YELLOWSTONE NATIONAL PARK — It's 10 a.m. on a frosty January morning. The vehicle for the Yellowstone Institute's "Winter Wolf Discovery" tour has pulled to the side of the road with six participants and the guide. We all gaze at a lone coyote that appears to be nonchalantly seated on the crest of a hill about 40 yards distant. The guide explains that the coyote may be considering whether or not it's safe to investigate a day-old elk kill that's in the bushes at the bottom of the hill.

Suddenly the coyote takes off running through the woods. Has he spied something interesting or is he fleeing the scene? We immediately know the answer when three wolves emerge on the hillcrest — two black females and a gray male. Wolves spell trouble for coyotes.

Everyone in the van gasps. Two hours into our tour, and we're spying wolves at close range. We hardly need binoculars, much less a viewing scope. The wolves saunter around for 10 minutes, occasionally running down the slope for a few bites from the kill before disappearing behind the hill.

Wolf reintroduction was extremely controversial (the caged wolves brought from Canada had to be protected by armed guards), yet the project is now largely deemed a success, at least in the park. In fact, Yellowstone is currently the pre-eminent wolf-watching site. People come from Japan, Norway, Australia and from all over the United States for the privilege — an estimated 200,000 people have viewed wolves at Yellowstone in recent years.

Winter is the optimal viewing season. As Douglas Smith and Gary Ferguson note in Decade of the Wolf; Returning the Wild to Yellowstone: "No doubt about it, the wolf's shining season comes in the heart of winter." Visibility is highest in winter because the elk are located in the meadows at lower elevation, and wolves follow elk. Still, it seems extraordinary that with 2.2 million acres in the park for animals to roam, so many stay near roadways.

Our guide, Shauna Baron, explains, however, that the roads were probably built where animal trails once existed. Moreover, in midwinter, the cleared roadways become convenient thoroughfares for bison, elk, foxes, coyotes and sometimes even wolves — as an alternative to sloshing through thick snow.

Elk at Yellowstone seem omnipresent. We practically trip over a few four-legged ladies strolling past when emerging from the entrance to the Mammoth Springs Hotel. These hefty ungulates can be seen in parking lots and schoolyards as well as in large herds, grazing or bedded down, on the snowy hillsides along the road leading to Lamar Valley. Yet as many elk as we see today, there were many more before the wolves arrived.

The impact of wolves on park wildlife and vegetation (the "wolf effect") has been rigorously studied and continues to be a hot topic. Though the elk herd is smaller, it's much healthier, contends Shauna, a wolf booster. Healthy elk and even elk calves are not the primary prey of wolves. A healthy elk can either outrun a wolf (35 mph versus 30 mph) or kick one to death. That means when the elk population is particularly strong, like this year, because of a wet summer that afforded ample vegetation, it's the wolves who suffer. Weakened wolves may die of starvation or be killed by other wolves, their number one foe in the park.

Thus these wily predators single out the weak and infirm; packs kill an elk every three to four days. So, it's not surprising the behavior of the elk in the park appears to have changed since wolves arrived. Being more fearful and apprehensive, the elk move more quickly through meadows, eating lightly as they go. The result has been a marked increase in willow growth along the meadow waterways — and this improved riparian zone benefits a number of species, including insects, frogs, fish, beavers and on up the food chain. Even bears benefit from having a year-round supply of protein.

The ultimate number of wolves at Yellowstone depends on the park's "carrying capacity" which is computed in terms of available food and extent of territory. Fierce territoriality is a wolf trademark. On our second day out, we stand on the western edge of Lamar Valley drinking in the beauty of this snow-covered expanse. Suddenly we hear in the distance the eerie sound of wolves howling — a fearsome melody that recalls legends of evil supernatural creatures.

Shauna guesses that the howls come from the Druid pack, a famous wolf clan that presided over Lamar Valley, lost control and then reclaimed dominance. From the other side of the valley other wolf howls emerge that could be either the Slough Creek pack, traditional rivals of the Druids, or a new pack called the Agates — now vying for this immense elk-rich region.

The visibility of wolves at Yellowstone has significantly enlarged knowledge of individual and wolf-pack behavior. Wildlife professionals as well as amateur enthusiasts can recount the soap-opera exploits of particular wolves including flirtations, infidelities and lifetime partnerships. They know which wolf was a patient mother or a nurturing dad and which pups grew up to become the alpha males and females leading the packs.

Traveling with the nonprofit Yellowstone Institute to observe wolves or any park wildlife is an obvious choice. The nonprofit was created three decades ago to partner with the park in offering educational courses (www.YellowstoneAssociation.org). Courses range from bird-watching to bear habitat; from wildflower identification to nature photography.

Course participants sometimes dwell in rustic cabins at Buffalo Ranch, built in 1907 in the heart of Lamar Valley, with a shared bathhouse and common dining hall. Our tour belonged to the "Lodging and Learning" series co-sponsored with park vendor Xanterra, so we enjoyed comfortable lodging and excellent meals at the old-fashioned Mammoth Hot Springs Hotel.

Our guide may have saved the best for last because, on the final morning of our stay, we again stood in Lamar Valley soon after dawn. Seventy years earlier, we learned, park service rangers had executed the last wolf in the park near this site. Now, instead of rifles, we peered through a viewing scope and saw 13 wolves, the entire Druid pack, their gray and black forms clearly visible on a slope about a mile away. Snow blew in our faces and a chill wind kept us alert, but no one complained. Our discomfort was small compared to the excitement and awe of witnessing wolves in the wild splendor of Yellowstone.