You can't step into a northern Wisconsin gift shop without seeing the dark red eyes and black-and-white spotted backs of loons stamped on postcards, magnets and T-shirts.

The common loon is a symbol of the Northwoods, its mournful call evoking images of warm summer days away from the hustle of daily life.

But the real-life birds may be in jeopardy, according to a recent study.

Wisconsin's loon population has dropped 22% over the past three decades. The study shows that the declines are likely due to lakes becoming less clear from climate change and land use.

Walter Piper, a behavioral ecologist at Chapman University in Orange, California, and an author on the study, said that reproductive success – or the ability of a loon to have a chick that lives to have its own offspring – is down in Wisconsin. It's only a matter of time until there are steeper declines, Piper said.

"I'm on pins and needles every year," he said.

Here's how climate change and land use are affecting the treasured Northwoods bird.

Loons need cold, clean water with natural shorelines

Common loons breed in freshwater lakes from Alaska across much of Canada, including parts of a number of other U.S. states, like Wisconsin, Minnesota and Michigan, which are the southern tip of their range.

Loons overwinter on the Atlantic and Pacific coasts, and then return to freshwater lakes in the Great Lakes Northwoods to breed and raise their young.

The bird needs clean, cold water lakes to nest, said Tom Prestby Wisconsin Conservation Manager at Audubon Great Lakes. Loons are visual hunters and rely on their underwater eyesight to dive and catch fish, he said.

Loons also need natural shorelines close to the water to nest, Prestby said. That's because loons have webbed feet that are more like flippers, he said, so they can't walk around on land, like other birds can.

Young and older loon chicks are dying at alarming rates

Piper and other scientists working on The Loon Project started monitoring loon breeding pairs in 1993. In total, they track 110 breeding pairs in Oneida, Lincoln and Vilas counties.

Piper's previous work with the project shows that life for loon chicks in northern Wisconsin is becoming harder.

Over the past three decades, there has been a steep decline in the ability of loons to produce chicks, according to their 2020 study. Both young and older chicks are dying at higher rates than recorded earlier.

One of the most dramatic declines is in the survival of young loons that have not yet started to breed, known as floaters.

In the 1990s, about half the floaters that migrated to the coasts for the winter would return to northern Wisconsin in the summer to look for territory, Piper said, referring to the time as the "roaring '90s."

Now, only about 16% return, he said.

Loons typically produce one brood of chicks per year with one or two eggs. But Piper said that broods with two chicks are becoming rarer.

And the chicks that do survive are 11% lighter on average than they were 30 years ago, putting their survival at risk.

Why are loon chicks getting lighter?

Piper and his colleagues wanted to see what is contributing to this overall population decline. So, in their most recent study, they wanted to figure out whether chicks were getting enough food.

The team looked at water clarity for 127 lakes in the northern part of the state from 1995 to 2021, using satellite images. They compared the satellite data from measurements taken directly from the lake to make sure the images were accurate.

Piper said they focused on water clarity in July because that is the most critical month for chick growth after they hatch in June.

They found there is a very close correlation between water clarity and chick weight, Piper said.

The most plausible reason for this is that adults can't find food as well in murkier waters to feed themselves and their ravenous chicks, Piper said.

Why are lakes becoming murkier?

Lakes are murkier in rainy years not because of the rain itself, but because of what is washing into the lakes, Piper said.

For instance, intense rain can wash sediment into lakes as well as nutrients, like nitrogen and phosphorus from fertilizers, that can incite algae blooms.

As climate change brings heavier and more frequent rainfall to northern Wisconsin, this will likely worsen over time, he said.

Will loon populations in the Northwoods continue to decline?

The scientists also started monitoring another population in Crow Wing and Cass counties in central Minnesota in 2021.

Although it's still early, Piper believes loons in Minnesota are heading in the same direction as those in Wisconsin.

Prestby is concerned that more severe rain events with climate change will not only make lakes less clear, but that it will wash away the natural shorelines that loons need — and even wash away eggs if the timing is right.

One of his biggest worries is that climate change may shift their range north and the treasured bird may no longer spend its summers in Wisconsin.

"No one really knows when or if, but it certainly is a possibility that someday we won't be in their breeding range anymore," Prestby said.

"That would be a very, very sad day."

This story was originally published by the Milwaukee Journal Sentinel. Caitlin Looby is a Report for America corps member who writes about the environment and the Great Lakes. Reach her at clooby@gannett.com or follow her on X @caitlooby.