water clarity

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Twenty years ago colleagues and I published a paper showing that artificial nesting platforms increase loon’s hatching success by 70%. Others have reported similar patterns. So there is no doubt that, on average, loons that incubate their eggs on artificial nesting platforms (“ANPs”) put more chicks in the lake than do pairs using natural sites. Moreover, our paper showed that greater hatching success produced by ANPs also leads to more fledged loons.

In the last two decades, ANPs have become an enticing tool used by loon conservationists to boost loon populations. This is not surprising. ANPs have proven to be effective, and they are rather easy to make and place in the water. So conservationists can plop a mess of ANPs in the water and feel pretty confident that they have added young loons to the population. And they can make a strong case to funding agencies that their actions might help loons avoid population decline. Indeed, many millions have been/are being spent in the U.S. to float ANPs as a means to mitigate the negative effects that oil spills in the Gulf of Mexico have had on the species.

Are ANPs really just as good as natural sites at producing young loons that reach adulthood? Or are platform-raised chicks not as likely to survive to fledging age as chicks hatched as natural sites? We must remember that loons pick the location of a natural nest, whereas humans choose the site where platforms go. So it seems quite plausible that platform-raised young face hazards that natural-raised young do not.

It is only now that I have large enough samples of nests from platforms and natural sites that I can run a head-to-head comparison. Despite my 32 years of Wisconsin data, only a small proportion of loons in the Wisconsin Study Area (e.g. 15 of 90 focal pairs in 2024; 17%) nested on platforms. In Minnesota, however, almost half of all of our focal pairs use ANPs (38 of 84 territorial pairs in 2024; 45%), so our sample of platform-hatched chicks has swollen markedly since 2021.

As the graph above shows, hatchlings from platforms are lost slightly more often than are natural-hatched chicks in both states. While the pattern shows up in both Minnesota and Wisconsin, the difference is quite small and does not reach statistical significance. In other words, we have no scientific evidence that chicks hatched on platforms suffer lower survival than those hatched at natural sites. The same can be said for chick loss in Wisconsin versus Minnesota, despite what appears to be a slightly higher rate of chick loss in the North Star State.

Frankly, I am relieved! It has become almost de rigueur to place an ANP in your lake to support the loons. If, for some reason, ANPs had been producing chicks likely to perish before reaching adulthood, it would have sent shockwaves through the world of loon conservation.

I am still not a great fan of nesting platforms. Why not? Because we have learned in recent years that nest predation is not the main problem loons are facing in the Upper Midwest. Remember, nesting platforms are a one-trick pony. They increase hatching success enormously and put more chicks in the water. But if chicks cannot get enough food to survive to adulthood or reach prime condition, then all of the platforms in the world will not help them.

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This seems a dark time for loons in the Upper Midwest.

Wisconsin breeding pairs fledge 26% fewer chicks now than they did 25 years ago. Our more limited data from Minnesota indicate low breeding success there as well. (A long-term study by Minnesota DNR confirms that chick production is decreasing in the state.) The decline in breeding success across the Upper Midwest concerns me. Do enough chicks still reach adulthood so that they can sustain the population of breeders?

But, as I have discussed in previous posts, loss of chicks while under their parents’ care is less of an issue than the escalating die-off of young adult loons after they leave the breeding grounds. Survival in this later stage of the life history is down over 80%. Of 99 chicks that we banded in 1998, 1999, and 2000, we had resighted 38 (38%) as adults by 2004. In contrast, we have reobserved as adults only 9 of 155 chicks (6%) banded between 2018 and 2020.*

Of course, these young adult returnees are troublemakers. They loaf on undefended parts of large lakes or on vacant small lakes. They intrude into breeding territories. Their visits force pair members to confront them physically and steer them clear of chicks. If the pair’s hints are not sufficient to drive the youngsters off, they are attacked. Naturally, the more of these 2- to 6-year-olds there are in the study area, the greater the chance that one of them evicts a member of the pair.

But these young loons are also the future. From their ranks come replacements for breeders that die each year. So young adults — warts and all — are essential to population stability.

The huge drop in the young adult population has turned our annual spring census into a stressful experience. In early May our Wisconsin and Minnesota teams race from territory to territory to see which of our marked breeders have returned and which territories from previous years are still occupied. Each year I fear that breeding lakes will be lost because the dwindling young adult population will be unable to fill breeding vacancies.

