Migrating pelicans arrive in Iola

IOLA – A flock of American white pelicans spotted at Iola Lake this spring has sparked concerns that the birds will quickly deplete the lake’s fish population, but experts say the reality is more complicated.

In late April, a video on social media showing about 50 pelicans on Iola Lake generated more than 1,500 reactions and 400 comments. Some locals commented that the birds would quickly decimate the lake’s fish population. One concerned commenter even urged residents to chase the flock off “or you won’t have any fish left.”

Dan Dembkowski, a fisheries research scientist with the Wisconsin Cooperative Fishery Research Unit at the University of Wisconsin-Stevens Point, said pelicans are piscivorous, meaning they eat fish.

“The extent of the influence on fish populations in Iola Lake would depend on a lot of different things like how many pelicans are there, whether they’re residents or transient birds, habitat complexity that lets the fish have a little bit of refuge, a lot of different variables are at play,” he said.

Ryan Brady, a Department of Natural Resources (DNR) conservation biologist with the Bureau of Natural Heritage Conservation, said American white pelicans are tip-up foragers that do not dive.

“They are swimming on the water and all they can really do is tip over and open up their large beaks and scoop up whatever they can get in that very shallow top portion of the water,” he said.

In habitats like Iola Lake, Brady said pelicans primarily target schooling fish, crayfish and amphibians.

“What makes up the bulk of their diet are these smaller non-game fish, but clearly they do eat some other fish and there’s plenty of evidence of them eating walleye or trout in some areas, and probably perch in some places, things like that,” he said.

Because their diet largely consists of non-game fish like carp, suckers and minnows, Brady noted the pelicans are actually “doing us a good thing by eating up invasive fish” that were not traditionally in the local waters.

According to a 2019 report by the U.S. Department of Agriculture Animal and Plant Health Inspection Service, American white pelicans can cause economic damage at commercial aquaculture facilities such as southern catfish farms, where densely stocked, five-foot-deep ponds provide a near-perfect foraging environment.

Dembkowski said a natural lake ecosystem is vastly different from a commercial fishery because fish are not concentrated at the same densities.

“The density of fish in Iola Lake is almost certainly lower than that, and with added habitat complexity like underwater vegetation and things like that, that likely reduces the effectiveness of pelican predation,” he said.

Dembkowski said it is difficult to measure the impact pelicans have on a lake’s fish population because many factors influence fish abundance. To determine the birds’ effect, he said researchers would need to analyze their diet and compare fish populations over time.

“They’re certainly fish eaters, but if they’re only there for a short period of time and are transient, just stopping through on a migratory route or something like that, it’s something that you raise your eyebrows at because it’s not something you see every day, but I would be a little bit more concerned if they took up residence there,” Dembkowski said.

Dembkowski said pelicans may add another stressor, but environmental factors are typically the primary drivers of a lake’s fish population.

Iola Lake covers 220 acres, reaches depths of about nine feet and contains panfish, largemouth bass and northern pike, according to the DNR. Brady said the flock of pelicans recently seen on the lake was likely stopping during its spring migration north.

The recent increase in American white pelican sightings across Wisconsin is part of a broader conservation success story. Though they are native to Wisconsin, Brady said pelican populations declined significantly in the state during the 19th and 20th centuries due to unregulated hunting, habitat loss and the effects of pesticides such as DDT.

Pelican populations began rebounding in the state in the mid-1990s, which Brady attributed to the banning of DDT, new hunting regulations, widespread wetland restoration and improved water quality.

While there were no known pelican nests in the state in the early 1990s, a 2025 survey documented more than 8,000 nests in Wisconsin. The nesting sites are primarily concentrated on isolated islands within large wetlands in the eastern part of the state, mainly across Winnebago, Brown, Dodge and Door counties, he said.

Though about half of the state’s pelican breeding population is located near Green Bay, the nesting colonies closest to Waupaca County are situated just to the south, near Lake Butte des Morts on the west side of Lake Winnebago.

For residents suggesting the birds should be chased off the lake, Brady said American white pelicans are federally protected under the Migratory Bird Treaty Act. The law makes it illegal for the public to shoot, disturb or harass the birds, and prohibits people from collecting their feathers or keeping mounted specimens.

“I think most people like seeing pelicans,” Brady said. “They see their comeback as a good thing. I think we should probably take the time to appreciate them instead of worrying about them taking things that we want.”