I am fearful of new challenges. In 1993, when I began to study the behavioral ecology of loons on a cluster of 12 Wisconsin lakes, doubt gnawed at me. How can one carry out meaningful, publishable, scientific research, if one’s study animals are large, aquatic, diving birds that range over huge territories, dive constantly, and must be followed in boats? Would my work be severely limited in scope, like that of researchers on porpoises, whales, and sea turtles? I had no training in field techniques for study of aquatic animals, only my childhood experiences paddling canoes over vast stretches of Lake Temagami in central Ontario. But my fascination with loons — which also grew during summers on Temagami — and my sense that canoes could be an effective means of tracking them without altering their behavior pushed me forward. And so, for reasons that I do not understand, I began to treat seemingly insurmountable problems with funding, logistics, and personnel as mere nuisances. And I ignored warning signals that any reasonable young scientist would have heeded. I began to study loons.

So it was in Minnesota. Although one might surmise that beginning a field project on loons in one state would be much like doing so in another, this is not so. True: loons are loons. We see many of the same behaviors, hear the same basic calls, and witness the same sorts of human-loon interactions in Minnesota that we have seen over the past 29 years in Wisconsin. But all else is new. Starting a major field study in the Crosslake area has reminded us that we have an army of friends, lake residents, and supporters in Wisconsin. These folks have housed us, fed us, carried us around in their boats at times, and — most important — provided us with a trove of information on our study animals to supplement our field data.

And our Minnesota study lakes are far larger than those in Wisconsin. Only a masochist would attempt to study loons on the massive Whitefish Chain — where about half of our Minnesota study animals reside — by canoe. So a growing list of Minnesota friends and supporters have provided us with boats — thanks, John, Mike, Mary, Keith, and Dawn! — that permit us to cover the big water. (By the way, several others have made our work possible by providing housing — thanks, Melanie, Charlie, Mary, Jim and Jon!) In fact, we have learned that we can move about far more easily on huge lakes than on the tiny lakes where most of our Wisconsin loons live. Moreover, we can hold our position in the water more effectively and work in greater comfort on the Chain, providing winds are calm.

However, loon capture is another matter. Having caught rather few loons on huge lakes in Wisconsin, I was concerned that my team would waste many hours each night scanning the dark water before our spotlight came to rest upon a tiny light smudge that would become, on approach, a loon parent and a chick that we could capture. In truth, we do spend somewhat more time searching for Minnesota loon pairs that we are accustomed to. Furthermore, locating loon families acoustically is more difficult in Minnesota, because Minnesota loons seem less vocal at night than their small-lake brethren in Wisconsin. But once located, loons in Crow Wing County have proved easier to capture. So my irrational fear that loon capture would be slower and more difficult in our new western study area was unfounded.

What progress have we made in Minnesota so far? Despite the ill-timed failure of an outboard motor that forced us to cut short our night and limp back to our boat landing using only a single canoe paddle and three tote box lids, we have marked 37

adults and chicks in four nights. We banded sixteen loons on Ossawinamakee alone last night. In a few hours’ time, five anonymous territorial loon pairs on Ossie have become a valuable set of individuals whose behaviors, life histories, and survival rates we can track to enrich our understanding of loon breeding behavior and population dynamics. Moreover, our experience in Wisconsin tells us that the brief capture and marking process leaves little or no imprint on loon behavior. Loons caught and marked one night act the next day as if the event never happened. They display the same casual indifference towards us and other humans that they showed on the day before.

On the other hand, we ourselves are greatly changed after we capture and mark loons. Marked loons are individuals to whom we are committed forever afterwards. Yes, we get scientific data from them. But marking creates a lifetime bond between observer and loon. We know these birds. We cheer as chicks we marked return as adults to the study area and claim territories. We mourn when marked parents lose a chick or abandon a nest. And we move heaven and earth to guard these individuals and come to their rescue, if they need it. It has proved impossible to maintain pure scientific indifference to our study animals.

In short, Minnesota loons are excellent study subjects. They ignore our visits to their territories and forgive us immediately after capture and marking. My initial fears and doubts about marking and observing Minnesota loons have subsided. We can now see that we will learn an immense amount about territorial behavior, breeding ecology, and population dynamics of Minnesota loons — if we are willing to shoulder the burden of an intensive field project in a new state on these most engaging birds.

