Big and burly, with a supersized orange bill, the once rare American white pelican is migrating through Illinois: ‘It’s just stunning to watch.’

Pelicans in Chicago? Increasingly, the answer is yes.

The American white pelican — a snow-white showstopper that weighs in at up to 30 pounds — has been spotted at Lake Calumet on Chicago’s South Side. The birds have been seen flying over the busy Dan Ryan Expressway, the historic three-flats of Lincoln Park and the neat bungalows of suburban Berwyn.

But the best time to see them is now, during their semiannual migration through Illinois, when hundreds rest and refuel near the Four Rivers Environmental Education Center in Channahon, 50 miles southwest of Chicago, and thousands descend on preserves such as the Emiquon National Wildlife Refuge in Lewistown.

“They’re such a big bird and they soar,” said Carl Giometti, a board member at the Chicago Ornithological Society. “You can get flocks of thousands of them, and it’s just stunning to watch them soar and hover on the wind right above you.”

As recently as the early 2000s, American white pelicans were so rare in Illinois that birders would travel hours to catch sight of one, according to American Birding Association webmaster Greg Neise, who has been birding in Chicago since the 1970s.

Theories abound as to why the birds began to appear in larger and larger numbers: Neise said that the pelicans, which traditionally breed in Canada and the Great Plains and migrate to the sunny Gulf Coast in winter, started breeding in northern Wisconsin, near Door County. He also pointed to the rise of invasive Asian Carp, a plentiful food source for the birds.

Others suggest that a storm may have knocked the pale giants — each with a 9-foot wingspan — off their traditional routes.

What’s clear is that the American white pelican, which was in marked decline in the 1960s, is more plentiful — and therefore more likely to be seen in the Great Lakes region — thanks in large part to decades of wetlands restoration nationwide, according to Andy Forbes, Great Lakes deputy chief for migratory birds at the U.S. Fish and Wildlife Service.

The American white pelican population is now estimated at a healthy 180,000.

In 1966, the overall breeding population was estimated at 40,000. Now the breeding population is estimated at 32,000 in Minnesota alone.

“It’s been a huge success story,” Forbes said.

This year’s fall migrants have already started massing near the Four Rivers Environmental Education Center, the closest place to Chicago for reliable large-scale viewing. On peak days, 200 or 300 of the birds can be seen swimming in shallow waters, according to Forest Preserve District of Will County program coordinator Erin Ward.

“They’re an incredible animal,” Ward said. “They can sense things. If there’s a hurricane coming, they’ll hang out here for a bit longer because they know.”

With big, orange feet and a hulking bill that expands to take in 3 gallons of water, the American white pelican has been described — by its fans — as peculiar, gangly and clownish. It carries a strong, fishy scent and looks too top heavy to get off the ground. Yet it’s a formidable flyer, with flocks soaring smoothly in precise formations.

“Pelicans all line up and fly in the same direction,” said Neise.

“When they turn on an angle you’ll see a flock of 100 or 200 birds up there — and all of a sudden they disappear, and when they turn back so they’re not head-on to you, they just reappear. It’s like they flash on and off in the sky.”

The birds, which can fly about 2 miles above the ground, learn migration routes from their parents, so there’s a good chance that the offspring of the pelicans stopping off in Channahon this year will take the same route in years to come.

White pelicans are larger than the better-known brown pelicans, which are often seen in Florida; they also have a different habitat range and don’t dive from above for their fish.

The Forest Preserve District of Will County is preparing for a Pelican Day celebration at Four Rivers Environmental Education Center on Sept. 25, with guided hikes to the sites where the pelicans are likely to be seen, presentations, exhibits and family activities. There’s no guarantee that the pelicans will still be in the area, Ward said, but the birds usually stay for two to four weeks in the fall.

And regardless of the birds’ travel plans, there will be pelicans on site. For the first time, “Hoo” Haven, a wildlife rehabilitation center, will bring two ambassador pelicans to the event.

The event is free but registration for hikes and presentations is required by Sept. 24. Ward recommends that those who want to see the pelicans on other days call the education center the morning of their visit to see whether the birds are in the area. The birds are often easiest to see in the afternoon, around 3 p.m., she said. Ward suggests bringing binoculars and a camera, and perhaps a portable chair. The longer you stay, the better your chances of seeing pelicans, she said.

In the past three to five years, the pelicans have become a fairly common sight in Chicago in spring, according to Giometti. At Lake Calumet, he has seen up to 40 to 50 birds at a time.

Neise quickly ticked off a half-dozen places in Illinois where he’s seen the birds. For those who are willing to make the effort, he said, there’s even the chance to observe them during cooperative fishing, in which the birds work together to herd their prey toward the shore, and then scoop up their catch with their giant bills.

“I’ve had feeding white pelicans so close I’ve been splashed by them,” Neise said.

nschoenberg@chicagotribune.com