In truth, we have lost several of our traditional territories in Wisconsin during the past few years. We did not find breeding pairs on Bridge, East Horsehead, Hildebrand, Miller, Oneida-East, Pickerel-North, Tom Doyle, Swamp, or Muskellunge (Lincoln Co.) in 2024. We seem to have lost one of our breeding pairs on Bertha Lake and another on Butterfield Lake in the Minnesota Study Area as well, although our data do not extend as far back there. Still, there has not been a wholesale loss of territorial pairs in the Upper Midwest, which one might have expected from the high mortality of young adults. So while we have far fewer young nonbreeders milling around, the decline in the territorial loon population is, as yet, small.

Thus, the loon population might be more resilient than we had feared. We have long known that the majority of young loons that return to the breeding grounds never settle on a territory. Perhaps the die-off of young adults merely reduces their number to those few that would normally claim territories anyway. It is a hopeful thought!

Meanwhile, my work continues in both states. I am connecting with water quality specialists in Wisconsin and Minnesota in hopes of learning why we are losing water clarity in July, which harms loon chicks. And I am searching feverishly — both on the breeding grounds and in Florida, where most of our birds winter — for the cause of the high mortality in young adults. These are not quixotic quests. I feel that people who love loons in the Upper Midwest will step up and help them if we can pinpoint the factors that endanger their population.

If you would like to support my efforts to conserve loons in Wisconsin and Minnesota, please consider a donation to our 2025 field effort. We squeeze all we can out of every dollar we receive.

* People sometimes ask me, ”Could these missing loons have simply gone somewhere else? Have they gone to Canada?” It is a reasonable question. Ecologists have marked and tracked movements of thousands of bird species as well as many other vertebrates. With the exception of nomadic species, though, territorial animals like loons stick to a rigid set of guidelines with respect to settlement. If it is still alive, a loon will return to the near vicinity of its natal lake as a young adult to look for a breeding spot. (This is especially true of males.)

The featured photo is by Hayden Walkush of the territorial female on Two Sisters-East. This photo is among the 1906 taken by the team this year as part of our study of whether or not loons can be distinguished using artificial intelligence.

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I thrive on routine and familiarity. When others gush about peculiar foods they ate as they slept in uncomfortable beds of strange hotels in foreign lands, I cringe. Yes, I laughed at Macon Leary’s decision, in “Accidental Tourist”, to eat at Burger King in Paris so that he would not shock his taste buds with new flavors. I knew his behavior was absurd. But my amusement was tempered by a harsh reality. I am Macon Leary.

Despite my disinclination to travel, I have to admit that visiting a new place can be curiously stimulating. In a new location, one’s brain is attuned to every novel detail — from the peculiar vegetation, scents, weather, road signs, and dwellings to the attire and speech patterns of the local humans and how they treat you. So it was two weeks ago when I visited lakes along the Gunflint Trail in Minnesota’s Arrowhead region.

The glacial lakes in this eastern gateway to the Boundary Waters are unusual. Most are long, slender, rather clear, and lie in an east-to-west orientation. The loons along the Gunflint Trail encounter many canoes and few motorboats. Observing this pristine habitat set me thinking about Upper Midwest loons in general. Could the factors that cause harm to loons in northern Wisconsin and north-central Minnesota — most of them related to humans — possibly reach them in this remote region?

Newly attuned to the contrast between lakes in regions of high and low human impacts, I sat down to take another look at loons and water clarity. I first looked to see whether masses of loon chicks from my Minnesota Study area (Crow Wing and Cass counties)* depend strongly upon water clarity, as we have recently found in Wisconsin. Regular readers of the blog will recall that the strong dependence of loon chick mass on water clarity is the hallmark of the recent population decline in Wisconsin.

Just as in Wisconsin, chick mass is dependent upon water clarity in north-central Minnesota.**

In Crow Wing County, Minnesota, chick mass increases with increasing water clarity. (Clarity calculated from satellite data and direct measurements available via the Minnesota LakeBrowser.)

Next, I examined climatic factors that affect water clarity. Is recent rainfall a strong determinant of water clarity in north-central Minnesota, as we have shown in Wisconsin? Yes it is.** As I have said many times before, rainfall appears to wash something into lakes that harms clarity.

Rainfall in loon lakes in Crow Wing County, Minnesota during the past 60 days causes water clarity to decline. (Clarity calculated from satellite data available via the Minnesota LakeBrowser.)

