population

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I have started to call it “the Great Void”. It is the period between a chick’s first autumn and the point — at 2 to 4 years of age — when it has matured, molted into adult plumage, and returned to the breeding ground to look for a territory. Why “void”? Because we know almost nothing about loons during this period.

The Great Void used to be a nuisance. It was frustrating to think that our birds were passing through so many critical life stages without us knowing where they were or whether they were alive. But we have now pinpointed high mortality of young adult loons as the greatest threat to the loon population of Wisconsin and, more recently, Minnesota as well. “Nuisance” no longer captures the depth of our frustration. We now have to admit that we know least about our loons during the time when it matters most. So I think we need to begin to describe the Great Void as a grave concern.

Yet we are not completely in the dark. We get a glimpse into the Great Void now and then. Here is the story of one glimpse we got in March of 2024 from the wintering grounds.

As soon as he spotted it, Jim “Crater” Anderson could see the bird was in trouble. Seabirds in Panama City, Florida do not lounge on the beach in late afternoon sun like tourists from Ohio. And this one was looking especially out of sorts. It was well above the high tide point, sitting in dry sand. Crater did not think twice about interrupting his daily 10,000 steps to come to its aid.

“That is not how a duck should sit”, Crater thought, looking at the bird. Indeed, with legs splayed right and left of its body and belly in the sand, it was a curious sight. The animal skootched awkwardly across the beach and flapped frantically as he approached to within five yards, making him wonder if its legs were broken. At that moment, he felt strongly that he must capture the bird and take it to someone who could help. He removed his grey hoodie and, crouching low to the ground to appear less threatening, crept still closer. “It’s okay, I am going to get you to someone who can fix you up”, he murmurred reassuringly.

The bird was not mollified by Crater’s soothing words. Now that he was within six feet, it whipped its head around and eyed him suspiciously. He steeled himself and grabbed it, enduring its painful nipping at his arms and hands. As quickly as he could, he swaddled the bird in his hoodie to calm it and walked briskly to Rick and Sheila Harper’s house. “They have parrots”, he reasoned. “They’ll know what to do.”

The bird he was carrying was bigger and heavier than he had thought it would be – much larger than any duck he had handled. Its bill was thick and dagger-like. Its legs were not broken, just connected at the very end of its body. And – this was the biggest surprise of all — someone had placed four brightly‑colored bands on the bird’s legs. “What is that all about?” he thought.

When he arrived at Rick and Sheila’s, Kim Youngbeck was also there. The four friends placed the bird in a cat carrier that was snug but secure and set about trying to learn what kind of bird it was and how they could help it. Sheila’s parents are birdwatchers who live in Park Falls, Minnesota. She sent them some photos in hopes that they could help with the ID. “That’s a loon!”, they announced with equal parts excitement and concern.

The Florida Fish and Game contact they spoke to informed them that a loon would not do well in captivity and that they should return the bird quickly to where they had found it. Dutifully, the friends walked back to the beach. Night had fallen in the hour or so since Crater had first captured the loon. Knowing that coyotes and raccoons prowled the beach at night, they decided to place it higher in the dunes than it had been at first. That seemed safer.   

Still, they worried about the loon sitting exposed in the darkness. The bird had not tried to get away from them after they placed it back on the sand. And when they went back to check an hour later, it had not budged. At that point, Kimberly volunteered to take the bird for the night.

Back at home, Kimberly wracked her brain to think what was wrong with the animal. Was it weak from hunger? Knowing that its diet was mainly fish, she offered it the only fish she could – some tilapia filets from the fridge — on a small plate. The loon showed no interest. She looked at the clock and realized that it was 10 p.m. Whatever they were going to do for this loon would have to wait until the next day. She turned the lights out, draped a sheet over the carrier, and hoped it would get some rest.  

The next morning Crater and Kimberly strategized again about the bird. It looked pretty healthy and fiesty, they agreed. They could see no reason to hold onto it any longer. Together they decided to return it to the ocean.

