We all love loons. So naturally we should take any step we can to help them. Right? In that light, artificial nesting platforms (ANPs), or loon rafts, would seem to be a no-brainer. Platforms make it easier for loon pairs to produce chicks.

ANPs fit neatly within the framework of loon conservation. Accepted enthusiastically by most loon pairs, they would seem to provide a perfect, low-cost solution to increase loon populations. They are easy to construct; a person with a modicum of carpentry experience can find plans online and build a platform in a day or less. So platforms provide a simple method by which a single loon enthusiast can improve the breeding success of a pair of loons for many years. Across the loon breeding range, platforms have become a panacea for bolstering reproductive success.

But are nesting platforms all that we need them to be? Now that loon populations appear to be in trouble in Wisconsin and perhaps even in Ontario — and now that some of the causes of declines are beginning to come into focus — maybe it is time for us to step back for a moment. Maybe we should ask whether platforms address the actual problems that loon populations face. To state it technically, can platforms mitigate the specific negative factors hurting loon populations and make populations viable in the long term?

We first need to recognize that platforms address a single, very narrow problem faced by loons. Loon pairs must sit on their eggs — in an exposed location — for 28 days. If a mammalian predator wanders by during that month, the nest is lost. Platforms solve this problem beautifully. They increase the rate of hatching by about 70%. But increasing of hatching success is all platforms do. Platforms put more small chicks in the water — a pleasing outcome for folks that deploy them — but they do nothing to help those chicks reach fledging age. They do not feed chicks; they do not protect chicks from predators. They do not boost adult loon survival. They have no effect on the rate of boat strikes or angling casualties or lead poisonings of adults and chicks. In short, if loon populations suffer declines owing to reduced hatching success, then nesting platforms are just what the doctor ordered. If declines are caused by anything else, then platforms would appear ill-suited to the task.

What do we know at this point about the status of loon breeding populations and factors that might threaten them? Precious little, I am afraid, especially if we are speaking of the entire species range. But we have begun to identify specific threats to loon populations in the Upper Midwest.

At present, the four most significant hazards to loons in northern Wisconsin appear to be: 1) larger populations of Simulium annulus, a black fly that targets incubating loons and causes massive abandonments of loon nests in May and early June, 2) decreased water clarity during the chick-rearing period, which increases chick mortality, 3) increased deaths of adult loons and chicks from ingestion of lead sinkers and jigs, and 4) a mysterious die-off of young adults in recent years that has caused the population of future breeders to plummet. Black fly numbers are highly dependent upon rainfall during the previous year, we have recently learned. More rain means more flies. Increased June and July rainfall also reduces water clarity during the month of July. Both increased black flies and decreased water clarity have become much more severe in the past few decades, probably as a consequence of increased rainfall from climate change. Lead poisoning is known to be a big problem for loons in New England; animal rehabbers in the Upper Midwest feel that lead poisoning has increased in frequency there in recent years. The severity of lead poisoning, of course, should depend upon how much angling occurs and the extent to which anglers switch out their lead tackle for alternatives that are not deadly to wildlife. Finally, we have measured a clear and sharp increase in young adult mortality in our study population in northern Wisconsin. We have no idea, at present, what its cause might be.

How well does the use of nesting platforms to boost hatching success of loons map onto the quadruple threat of increased black flies, decreased water clarity, lead poisoning, and spiking mortality of young adults? With respect to black flies, platforms might mitigate the problem somewhat. Platform-nesting loons suffer abandonments just as severely as do loons nesting at natural sites, but the increased hatching success of second nests on platforms offsets the hit to hatching success caused by black fly-induced abandonments of first nests. Platforms, of course, have no impact on the decreased growth rate and increased mortality of loon chicks owing to declining water clarity and the resultant difficulty of feeding chicks. Likewise, platforms cannot affect the incidence of lead poisoning in an area. And platforms cannot possibly save young adult loons from whatever has caused them to die at such an alarming rate in recent years.