Our work in Minnesota is just beginning. Although we have great support from the National Loon Center and seem to be getting lots of folks from across the state interested in our work, there is much left to do. At present, we are scouting lakes in the Crosslake area and hoping to find chicks so that we can band the chicks and their parents. Only through this arduous process can we establish a large study population, measure survival rates, and construct a population model for Minnesota loons. So far we have only fifteen banded birds in our entire Minnesota study area.

Make that sixteen. On Wednesday, Katy and Jordana found a new nesting pair on Lower Whitefish. This duo — the nesting loons, not Jordana and Katy — has the distinction of using the oldest, most sunken, washed-out nesting platform that we have yet seen in Minnesota. (Most nesting platforms that we have found in our new study area are quite bouyant and well maintained.) The platform location is also exposed to a substantial wind fetch, not to mention endless wakes from passing boats. And yet, drawn to this location by the predator-resistant nesting opportunity, a pair of loons has made this site their home.

Jordana shared the news of this new nesting pair with me in the most thrilling possible way. She told me there was a nest and sent me a video of one of the pair members swimming underwater and behaving protectively towards it. I immediately ran the video and caught an unmistakable sparkle on the bird’s left leg. (Note the bright white spot on the left leg of the loon in the featured photo and the video below.) The sparkle told me that the bird had a silver band on its leg that was catching the sunlight; the fact that the left leg was banded told me that this loon was an “ABJ” (adult banded as a juvenile) and not an “ABA” (adult banded as an adult). Hence, this loon, when we capture it and confirm its age and natal origin from the number on its USGS metal band, will be the first known-age individual in our Minnesota study area.

So this is not just any pair of loons. No, this Minnesota loon pair represents a first for the new Minnesota study area, because one of the two pair members is an individual whose age can be known precisely. Kevin Kenow of the USGS captured and marked this silver-banded loon as a chick four to six years ago on a different part of the Whitefish Chain. At present we must say “four to six years ago” because Kevin placed only a single band on the left leg of this bird, and he banded six other loon chicks similarly. Until we capture it, we will not know which of those seven chicks grew into this breeder. However, we can be virtually certain that the banded loon is a male, because most females settle to breed many miles from their natal lake.

Why am I so excited to see this young adult settle in our study area? Because one very important demographic parameter we seek to measure in Minnesota loons is the survival rate of juveniles and young adults. This, you may recall, is the cohort of the Wisconsin loon population that has suffered a high rate of mortality in recent years and thrown that population into decline. While we will be able to estimate the survival rate of breeding Minnesota loons — a crucial parameter in its own right — after another year or two of work, it will take five years or so before we have seen enough settlements of ABJs like this male to produce a good estimate of young adult survival in Minnesota. But the sight of this first young settler shows that we are on the road.

Although I am stuck in California teaching for another few weeks, others have been hitting the lakes. Based on thirty or so lakes from which I have had reports — mostly Linda’s work, but also a few lake residents — we have an early read on the return rate of adult loons from last year.

Let me explain. April and May are exciting months for the Loon Project, because we hustle from lake to lake to see which of our banded adults have returned and which have not. In a typical year, the vast majority of our study animals have managed to survive the winter, navigate fall and spring migrations successfully, and take possession of the territories they occupied the previous year. The figure hovers around 80 to 90%. A high rate of annual survival is vital to our population. The low reproductive rate of loons is sufficient to sustain the population only because most adults survive each year.

During years when I am able to steal away from my pedagogical commitments, I find these “censusing” visits oddly thrilling. On my first lake visit of the year, I fancy that the male and female both pause for a moment, wheel in my direction, and think, “Where’s he been?” This might not be pure imagination; after all, I have been observing most of these individuals for a decade or more.

Last year seemed an exception to the typical high rate of adult return. Fully a quarter of the adults that we left behind safe and sound in the early fall of 2019 failed to come back in the spring of 2020. While some of these adults had merely been evicted from their territories, most were dead. Coupled with our recent finding of population decline in northern Wisconsin, the low 2020 return rate weighed on my mind last spring. On the other hand, return rates bounce around. So I tried to avoid jumping to the conclusion that adult survival was going downhill.