The two friends took the carrier to the beach and removed the loon. This time, though, they let it go at the water’s edge, where the waves were breaking on shore. With furrowed brows and hands on hips, Crater and Kimberly watched as the bird bravely faced the waves and began to crawl towards the ocean. It was not pretty. On five occasions, a wave caught the loon and hurled it backwards several yards towards the beach. Kimberly was reminded of videos she had seen of tiny sea turtles heroicly battling the surf to reach the sea after hatching. The bird did not give up, however. Eventually it was able to take advantage of a lull between waves, reach water deep enough for a dive, and plunge beneath the crashing surf. Kimberly and Crater cheered to see its head pop up thirty yards from shore, well beyond the surf zone.

After a late March sojourn with beach-going humans, the loon, which we had banded the previous summer on West Twin Lake in north-central Minnesota, was back where it belonged — and looking none the worse for wear. We have no idea what brought this nine-month-old to shore.

We got a second, more sobering glimpse into the Great Void in late August 2025.

Battered by stiff winds and high waves from Hurricane Erin, the loon sat within the surf zone on Rockaway Beach in Queens, New York, twelve miles southeast of the Statue of Liberty. Waves crashed over it — even submerging it entirely on occasion. Susan Garman and her ten-year-old son Justin had made a quick trip to the shore to gawk at the surging whitecaps. But when they spotted a large bird that was being pummeled by waves and seemed unable to help itself, their light-hearted jaunt to marvel at nature’s fury took a serious turn.

They hurriedly shed their shoes, waded into the surf, and approached the bird. It looked as bad as Susan had feared it would: dazed, bedraggled, and water-logged. Worse still, the bird showed little fear of Susan and her son when they approached it. “You’re hurt, aren’t you?” she said to the animal, a comforting, motherly tone in her voice. “We are going to help you”.

Yet after she had gathered the bird up, Susan’s concern deepened. She had hoped to feel a smooth, reassuring mass of pectoral muscle when her fingers reached around its chest and belly, but instead, she encountered the sharp protruding keel of its sternum. So it was also emaciated. “Oh, buddy, I am so sorry!”, she whispered. It lifted Susan’s spirits slightly to see that the bird had four bright color bands on its legs. Her mind now racing, she reasoned that the person who had marked this bird would surely wish to help them save it.

She and Justin carried the bird to their home to do what they could. They nestled it in some blankets in the kitchen; it made no objection. Susan Googled “injured bird”, and found some local rehabbers and veterinarians, but no one that she reached could or would help. Justin submitted a photo of the bird to Google Lens to try and identify it. Lens came back with: “The bird in the image is a Common Loon.” “A loon!”, Susan repeated, trying to square her recollection of that glamorous northern species with the unsightly mass of soaked, tousled feathers on her kitchen floor. She and Justin were cheered by their ability to identify the bird they had rescued. They finally seemed to be getting somewhere.

But the loon was very weak and slipping away. “We are here with you”, was all she could muster, her voice softer and breaking from sadness and frustration. Finally, the loon stretched its head forward for a moment, pulled it back again to rest on its chest, and let out its last breath. Crushed by the loss herself, Susan looked for a positive to share with her distraught son. “At least it did not die alone”, she offered.1

We will have to record many more encounters of our young marked loons before we can shed much light on the alarmingly high mortality of loons during their first few years of life. Meanwhile, I am keeping my fingers crossed that other loons of ours who are in need of aid find such generous, compassionate people as these two youngsters did.

1 – We had banded the loon that Susan and Justin found as a chick on Upper Hay Lake, near Pequot Lakes, Minnesota, in July of 2024. So it was just over a year old when it perished. From the work of Kevin Kenow and his team, we know that loons from the Upper Midwest that winter off of Florida make their way up the Atlantic coast to spend the summers of their first and second years of life as far north as the Gulf of St. Lawrence. Thus, this young bird was probably on its way back to the wintering grounds in Florida.

Our paper on the Silver Spoon effect in loons has just been published online. You can read it at:

https://link.springer.com/article/10.1007/s00442-025-05836-8?utm_source=rct_congratemailt&utm_medium=email&utm_campaign=oa_20251124&utm_content=10.1007/s00442-025-05836-8

The top photo is of the loon from Panama City Beach, Florida. Photo by Jim Anderson.