On the whole, then, floating nest platforms do not appear to address effectively the threats faced by loon breeding populations (to the extent that Wisconsin represents loon populations generally).

While that quick analysis might seem reasonable, I have ignored one crucial fact about loon nesting habitat and platforms. Platforms often provide loons with an opportunity to breed in lakes or parts of lakes where they otherwise could not because of the absence or poor quality of nesting habitat. In other words, platforms actually create new nesting habitat. If the new nesting habitat that platforms make available contains enough food that parents can fledge the chicks they hatch there, platforms might provide “bonus chicks” that give the loon population a boost. *

Of course, platforms are so enticing to loons that they must be deployed thoughtfully. A platform placed on a very small lake might lure a pair of loons to use it but result in starvation of the chick(s) because of food limitation. Since a pair lured into such a tragic situation might otherwise have nested and reared chicks successfully elsewhere, such misuse of nesting platforms exacts a cost on the breeding success of the population. (Loon conservationists recognize the pitfalls of using nesting platforms thoughtlessly and only deploy them where they are likely to do more harm than good.)

While loon platforms seem effective at boosting loon populations in some respects but appear ineffective or even harmful in other respects, what conclusion can we reach? Lacking hard data, we can only speculate. However, it is probably safe to conclude that judicious use of nesting platforms in lakes or parts of lakes that lack good nesting habitat adds enough “bonus fledglings” to the population to make platforms an effective conservation tool. Indeed, with the list of threats to loon populations growing, we might soon face a situation where we are casting about for new loon habitats with plenty of food but nowhere to nest — so that we can rely upon platforms to place a good many more chicks in the water.


* Population ecologists will recognize a potential flaw in my reasoning. Even if platforms result in a huge increase in fledged chicks in a population, density-dependent mortality during winter or migration (e.g. owing to food shortage) might wipe out all of these extra individuals. In that case, platforms would not be an effective conservation tool. In fact, increased adult mortality from a variety of causes could produce population decline even in the event of huge “bonus” chick production via platforms.

I am never prepared for chick loss. As a scientist, I know that the first several weeks of life are fraught with danger for loon chicks. Have they developed normally? Can they thermoregulate properly? Are they able to dodge eagles, muskies, and snapping turtles that can devour them when small? Are their parents aggressive and vigilant enough to keep intruders at bay, which might otherwise kill them with a few well-placed jabs? Is there sufficient food in their natal lake to sustain them and support their rapid growth? And these are merely the natural threats to chick survival.

As hazardous to chicks as natural dangers, or perhaps more so, are threats that humans pose. Sometimes these are direct impacts; humans drive their boats rapidly and often strike chicks, which cannot elude them as deftly as adults. Anglers’ lures and baits, recognized as unnatural and avoided by most adult loons, are sometimes gobbled up uncritically by chicks, which are just learning what they can and cannot eat and must gorge themselves in order to grow. The hooks — and especially lead jigs and sinkers that they ingest at such times — pose a grave risk to the youngsters. A more insidious and dire threat that we have seen recently is the decline in water clarity in northern Wisconsin in the past decade, which makes it difficult for chicks and parents to find food and likely explains much of the reproductive decline we have seen there. (We will soon determine whether water clarity is declining in loon lakes in Minnesota as well.)

Although I am acutely aware of the increasing dangers that loon chicks face, I struggle to adjust to the steady drip drip of chick mortality in Wisconsin and Minnesota. When the Rush-USA Point pair lost their chick, I reasoned, “Well, that territory gets high boat traffic; it is hard to keep a chick alive there.” I justified the loss of the Cross-National Loon Center chick and the two chicks hatched by the Rush-Hen pair in the same way. I was a bit numbed by the time I considered the loss of the two young chicks of the Eagle-East pair.