Recent reports from the lakes this year have placed concerns about adult survival front and center again. Each of Linda’s almost-daily census visits seems to bring fresh news about a missing adult or breeding pair. Early on, Linda reported that a new male had replaced the long-time resident male on Manson. Okay, that happens, I thought. Nothing to worry about. The Deer Lake female, freshly marked in 2020, also turned up missing. A Halfmoon Lake visit brought no better news; the 2020 female from there was gone as well. Hildebrandt and Julia, always occupied by pairs and frequent chick producers, were vacant. Linda’s trip to Nokomis Lake was most devastating of all. Towards the eastern end of the lake, both members of a long-term pair with a consistent record for rearing chicks were AWOL. And Linda turned up only one unmarked loon from the entire 2200-acre Nokomis flowage, which usually supports three breeding pairs.

He did not know it, but Al from West Horsehead produced the straw that broke the camel’s back. His report from this morning that the 8-year-old West Horsehead male had been replaced by a 6-year-old male from neighboring East Horsehead hit me especially hard. The sample had become large enough that I could not longer deny the pattern. Looking at the number of returns right now, we have found only 21 of 31 adult loons that should be on territory. Now, we will track down some of these missing birds. A few will be alive and breeding on a seldom-visited lake near their old territory. And that will give us a momentary lift. But an adult return percentage in the low-70s, as we are seeing for the second straight year, will not sustain our breeding population for long.

By training I am a behavioral ecologist. That means that my background and experience help me understand what behavioral answers have evolved in response to the ecological problems animals face, like avoiding predators and finding a mate. So I am especially interested to learn why loons that are rearing chicks abandon them for periods of an hour or more to visit the neighbors, and why female territory holders are able to surrender their territory to a superior opponent and live for another day while male territory holders in the same predicament seem unable to sense the danger and often die in territorial battles. But such questions pale when compared to a single, burning question we have faced for the past year on the Loon Project: “What is causing the northern Wisconsin loon population to decline?”. That question has become a nagging source of unease that prevents me from feeling fully comfortable anywhere and at any time.

There are many possible reasons for the decline: the exploding eagle population, decreased fish numbers, human impacts like increased boating or angling. And, of course, climate change, which impacts temperature, rainfall, and extreme weather events, is the elephant in the room. Learning about and systematically eliminating each potential cause of the decline will require me to find and collaborate with other scientists who know about fish, eagles, human impacts, and climate. In other words, cracking this nut will force me far outside my comfort zone.

We have glimmers. My collaboration with Sarah Saunders showed us that increased rainfall, increased human settlement, and the North Atlantic Oscillation – a broad-scale climatic event that influences weather in the northern Hemisphere – are all linked to both lower breeding success and lower adult survival of our loons.

A month or so ago, Linda and her husband, Kevin, speculated that increased boat traffic on large lakes might be the cause of the reproductive decline of loons in Wisconsin. They reasoned that more big boats might churn up the water, reduce water clarity, and make it harder for loons to find their prey under water. Such a scenario might make chicks grow more slowly now than 25 years ago and cause higher chick mortality.

Water clarity has always been a prime suspect among factors likely to influence loon survival and breeding success. As visual predators, loons must be affected by water clarity. Right? Yet we have no evidence to date that clarity affects loons. Brian Hoover’s recent paper, for example, showed that juvenile loons try to forage on lakes similar to their natal one in pH, but not in clarity. Our analysis from several years ago showed that young loons tend to settle on breeding lakes similar to their natal one in overall size and pH – but, again, water clarity is not a factor. Moreover, a glance at our study lakes shows that loons survive well and produce chicks on lakes that range from crystal clear (20 feet of visibility or more) to very murky (4 feet or less of visibility). If loons live and breed successfully on lakes that vary so greatly in clarity, perhaps clarity simply does not matter at all.