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Following a long summer of capture, marking, and field observation, we have a new tranche of loon data from Wisconsin and Minnesota. The picture in Wisconsin does not change greatly from year to year. There we already had 32 years’ worth of research findings before 2025. But each successive year in Minnesota — where our research began in 2021 — increases our understanding of that population immensely. And with our improved knowledge of Minnesota loons, the status of the loon population across the Upper Midwest is coming into focus.1

Three demographic parameters together dictate whether a population of animals is increasing, decreasing, or stable, These factors are: 1) survival of breeding adults, 2) reproductive success, and 3) young adult survival. Recent measurements have shown us that the Wisconsin population is declining. And we know very well which of these parameters is responsible for the decline. If we compare our growing dataset in Minnesota to the trove of data we have from three decades of research in Wisconsin, we can learn whether or not Minnesota loons are headed in the same direction.

First, let’s look at survival of adult breeders. It should not be surprising that the most important single indicator of population dynamics (i.e. whether a population is stable, increasing or decreasing) is the rate of survival of its adult members. There is good news from the Wisconsin Study Area. The survival rates among territorial females and males both have been stable for the past three decades (Figure 1). This finding implies that once loons reach adulthood, they survive and hold their territories well. The decline that we are seeing in the Wisconsin population, then, must come about because of problems that occur before loons settle on territories.2

Figure 1. Annual survival rates of adult breeders on territories.

What about survival of territorial breeders in Minnesota? From measurements in 2022, 2023, and 2024, it appeared that adult survival in Minnesota might be lower than that in Wisconsin (look at these years in Figure 2, below). However, each year we get a better “read” on these numbers because our sample of loons becomes larger and more representative of the overall population. So the 2025 adult survival numbers are the most reliable ones we have to date. As you can see from Figure 2, there is no evidence for a

Figure 2. Survival rates of adult breeders in Wisconsin and Minnesota from 2022 to 2025. (Sample sizes are shown above each bar.)

difference in survival rates of territorial adults between Wisconsin and Minnesota. Minnesota, like Wisconsin, is seeing good adult survival. Again, this is good news!

Now let’s turn to reproductive success in the two states. Since we learned recently that the silver spoon effect is strong in loons, we know that we must look both at quality and quantity of loon chicks produced to get a good sense of how well a population is reproducing.

First let’s look at quantity. As Figure 3 shows, chick production in each region fluctuates greatly from year to year according to ice out date, severity of black flies, water clarity

Figure 3. Chicks fledged per territorial pair since 1995 in the Wisconsin Study Area and from 2021 to 2025 in the Minnesota Study Area. (Dotted line shows the trend in Wisconsin.)

in July, and other factors. Overall, however, chick production has decreased significantly in Wisconsin during the past three decades. Adult breeders are simply not producing as many offspring now as they did 30 years ago.

While Wisconsin data show a clear decline in number of chicks produced, it is too early to discern a trend in Minnesota. Chick fledging rate simply bounces around too much from year to year to see a pattern. We can say that chick production is at a similar level in the Wisconsin and Minnesota study areas. However, note that 2025 was a banner year for chick production in Minnesota and a poor one in Wisconsin.

Next we need to look at the quality of loon chicks that Wisconsin and Minnesota are producing. Our recent work has shown that chicks that fledge at low weights are much less likely to survive to adulthood and produce chicks themselves than are their heavier peers. Chick body condition has been falling for the past few decades in Wisconsin (see Figure 4, below).

Figure 4. Average body condition (mass divided by age) of chicks in Wisconsin from 1998 to 2025 and in Minnesota from 2021 to 2025. (Trendline shows Wisconsin pattern.)

The five years of data we have on body conditions of Minnesota chicks are not as many as we would like, but the numbers are consistent. Chicks fledge in Minnesota at similar — or even slightly worse — body condition than those in Wisconsin (Figure 4). We can infer that Minnesota is suffering from the same challenging chick-rearing conditions that have plagued Wisconsin (probably declining water clarity).

The third and final piece of the puzzle that we need to understand population dynamics is the survival of young adults. These birds are the breeders of the future that have not yet settled on territories. They range from three to about six years of age.

If you have been following my blog closely, you know that young adult survival of Wisconsin loons has seen the most dramatic decline among the three critical population determinants. That is, adult survival has held steady, and chick production has fallen somewhat, but the return rate of young adults to the breeding grounds has been abysmal — far below what it was a quarter century ago (see Figure 5, below).

