WTTW: This time of year, Chicago is typically awash in migratory waterfowl, as visiting birds spend the winter hanging out on Lake Michigan and area rivers before heading back north in the spring.

These mergansers, coots, scaups, buffleheads and goldeneyes — just to name a few — aren’t necessarily rare or endangered, but their appearance does make for an exciting change of pace among local birders.

So when word began to spread that one of these guests, a white-winged scoter, had been spotted on the North Branch of the Chicago River, folks grabbed their binoculars, scopes and cameras and headed to Chicago’s River Park for a look.

These skilled photographers came away with some stunning images of the scoter, which they shared on social media. And in the process, the birders inadvertently provided a couple of researchers at Loyola University with a key bit of documentation they hadn’t anticipated — one that proved without a doubt what, until now, had only been a theory.

There, in the beak of the scoter, was quite the catch: a red swamp crayfish, clear as a bell, about to go down the gullet.

The curious cluster of non-native swamp crayfish (Procambarus clarkii) at River Park, where the North Branch and North Shore Channel converge, happens to be a focus area of study for Loyola professor Reuben Keller, who specializes in aquatic invasive species. One of Keller’s graduate students, Tava Oosterbaan, had recently wrapped up a study looking at the presence of microplastics in the crayfish.

While it had already been established that fish in the river were eating the crustaceans, it was pure speculation birds were doing so as well.

“We haven’t seen a bird with this crayfish in its mouth in our river,” Oosterbaan said. “When we got those photos and we got to see them, it was kind of like a ‘Eureka.’ OK, it’s definitely happening, they’re definitely consuming crayfish. We can say it because now someone has seen it and taken a photo of it. It was so exciting.”

Mike McCawley, one of the birders who photographed the scoter, didn’t set out to make a contribution to science. He just wanted to catch a glimpse of an odd duck that’s typically camera-shy and elusive.

White-winged scoters (Melanitta deglandi) breed in the boreal forest of northern Canada and Alaska and during winters, most head for the Atlantic and Pacific coasts, but some make their way to the Great Lakes.

They tend to prefer big open waters, which can make it difficult to photograph the birds, McCawley explained. To have one on the Chicago River was a chance to see one up close.

But there are no guarantees in bird watching. McCawley spent an hour on the bank at River Park scanning the water for the scoter, to no avail. And then his luck changed.

“I was about to leave when a gentleman across the river alerted me that he’d spotted the scoter and pointed him out to me,” McCawley said.

White-winged scoters have a tell-tale patch of white against otherwise black feathers, and males have another dash of comma-shaped white around their eyes, plus an orange-tipped beak. There was no mistaking the bird.

“I watched him dive and reappear a bunch of times and in one of those re-surfacing moments he was wrestling with this large crayfish,” said McCawley, who managed to snap a photo before the scoter downed the crayfish in a single gulp.

“It was certainly a rare and thrilling moment to witness and to capture,” he said.

Thrilling, but in light of Oosterbaan’s research, also concerning.

After trapping red swamp crayfish along the length of their North Branch/Channel stronghold, and then dissecting them and analyzing their stomach contents, Oosterbaan made a surprising discovery.

The amount of microplastics contained in the crayfish guts was “startling,” Oosterbaan said.

Compared to all other existing literature on crayfish, the specimens from the Chicago River contained microplastic loads anywhere from 10 to 300 times greater than previously recorded. (Microplastics are defined as less than 5 millimeters, or smaller than a pencil eraser.)

“There are no numbers higher than ours — that I know of yet,” Oosterbaan said.

In general, the plastic was in the form of microfibers — small fragments of polyester, acrylic and nylon — shed off clothing and other fabric items such as bedding or carpets.

Most surprising was the way the fragments often clumped together into “fiber balls” in the stomachs of the crayfish, growing over time.

“As the crayfish is eating more of these microplastics, they’re getting tangled in this bundle. When the fiber ball gets too big, they can’t pass it out, … they can’t throw it up, they can’t digest it, it just kind of gets stuck in them,” Oosterbaan said.

The long-term consequences of these fiber balls, a newer phenomenon that’s also been observed in other species including crabs, is unknown.

In red swamp crayfish — omnivorous and notably indiscriminate eaters — microplastics may have found their ideal consumer.

“We even found pure mud in their (swamp crayfish) stomachs. They are just shoveling anything into their mouth,” Oosterbaan said. “If there’s microplastics anywhere in the environment, they’re probably doing a good job hoovering it up.”

And when a scoter, or other visiting diving duck, in turn swallows a swamp crayfish whole, all of those microplastics — including fiber balls — are going down the hatch, too.

What does this mean?

Minimally, Oosterbaan’s results suggest crayfish might be a significant vector when it comes to microplastics entering the food chain, given how many other organisms eat crayfish.

But the research also raises a host of new questions: Is the concentration of microplastics unique to the Chicago River, specifically in a stretch downstream of a wastewater treatment plant (see sidebar)? Or would the findings be similar in other urban bodies of water? Do all crayfish consume a large amount of microplastics or is this something unique to the red swamp species?

“This is pretty new territory,” Oosterbaan said. “It does call for more research.”

In an interesting twist, Oosterbaan also sampled invasive zebra and quagga mussels found in the same channel as the red swamp crayfish. Their uptake of microplastics, by contrast, was extremely low.

“The funny thing about mussels is they operate on this level where they actually do naturally discriminate between particles they ingest,” Oosterbaan said. “We think that the zebra mussels, they’re either not holding on to the microplastics long or they’re not accepting them readily to begin with.”

And here’s where the white-winged scoter reenters the conversation.

Scoters love to eat mussels, which they swallow shell and all. And one of the reasons they’re turning up in the Great Lakes in larger numbers is because of the all-you-can-eat buffet of zebras and quaggas.

“If these birds are coming here and they’re gorging themselves on invasive mussels that also are not huge microplastics sources, I think that’s great news,” Oosterbaan said.

Chicago birders nabbed a photo of that, too.

Red swamp crayfish shouldn’t be in the Chicago River. Their presence, Reuben Keller has long theorized, is likely due to aquarium releases. And their persistence in the area around River Park, he suspects, could be due to the site’s location downstream of the O’Brien wastewater treatment plant.

“It disgorges relatively warm water year-round. We think that’s really important during the winter. It keeps the water warm enough that this southern species can survive up here,” Keller previously told WTTW News.

That same treatment plant is also potentially the source of the microplastics observed in the crayfish, Keller said. Or not. Or just one of many sources.

At this point, per the Environmental Protection Agency, microplastics have been found in every ecosystem on the planet, including Antarctica.

Allison Fore, a spokesperson for the Metropolitan Water Reclamation District (MWRD), said most microplastics in the wastewater stream are removed during preliminary and primary treatments processes, but conceded there are “considerable challenges and costs to remove all microplastics … especially considering the approximate 400 billion gallons we treat each year.”

There are other ways microplastics can find their way into the Chicago River and North Shore Channel, Fore noted, including stormwater runoff and the breakdown of larger plastic waste people dump along the banks or toss directly into the waterway.

“The district is currently studying the sources of microplastics to our (wastewater treatment plants) and what is removed through our existing treatment processes,” Fore said. “Ultimately, it comes down to source control and all of us as consumers to limit the amount of plastic that could potentially enter our environment.”

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