A WOLF approaches her target, staring with the intense gaze of a predator, her every muscle tensed for action. The young bull elk turns to face the threat. There is a long moment of suspense while the animals size each other up. Then the elk puts his head down and charges at the wolf. The canine hunter turns tail and runs.
In the Rocky Mountains of Yellowstone National Park and central Idaho, such scenes have been played out regularly in the seven years since wolves were reintroduced. For decades before, opponents of wolf restoration had argued that elk herds might not withstand wolf predation. As it turns out, both wolves and elk are flourishing. In fact, the entire mountain ecosystem has benefited. For biologists it is a rare opportunity to watch as the pieces of a disrupted ecosystem fall back into place. The success story should also be good news for conservationists fighting to protect or re-establish carnivores in other mountain areas.
The last native Yellowstone wolves were killed in 1930s, following a long campaign of poisoning and shooting. But today the mountains in and around the park are home to some 200 wolves living in 19 packs. Their numbers are increasing, and other local residents have no choice but to deal with them. “The learning curve for elk has been steep,” says Steven French of the Yellowstone Grizzly Foundation. “The first year the wolves were back, elk just stood around almost thinking that these were nothing more than big coyotes,” says French. “But they quickly learned that wolves are a serious threat.” Though these particular animals had never experienced wolves, evolution had equipped them to cope. “These animals evolved over several million years with predation. It’s part of their make-up to understand predators,” says Douglas Smith, leader of the Yellowstone Wolf Project.
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The main factor influencing elk mortality turns out to be severe weather (Journal of Wildlife Management, vol 65, p 998). In 1997, when elk were weakened by an unusually harsh winter, wolves killed 26 per cent of those they tried to attack. The following year, when the winter was mild and the elk were healthier, the wolves’ success rate was only 15 per cent. In recent years, mild winters have allowed elk numbers in the park to increase, even as the wolf population grows.
Elk are undoubtedly the wolves’ primary prey, but they are unlikely to be eaten unless they are too sick, hungry, old or young to defend themselves. An elk strong enough to stand its ground seldom falls to wolves. “To some, this sounds like a fairy tale or a government snow job,” says Smith. “The finding that healthy elk can face down wolves is not a surprise, but this has to be proved repeatedly because people like to believe wolves can kill anything they want.” In fact, several wolves in the park have died of wounds inflicted by slashing elk hooves or antlers.
Observing wolves re-establish relations with their prey has highlighted the delicate balance between species. And watching them interact with the other Yellowstone top predator, the grizzly bear, reveals an even more complex relationship. Grizzlies survived the anti-predator blitzkrieg that wiped out wolves, so they have the advantage of uninterrupted residence in the park. They are also bigger than wolves. But that doesn’t mean they always have the upper hand.
“There’s a balance of power involved in who usurps a kill from whom,” says Chuck Schwartz of the US Geological Survey Northern Rocky Mountain Science Center in Montana. Wolves often give in to a bear rather than risk injury fighting to keep a meal. “Adult male bears are able to take kills away from wolves regardless of the size of the pack,” says Schwartz. “But a large pack of wolves can succeed in taking a kill from a smaller bear, a female or a sub-adult.”
Yet most interactions between Yellowstone’s two top predators are benign. French recalls the first encounter he witnessed between grizzlies and reintroduced wolves. A mother bear with two cubs came across a small wolf pack. Three young wolves ran towards the bears, which began to retreat, until the mother turned and stood her ground. As the wolves walked away the cubs began chasing them in a playful manner. Eventually all the animals disappeared into some woods. When French next sighted the grizzlies, they still had two of the yearling wolves in tow. For the next two days, he watched as the wolves fed on the leftover meat of prey brought down by their burly bruin neighbours.
In other situations, the roles may be reversed. Until the reintroduction, hungry grizzlies emerging from hibernation in early spring would feast on the bodies of elk and bison that had succumbed to harsh winter conditions. With the wolves around, there are now few such unclaimed carcasses for newly awakened bears. The grizzlies’ response has been simple: raid the wolves’ larder. “We’ve tracked bears right out of their dens, over the snow, straight to wolf kills,” says Smith.
He reports seeing wolves and grizzlies bed down amicably near each other, but when a bear gets near a wolf den, protective adult wolves buzz around the intruder like a swarm of angry gnats. “Two weeks ago I saw a wolf sneak up behind a bear as it was retreating from the wolf den, and bite it right on the butt,” says Smith. But usually they keep their distance. “I’ve seen a lot of wolf-grizzly interactions, but never before has one made contact with the other.”
Wolves have a much more violent relationship with another important Yellowstone predator, the coyote. Coyotes sometimes try snatching a meal at a wolf kill, but they do so at their peril. The wolves will most likely attack, and Robert Crabtree of the Yellowstone Ecological Research Center has found that out of 200 recorded clashes between wolves and coyotes, 28 resulted in the death of one or more coyotes.
Crabtree estimates that the coyote population has halved since the wolf’s return – and this is no bad thing. During the wolf’s long absence, coyotes in Yellowstone reached some of the highest population densities ever seen in North America. While the coyote ruled, other medium-sized predators couldn’t compete, and their numbers dwindled. “With the wolf back in place as a top carnivore,” says Smith, “biodiversity is greater.” Sightings of red foxes are up, especially in the areas most heavily used by wolves. Wolverines, lynx and fishers, a rare species of weasel, are also likely to increase. “The return of the wolf is the best thing to happen to Yellowstone in the past century,” says Smith.
Not everyone sees it that way. Like most mountain habitats in the developed world, Yellowstone and the surrounding wilderness of central Idaho are an island in a sea of human habitation. Wolves that roam outside this wilderness are already being killed or relocated by landowners concerned for their livestock. It’s a conflict that is being played out in many of the world’s mountainous regions.
The successful reintroductions at Yellowstone may help advocates of predator conservation elsewhere, but Smith, for one, expects a difficult fight. “It’s tough to find places that are wild enough to hold wolves,” he says. “The whole key is preserving habitat, and when you look at projections for growing human populations, the future does not seem promising for large carnivores.”
- Carnivores in Ecosystems: the Yellowstone experience, edited by Tim Clark and others, Yale University Press (1999)