Figure 5. Return rates of chicks to the breeding grounds 2 to 4 years after being banded as chicks in Wisconsin. (Data are missing for 2000 and 2007.)

We have been on pins and needles to see if this distinctive and rather alarming Wisconsin pattern is present also in Minnesota. Fortunately, our understanding of young adult survival has grown by leaps and bounds in Minnesota this year. Why? Because: 1) we started banding Minnesota chicks in 2021 and have done so every year since then, 2) most young loons return to the breeding grounds at three or four years of age in adult plumage, and 3) we regularly record identities of these young birds as intruders and loafers within our study areas. Thus, 2024 gave us our first glimpse at young adult survival in Minnesota using the crop of 26 chicks banded in 2021. And 2025 provided an even better window onto young adult survival there, since we could look at the return rate of 64 banded in 2021 and 2022 combined.

What do our findings show so far? In 2021, we banded 52 chicks in Wisconsin. Of these, 7 had returned as of 2025 (13.5%). We marked 28 chicks in Minnesota during 2021, and only one has so far been spotted as an adult (3.6%). For chicks banded in 2022, the numbers that have returned in Wisconsin and Minnesota, respectively, are 5 of 44 (11.4%) and 4 of 36 (11.1%).

These numbers tell a clear story. The percentage of young adult loons returning as adults in Minnesota is well short of that expected in a healthy population (a rate of about 41%). That percentage is also far below what we have seen in the past in Wisconsin (note the return rate in the 1990s and 2000s in Figure 5). In fact, the low return rate of young adult loons in Minnesota closely mirrors the dismal rate in Wisconsin.

In summary, it has taken five years to be confident of how the loon population in the Minnesota Study Area is faring. But our data now show that loons in Minnesota — at least those in Crow Wing and Cass counties, where we work — exhibit the same set of quirky demographic patterns that typify loons in Wisconsin and have set in motion a decline in the overall population there: 1) strong and stable adult survival, 2) poor reproduction in terms of both number of chicks and body condition at fledging3, and 3) a massive and diagnostic plunge in the survival rate of young adults (which are future breeders).

We have work to do.

1Thanks to Sheila Johnston, who took this photo of a molting adult loon on Gull Lake, which is just south of the Minnesota Study Area.

2I know. I just published a blog post in which I mourned the losses of many male breeders in the Wisconsin Study Area. I am still concerned about these losses. But in the long-term, which spans over three decades, adult males and females both have survived well. So I am hoping that the loss of several old, established male breeders this summer in Wisconsin was a blip.

3As noted earlier, it is too soon to tell from our data whether the number of chicks fledged is declining in Minnesota. We will gather those data over time. But we already know that Minnesota loon chicks are fledging in poor condition, just like Wisconsin loons. It is worth noting that the Minnesota Loon Monitoring Program, which has counted chicks across the state since 1994, reports a long-term and statewide decline in chick numbers.

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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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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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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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A few years ago, a non-scientist collaborator of mine suggested that I place transmitters on loons. This was a cool idea in many respects. Transmitters would permit us to monitor loons’ locations in real time and share those data with the public on a splashy website. I agreed that the technique would be thrilling and draw lots of public interest. But when the surge of adrenaline subsided, I was left with two troubling questions. First, what scientific hypothesis could we test with transmitters? Second, how would attaching transmitters to loons help us conserve loon populations in the Upper Midwest?

I am not knocking the technique. Transmitters are a potent tool used by animal ecologists to learn about patterns of migration, dispersal, and nomadism. Kevin Kenow and his collaborators employed satellite transmitters to show that typical adult loons breeding in Wisconsin and Minnesota spend the fall on Lake Michigan before heading south for winter. Kevin’s team also learned that juveniles remain on or near their natal lakes until late November, at which time they make a beeline for their winter quarters. So transmitters have helped us pinpoint times and places that are crucial to the annual survival of Upper Midwest loons. At present, though, there is no burning question concerning loons that transmitters might address.