So loon chick survival is highly dependent upon water clarity across the Upper Midwest. And water clarity declines after rainfall across this region as well. These findings hold for two study areas 200 miles apart comprising lakes with extensive shoreline development and human recreational activity.

What about remote regions like the Gunflint Trail? We have no loon data from this region, so we can only infer loon chick condition on the basis of water clarity. Fortunately satellites pass over these lakes just as they do the lakes of northern Wisconsin and north-central Minnesota. Therefore we have just as crisp and complete a picture of water clarity along the Gunflint Trail as we do anywhere else.

First, a hypothesis. I have said countless times that fertilizer linked to lakeside lawns is a prime suspect for the “rainfall effect”. That is, water clarity probably declines after rainfall because of fertilizer and other matter from lawns that washes into lakes and triggers phytoplankton growth. This is just a hypothesis. I could be wrong. But the comparison of Crow Wing County lakes to Gunflint lakes permits a test of the hypothesis. A lack of a rainfall effect along the Gunflint Trail — that is, no negative impact of recent rainfall on water clarity — would support the hypothesis.

Rainfall in the Minnesota Study Area (Crow Wing County) is associated with a decrease in water clarity. In contrast, recent rainfall is linked to an increase in clarity among lakes along the Gunflint Trail.

As the above graph clearly shows, rainfall does not negatively affect water clarity among lakes along the Gunflint Trail. In fact, recent rainfall in the region is associated with a slight increase in water clarity. This finding is crucial. It strongly suggests that human development and/or activity is causing the rainfall-associated decline in water clarity in Upper Midwest lakes.*** This means that we can begin to narrow the scope of our investigation into clarity as a cause of chick mortality.

Every scientific investigation exposes at least one puzzle. Here it is. If water clarity in the Gunflint region is not negatively impacted by humans, we would expect high loon breeding success there. Yet long-term data from nearby portions of Cook and Lake counties (monitored by the Minnesota Loon Monitoring Program) show a steady decline in both adult and juvenile populations. ****

I have said, “It is such a relief to be home” so many times after returning from my summer field work that my wife now only smiles faintly to hear it. I love the lakes and loons of the Upper Midwest but remain the same unadventurous homebody now as before. Still, it is gratifying that my recent plunge into unfamiliar terrain led to new insights about loon conservation. Maybe I should stray from the beaten path more often.

* Thanks to Sheila Johnston for the featured photo. Sheila snapped a picture three days ago of the grown-up chick and it heavily-molting male parent on Bass Lake near Nisswa, Minnesota.

** These are “statistically significant” patterns. That is, they exceed the threshold for results to show a clear non-random effect.

*** Obviously, there are other possibilities, which we must examine.

**** We are getting into the weeds here. But — as Phyllis Sherman has reminded me — the Cook/Lake index area surveyed for the MLMP is not as remote as the Gunflint Trail area. Inspired by Phyllis’ comment, I took a look at water clarity within the Cook/Lake Index area lake specifically. They show a very weak rainfall effect on water clarity. So the puzzle persists. Loons are struggling to reproduce on remote lakes whose clarity is largely unaffected by human activity. Black flies, I understand, are a severe problem in the area. It is possible that black flies alone — or black flies together with other ecological factors yet unknown — account for the local population decline.

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If aliens landed on Earth’s surface to investigate its life forms, they would be puzzled by the coexistence of common loons and humans. True, loons spend almost their entire lives on the water, where they are relatively free of dangers from humans and other terrestrial vertebrates. But loons require solid ground for nesting, safe “nurseries” for rearing their chicks, and abundant food to keep themselves and their chicks alive. How, then, can loon populations persist along the southern periphery of the species range, where humans and human recreation threaten all three basic requirements?

The ability of loons to thrive in regions of intense human building and recreation vexed me for several years in the 1990s, when I first began my long-term loon research. I could see that most people venerated loons and took pains to protect them. But the sheer abundance of humans surrounding, approaching, and fishing near adults and chicks during the spring and summer made the tasks of hatching young and rearing them to adulthood seem daunting. How did loons manage to raise any young in the northern U.S. and southern Canada?

