As we squinted out over the Mississippi River backwaters from the observation deck at the Trempealeau National Wildlife Refuge, we could make out a big, bright-white form in motion on the marsh, flapping in the distance.

The giant spotting scope brought it into focus — a flock of about 50 tundra swans stopped on their way south, standing out amid the gray of an even bigger flock of Canada geese.

Stephanie Edeler, a wildlife refuge specialist at the Wisconsin sanctuary, pointed out a bald eagle nearby.

"We get tons of pelicans out here, too, and river otters," she said.

We had come to experience the bird haven that the refuge's isolated backwaters provide. Sandhill cranes land on its dikes, and coots gather by the thousands. It was a great spot for my family of four's first real foray into birding.

Franklin D. Roosevelt had birds in mind when he established the refuge's original 700 acres back in 1936, and it has since grown to 6,446 acres of protected deltas, marshland, woods and prairie in the Driftless Area of southern Wisconsin.

It is a gem amid the many national refuges along the Mississippi flyway extending from Canada to Mexico. Refuge staffers and visiting ornithologists have recorded more than 283 species of birds in Trempealeau, and each May, the sanctuary hosts a migratory bird festival, celebrating the arrival of yellow-rumped warblers, orchard orioles and other songbirds.

Birds were migrating in the other direction when we set out down the Great River Road south to Trempealeau in late fall. The air was chilly and the bluffs in the distance were already a wintry shade of purple on the Minnesota side of the river, south of Winona.

We stopped for the night in the small village of 1,529, whose Main Street slopes right down to the river.

Built in 1871, the Trempealeau Hotel has a historic but unpretentious and fun feel, with a small dining room and a mounted snapping turtle on the wall overlooking the vintage bar. When new owners took over in 2012, they kept the place's (rightfully) famous vegetarian walnut burgers on the menu and added locally sourced meats and fresh pasta. Trains rumbled by right outside our window as we ate, riling up our two girls, who pointed and called out every time, watching for the caboose. The trains' charm wore off a little as the night went on, but luckily we are all deep sleepers.

The next morning, we had breakfast at the cozy Garden of Eatin' in nearby Galesville and headed for the refuge.

The Trempealeau National Wildlife Refuge is a place where the changing of the seasons is especially vivid, marked by shifting colors and thousands of migrating birds.

When we traveled the loop of the refuge's 4-mile "prairie's edge" drive, the purple and pinks of wild lupine and other wildflowers were long gone from the refuge's rolling sand prairie, replaced by the vibrant reds of little bluestem and gold of Indian grass.

Wisconsin's Great River State Trail, part of the 3,000-mile biking route called the Mississippi River Trail, ends in the refuge, and the setting is a stunning place for a ride. The region's unique "driftless" topography was created when the glaciers came through the surrounding lands but avoided passing over certain areas. The wind blew the sand and silt left behind by the melting glaciers and created the many mounds and hills that make this place different from other parts of the Midwest.

We vowed to return with bikes and our Burley trailer for the girls. And maybe a real camera. The refuge is the kind of place where wildlife photographers are often rewarded — snapping plenty of birds, of course, but also sunning turtles, swimming muskrats and otter at play.

The refuge's dikes and control structures mimic the natural flooding and drought cycles that were there before the locks and dams controlling the Mississippi River's levels were built. The dikes themselves are now popular places to walk, hike or bike. Edeler suggested we check out Kiep's Island Dike.

The dike's road was lined with reddish-gold prairie grasses and shrubs with yellow foliage still clinging to the branches, standing out against the purple river bluffs rising in the background.

Once enough snow blankets the prairie and woods, the refuge's hiking trails become snowshoeing and backcountry cross-country skiing trails. Refuge staffers don't groom them, depending instead on visitors to break trail. They make pairs of snowshoes available at the refuge office when it's open.

Out on the observation deck, our 4-year-old wanted a closer look at the tundra swans, but struggled to keep the scope pointed on them. Edeler told us that an even greater number of the beautiful birds had been spending time in the refuge before some patches of ice moved in, sending them down to spots a little farther south. She told us the swans were still gathering by the thousands in open waters downriver in Brownsville, Minn.

We decided to take her advice and follow their path (though not as the swan flies). We drove about 44 miles south, crossing back to the Minnesota side of the river just north of La Crosse, Wis., my husband teasing the girls that we were on the hunt for "snow loons."

"Tundra swans!" we corrected him.

We were very glad we made the extra drive. The Brownsville Overlook off Hwy. 26 offered quite a spectacle — much of the river was covered in white, as thousands of swans filled the waterway.

Right near the overlook, hundreds of the birds were gliding around and diving under the water to dig for arrowhead tubers. While we didn't need binoculars to watch them, the overlook's scope brought their antics into even greater focus.

Experts at the Upper Mississippi River National Wildlife Refuge, which runs adjacent to the Trempealeau refuge in places but also extends for hundreds of miles up and down the main waterway, keep bird counts online. They posted that as many as 10,000 tundra swans were gathered around the islands south of Brownsville during our visit.

On several weekends in late fall during the swan migration, naturalists from the Upper Mississippi River refuge staff the Brownsville Overlook. The refuge also hosts a "swan watch" bus tour — which leaves from Winona and stops at two overlooks where the birds can be easily seen — each November.

During our visit, two naturalists gave a talk to a busload of elementary schoolchildren, measuring kids' "wingspans" as they spread their arms wide. Later, they fielded questions from our eldest daughter and pointed out the ducks and eagles that had joined the long-necked cobs (male swans) and pens (female swans).

Tundra swans were once called "whistling" swans because of the sounds their wings make in flight.

But even on the water, the gathered migratory flocks made a great ruckus of sound. Bugling calls of "hoo-ho-hoo" and noisy honks rose from the river, creating a sonic experience unlike anything we'd ever heard.