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Study finds loon populations decreasing due to poor water clarity in lakes, an effect of climate change

Loons at Sylvania Wilderness in the Ottawa National Forest.
Katie Thoresen
Loons at Sylvania Wilderness in the Ottawa National Forest.

Northern Wisconsin lakes are less clear than they were 30 years ago.

That’s led to a decrease in loons, who rely on clear waters for hunting fish.

If you’ve spent time on northern Wisconsin’s lakes, you’ve probably heard the eerie, iconic call of the loon.

Since 1993, Dr. Walter Piper has been studying the state’s loon population through the Wisconsin Loon Project, which he leads.

A Professor of Biology at Chapman University in Orange, California, Dr. Piper was initially interested in the bird’s aggressive territorial behaviors.

Each year, over time, however, his team realized that loon broods were shrinking.

He recently publisheda paper in the journal Ecology in which he found that as our climate warms and rainfall increases, lakes are becoming inundated with runoff materials, leading to worse reproductive outcomes for loons.

“I started to think, wow, these chicks don't seem to be as big as they used to be. And they're not as heavy as they used to be,” said Dr. Piper.

Loons can have either one or two chicks, but these days, almost every brood Dr. Piper’s team finds only has one chick.

“It's almost like a, like, exciting when you see the two chick brood, they become just unusual to see that,” said Dr. Piper.

After noticing this substantial reproductive downturn, his team needed to figure out what could conceivably be causing this pattern.

Loons are visual hunters, relying on the clarity of water to discover prey.

Using satellite data, they compared water quality of lakes with chick mass data and found the clearer the water, the fatter and healthier the chicks.

Over the past 30 years, lakes in northern Wisconsin have become less clear, but researchers aren’t exactly sure why.

As the climate warms, rainfall increases and more materials wash into lakes, reducing clarity.

But Dr. Piper’s team isn’t sure what material is the main offender, whether it’s organic matter, nutrients like fertilizers, septic leakage, or something else.

“But that's our next goal is to try to narrow down what exactly seems to be washing into these lakes to make them less clear,” explained Dr. Piper.

Loon populations are also threatened by lead poisoning from lead sinkers used by fishermen.

Safer, nontoxic alternatives like ceramic or tungsten sinkers protect adult loons, who will die within a week of ingestion of lead.

Dr. Piper says loons don’t need one more thing killing them.

“It may be that this reproductive decline is something that the population would survive, but if you're in addition, killing adults, needlessly with lead sinkers, you know, that's a shame,” said Dr. Piper.

In a number of states in New England, there’s a ban on lead jigs and Dr. Piper thinks this may support the loon populations out there, which tend to be healthier.

You can keep up to date with the Wisconsin Loon Project by checking out Dr. Piper’s blog.

Hannah Davis-Reid is a WXPR Reporter.
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