What questions are most pressing with respect to Upper Midwest loons? With another year behind us and the 2024 field season looming, let’s take stock. How healthy is the population of loons in the Upper Midwest? And how can we best use our resources to protect them?**

Population Surveys

Two broad censuses carried out by armies of volunteers look at loon populations across large swaths of Minnesota and Wisconsin during late July. These counts are prone to fluctuations caused by changes in personnel and weather conditions during a narrow window of data collection. Still, they provide valuable large-scale “snapshots” that, in the long run, tell us how each population is faring. Furthermore, by comparing Minnesota and Wisconsin snapshots side by side, we might discern a broader regional trend.

Wisconsin’s LoonWatch survey has been carried out every five years since 1976. The survey showed robust statewide gains in loon numbers during the 1980s, 1990s, and 2000s. The most recent survey, however, revealed a decline in the Wisconsin loon population between 2015 and 2020. (The next survey will occur in July 2025.)

The Minnesota Loon Monitoring Program generates data annually and is based on six “index” areas. The enhanced geographic dimension to the MLMP survey suits Minnesota’s loon population, which is three times the size of Wisconsin’s. From 1994 to 2010, populations in two of six areas increased, two declined, and two were stable. But trends have shifted downwards in recent years. Since 2010, two areas have been stable, two have declined slightly, and two have fallen sharply. Surprisingly, the strongest, most consistent declines have occurred in the two most northerly areas (Cook/Lake and Itaska).

If we stitch Minnesota and Wisconsin surveys together, we can see that the Upper Midwest loon population as a whole increased (Wisconsin) or remained stable (Minnesota) during the 1990s and 2000s. We can also detect an apparent decline across the region that began in about 2010 in Minnesota and five years later in Wisconsin.

Poor Breeding Appears to Explain the Wisconsin Decline

Our breeding data from Wisconsin shed light on the recent population decline there. During the 1990s and 2000s, Wisconsin breeders raised healthy chicks with high survival. Brood size was split 50/50 between one- and two-chick broods. Beginning in 2010, however, chick survival and mass fell, and only 20 to 30% of broods contained two chicks. Furthermore, young adult survival plunged by 60% in Wisconsin from 2000 to 2015. Thus, poor breeding success and loss of young adults seem to be driving the population decline. There are simply not enough young loons being produced to replace adults that die.

Wait a minute. The breeding decline began around 2010, whereas the population did not begin to fall until after 2015. Are these results consistent? Indeed they are. Most loons do not settle on territories until they are five to ten years old. Therefore, several years must pass before poor breeding success is “felt” in the adult population. Hence, a statewide population decline beginning in about 2015 is what we would expect from a reproductive downturn 5-10 years earlier.

Hints of a Similar Pattern in Minnesota

We have only three years of detailed breeding data from the Minnesota Study Area. These data are too few to make robust comparisons with population trends from the MLMP. Still, we can report two preliminary patterns from the state. First, the adult return rate in Minnesota (80 to 83%) has consistently run 5% below that in Wisconsin.* Second, 31% of all fledged broods in our Minnesota Study Area from 2021 to 2023 contained two chicks. This number puts Minnesota in line with Wisconsin, where the paucity of two-chick broods reflects challenges faced by breeders since 2010. The 2022 MLMP report too cites reduced chick production in recent years as a potential cause for concern. At first glance, then, the loon population in Minnesota seems to be facing the same difficulty as its neighbor to the east.

Environmental Causes of the Decline

Thus, the loon population across the entire Upper Midwest seems to be in decline owing to reduced breeding success. This is vital information. But if our knowledge ended there, we would stand no chance of fixing the problem. To do so, we must identify the precise environmental factor or factors that impair loons’ ability to breed. In the past few years, of course, we have learned that decreased water clarity and increased black flies are two such factors in Wisconsin. That is a good start. However, it will improve our understanding — and strengthen any case we might wish to make for using local, state, and/or federal resources to mitigate the problems — if we can extend these findings from Wisconsin to Minnesota.

The Plan for 2024

2024 is going to be a pivotal year for the Loon Project. Why “pivotal”? Because we have built a conceptual and logistical platform in Wisconsin for understanding the entire Upper Midwest loon population. And we have painted a clear picture of a declining Wisconsin population and its causes. In 2024 we must pivot towards Minnesota.

