Fewer loon chicks surviving due to climate change, researchers say

For three decades, David Johnson has guided nature lovers in early spring to northern Illinois lakes to hear the eerie yodeling of hundreds of common loons.

Within the next 30 years, however, there may be few if any migrating loons in Illinois, according to Walter Piper, a researcher and professor of biology at Chapman University in Orange, Calif.

Loons, which winter along the Atlantic and Pacific coasts and migrate through the Midwest to nest farther north, are not successfully raising as many chicks as they have in the past, said Piper, who has studied the birds in Wisconsin for years.

“Increased rainfall associated with climate change is washing organic matter into northern Wisconsin lakes, reducing water clarity, and making it harder for adult loons to find food for their chicks,” Piper said.

One of Piper’s studies, published last month in the journal Ecology, suggests that climate change, through water clarity, profoundly affects freshwater ecosystems. The extra moisture has also increased the population of black flies, which can disrupt nesting loons.

“Climate change could result in long-term decline of the loons and their breeding ranges,” predicted Piper, who runs the Wisconsin Loon Project. “We could lose all U.S. breeding populations. We could only have loons breeding in Canada. That would be tragic.”

Loon reproduction, however, is also declining across southern Canada, where the Canadian Lakes Loon Survey has been tracking their breeding habits for the past 40 years.

“The number of babies just goes down and down and down,” said Doug Tozer, director of waterbirds and wetlands for the conservation organization Birds Canada, which coordinates the loon survey.

The reasons are unclear, but Tozer said he thinks the decrease in Canada is related to rising temperatures causing an increase in mercury pollution. Tozer has co-authored papers looking into the connection between the drop in the loon population and mercury, acid rain and climate change, among other factors.

“The number of breeding loons in southern Canada is also starting to decline. This is what we’ve all been dreading,” said Tozer, who has joined forces with Piper to work on a project analyzing all loon data from North America.

Karen Lund of Genoa, who does annual loon surveys with Johnson in northern Illinois, worries about those statistics. “It would be sad if there will be fewer loons and that people of the next generation might not see or hear them,” she said.

Loons once nested in Illinois, Indiana, Iowa and Ohio, but now they breed in Michigan, Wisconsin and Minnesota. They also breed in the New England region and a few northwestern states including Montana, but most nest in Canada. Illinois’ last breeding pair of loons was recorded in 1892 in Lake County. Reasons for their demise could include habitat destruction, pollution and other factors, Piper said.

Loons can live to be 30 years old, he said, but if they’re not producing enough chicks their numbers will keep dropping. Loons typically raise two chicks annually, enough to replenish their population.

“Overall, Wisconsin’s adult loon population has fallen an estimated 22% in the last 25 years,” Piper said.

Each year for decades, Johnson, who is from Buffalo Grove, Ill., has picked one day in late March or early April to gather data on migratory loons in the Chain O’ Lakes area. He said he has noticed a drop in numbers. “But I wouldn’t say it’s precipitous.”

“Our highest count was 676 on April 6, 2013, but 401 this year is a good number, too,” he said.

Still, Johnson said he thinks Piper’s findings are “concerning.”

Piper heard and saw his first loon in the north woods as a child. “I was in Ontario on a lake,” Piper recalled. “I was underneath my warm Hudson Bay blanket and in our primitive cabin on the lake shore and heard this ethereal, haunting sound coming across the lake.”

Piper began researching loons in 1993, focusing on territory defense, habitat selection and breeding behavior in three counties in Wisconsin. He nets and weighs adults and chicks, and fits them with leg bands for identification.

“Over the years, I started to realize that the chicks weren’t as heavy as they used to be at a certain age, and sometimes only one chick instead of two would survive,” Piper said.

His data showed that the total weight of chicks four to five weeks old had decreased by 11% over the past quarter-century. “That equates to more chick mortality. I had to explore this and find out what’s going on.”

Piper worked with Max Glines and Kevin Rose, water clarity specialists from Rensselaer Polytechnic Institute in Troy, N.Y., who co-authored the study published in Ecology. They gathered data from the lakes where the loons he studied were breeding. They discovered water quality had declined at the same time rainfall had increased.

“That link between rainfall and water clarity is quite strong,” Piper said. “We can clearly point to rainfall as the culprit. Heavy rains, especially in July when adults are feeding chicks, make the water cloudy, making it more difficult for parents to see their prey. The chicks really suffer,” Piper said. “The parents cannot find enough food.”

Piper began similar studies in Minnesota in 2021. He also will work with colleagues to find out what kind of substances rainfall is bringing into the lakes.

“We haven’t nailed down exactly what it is that’s washing into the lakes that make them less clear,” he said. “It could be fertilizer, pet waste or something else. We have to get to the bottom of this.”

Piper’s loon conservation work has also shown that loons abandon their nests when harassed by black flies. Black fly populations have increased in the past few decades in Wisconsin, he said. Their population is boosted by more rain.

In 2020, nearly all loons nesting in 108 lakes abandoned their nests due to black flies, and that is related to climate change, Piper said. “Only three breeding pairs were able to nest, because of black flies,” he said.

Tozer said what’s happening with loons in one breeding region may be different in another.

“I think it’s going to vary regionally, what the problem is,” he said. “Water clarity looks like one of the smoking guns in Walter Piper’s area. Southern Canada, it might be mercury. In other places, it will be something else.”

But the reasons, they believe, are all related to climate change. They are working with postdoctoral students to analyze data on loons throughout North America. This information includes long-term data from research projects in individual states and across particular regions.

“We cannot control rainfall or climate change,” Piper said. “It’s an ocean liner we can’t turn around rapidly.

“If there are changes people can make, it would be to take better care of their shorelines,” he said.

Piper said more research is needed to find ways to help loons so people like Johnson can continue to watch them, hear their otherworldly calls and introduce them to others.

“I am crazy about loons,” Johnson said.

He’s been that way since he was 18 years old and heard his first calling loon in northern Wisconsin. “It was a starry night and the loon was wailing,” he recalled. “They still nest there — I think.”