The lone bison is breathing little clouds. They look like frosty speech bubbles that the chilly North Wind juggles through the crisp air, until it loses interest and blows them apart with one powerful puff. The old bull stands in the snow, quiet and motionless. The white stuff reaches almost up to the buffalo’s hips, and more fresh flakes are falling onto his shaggy coat. His massive back is already dusted like a powdered sugar cake-topping.

It’s another cold winter morning in Yellowstone National Park, with temperatures dipping to 5° F (-15° C). Here, in Wyoming’s northwestern corner, the frosty season lasts six long months.

I can see through my binoculars thin icicles extending down the bison’s muzzle, and the thick fur fringes under his mouth are frozen stiff in an icy moustache. The poor creature must be dreadfully cold.

Bjorn Anderson grins. “I bet the bison is not nearly as cold as you are,” he says. “Look, he is perfectly insulated. Not even the snow on his shoulder hump is melting.” The giant animal doesn’t move in order to save precious energy, which is difficult to replenish now, when food is scarce.

It takes a lot of strength to use his giant head as a snow plow, to dig deep down for the last bits of leftover grass. Bison are pretty smart, Bjorn surmises. And he should know, as every day he shuttles tourists through the park and past the heavyweight beasts in a canary-yellow snow coach.

Canary-yellow Bombardier snow coaches carry winter visitors through Yellowstone National Park.

Most park roads are closed to wheeled private traffic from the first Monday in November until mid-March. Annual snowfall averages about 150 inches (3.8 m). Higher elevations can easily receive even more. To reliably clear the park’s 310 paved miles (499 km) on a daily basis would be a tremendous (and expensive) effort — almost impossible to keep up during the occasional violent blizzard.

For the safety of visitors, only tracked “over-snow vehicles” with ski-like runners in front and tank-like treads, like tour guide Bjorn’s vintage Bombardier, are allowed on Yellowstone’s groomed winter roadways.

“Had enough northern exposure?” Bjorn asks jokingly as he notices the frozen red tip of my nose. I could easily compete with Rudolph the red-nosed reindeer, now. So I nod and pull my head back into the vehicle as Bjorn closes the two roof hatches through which his passengers had peeked at the frosty bison. He turns the ignition key and the engine howls.

The Bombardier, built in 1978, makes a deafening noise. Perhaps I should have taken some of the earplugs that Bjorn knowingly offered to his nine passengers when we first climbed into the vehicle at Flagg Ranch Resort, the starting point of our bumpy, 45-mile (72 km) journey to Old Faithful Snow Lodge, in the heart of Yellowstone National Park.

If only he hadn’t boasted at the same time that we would be the “lucky ones,” riding in Bombardier’s “luxury” edition, as coach number 710 had been especially padded and soundproofed to carry the Olympic torch part of its way to Salt Lake City’s Winter Games in 2002.

After his enthusiastic praise, I couldn’t possibly expose myself as a wimp and reach for the earplug box. No ear plugs for me. “Thank you very much.” My fellow passengers had also declined. So we are all enjoying the authentic background noises of an endangered species of snow coaches.

Less than two dozen of these historic snow crawlers still belong to the active park fleet. Invented in the 1940s by Canadian Joseph Armand Bombardier, all Yellowstone Bombardier models stem from the late 1970s. Many a time they have been scheduled to be replaced by quieter and environmentally cleaner alternatives.

Yellowstone concessionaire Xanterra Park & Resorts, which operates all hotels, restaurants and ski-rental facilities, and also runs sightseeing tours and shuttle trips to and from park hotels, is already utilizing a new generation of more comfortable snow coaches on some routes — ordinary minivans modified to run on tracks, instead of wheels.

Independent tour operators also offer sightseeing trips in modern track vehicles. “Not nearly as well geared to master extreme snowy conditions as my old lady here,” Bjorn Anderson proudly declares, and pats the dashboard of his trusty snow machine.

We glide through silent pine forests where trees wear puffy snow hats, and over wide, open clearings, that are, in reality, frozen lakes. We drive past murmuring creeks fed by hot thermal springs where we are told elk wade through the water to warm their hooves. Waterfalls plunge down snow-padded cliffs. White spume sprays shivering aspen trees, freezes, and wraps the bare trees into a sparkling garb of frozen water droplets.