in 65 packs in Yellowstone's northern range. The largest and, in Crabtree's estimation, most successful is the Bison Peak Pack.
Although coyote packs generally comprise two to ten animals led by the most dominant male and female, called the alpha animals, the Bison Peak Pack, during one bumper-crop breeding season, included 11 adults with 12 pups. This small army was made possible, Crabtree believes, because the pack's territory lies on some of the richest land in the Lamar Valley, a site replete with rodents and herds of hoofed prey.
Like all coyotes, the Bison Peak animals maintain their territorial pawhold by leading lives reminiscent of Shakespearean drama. The alpha male and female rule like a king and queen, and only they produce pups. The lower-ranking, beta animals exist mainly to serve the alphas' fiefdom. Likely to be pups from previous years, the betas help to raise subsequent litters and protect the territory.
The alpha male decides when and where the pack will hunt and is almost invariably the first of the pack to attack, going head to head with animals such as elk, which may outweigh him more than twentyfold. This leadership role comes with a price: The face of one former Bison Peak alpha male was heavily scarred by the travails of predation and intraspecies warfare.
The Bison Peak's territory, like that of all packs, adjoins the domains of other coyotes. Occasionally, neighboring packs transgress on one another's land. If caught, a snarling battle may ensue. However, coyotes are gifted in the art of biological diplomacy. Inherited behaviors--certain vocalizations and body postures--indicate submission, surrender and retreat, allowing interlopers to escape alive. Friendly meetings also occur between members of different packs. Crabtree has seen the alpha female from the adjacent Amethyst Pack pay amiable visits to Bison Peak coyotes. He suspects that her father was once a Bison Peak beta.
In Yellowstone, alphas usually ascend to their positions when two to five years old and may hold on to them for years. Though the average coyote lives only six years, Crabtree says, many beat the odds. The oldest on record was a Colorado animal that lived 16 years. One former alpha female of the Bison Peak Pack was more than 13 years old when she was killed and eaten by a cougar.
The death of an alpha offers a chance for one of its beta offspring to advance in coyote society. A younger male in the Bison Peak group took over after the alpha male was killed by a snow plow as he crossed the Lamar Valley road one winter day. But betas do not always wait until an alpha dies. Sometimes, like an ambitious prince, a beta will make a power play against a reigning monarch: "In about half of territorial takeovers," Crabtree says, "betas throw out the alphas. In the other half, outside loners do the job."
Loners wander a social and biological netherworld in the unclaimed margins between territories. Mature animals that lack a home, loners make up about a fifth of the coyote population and are ever vigilant for signs that an alpha is losing power or has died, offering a chance to take over. When an alpha is deposed, it generally takes up residence on the fringes of its old territory.
Alpha males and females mate for life. Courtship begins in December in Yellowstone as the paired animals work in tandem to mark territorial boundaries with sprays of urine. The alphas mate in February, and pups are born in April in underground dens.
A pack may have as many as 10 den sites on its territory and may move young pups from den to den, perhaps to avoid other predators or to reduce the chance of insect infestation. Coyotes use dens handed down from previous generations. The Bison Peak Pack in 1992 was using a den at which biologist Weldon Robinson had captured pups in 1946. Crabtree has discovered that at least 75 percent of the dens in the Robinson study are still in use.
Coyotes use dens only for sheltering pups. At 12 weeks of age the pups begin to travel with the adults, and the pack abandons den life. Kazia Hatier, one of Crabtree's graduate students, found that the highest pup mortality occurs from mid June to early August as the pups enter the world beyond the den. Generally, only two pups from an average litter of six survive into adulthood. Much of pup success depends on food availability. Alphas always eat first. If nothing is left over, pups and betas may starve.
Which suggests that the life of a predator, even in a place like Yellowstone, is not an easy one. Of 6,433 encounters between coyote and prey that Eric Gese, a doctoral student working on the coyote project, has tallied, only 1,545 concluded successfully for the coyote. Nevertheless, Crabtree's research has shown that coyotes as a species annually kill more elk than any other park predator. In the northern range, home to 20,000 elk, coyotes yearly take about 1,350 elk, grizzlies 780 and cougars 612.