Thanks to the hard work of our field crews, seed money from the National Loon Center, and the growing ranks of folks in Minnesota, Wisconsin and elsewhere who support our work logistically and financially, we have spent three productive years in Minnesota. We have identified 115 territories in Crow Wing and Cass counties that constitute our Minnesota Study Area and marked adults in about 3/4 of these territories. Our task now is to place a large enough team in the field to collect high-quality breeding data from our new Minnesota study lakes.

We will use methods in Minnesota that have proved successful in Wisconsin since 1993. In the spring we will clear cobwebs from our canoes, head to our 115 study lakes, and confirm the return or non-return of each pair member. On subsequent weekly visits single team members will locate and identify each pair member and document their nesting status or number of chicks. Most critical to our effort will be recording causes of nest failure and chick loss, because, of course, poor breeding success is the root cause of the Upper Midwest population decline.

Our growing sample of survival data from adult return rates will allow us to build a population model for the Minnesota Study Area. In addition, accumulating return records will allow us to determine whether the curiously high annual mortality of Minnesota adults that we have measured by three separate means holds up over time. If so, we will try hard to identify the source of the mortality, which would be very costly to the population.

Following the field season, we will determine whether the low breeding success in our Minnesota Study Area persisted in 2024. Then we will turn our attention to environmental factors that are causing nest failure and/or loss of chicks in Minnesota. That is, we will follow up our increased field effort with a statistical search for likely causes — especially water clarity, black fly populations, and weather patterns — that might be driving a breeding decline. It will likely take several years of intense field work to get a clear picture of such causes.

Support for Our Low Tech Approach

As you have surmised, our future promises to be unglamorous and low tech. We will not use drones, satellite transmitters, amphibious vehicles, or hovercraft to collect data. Instead, trained observers will employ the field techniques that have gotten us where we are today. We will carry our canoes to boat landings, put paddles in the water, find loons, and collect as much data as grit and elbow grease allow.

Now I am asking for your help as we do this important work to save loons in the Upper Midwest. If you believe in our work and wish for it to continue, please consider a tax-deductible donation to support us. In keeping with our theme of simplicity, we run a lean operation. None of our funding goes into the pockets of senior researchers. This year we will use our funds to support: 1) field interns who visit study lakes by canoe and collect data (about $6,000 for each of four interns covers a monthly stipend and reimbursement for gas); 2) lodging for the interns and myself (about $10,000, if recent experience is a useful guide); 3) economy airfare for me to make two trips to and from the Upper Midwest and gasoline for the motorboat we use to cover breeding pairs on the Whitefish Chain ($1800); and 4) color bands for marking loons and costs to replace broken equipment and needed supplies ($4,000). So I estimate our need to be about $40,000 for the expanded 2024 field effort in Minnesota.

By the way, we currently have enough funding in place to support a modest field effort in Wisconsin. However, increased funds directed to Wisconsin would also strengthen our effort in this most valuable long-term study population. You may earmark your donation to go towards our Wisconsin work, if you so choose.

You may use this link to go to our “Donate” page. Thanks for any support you can give us. We promise to make every penny count! 

The Future

Our future prospects seem bright. In addition to cultivating a large number of supporters across the Upper Midwest, we are forming an Upper Midwest research team. Obtaining funding is always uncertain, but our new collaborators have a good track record of acquiring major regional funding. We will apply for such funding this year and, if we are fortunate, might receive it by late 2025.

If all goes well, lake dwellers in Crow Wing and Cass counties will soon get used to the same peculiar sight to which lake residents in Oneida and Lincoln counties have become accustomed: paddlers in solo canoes, wearing bleached PFDs and binoculars, scanning the lake’s surface ceaselessly for loons.

FOOTNOTES

* This pattern is enigmatic. I can think of no reason why Minnesota loons should die at a higher rate than Wisconsin loons. One hypothesis is that the pattern is the higher density of loons in the Minnesota Study Area than the Wisconsin Study Area results in greater competition for territories in Minnesota. If so, what appears to be a low adult survival rate might instead be a higher rate of eviction. From a conservation standpoint, we must hope that eviction explains the apparent difference. If Minnesota loons truly die at a substantially higher rate than Wisconsin loons, Minnesota birds would have to offset that mortality rate with considerably higher breeding success.

