– To the casual observer, the Sax-Zim Bog is not particularly scenic in winter.

It’s a vast stretch of flat, snow-covered, frozen ground punctuated by trees, sometimes in clumps, sometimes standing alone. Every so often, there are the remnants of a rotting, collapsed barn, a vestige of the misplaced optimism of a farmer who had hoped to tame the soggy ground only to discover that the bog usually wins such jurisdictional disputes.

Of course, the bog doesn’t get many casual observers. It’s tucked into a remote corner of the Iron Range that few Minnesotans visit. Bird-watchers, on the other hand, travel from all over the country to get there.

Every February, the immense bog — more than four times the size of Minneapolis — offers extreme birders the prospect of spotting birds that have migrated from northern Canada, species seen nowhere else in the lower 48 states. To these devotees, seeing birds that others haven’t seen is what it’s all about.

“It’s like a big, lifelong Easter egg hunt,” said Mike Hendrickson, founder of the bog’s annual Winter Birding Festival. “Every state has different eggs, and everyone wants to see them all. Northern Minnesota has its share of very special eggs, and people will go bonkers over that.”

This year’s festival attracted people from such far-flung — and warm — locales as Southern California, Texas and the bay area of Florida. They bundled up in sweaters, coats and layers of sweatpants to withstand the bog’s near-zero temperatures. In their heavy work boots, they tromped across northern Minnesota’s tundra, striking the pose of big-game hunters, shooting with cameras outfitted with 2-foot-long lenses.

Their window of opportunity is limited. It was mid-month and, if normal migration patterns held, the birds would be heading back north within a week or two.

“They sort of eat their way down here, moving farther south as they run out of food,” explained Frank Nicoletti, a researcher at the Hawk Ridge Bird Observatory in Duluth. As soon as the weather begins to warm up, the birds start eating their way north again, usually leaving the bog by the first of March.

That was enough to draw 150 birders — the point at which the birding festival caps participation — to Meadowlands, a town of 134 people that sits on the edge of the bog about 45 miles north of Cloquet.

“The festival is a big deal because the bog is a big deal,” Hendrickson said. It doesn’t matter that most Minnesotans haven’t heard of it. The birders have, and so, apparently, have the birds. More than 240 species have been spotted there.

A frosty start

Before dawn, the birders gather in Meadowlands, where they board schoolbuses staffed by professional guides and, no small perk, drivers who know where the heated bathrooms are.

Nonetheless, heat was in short supply early in the day. As the birders climbed aboard the buses, the windows quickly fogged over. No one was about to miss a sighting, so there was only one thing left to do: Open the windows.

Sid Crawford, who had come from Florida to attend his fourth festival, took the chill in stride. “I don’t think it’s uncomfortable,” he insisted. “I think it’s invigorating.”

As the trip began, Nicoletti instructed everyone on board to keep vigilant watch and yell out if they saw anything promising. “Look for blobs in bushes and trees,” he instructed.

The most exciting sighting of the day wasn’t a blob. It was barely a speck: a boreal owl, which, weighing a mere 4 ½ ounces, is one of the smallest of its kind and among the rarest of sightings.

The busload oohed and ahhhed, clicking their cameras like a tour of Hollywood stargazers who’d seen Brad Pitt and Angelina Jolie strolling down the sidewalk arm-in-arm with George Clooney.

“The only way this could be better is if the bird had hopped on my shoulder and said, ‘Take me home with you,’ ” said Ed Newbury, a retired Episcopal priest from Nebraska.

That’s birding

There is no official bird-watching motto, but the phrase “That’s birding,” certainly could qualify.

The folks on one bus hiked for 20 minutes through deep snow in search of a woodpecker that might have been dining recently in a grove of trees. It had moved on by the time they got there. Lars Benson, who was leading the hike, turned to the group and said, “Well, that’s birding.” Without a grumble, the group turned around and hiked back to the bus — for another 20 minutes.

Just as the bus was about to return to Meadowlands for the day, word came about a great gray owl sighting. The bus immediately set off on a wild goose (or in this case, wild owl) chase that zigzagged across a corner of the bog for more than an hour while the birders kept their posts at the windows (which, by this time, could be closed).

Several times, a birder would holler “Stop!” only to be followed by moans of disappointment at the discovery that a blob in a bush was, in fact, just a blob.

Nicoletti finally called off the search by announcing, “That’s birding.”

Still, no one went home disappointed. Most of them had seen new species, including pine grosbeaks, hoary redpolls, northern shrikes, gray jays and boreal chickadees.

The sighting didn’t have to involve a rare bird. Watching a bald eagle that sat regally atop a tree just off the road, Illinois birder Michelle Kolb sighed.

“This is birding nirvana,” she said.