I find it easier to stomach brood reduction. When broods decrease from two chicks to one, I take solace in the survival of the remaining chick. So it went at Upper Whitefish-Steamboat, Ossie-Island, and Sand this year. Very often brood reduction of this kind comes about because food is limiting; the death of the smaller chick actually gives the larger chick a fighting chance to make it.

What stings the most is loss of chicks that have reached four weeks of age. In the past few days, two chicks that had attained this milestone perished in the Minnesota Study Area. (The NLC is awaiting necropsies on both individuals.) Quick inspection of the Lower Hay-Southeast chick that lost its life and washed ashore earlier this week showed what appeared to be traumatic injury on the back, suggestive of a propeller strike. When you consider that the Lower Hay-SE territory is right next to a major public boat landing, this likely cause makes sense. The second deceased chick, from Clear Lake, was 32% lower in mass than its sibling; thus it was falling far behind in acquiring food from its parents. So this looks like classic brood reduction. Indeed, Kate Marthens, one of our Minnesota field team, reported that this chick was not keeping up with its family on the day that it was found dead, an indication that brood reduction was imminent.

The significant increase in mortality of loon chicks of all ages (i.e. both younger and older than five weeks of age) is a hallmark of the current population decline in Wisconsin. I should be learning to cope with it — preparing myself to face it in Minnesota too, if our growing sample there reveals the same trend. But that is more easily said than done. It still hurts like the devil to lose a chick.


Featured photo — One of our largest chicks in Wisconsin is that on Little Bearskin Lake. It was alive and kicking as of this writing! (Molly Bustos, a Wisconsin intern, holds the bird.)

Yesterday, I heard the cheerful, buzzy calls of Japanese White-eyes* flitting about in the trees in my backyard. They are handsome and engaging little birds, but they don’t belong in southern California. They never lived here before humans did. As recently as ten years ago, white-eyes were quite difficult to find in the area.

A few weeks ago my wife, son, daughter, and I visited my ailing mother in Houston. On our first morning there, we were awakened by the incessant cooing of White-winged Doves*. They too are a striking species. The flashy white stripes on their wings and tails set them apart from the more familiar and homely Mourning Doves. Even the ceaseless calling of White-wings is rather pleasant. Don’t trust me on this; the abundant murmurings of this species inspired Stevie Nicks to write an entire song about them. But White-winged Doves have not always lived in the Houston area. I remember scouring trees around the Galveston County Courthouse in vain for this species with my mentor, Fred Collins, on a Christmas bird count a half century ago.**

Of course, while new species colonize new regions; well-established residents also vanish. In the Upper Midwest, the Piping Plover, a cute little shorebird, has recently become severely threatened. Though I have never seen a Piping Plover in all my years in Wisconsin and Minnesota, I do have experience with a second threatened species, the Black Tern. These agile fliers flit about marshy areas, plucking insect larvae and small vertebrates from the water and vegetation. They are appealing birds — with jet-black bodies that contrast tastefully with greyish wings and tail. But it is a longshot to find them in the Upper Midwest nowadays. What seemed a healthy breeding colony fifteen years ago on Wind Pudding Lake in northern Wisconsin — where we have always had a breeding loon pair — has disappeared altogether. It has been so many years since I last saw Black Terns on Wind Pudding that I have stopped looking for them there.

In short, my years as a bird-watcher have taught me that populations of birds change dramatically over time. Some species magically appear in new places, and other species disappear. I suppose it is my first-hand experience with the dynamics of avian populations that infuses my current research on loon populations in Wisconsin and Minnesota with such urgency. This is why I sweat the black fly season in May and June, worry about boat strikes and lead poisoning, and am in a bit of a panic over the recent loss of water clarity in the region. I have now seen — as I had not in 1993 when my loon work began — that birds can disappear.


* Photos by Natthaphat Chotjuckdikul and Ted Bradford from eBird.