** The beautiful featured photo, as usual, is by Linda Grenzer. It shows a foot waggle by two-year-old male that tried to claim her lake as its territory this past summer. We are slightly worried that this youngest-ever settler is a sign of population decline in Wisconsin, because four-, five-, and six-year-old nonbreeders would normally outcompete it for this territorial opening.

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I did my graduate work at the University of North Carolina-Chapel Hill. My advisor and I spent tooth-chattering mornings from November to April sitting in blinds and watching 300+ color-marked white-throated sparrows compete for seeds at feeding stations. We learned a good deal from this work. We now understand how aggressive behavior affects the survival and local movements of this species.

Many lake residents and outdoorsy types in Wisconsin and Minnesota recognize white-throated sparrows from another time of year. These striking little birds sing distinctive, whistled songs in late May and June along forest edges in the Upper Midwest. Although they are more understated, the calls of white-throats typify northern boreal forests much as loons’ calls symbolize northern lakes.

White-throated sparrows live two very different lives in summer and winter. We witnessed part of the transition between these lives in North Carolina. During early May, the undisciplined hordes of sparrows we had grown accustomed to seeing broke up into smaller flocks. In mid May, they spurned the seeds we offered and fed instead on protein-rich buds they found in treetops. By late May, our sparrows had left for the north country.

The departure of our study animals left us with mixed feelings. On the one hand, it gave us a much-needed break from the daily grind of field work. On the other hand, it left a void and a puzzle. Where had our birds gone? Were they New England breeders that serenaded summer hikers in the White Mountains of New Hampshire with their plaintive calls? Or had they headed inland towards the Upper Great Lakes where they crooned to cottagers on lakes? Perhaps they had ventured to northern Ontario, Manitoba, or even the Northwest Territories. If so, they likely belted out their songs with no human around to enjoy them.

I spent many hours pondering summer destinations of our wintering sparrows. I felt — quite irrationally — that there must be some way to learn where they migrated to breed. Could some distinctive wisp of vegetation or a sticky residue from berry or insect from the breeding quarters become lodged in their feathers or stuck to the bill; survive the journey southwards; and still be detectable in North Carolina in October? Perhaps. But no researcher, to my knowledge, has ever determined the migratory origin of a small songbird by such a means. Eventually I gave up on my fanciful notion of learning where our sparrows spent the six months when they were not in our company.

Other scientists did not give up on the dream of linking breeding and wintering areas. Indeed, for a few decades now scientists have used stable isotope analysis to detect geographic movements of itinerant animals. Stable isotopes are different versions of a chemical element with different masses. For example, most hydrogen atoms (over 99.9%) occur as H-1, which has no neutron in the nucleus. But a few hydrogen atoms take the form of H-2, which possesses one neutron and weighs twice as much. Here is the key point: water droplets in rainfall in each geographic region contain a characteristic tiny percentage of H-2 (.02% in one place, .008% in another). And living things absorb water so that they too contain a ratio of H-2 to H-1 in their bodies that is distinctive to the region they inhabit.

Measurement of stable isotopes is especially useful to bird biologists because of feathers. Feathers are not living tissue. They are keratinized structures that grow from living tissue and, once formed, no longer receive a blood supply. So the stable isotope ratio within feathers does not track the current environment like that in skin, blood, or muscle. Instead, feathers are a time capsule that contains the stable isotope ratio at the time and place of their formation. When a bird grows new feathers in one place and migrates to another, its feathers retain the stable isotope signature of the molting location.

Loons grow fresh wing feathers on the wintering ground prior to migration. This means that wing feathers of breeding loons bear the isotopic signature of their winter quarters. Thus, a small wing feather we clip in July can tell us where a specific breeder spends its winters.

We have some understanding of loon migration and wintering patterns, thanks to the work of Kevin Kenow, Jim Paruk, and their co-workers. Furthermore, recoveries of banded loons have helped us sketch out the wintering range of our Wisconsin and Minnesota breeders (see map below). However, we cannot tell where any particular loon — like the territorial female on Roosevelt-Southwest — winters.

Sources and destinations of loons banded in Wisconsin and Minnesota. Light blue lines are paths of adults; dark blue lines indicate first-winter birds.