Most of the elk that coyotes kill are calves, preyed upon mainly in early summer. During the warm months, coyotes also take advantage of the park's rodent smorgasbord. Crabtree was surprised to find how large a dent coyotes can make in rodent populations. "In the Lamar Valley," he says, "they take 23.6 percent of all pocket gophers, 35.2 percent of ground squirrels and a huge 76.2 percent of all voles."
In winter, a fresh stock of elk calves is months away and rodents are scarce, so coyotes turn to killing adult deer and elk. Even ailing elk make impossible quarry for a lone coyote. But Yellowstone coyotes have numbers on their side, attacking as packs. They also use patience as a weapon. A park ranger once reported a pack of coyotes that for seven days besieged an elk that had taken refuge in a stream. The pack finally killed the elk when fatigue drove it ashore.
Even when food is readily available, coyotes do not come easily to their place at the table. Other predators demand a seat, too. Cougars, Crabtree believes, kill 5 to 10 percent of the park's coyote population every year. And now the coyotes have to contend with the gray wolf.
Prior to extinction of the wolf in Yellowstone, the park's canines lived under a distinctly hierarchical system in which wolves dominated coyotes and coyotes dominated red foxes. The extent to which wolves persecuted coyotes in Yellowstone is unknown, but one of Crabtree's studies found that 71 percent of interactions between coyotes and foxes in the Lamar Valley are aggressive, with 40 percent fatal to the fox.
Now it may be the coyote's turn to experience suppression. In the year following the Yellowstone wolf release, Crabtree recorded that the newcomers had killed 12 adult coyotes in the Lamar Valley. He estimates that wolves may have accounted for a total of 48 dead coyotes since the first release, perhaps 25 percent of the Lamar coyote population. "Wolves will be a lot more effective at controlling coyotes than the old park trappers ever hoped to be," Crabtree says.
Crabtree and the park's wolf biologists have discovered that who beats whom among coyotes and wolves is a matter of numbers. In the Lamar valley, the dead coyotes were the victims of nine resident wolves. But in a north-central part of the park called Blacktail Plateau, where only two wolves have set up shop, it's a different story. Wolf biologist Michael Phillips discovered last winter that this duo was killing far more elk than he would have expected. Subsequent research showed that a pack of six coyotes was driving the wolves off their kills, forcing them to hunt more frequently than they ordinarily would.
Such data only hints at things to come. One of Crabtree's studies suggests that, with wolves in the equation, elk, bison and moose numbers may be trimmed by 8 to 20 percent. Coyotes are likely to decline, perhaps steeply. If they do, pronghorn--heavily hunted as fawns by coyotes but too small to interest wolves--may increase. And how will a drop in coyotes affect voles, the rodents of which coyotes devour so many? Will grasslands, eaten by a growing rodent horde, suffer? Or will red foxes, freed of coyote suppression, glut on the rodents and experience a population boom?
The federal government released 17 more Alberta wolves into the park last April. This will increase pressure on the coyotes, but perhaps they will be up to it. "Yellowstone coyotes are bigger and stronger than those elsewhere, perhaps because, in the absence of wolves, they have turned to hunting big game," Crabtree says. "The loss of wolves may have yielded a super coyote, so maybe they'll hold their own against the wolves. Or maybe they'll sink back to underdog status. That's one of the big questions that I hope to answer in the future."
Roger Di Silvestro, a senior editor on this magazine, sometimes wishes he had been raised by wolves.
Watch Wolves On NWF Television
National Wildlife Productions, NWF's TV and film division, tells the wolf-reintroduction story in "The Wolves Return to Yellowstone," airing on TBS Superstation initially at 9 p.m. E.S.T. Sunday, November 3, and three more times in ensuing weeks. The program, hosted by Matt Fox of television's "Party of Five," documents every detail of the highly controversial recovery effort, from the battles at public hearings to the release of wolves in Yellowstone.
Restoring the Wolf
The National Wildlife Federation has campaigned for wolf reintroduction since the early 1980s. Tom Dougherty, NWF's Western Staff director, served on the federal Wolf Management Committee, helping to develop the reintroduction proposal. Such efforts yielded an outpouring of public support and resulted in release of wolves in Yellowstone and Idaho beginning in 1995. Recently, NWF helped defeat a lawsuit brought by Montana ranchers to stop the release of more wolves. "Our efforts would not have been successful without active public support," says Dougherty. "Wolf reintroduction demonstrates the flexibility of the Endangered Species Act and shows that large predators can coexist with humans."