** In fact, the picture is a bit complicated in the case of this species. White-winged doves occurred commonly in the southwestern U.S. 100 years ago, but the population was devastated by the expansion of the citrus industry. However, in the past three decades, the species has begun to nest in citrus trees and has come roaring back.

It is often said of field biologists that we resemble our study animals. I guess it is true. No, I am not aquatic. Nor do I subsist on a diet of fish, crustaceans, insect larvae, and the occasional mollusk. I did not even engage in a dangerous battle to secure my mate and territory. But, like loons, I enjoy being alone.

One of the joys of my profession is the time that I spend alone in a canoe, watching loons and taking in the beauty and simplicity of their lives. When your world is distilled down to watching the sky for other loons and bald eagles, chasing fish under water, and preening from time to time to take care of your feathers, life seems pretty straightforward. During those moments when I am with loons, their few concerns are all that matters. At such times, the headaches of keeping a major research project afloat, supporting a young field staff, repairing or replacing broken equipment, publishing scientific papers, and sharing engaging stories, photos, and video via social media vanish.

Loons would seem to gain even more than I do from avoiding crowds, especially at this moment. As a migratory species that winters along oceanic coasts, summers on northern lakes, and uses a variety of lakes and rivers in between, common loons appear at great risk from the current outbreak of highly pathogenic avian influenza. After all, waterfowl like ducks and geese, which share these waterbodies with loons, are known to be important hosts for the virus. Yet to date, loons seem to have avoided the epidemic of HPAI that has decimated other aquatic birds in the United Kingdom and eastern North America. How have loons dodged this juggernaut? Mostly by breeding solitarily, instead of gathering in dense breeding colonies on oceanic islands, where the virus spreads quickly via saliva, respiratory droplets, and feces.

Loons’ ability to avoid massive mortality events from HPAI is welcome news. After all, they already have had to contend this year with a late ice-out that has delayed their reproductive efforts and a higher-than-usual population of Simulium annulus, the black fly that singlehandedly makes May a miserable month. Yet some pairs have remained steadfast. At long last this week, several breeding pairs in Minnesota and Wisconsin Study Areas have hatched chicks, like the ones in the photo above from Ossawinnamakee Lake (photo by Keith Kellen). Maybe things are beginning to turn around!

Each spring I feel my adrenaline level rise as we carry out the annual census of returning loons. This practice seems mundane, at first glance. During the census, we simply visit all loon territories and identify each territorial loon we find from its colored leg bands. But since I have gotten to know many of my study animals quite well, I wait with bated breath to learn whether Clune (the famously tame male on Linda Grenzer’s lake, whom I have known since he was a chick) comes back. I feel almost as strongly about Clune’s son, who settled 6 km away, on tiny Virgin Lake. I even have a soft spot for the comically skittish female on Silverbass Lake. She routinely appears down at one end of this long skinny lake, seems to wait for us to paddle in her direction from the other end, and then races by us underwater and reappears at the end of the lake we just vacated. She is so notoriously hard to approach that her very skittishness has become a useful identifying trait. In Minnesota, I was anxious to see whether the young male of unknown identity on Lower Whitefish — who nested rather recklessly on a water-logged artificial nesting platform exposed to the powerful west wind and waves — would return from the winter and try that move again or learn from his mistake and seek a more protected location. (I am happy to report that all four of these loons are back this year.)

Apart from the relief or dejection we feel when we spot our familiar study animals — or don’t — loons’ tendency to return provides critical scientific information. A tally of the proportion of all adult breeders that returned from the wintering grounds in the spring tells us about survival between late summer of the previous year and early spring of the current one. Of course, territorial eviction muddies the water. That is, a loon can either fail to return to its previous territory because it is dead or because a competitor has driven it off of its territory and forced it to move elsewhere. So we must be cautious in interpreting return rates. Still, they provide us with a crude metric of survival.