I cannot answer this question completely. I am still amazed at the abilities of adults and chicks on busy lakes to dodge motorboats and jetskis as well as they do. And it continues to surprise me when adults fledge chicks from small lakes where food seems limited. However, detailed study of loons’ nesting patterns allowed me to solve one riddle: how loons enjoy high nesting success despite intensive shoreline development.

One would think that shorelines are essential to nesting loons. Loons have to nest along shorelines, right? And humans build summer homes along shorelines too. So loons and humans would seem to be direct competitors for shoreline habitat. But it is not so. Why not?

The answer is deceptively simple. Well-drained “upland” shorelines provide the best sites for building lakeside homes. Upland sites are free of boggy or marshy vegetation. At the same time, upland shorelines provide poor nesting habitat for loons. Most loon eggs placed on upland shorelines end up in bellies of raccoons that take advantage of the comfortable footing they provide to look for easy meals. Experienced male loons learn to avoid placing nests on dry, upland shorelines.* Instead, they usually locate nests on islands, marshes**, or bogs hard for terrestrial predators to reach.*** So one key to loons’ ability to coexist with humans is merely loons’ preference to nest where humans cannot build.

Hodstradt Lake in the Wisconsin Study Area illustrates the complementary use of shorelines by loons and humans. Hodstradt is a 119-acre lake that has beautiful clear water with a slightly greenish hue. The lake is full of fish but completely encircled by lake homes. There is no island, marsh or bog in Hodstradt — only a peninsula in the southeastern corner (see screen grab below from Google Earth). Almost all nesting attempts by loons on Hodstradt have been on the end of that peninsula. High water caused by heavy rainfall in the past decade submerged the narrow spit connecting the end of the peninsula to the mainland, making it a small island. Whether an island or a peninsula, though, the land is low lying and impossible to build on. Hence it provides permanent nesting habitat for loons that is off limits to humans.

A similar situation exists for many loon pairs in the Minnesota Study Area. The seven pairs that nested this year on massive Cross Lake provide a good example. Three of these pairs nested on small uninhabitable islands; three nested among dense cattail patches in marshy coves; and one used an artificial nesting platform. (Five of these pairs hatched chicks.) Thus, the “Jack Sprat” nature of loon and human shoreline use can be seen in both Wisconsin and Minnesota. With rare exceptions, sites safe for loon nests are sites where humans cannot or will not build.

So adult loons are able to put chicks in the water despite extensive shoreline development. This would seem to be cause for celebration. In a cruel twist, though, shorelines altered to support suburban-style homes, lawns, and driveways have increased runoff. Although we are still working out the details, it appears that higher runoff has, in turn, produced a decline in water clarity and decreased chick mass, probably because adults cannot see fish well enough to provision their chicks adequately. In short, shoreline development negatively impacts loons during the second critical breeding phase: chick-rearing. Indeed, the sharp increase in mortality of chicks and young adults in the past two decades has become our number one concern with respect to the Upper Midwest loon population.

If there is a silver lining, it is this. Loons are resilient. They have been able to find nesting sites and sustain a high hatching rate despite everything humans have thrown at them. Perhaps we can help loons reverse the decline in chick survival, if we can learn precisely what is driving the drop in water clarity. This will be a massive challenge. But I have to believe that loons can come back from this setback. It keeps me going.

* We learned 16 years ago through marking of loons and systematic tracking of nest placement that male loons choose the nest site. For those not interested in looking at the science, we know this from two facts. First, loon pairs learn where to nest by trial and error. That is, they tend to reuse a site where they hatched chicks the previous year but move to a new nest location after egg predation. This logical nesting strategy is called the “win-stay, lose-switch” rule. Second, loon pairs in which the female pair member returns from the previous year but the male pair member does not usually do not reuse a successful site from the past year. In contrast, pairs consisting of the male from the previous year and a new female tend to reuse successful sites. In short, pairs with new male members do not use the win-stay, lose switch rule. They act as if they have forgotten where the best nesting site is.

** The featured photo is of Clune, Linda Grenzer’s favorite male loon, who bred for many years in her lake in Wisconsin. He is incubating eggs in a marshy corner of the lake that, predictably, is devoid of homes.

*** Of course, humans often accomodate loons’ nesting preferences by placing artificial nesting platforms along lake shores. Platforms provide very attractive nest sites for loons.

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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.