Nudged by Linda and Kevin to look once more at water clarity, I finally had some success. When two new collaborators at Rensselaer Polytechnic Institute provided me with thirty years of water clarity data based on satellite overpasses from my Wisconsin study lakes – and I plugged those data into my statistical models – suddenly clarity mattered. To be specific, mean water clarity during July was a significant predictor of chick mass. Clear water produced fatter loon chicks! Furthermore, chick survival decreased significantly in cloudy lake conditions.

Wait……what does this pattern mean? If you are like me, you think of water clarity as being constant or static for a lake. That is, you consider Two Sisters Lake as a very clear lake and Pickerel Lake as a murky lake. And you are correct. But those lakes – all lakes – fluctuate in clarity seasonally, annually, and even over days or weeks. Runoff events caused by rainstorms reduce clarity, for example, because silt and other materials are carried by streams into lakes. So you can have a bad few weeks or month for clarity on a lake that is generally quite clear. And a very clear lake can gradually become less clear over the years. The new satellite data are showing us that such short-term fluctuations in water clarity are associated with lower chick mass. It is a conceptual leap, but the obvious interpretation here is that short-term losses in water clarity impair foraging by loons and reduce the amount of food they are able to provide for their chicks.

It is early days. My collaborators are refining their estimates of water clarity from the satellites for northern Wisconsin and promise improvements by October. Meanwhile, I am left to ponder two things. First, water clarity in northern Wisconsin has declined over the past ten years, as the featured graph shows. Second, if recent declines in lake clarity really do hurt loons’ ability to catch prey for their chicks, what can a single loon researcher do about it?

We are not the only people who study loons. In fact, dozens of researchers from Iceland to Montana…from Alaska to Massachusetts…and from British Columbia to Newfoundland have done so. And that is to say nothing of loon study that occurs on the wintering grounds.

Loons are, of course, engaging animals. It puts a spring in my step just to tell people that I study them. And the same is true of dozens of undergrads, Masters’ students, and loon enthusiasts who have chosen to spend time with these odd and fascinating birds.

But spending time with loons and gaining useful knowledge about them are two different things. Much of the basic information about the life-history of the species — where they nest; when they arrive on lakes in the spring; what their predators are — has been understood for some decades. So folks who observe the behavior of loons during the breeding season, even with a keen eye, have a hard time contributing to our knowledge of the species.

There is an exception. Marking of animals for individual identification throws open the door to an abundance of exciting and useful research questions. Once we had marked a few dozen loons in the 1990s and begun to follow their lives closely, we quickly put to rest the abiding — though scientifically implausible — legend about the species: that they mate for life. We now know that a typical adult has several different mates during its lifetime. More profoundly, we now know that loons are decidedly unromantic. A loon’s bond is to its territory, not its mate. When loons fight, they fight to retain their ownership of a territory — and to remain paired with whatever individual of the opposite sex has succeeded in maintaining its own bond with the same territory. Having loons banded has forced us to recognize the shocking fact that established breeders whose mate is evicted by a competitor simply pair quickly with the competitor, leaving their previous mate on its own to cope with the loss (on a new territory).

Marking of loons also exposed a peculiar finding about the species: that males choose the nest site. Since we have breeding pairs marked, we have measured statistically how males take the lead when pairs are nest-searching. More to the point, we have shown that the disappearance of a male breeder causes a territorial pair to “forget” nesting locations that they used successfully in the past.

While color-banding of loons is immensely valuable for behavioral study, it is even more so for monitoring populations. This is easy to understand. Once you start marking animals and systematically working to resight them, you learn at what rate they return annually to breeding territories. Instances of return or failure to return allow us to construct a population model to estimate adult survival. And if resighting efforts take place within a tight cluster of study lakes that are visited regularly, a researcher can refine the population model by accounting for those frequent cases wherein an adult loon failed to return to its lake not because of mortality but because a competitor evicted it and forced it to move to a new breeding lake nearby.

In fact, it is our intensive — almost obsessive — efforts to relocate adults lost from their original territories that makes our study methods unique. The obsession extends to loon chicks as well. That is, we search far and wide to find the breeding territories of loons that we banded when they were four to six weeks old. To date, we have discovered 183 chicks that matured and settled on territories 4 to 11 years later. These data further improve the population model, because they permit us to estimate survival of chicks to adulthood. Linda found our latest case of settlement by an adult-banded-as-chick on Manson Lake just yesterday. She tells me that this is the first instance in which she took a photo of a chick (above photo of the 2013 family on Jersey City Flowage) and then snapped another of that same loon after it had returned as a territorial adult (see photo below of this eight year-old yodeling yesterday on Manson Lake).