Let’s look at return rates throughout the study. What is clear from a quick inspection of the graph below is that loons in the Wisconsin Study Area have fluctuated in their tendency to return, coming back at a rate of over 90% in great years and just above 70% in dismal ones. (Minnesota study loons returning in 2022 also fell within this window, as the graph shows.)

Perhaps the most striking pattern is the lack of concordance between return rates of each sex. In other words, knowing that it is a bad year for male survival tells us nothing about female survival. True, there are some years in which male and female survival seem to go hand in hand — look at 2005-2009, for example. But male and female rates seem to run in opposite directions between 2010 and 2017. Overall, there is no statistical tendency for male survival to be correlated with female survival.

We can draw an important — though tentative — conclusion from the fact that male and female survival do not vary in concert. Major loon mortality events outside of the breeding season do not seem to drive annual loon survival strongly. If major die-offs during the non-breeding period (i.e. winter and migration) were a major cause of loon mortality, then male and female numbers should be correlated, because the sexes use similar migratory routes and winter quarters and should suffer in parallel each year.

The most interesting and potentially worrisome pattern we could spot in the annual return rate data would be a decline in survival of either males or females. As you can see from the color-coded dotted lines, female return rate has actually shown a slight rise over the past 29 years. On the other hand, male return rate has declined slightly, though not significantly, during this period. Still, since we already know that males are struggling to maintain optimal body mass in the Upper Midwest, it is disconcerting to see male survival decrease in a way that seems consistent with the mass loss.

Of course, while making the rounds of territorial pairs, we also notice if a territory is vacant or occupied by a lone adult after having supported a breeding pair the previous year. And therein lies a bit more troubling news. Ten of 118 Wisconsin territories that were occupied in 2021 are now vacant or inhabited by loners. We have also recorded two new territories in lakes not used for breeding last year, so the net loss in territories is only eight. Still, this was not the picture we wished to see in a population that has been on a downturn. (Though we are only learning about the Minnesota Study Population, it appears that only one territory among seventy or so that we have visited so far fell into disuse this year after having been occupied last year.)

Let’s put aside worrisome population patterns and turn to news of the moment. It is early June in the North. This is a time of great hope for loons. A few breeding pairs in our Minnesota and Wisconsin study areas — like the Lower Hay pair in the photo — were fortunate enough to dodge both black flies and raccoons and are on the brink of hatching young. Many more have rebounded from early setbacks and renested. If we are lucky, we still have the potential for a good crop of chicks in both regions. Lacking any more effectual means of bringing this about, I will keep my fingers crossed.

What if we had an early warning system in loons that could alert us to population decline, like the proverbial canary in a coalmine?

Male loons might serve as such an early warning system. That is, careful monitoring of the health of male loons might provide a good indication of the health of the loon population as a whole. How is this possible? Because the more we study the breeding ecology of loons, the more stark differences we find between the sexes. And — more to the point — male loons have some chinks in their armor that females do not.

Most fundamentally, males are 25% larger than females. Greater size places greater energetic demands on males. Males are living “closer to the edge” than females and might often fail to acquire enough food during the season to maintain good body condition. Thus, a decrease in the quality or quantity of food — which could set in motion a population decline — should strike males first and hardest. Indeed, as the graph below shows, the average mass of male loons has declined in northern Wisconsin over the past 30 years in a way that suggests they are having more time finding food now than they used to. (Note that females have not declined in mass during the same period.) The obvious conclusion: something in Wisconsin lakes has changed in the past three decades that has impaired males’ ability to feed themselves.

Average masses of male and female loons in northern Wisconsin, 1991 to 2021. Male mass has declined significantly during this period, while female mass is unchanged.

Long before I discovered that male masses were in decline, I had begun to worry about male loons. You see, male loons live shorter lives than females. This means that there are simply fewer adult males around. In fact, the majority of non-territorial adults (“floaters”) in the loon population are females. Since males are in short supply, the loss of an adult male breeder on a lake or territory sometimes leads to that territory becoming vacant. In fact, in 23 of 24 well-documented instances where an adult breeder’s death was associated with a territory vacancy, the dead breeder was a male. Vacant territories are, of course, a harbinger of overall population decline.