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Many of my colleagues fear ChatGPT. They fear that students will use this new online tool based on artificial intelligence to generate papers and answer questions on homework assignments that students are meant to tackle themselves. Their fear is legitimate. Why? Because if you read ChatGPT’s answers to a range of questions, you notice something rather quickly. ChatGPT generally produces plausible, thoughtful, coherent responses. Furthermore, ChatGPT writes well — at least compared to what I see from most of my undergraduate students. In short, ChatGPT creates headaches for instructors. It is forcing us to reconsider how we evaluate our students.

On the other hand, I was excited to learn what this new AI tool would produce when asked about loon biology. I asked ChatGPT: “Do loons mate for life?”. It responded:

While common loons often return to the same breeding territories and may reunite with the same mate from the previous year, these pair bonds are not necessarily permanent. After the breeding season, loons typically migrate to coastal or open water areas for the winter, and their social behavior can be more flexible during this time. When they return to their breeding territories in the following spring, they may or may not reunite with the same mate.

Now, this is not a terrible answer. ChatGPT is correct when it suggests that loons do not mate for life. But its mention of migration is off-topic. Its point regarding “social behavior” during winter is irrelevant. Its statement that loons “may or may not reunite with the same mate [in the spring]” is grossly misleading. And ChatGPT has entirely failed to mention the chief reason why loons do not mate for life: territorial eviction.

ChatGPT’s responses to loon-related questions are similar to its answers on other topics. The program searches the web for information from which to build its responses. But because these responses draw information from countless online sources, they include the good, the bad, and the ugly. In short, ChatGPT gives you a blur of “conventional wisdom” about any topic, not rigorous and precise scientific truth. Its answers are, for the most part, uncontroversial, vague, and riddled with caveats.

I turned my attention to loon conservation. When I asked, “Are any common loon populations in trouble?”, ChatGPT came back with:

As of my last knowledge update in September 2021, the status of loon populations, particularly the Common Loon (Gavia immer) in North America, varied by region and was a subject of concern in some areas. Common Loons were classified as a species of “Least Concern” by the International Union for Conservation of Nature (IUCN) due to their relatively stable population at the global level.

However, it’s important to note that local and regional populations can face significant challenges, including habitat loss, water pollution, lead poisoning from ingesting fishing tackle, disturbance from boating and recreational activities, and climate change impacts on their breeding and wintering grounds. These factors could affect specific loon populations and lead to localized declines.

ChatGPT is spot on in some respects. Loons are in no trouble globally. And the status of populations varies from one region to another. But the program uncritically lists many anthropogenic factors that might harm loon populations and provides no specific information. One might infer from ChatGPT’s statement that we must solve all of the problems listed in order to preserve loons. Or perhaps loon populations face many obstacles but none is severe enough to cause serious harm. In truth, we do not know which, if any, of the listed factors might endanger loons. Furthermore, ChatGPT has failed to mention two factors — exploding black fly populations and decreased water clarity — known to harm loon populations in the Upper Midwest. If this had been a class assignment, ChatGPT would have earned a “C-“.

ChatGPT’s take on factors threatening loons sounds eerily familiar to what we loon conservationists often say. (I include myself in this group.) That is, we often settle for a ChatGPT-caliber pronouncement about loon conservation. We say or imply that if we: 1) enact a lead ban, 2) reduce human settlement on northern lakes, 3) eliminate water pollution, 4) keep boaters away from adults and chicks, and 5) halt climate change, then we can save loons. These goals, of course, range from difficult to impossible to achieve.

A ChatGPT-like approach will not save loons. We simply cannot eliminate all threats. In fact, many factors that loon conservationists perceive as threats pose little or no hazard. The best example is human recreation. While lead sinkers are a danger to loon populations because of the many breeding adults they kill each year, loons are well-equipped to handle boaters. Loons tremolo, wail, or yodel when boats are too close to them or their chicks. They penguin dance, charge, and dive noisily at boats that creep close to their nests. Humans usually interpret these warnings correctly and back away in short order. Moreover, the low rates of mortality and nest abandonment attributable to boating activity indicate that loons tolerate human interactions well.**

How do we distinguish between relatively benign environmental factors, like boating, and those that truly endanger loon populations, like black flies, lead sinkers, and water clarity? Science. Only science will save loons. If the Minnesota loon population is declining and 50% of loon deaths result from lead poisoning, the folks in Saint Paul will take notice. If Wisconsin loons fledge 40% fewer offspring nowadays than in 1995 because of lower water clarity, that will make headlines in Milwaukee. And if the fledging rate across the Upper Midwest is 30% lower owing to black fly-induced nest abandonments, that might turn apathy concerning climate change into action.***

