climate change

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It was just a bag in the water. But it was a large white plastic bag, one flap of which protruded above the surface of Little Pine Lake in our Minnesota Study Area. As Evrett, Isaac, and I paddled across the southern end of Little Pine to begin our observations of the Dream Island loon pair, the bag caught our eye and sullied the otherwise idyllic Northwoods scene. Looking to leave the lake a bit cleaner than when we had arrived, we fished the bag out of the water.

The writing on the bag told the story.

I have a confession to make. I come from a family of non-gardeners. When we see a beautiful tree or flower, we savor it. But the notion that some act of ours might alter the health or appearance of a plant is altogether foreign. A product of suburbs of large cities, I have grown accustomed to gazing at the verdant, manicured lawns and gardens of neighbors — then turning to look ruefully at my own. Yet jealousy of my neighbors’ lawns is not enough to induce me to follow their lead.

Of course, the suburbs are one thing. Lakeshores are quite another. The bag that Evrett fished out of Little Pine suggested that a resident on Little Pine was placing fertilizer on their lawn. While the decision of how to treat one’s lakeshore is up to each individual, it has consequences for all of us. Inevitably some of the high-nitrogen and -phosphorous fertilizer that produces a lush green lawn by the lake washes into the lake when it rains. Lake phytoplankton — free-floating, microscopic algae that inhabit all lakes — are starved for nitrogen and phosphorous just like grasses and trees on land. So adding fertilizer to lakes causes higher-than-normal growth of phytoplankton, which reduces water clarity and can have a variety of more serious impacts on lake-dwelling animals and plants.

It is too early to tell whether lawn fertilizer is at the root of the water clarity loss in the Upper Midwest during the past quarter century. We do know that heavy rainfall causes low water clarity. And we know that low water clarity hinders loon parents’ feeding efforts and produces emaciated chicks. But while we investigate the specific cause of water clarity decline, wouldn’t it be prudent for lake residents to stop using fertilizer on lakeside lawns, in case loon chicks are unintended victims?

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By the way, Wisconsin Public Radio did a short segment on our study and on the decline in water clarity we have reported recently. If you wish to hear how I sound after a day of field work and a bit too much coffee, you can find it at this link.

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At a March meeting of loon researchers in New Hampshire, John Cooley of the Loon Preservation Committee showed that the recent increase in severe rainstorms in the Northeast has made flooding of loon nests a routine cause of nest failure there. John’s report was eye-opening to me for two reasons. First, nest floodings occur seldom among Upper Midwest loons, so his result showed that environmental threats facing loon populations vary regionally. Second, and more important, John’s findings pushed me past a personal cognitive tipping point. I now see clearly that climate change, which has negatively impacted plants and animals worldwide, has not spared the common loon.*

I must admit that I was among those who hoped that loons might dodge climate change. I have long understood that hundreds of terrestrial birds are being adversely affected by changing patterns of temperature and rainfall. But loons are aquatic, I reasoned. Maybe they are different.

In fact, the list of climate-related factors known to harm loons is growing. In addition to the new flooding threat from storms that John’s talk revealed, the list includes black flies, which are getting worse owing to increasing annual rainfall. And our just-published paper shows yet a third problem that rainfall poses for breeding loons. In a nutshell, July rainfall reduces water clarity, which hinders loons’ efforts to capture fish to feed their chicks. This problem has led to a decline in chick mass and increase in chick mortality over the past 25 years in northern Wisconsin. If you are keeping score, we now know of two climate-related patterns that reduce hatching success of loon eggs and one that increases mortality of chicks after hatching. It is no wonder that loon reproductive success is falling across most of the breeding range, including its heart, in Canada.

These are not short-term patterns likely to reverse themselves in a year or two. Flooding, black flies, and water clarity have been getting worse for at least 25 years. No rational person who has seen these data and is capable of looking at the world with an objective eye can doubt that climate change is harming loon populations.

What now? Do we resign ourselves to loon population decline in the Upper Midwest? Do we accept the models that show the breeding range shrinking northwards until the species no longer breeds in the United States by 2050 or a bit later? Do we sit down with our children and grandchildren and explain to them that they will have to go to Canada to see the birds whose charismatic presence near our summer homes has so enriched our lives? I don’t think so. We cannot reverse climate change in a hurry. We cannot stop rain from falling. But continued field research might allow us to pinpoint climate-related hazards faced by loons — such as the precise identity of the material that rain is washing into lakes to reduce water clarity — and use that information to mitigate the harmful effects of climate change. The current picture is disheartening, but we must do what we can to save loons.

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*Featured photo by Linda Grenzer on April 8. Loons, mostly males, have begun to trickle back to the Northwoods. Linda took this photo of the male that has bred for 12 years on Deer Lake in Lincoln County. But here he is exploring nearby Muskellunge Lake, to which the longtime male resident did not return in 2023. It will be interesting to see if he settles on Deer Lake, where he has experienced seven nest failures in a row, or moves over to Muskellunge, which has a very good track record of chick production.