Brigham City » Spring is winging through Utah this week and resting on the receding ice in the marshes east of the Great Salt Lake.

The lengthening days and opening waters have prompted the fleeting return of thousands of tundra swans from California, and hundreds were standing on ice shelves and preening Saturday during the Bear River Migratory Bird Refuge's annual Tundra Swan Day. Dozens of Utahns drove slowly along the dikes between canals and marshes, stopping here and there to zoom in on the big white birds and verify their species by spotting the little yellow stripe arcing forward from the eye.

The swans mostly sunned themselves and rested on the ice. Now and again, they stretched backward to rub bills between wings, or slipped into the shallow water to dredge food from the murk.

"Elegant," Sylvia Wilcox said, explaining the attraction that brought her and a friend north from Salt Lake City. "It's just amazing to see them out here on a tundra, so to say, just resting. The whole life cycle is just fascinating.

"This is a stopover point that's so important to them. That's what's so exciting to me: You just get a sense of the links."

The flat water before the swans reflected the snowy Wasatch range to the east and the beige Promontory Range to the west, depending on the vantage.

Tundra swans are known as whistlers, and they're smaller than the trumpeter, which lacks the yellow stripe. Refuge biologists say most of these whistlers come year after year from the Sacramento-San Joaquin delta, bound for Canadian or Alaskan nesting grounds. The freshwater along the Great Salt Lake is a rare oasis of aquatic plants and invertebrates along their migration.

Many of Saturday's birdwatchers were treated to -- or perplexed by -- one big bird that wasn't like the others.

"What's that big black one?" one man asked.

"I don't think it flew in from Australia," a U.S. Fish and Wildlife Service employee said through a rolled-down window as he drove by on the gravel dike.

Yet that's where it belongs, naturally. A black swan with a red bill stood among the white whistlers on the ice, preening like the others and generally looking like he knew the drill as well as the others. Volunteers who set up spotting scopes for the public guessed that the black swan may have escaped from a zoo and joined the migration.

"He doesn't belong here, but he's found some buddies," said volunteer Louise Brown, who makes a daily migration of 90 miles from Kamas to see the refuge birds and help people understand them. "He's causing quite a stir. I guess he's thinking, 'These guys look healthy. They know where the food is.' "

Tundra Swan Day also included birding and digital photography classes at the refuge headquarters. Refuge Recreation Planner Betsy Beneke said a sunny and warm weekend in mid-March is a good time to draw people out into nature.

"Everybody's kind of got cabin fever," she said.

The swan migration continues this month, and visitors can pick up brochures for self-guided refuge tours at a kiosk on Forest Street west of Brigham City.

bloomis@sltrib.com