So if you are an unprincipled student being taught by an inattentive instructor, ChatGPT might earn you a “B” on your history paper. And if you cannot get the wording right in a letter to a client or colleague, ChatGPT might provide suggestions. But we loon conservationists should resist the uncritical, shotgun approach that ChatGPT takes to addressing questions. If we are going to preserve loon populations that we treasure, we must first collect data. And then, in our communications with the public, politicians, and the media, we must highlight the specific environmental hazards that science has shown to be dangerous to loons.

* The featured photo was taken a week ago by Linda Grenzer of an adult male from Lake Winter, Wisconsin that swallowed a lead sinker. Though the sinker was surgically removed by Raptor Education Group in Antigo, the male died two days later from the lead it had already absorbed.

** I might be biased by my work in Wisconsin and Minnesota in my conclusion about loons coping with boating activity. It is conceivable that boats do cause enough nesting failure and/or chick mortality in some regions to threaten loon populations. We do not have data to show such a pattern, however. If you know of such data, please let me know.

*** I made up these three numbers. We are still collecting data on loon mortality caused by lead sinkers. Only recently have we learned about the threats of black flies and loss of water clarity. We and our partners are recording many lead-poisoned loons these days. We will publish an estimate of lead’s impact within five years. Robust estimates of the impacts of black flies and water clarity on loon populations in Wisconsin (and possibly Minnesota) should be available by sometime in 2025.

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I should have known all along. I should have known last May, when the ancient outboard motor we had just bought to cover the Whitefish Chain spewed a foul rainbow sheen onto the water’s surface and belched a caustic purple cloud that momentarily blinded us. I should have known as I filled huge tanks of gasoline at the Holiday convenience store in Crosslake, hefted them down to the dock, and hooked them up to the belching motor. I should have balked at the absurdity of using a filthy, fossil-fuel-guzzling outboard to study an animal that requires clean air and water.

Instead, I shrugged. “This is how people get around in the Northwoods”, I thought. “This is inevitable. This is the environmental cost of studying loons on big lakes.”

In my own defense, my understanding of proper boating practices became ingrained during my childhood. Back then, when we needed to provision our cottage on an island on 40-mile-long Lake Temagami in central Ontario, we took our little 2-stroke outboard over to the Ojibway Store on Devil’s Island. I still recall taking in the pleasing aroma of balsam fir mingled with mixed gasoline as we listened to the soft lapping of waves against the store’s dock. At the time, my major concern was whether Mom would treat us to Burnt Almond bars when she had finished ordering our groceries. Gasoline was just an innocuous part of the landscape we inhabited.

Indeed, to folks of my generation and generations adjacent, the angry whine of an outboard motor, the slap of a stiff wind in our faces, and the sight of parting, churning waters behind us seem inextricably linked to the pungent smell of gasoline.

But it need not be so. There is a growing market for electric outboards (and inboards) that can replace gasoline motors smoothly and are far cleaner (of course), quieter, and — according to what experts say — very reliable and low-maintenance. I have been researching this.

Why have I experienced this sudden desire to go electric on the water? Two reasons. First, the last two Wisconsin field teams and I faced an absolute nightmare every time we tried to start up our vintage 9-horsepower Evinrude. I did not collect data on our efforts, but I believe we averaged 43 almost-shoulder-dislocating tugs of the starter cord per lake to get that dirty old 2-stroke started. I have had it! (I believe Sarah ’22, Molly, Claudia, Chris, Tia, Bailee, and Sarah ’21 will applaud this move.)

Second, I can no longer deny the obvious. The relentless march of climate change has begun to hurt loons in the Upper Midwest. We can see it in the increase in the May black fly population, which forces loon pairs to suffer horribly as they to incubate their eggs, often to the point of abandonment. And it is even more evident in the sharp decline in July water clarity during the past quarter century (see below) — a decline that impairs loon parents’ ability to find food to feed their chicks. Both increased black flies and decreased water clarity, we now know, come about in large part because today’s warmer, rainier summers produce more flowing water that: 1) supports increased black fly reproduction and 2) washes more matter into lakes that reduces clarity.