We are still going strong in Wisconsin. Each year that passes improves our known-age data on adults and chicks banded as long ago as 1993. This year, though, through a brand new partnership with the National Loon Center in Crosslake, we are bringing our technique of intensive mark and resighting to Minnesota. In the next several years, we hope to share better tidings with lovers of loons in central Minnesota than we shared recently with loon enthusiasts in Wisconsin.

My family took a vacation this past week to the East Coast. It was not a typical vacation. We boarded our eastbound flights nervously, wiped our seats obsessively with the comically-small towelettes provided by flight attendants, cinched our masks high over our noses, and glared with disapproval at fellow passengers who failed to do the same. Upon arrival in Boston, my daughter and I waited for three hours in 96-degree heat for a COVID test (both were negative) and then rushed back to the airport to meet my wife and son. Ultimately, though, we all arrived in Vermont for a five-day vacation with family members who could also boast of recent negative tests.

Even without the added stress of coronavirus, I had expected to struggle on this vacation. I loved vacations when I was a child. My parents would throw their four kids into one of those monstrous Chevy station wagons with fake wooden side panels and drive northeast along the interstates from Houston on our annual odyssey to New England. We loved the highways, the motels, the afternoon stops for soda, singing madrigals in the car at night, playing the alphabet game with road signs — and even the adventures we had after occasional tire blowouts. But age has made me hunger for the sound nights of sleep that go with routine and a familiar bed. So when my wife described her plan for a New England holiday — to begin immediately after my daughter and I had buttoned up our canoes and car in the storage box in Rhinelander — I sighed. “Ok”, I said, “that sounds like fun!”.

Despite their many drawbacks, there will always be one big positive about vacations: vacations bring an exciting change of scene. In meeting new people and taking in new sights and smells, you are able to compare — consciously and unconsciously — your vacation spot to what you have seen elsewhere. As a scientist, I appreciate the new connections my brain makes when I move from one location to another.

As it turned out, our visit to Vermont provided an unexpected comparison of two loon populations headed in opposite directions. One of our outings took us kayaking on Kent Pond, near Killington. “Pond” is a misnomer; Kent Pond is a dammed lake that covers 71 acres. According to Eric Hanson, who has been following Vermont loons for almost as long as I have been covering those in northern Wisconsin, the first attempted loon nest on Kent Pond occurred in 2009, and the first chick fledged in 2011. So, Kent Pond — and southern Vermont generally — illustrates how loons can settle in an area, begin to breed, and establish a new population. After I had adjusted to sitting so low in the water and using the quirky two-sided paddle to propel my kayak forward, I joined my daughter and the rest of our party as they sought out the loon pair that inhabited the Pond. We caught up with the tame adults and their two nine-week-old chicks along the northeastern shoreline. The larger chick swam and preened casually and lagged behind the family, while the smaller chick approached and hounded its parents for food unceasingly. Their size and behavior made it clear that these were two strapping chicks. Their wing flaps, moreover, exposed fully adult-sized flight feathers that will soon lift them off of the Pond and permit them to explore other lakes in the area. (I took no photos of the Kent family, but Linda’s photo of a rare two-chick family on her lake is similar.)

After gawking at the two monstrous chicks on Kent Pond for a time, I explored the Pond a bit more and was reminded of one of my study lakes in Wisconsin. Like Kent Pond, Currie Lake is rather round in shape and has two small islands near its center. Like Kent, Currie also hatched two healthy-looking chicks in June 2020. But Currie lost one chick in its first week and the other chick before it reached two weeks of age. In other words, the chick loss this year at Currie exemplifies the current reproductive downturn in the northern Wisconsin population. The two adult-sized chicks at Kent, on the other hand, well represent the Vermont loon population, which continues to grow and expand. (Below is a plot of the size and breeding success of loons in Vermont from the Vermont Center for Ecostudies.)