Why does it matter where a specific territorial loon spends the winter? Because we have burning questions about conservation of Wisconsin and Minnesota loons that require fine-scale understanding of migratory patterns. For example, does use of certain wintering areas lead to low survival for Upper Midwest breeders? Do poor years for adult returns in Wisconsin and Minnesota correspond to “die-offs” in specific wintering areas? Does the low annual return rate of adults in Minnesota (compared to Wisconsin) indicate unfavorable conditions in their more westerly winter range (see figure above)?

In fact, we have many more questions of this kind. To answer some, we will need ecological data from the Gulf of Mexico and Atlantic Coast. At the moment, however, subtle information locked within the feathers of our study animals and transported by them from wintering to breeding grounds is giving us hope that we will soon have a better understanding of common loon survival throughout the year.

Thanks to Linda Grenzer, who took the cool photo of the male from Halfmoon Lake coming in for a landing some years ago.

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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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Perched on the bow of a small motorboat in the middle of the night, I sweep a spotlight back and forth across the lake’s surface. My goal is simple. Find any small item resting on the dark water that catches the light. “Buoy”, Claudia proclaims in my ear as I freeze the spotlight on one such object that, at first blush, appears to be a loon. “No”, she barks a moment later, when I find a floating clump of vegetation. But shortly afterwards, the light falls upon something small, fuzzy, and brownish that becomes more and more loonlike as we approach it. I hand the spotlight backwards over my head to her, scooch as far forward as possible on my knees, and glance at the net to confirm it is untangled. Richard slows the boat and turns towards the loon family. “Adult!”, I whisper to Claudia — needlessly, because we had already agreed that we would first attempt to catch the parents. She trains the light on the larger of two adults whose physical features become dimly visible as we pull within fifty meters. On this occasion, luck is on our side; the male and female become alert as we draw near, but neither dives. We net the male without difficulty and, shortly afterwards, the female. The chick dives once after we fix him in the light. Seconds later, attracted by my loon calls, he wheels, swims towards the boat, and dives smoothly into the net that I place in his path. We quickly text Terri so that she can prepare the bands and datasheets on shore. Twenty two minutes later we have marked and weighed all three loons, transported them back to the capture site, and released them. Then it is on to the next lake.

One’s world narrows during loon capture. In the moment, all that matters is whether we netted this or that adult or chick we wished to band. Now that the sleep deprivation and tunnel vision of the capture period has subsided — and our nips and scrapes from loon bills have mostly healed — we can look back at our achievements over the season as a whole.

Between West Fox Lake in Minnesota, where our efforts began, and Oneida Lake in Wisconsin, where we wrapped up our season, we captured and banded 134 loons this year. Terri and Richard saved us in Minnesota with their expert boat-handling and organizational skills. Emily and Danny from the Wisconsin team were essential to our capture there. A huge thank you to all team members, who made 2023 a great year.

The research landscape differs starkly between the two study areas. In Minnesota, breeding pairs on Kego, Mitchell-East, Mitchell-West, Goodrich-Southeast, O’Brien, Clamshell, Kimble-West, Margaret, Big Trout-Far West — and dozens of other territories — got bands for the first time. The return or non-return of these adults in future years will allow us to refine our estimate of adult survival in the region and build the first-ever quantitative population model for the state. Thanks to our growing list of Minnesota partners and friends, who greased the skids for our work there with donations of funds, lodging, field work, lake access, advice, information about loons on their lakes — and moral support!

Having marked almost all adults in the Wisconsin Study Area decades ago, we now focus on marking chicks. Chick mass, we now know, provides a convenient assay of water clarity during the chick-rearing period. While we have already shown that increased black fly populations and falling water clarity have dealt the Wisconsin loon population a devastating one-two punch, there is more work to be done in the state. If we can pinpoint the exact environmental factor that reduces water clarity — our current research target — we might learn how to stem the population decline.

All of our research findings require loon capture. Although it is not foremost in my mind at those moments when I am kneeling in the bow of a small motorboat and inspecting fuzzy brown spots on the water, our work — our ability to learn about loon populations and what ails them — depends critically upon catching loons, weighing loons, and knowing who they are.

Thanks to Barbara Krimmer of South Two Lake in Wisconsin, who took this nice photo of the female (left), male (right) and two big chicks there.