So I have finally figured something out that I should have guessed before. Climate change is hurting loon populations in the Upper Midwest in multiple, measurable ways. Cutting back on fossil fuel usage where I can will help slow this damaging pattern. And that is a step in the right direction.

on

One often hears that clear water is a benefit to loons — if not an outright requirement. The entry for the “Common Loon Habitat” section in Birds of the World, for example, opens with “[Loons] prefer clear lakes….”. The Cornell Laboratory of Ornithology’s page dedicated to the common loon begins with: “The eerie calls of Common Loons echo across clear lakes of the northern wilderness”.

An association between loons and water clarity seems reasonable. After all, loons are visual predators. Why would they spend time in water through which they cannot see?

Yet I learned in Wisconsin in the mid 1990s that loons do not strongly favor clear water. While many of my study lakes, like Alva and Two Sisters, are quite clear and produce chicks regularly, many others, such as Hancock and Oneida, are both turbid and productive. In short, loons in the Upper Midwest thrive and fledge chicks on lakes that vary between 3 and 20 feet of visibility. Indeed a scientific analysis showed that water clarity is not among the factors that dictates use of a lake by loons.

If you think about it, you can understand why a migratory species like the common loon does not overspecialize on water of a certain clarity. As we know from Kevin Kenow’s work, loons fly hundreds of miles across largely unknown terrain and then must land on a waterbody somewhere. If they are in desperate need of a meal at such times — as we might presume — they had better not be too finicky about the menu and the eating conditions. Flexibility must be especially important among juveniles migrating south for the first time, who are crossing terrain that is entirely unfamiliar to them and must find food nevertheless. And, of course, migration begins or ends in the Gulf of Mexico or Atlantic, where both diet and water clarity are entirely different from that during the summer months.

Wait. I posted a blog in the spring detailing the importance of water clarity to loon foraging success and explaining how rainfall was washing material into lakes and reducing clarity to loons’ detriment. Am I now taking that back? No indeed! Water clarity IS important to loon families in July. At that time of year, loon chicks gain mass much faster if the water is clear, and their adult parents maintain body mass better when water is clear. But further analysis has revealed an additional factor that is not so straightforward. I learned just a few weeks ago that loon chicks and their parents actually show lower mass in July in lakes that have high long-term clarity. That’s right; loons have higher masses when short-term water clarity is high but lower masses when they are in normally-clear lakes!

Just to be very plain here, I am saying that short-term water clarity (during the month of capture) increases loon masses because they probably see their food more easily, but some factor related to long-term clarity (how clear the water is on average, over many years) actually makes it harder for loons to put on mass. How do we make sense of this brain-twister?

We can only speculate about the long-term water-clarity-related factor that hinders loons’ foraging. However, there is a prime suspect. Human recreation is strongly correlated with lake water clarity. In other words, people like to spend time boating, fishing, and swimming in clear lakes. During the time when loon parents are trying to stuff their chicks with food, we humans are out there complicating the process by frolicking about in their vicinity. It seems quite plausible that this burst of human activity causes loons to lose precious foraging time and perhaps also access to their favorite foraging spot, if humans are using it. So we can easily see how human activity might cost loons some food and thus reduce mass.

If I am correct that humans impair loon foraging in clear lakes, then we can count breeding on a clear lake as a mixed blessing for loons. Clear water makes food easy to see and catch, but it brings hordes of humans that loons and their young must avoid — which cancels out a good deal of this advantage. Now, if a loon pair were to breed on a lake that had clear water and was inaccessible to humans, they would have it made! Sadly, this seldom happens in our neck of the woods.

In addition to this cool but somewhat distressing news about loon biology, I have distressing and not at all cool news about the Loon Project. We have just lost our primary funding source and are therefore going to be a bit tight for 2023 and perhaps beyond. I am hoping to use a “rainy day fund” to make it through 2023 in Wisconsin. Continuation of the work in Minnesota, which we began only two years ago, is now very much in doubt. If you can consider a donation to help us fight through this lean period — so that we can continue to learn about loon biology in ways that might help preserve the Upper Midwest loon population — we would really appreciate it.

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Photo: The male of the Little Pine-Dream Island breeding pair spent a good deal of time off of the nest in late May of this year, because of black flies. He and his mate fought off the flies, incubated their eggs and fledged two chicks this year. Little Pine Lake, on the Whitefish Chain, is relatively clear, and the male’s purple and white bands are easy to make out.