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I am not a bitter person. I try hard to look without jealousy at those more fortunate than myself and be happy for their situation and not sad about my own. But those two big, fat, sassy chicks at Kent Pond — and the population of which they are a part — showed me a portrait of loon ecology that is becoming distressingly unfamiliar.

I feared in May that 2020 would be a forgettable year for breeding among loons in northern Wisconsin. As many followers of the blog may recall, I wrote numerous posts this spring and summer warning of reproductive struggles of loons in Oneida, Lincoln, and Vilas counties. Before I was even able to visit my study lakes in late May, the die was cast. Black flies, Linda told me in early May, were worse in 2020 than any year during the 28-year study — worse even than in 2014, when about 80% of all first nests were wiped out by the relentless blood-suckers. Indeed, only 3 breeding pairs out of the 109 that we followed this year were able to incubate to hatching a nest that they began in May. The flies were a painful punch to the gut from which the breeding population never recovered.

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Despite the huge setback caused by the flies, most pairs forced to abandon their first nesting attempt renested in June. Many such pairs used promising nest locations on islands, protected boggy shorelines, or marshy mounds formed from emergent vegetation; still others placed their eggs of artificial nesting platforms anchored on lakes by lake residents anxious to boost their efforts. And so, in spite of the challenges, many nesting pairs hatched late chicks. These successful pairs included several on lakes that had not produced chicks in many years, such as Hodstradt, Shepard, and Dorothy. They included a few lakes where entirely new breeding pairs had settled, found good nesting places, and hatched young, like South Two, Silver, and Miller. Finally, one breeding pair — on Baker — performed the most impressive feat of all, raising their own loon chick in 2020 after having reared a mallard duckling to fledging in 2019.

Yet all of these heart-warming breakthroughs combined were not enough to lift the breeding rate this year to respectability. As the graph shows very clearly, 2020 continued the steady decline in the reproductive fortunes of northern Wisconsin loons that began over two decades ago. The decline is marked not only by increased black fly harassment but by increased losses of chicks after hatching — both young and old chicks.  Altogether 9 of our pairs patiently sat on their eggs for 4 long weeks only to lose chicks in their first week of life. An additional 8 pairs reared chicks past the “danger period” of the first two weeks but lost one or both chicks later (and a few more, perhaps, will be lost in the coming weeks). In short, we can no longer breathe a sigh of relief after chicks hatch — or even after they reach 2, 3, or 4 weeks. As a matter of fact, I no longer know at what age we should count chicks as having survived. Mortality of chicks of all ages is much higher now than in the 1990s or early 2000s. Statistically, 31% more young loon chicks (<2 weeks) die now than before, and the death rate of old chicks (>5 weeks) has increased by a staggering 81% in the past 28 years.

After having blithely focused my attention on the territorial behavior of loons for a quarter century, I am now compelled to look at what is causing the sharply higher mortality among chicks and young adults. I feel as though I owe it to the folks who live on the lakes of the Northwoods and imagined that they would always hear the sounds of loon calls echo across the water. And I owe it to the loons themselves.

I sometimes dwell on the negative. In fact, those who know me well no doubt would regard that as an understatement. Strangely, I myself forget that I possess this trait. As a result, I often careen downwards over periods of days or weeks, seeing one after another of the unpleasant aspects of a certain committee I sit on, a basketball team I watch, or a politician whom I hear speak. Eventually though, my negative jag launches me into something unambiguously positive that contradicts all earlier evidence and forces me to pause and reconsider.

So it has been in recent weeks, as I have worked on a team of loon biologists revising the common loon account for Birds of North America. While the long-term, downward trajectory of my study population had me in a funk, talking to and working with these folks (especially David Evers) has given me a broader, more balanced view of how loons are doing along the southern edge of the species range. This has turned me around.

As Dave pointed out to me, the picture of loon breeding in other parts of the U.S. is quite a bit rosier than in northern Wisconsin. While not all of the data are reliable, there seems no question that loons are thriving in Maine, New Hampshire, Vermont, and Massachusetts, having experienced double-digit increases in adult populations in the past decade. These findings contrast sharply with Upper Midwest loon populations, which have shown little or no change. In Minnesota and Michigan, according to our latest measures, populations are merely stable. Wisconsin loon populations, while they increased greatly during the 1980s, 1990s, and even early 2000s, have been measured as stable or declining in recent years.

