While on a recent visit to the Chicago Botanic Garden, Ann Harness spotted a creature she’d never seen before. The tall brown bird with a long bill looked like a cross between a rail and a heron.

It was a limpkin — far from its home.

The bird lives in tropical areas, from southern Florida to the Caribbean islands, Mexico and Central and South America, where it gives a piercing cry from its wetland habitat.

Harness’s sighting was one of at least 24 in Illinois this year.

“Limpkins spend their time in wetlands and aren’t that easy to see, so there’s probably a whole bunch more that we don’t know about in Illinois,” said Mike Ward, an avian ecologist with the Illinois Natural History Survey.

Geoff Williamson, recording secretary of the Illinois Ornithological Records committee, agreed.

“Of all the bird species that have expanded their range northward into Illinois, the limpkin is the most dramatic,” said Williamson, a longtime Chicago resident.

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Though climate change may quickly come to mind as a reason for the expansion, biologists say this phenomenon has a lot more to do with the introduction into the United States of several nonnative snail species, a new food source for the limpkin.

Others have been seen this year at McGinnis Slough in Orland Park, McHenry Dam in McHenry County and Grass Lake in Lake County. Two were reported at the Nygren Wetlands in Winnebago County, and others have been found farther south in counties such as Bureau and Johnson, where two were seen together.

“Illinois had its first (sighting) in 2019 (in Olney), then two each during 2021 and 2022, and now I can’t keep pace with the records in 2023,” Williamson said.

Hundreds of nature lovers are traveling the state to document this species for their state and county lists.

The Chicago Botanic Garden limpkin has been seen most days since Aug. 13, and some of the others are also still around.

The limpkins are feasting on mussels and snails, using their uniquely adapted bills to retract the mussel or snail from inside its shell.

Once nearly wiped out in Florida, the limpkin has recently spread to the Carolinas, Alabama, Mississippi, Georgia and Louisiana, where it successfully nested.

In the late 1990s, limpkin populations were declining in Florida as wetlands were drained and their main food supply, the native Florida apple snail, was decreasing. In the mid-2000s, various types of apple snails native to Central and South America as well as Asia were introduced to the United States, often for use in aquariums.

The nonnative snails have been tossed outdoors into waterways, and their populations began to explode.

Limpkins began eating the nonnative snails and increasing their numbers in Florida. They may have started to move northward as a result.

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Other Midwest states documenting wandering limpkins within the last few years include Missouri, Iowa, Wisconsin, Minnesota, Michigan, Ohio and Indiana.

Ward said potentially more droughts in the South due to climate change could affect the limpkins’ movements.

“They have to move and find better habitat for feeding,” he said. “But I don’t think that is explaining the overall increased population of this species.”

As with other water birds, the limpkins may be engaging in what’s called post-breeding dispersal. After leaving their nests, immature birds like little blue herons often fly north seeking food, then fly back south for the winter.

“Though considered nonmigratory, limpkins may now be engaging in this new kind of behavior, and food supply and increase in population could be causing it,” Ward said.

Meanwhile, the nonnative snails are causing problems in aquatic ecosystems in Florida, Louisiana and other states.

Officials hope the limpkin may help keep the invasive species in check. But it will be difficult, because many of the introduced snails can reproduce twice as rapidly as the native ones, according to the Florida Fish and Wildlife Conservation Commission.

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While Illinois does have the invasive Chinese mystery snail, often considered an apple snail, it also has 75 more mussels, snail and clam species the limpkins can eat. Mussels, snails and clams belong to the large group of aquatic creatures called mollusks, soft-bodied organisms without backbones enclosed in a hard shell.

“That’s a niche the limpkins seem to be taking advantage of in Illinois,” Ward said. “They seem to be hanging out in wetlands with a good population of snails and freshwater mussels,” he said.

The limpkins have been documented eating both native and nonnative mollusks in Illinois and Iowa.

Stoil Ivanov, who has videoed many rare and common birds in the Chicago area, took a video in late August of the limpkin at the Chicago Botanic Garden as it pried open a large mussel. It took the limpkin at least four minutes to get at the meal inside the hard outer shell.

Even birders who don’t consider themselves “chasers” have gone to see a limpkin discovered near where they live in Illinois.

“Normally I don’t chase vagrant species,” said Wanda Supanich of Libertyville. But the limpkin has been at the Chicago Botanic Garden for so long that she said she felt “obliged to make the effort to see it, and I’m glad I did.”

It took her three tries. She accompanied a group lugging their heavy scopes for a mile on a hot day before reaching the spot where it had last been seen. Within 15 seconds, they saw the bird. “It grabbed a huge freshwater clam and moved into the shadows to hammer the shell open,” she said.

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Supanich, Harness and other birders and biologists wonder what will happen to the lingering limpkins when cold weather comes.

“Since they’re not normally migratory, they might not have a clue what to do having never experienced winter,” Harness said. “I’m heartbroken thinking about it.”

A limpkin seen in Ohio a few years ago remained there until December, and a video shows it feeding on snails buried by ice.

The bird later died after a cold spell in the state.

Williamson said he doesn’t think limpkins can survive winters in the North, but he doesn’t know whether they will die or retreat south in winter and then move back north in spring.

“Biologists still don’t understand the mechanics of this invasion,” he said.

Harness hopes the limpkin she discovered starts flying south soon so it can find food in winter. “I’d like to think it will figure out what to do,” she said.