So the overall picture of loon populations along the southern edge of the breeding range is mixed. But things look so good for the species in New England that, even after considering the slightly negative recent trend from the Upper Midwest, we must conclude that overall the U.S. loon population is doing fairly well.

The uneven geography of loon population patterns raises an important issue. Could the burgeoning New England loon population supply young adults that settle in the Upper Midwest, breed there, and thus rescue our struggling population? No, this cannot happen, because young loons do not disperse far from their natal lakes to breed. A few of the chicks that we have marked in Wisconsin have made it to Michigan, and one or two of these thousands probably has settled in Minnesota (though we have no reports to date), but none has gone farther afield than that. The stability of the Upper Midwest loon population relies solely upon the successful reproduction of Upper Midwest adults. In other words, we are on our own.

Still, the mere fact that loons are reproducing well and expanding their population somewhere is heartening. It suggests that factors causing the decline in the loon population in Wisconsin might be local ones, not sweeping ones, like climate change. Or it might mean that factors that could lead to loon population declines — whatever those factors are — can be reversed by intense local conservation efforts, such as occur in New England states.

At any rate, I am looking at the world a bit more cheerily now, after learning about thriving loon populations in New England. With my tunnel vision always focused more on things loon than things human, there is reason for hope.

I have just finished a rough draft of a manuscript describing the population decline of loons in my study area. That effort forced me to count and calculate, estimate and project. I like math, so the work was not unpleasant. I thought that I would pause and share some of the numbers I produced. First, let me share a complex graph!

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This graph shows two sets of values over an 18-year period. The blue line shows the proportion of all adults in the population that are floaters — that is, adults that lack a territory. This group includes both adults too young to have settled and old adults that have been evicted from a territory. The grey bars show the number of chicks banded in the study area three to four years before, adjusted for the number of territories covered those years. In short, the bars show how good the breeding years were in the study area three to four years before. I plotted things this way because three- and four-year-old loons make up the bulk of the new floaters each year, so by comparing the grey bar to the blue line, you can see what impact the breeding success three to four years ago had on the floating population. We expect that lots of chicks produced three to four years before will produce a surge in floater numbers. So the blue line should track the grey bars.

Okay, now let’s see what we can learn from the graph. Notice, first, that the blue line descends overall. This means that the proportion of the adult population made up of floaters declined during the past 18 years. Notice, next, that the grey bars are roughly the same height throughout the graph, which means that chick production was relatively stable over this interval. Already you should be thinking that something odd is going on. The blue line is NOT tracking the grey bars as closely as we expected. The bars and line DO track each other pretty closely at many points, however. For example, the stable chick production from 2002 to 2006 is paralleled by the stable floater population. 2008 went as we expected: good chick production 3-4 years before meant a positive bounce in the floater population. 2013 saw a loss of floaters, as we expected from low chick numbers 3-4 years before.

Now, focus on the last four years. Floater number had fallen to less than 40% of the adult population by 2015. Huge chick production from 2012 and 2013 should have “rescued” floater numbers in 2016 (caused them to spike upwards), but we only see a small bump up in floater numbers that year. And 2017 is worse as, despite big crops of 3- and 4-year-olds, there is a sharp downward turn in floater numbers! Likewise,  2019 should have seen an uptick, but floater numbers actually declined to an all-time low.

I know it is messy to look at this plot. If you find my fine-scaled analysis too picky, forget about the trees I have been discussing and look at the forest. Chick production during the past 18 years has been okay, yet consistently we see fewer floaters than we expect. This is the main puzzling finding of the paper I have written.

It is the mysterious loss of floaters, in fact, that seems to imperil the population of Oneida County loons. We estimate that there are about half as many floaters now as in the late 1990s and that the entire adult population has fallen by 22%. We do not know what is happening to the missing floaters — whether they are dying in their first fall, on migration, or perhaps during winter. But those floaters, which are  future breeders, will have to stage a comeback to get the population back on track.