Sadly, recreational fishing does not help the situation. Possibly because males’ greater size makes them a bit more desperate to feed themselves, male loons are twice as likely as females to be hooked by anglers or become entangled in fishing line. This pattern is well-documented in New England loons, but the same scenario plays out in the Upper Midwest. Specifically, of 47 known fishing entanglements among our study animals, 33 involved males, and only 14 involved females. Angling mortality, then, exacerbates what is already a female-skewed sex ratio owing to early male senescence.

It is difficult to predict the future, but I think you can see why I am concerned. Male loons appear to be in trouble. We cannot say for certain whether mass loss by male loons will cease or continue. Furthermore, we have no evidence to date that the 4% net loss in mass by males since 1991 has negatively affected their survival. So it is too early to panic about these patterns. But it is also hard not to feel like a miner glancing anxiously at his lethargic canary.

I have said a number of times that we do not know how the Minnesota loon population is doing. That blanket statement is misleading. In fact, two well-organized efforts to gather data on Minnesota loons — both run by the DNR and staffed by armies of citizen scientists — have been under way for decades. These massive efforts have given us glimmers of information about the status of loons in the state that I will summarize here.

The Minnesota Loon Monitoring Program

Begun in 1994, the Minnesota Loon Monitoring Program relies upon volunteers to count loons within six regions in the state and produces a summary report every five years. A second project, the Volunteer LoonWatcher Survey, also run by the DNR, began in 1979. Since the MLMP aligns closely with one important goal of our Minnesota work — assessing the status of the Minnesota loon population — I will limit my comments to that survey.

Loon density (number of loons per 100 acres of lake), according to the Minnesota Loon Monitoring Program. (From 2020 report by Krista Larson; Minnesota DNR. Reproduced with permission.)

What Do the MLMP Data Show?

Of course, using volunteers — some without boats and binoculars — to measure loon numbers increases uncertainty in measurement. But despite inevitable fluctuations in measurements from individual regions and years, the MLMP survey seems to be an effective tool for estimating loon populations. So it is reasonable to look at MLMP data and expect to see meaningful patterns.

One of the first patterns you notice in the MLMP survey data is the noise within it. The true density of loons on lakes within each region of Minnesota should not vary much from one year to the next, because loons are long-lived and reproduce at a low rate. Yet the MLMP data show huge fluctuations in loon density from year to year, especially in Itasca, Otter Tail, and Becker Counties. That substantial scatter in the data is important, because it makes interpretation difficult.

Second, despite the noise, it is clear that the density of loons varies greatly between regions. The DNR’s analysis shows only one loon per 100 acres of lake in Kandiyohi County (southwestern part of the state) but three or more loons per 100 acres in Itasca County (northern part). The four other surveyed regions — Becker, Otter Tail, Aitken/Crow Wing, and Cook/Lake — have loon densities that fall between these two extremes. Differences in density across the state are significant, because they help us identify regions of particular importance to a species. With apologies to loon lovers in southern Minnesota, if loons are three times as dense in Itasca County as in Kandiyohi, then Itasca is a much higher conservation priority. (This sort of “triage” perspective is the bread and butter of conservation biology.)

Third, population trends — the aspects of the survey in which we are most interested — are dimly visible within the data, despite year-to-year scatter. According to the DNR analysis, two regions — Cook/Lake and Itasca — have seen small declines in loon density since 1994; one — Otter Tail — has seen a small increase; and the other three regions have experienced no significant change. These conclusions highlight one difficulty we face in assessing the MLMP results. If there are two bits of bad news and one bit of good, what do we conclude about Minnesota’s loon population as a whole?

According to the DNR summary, “MLMP results suggest that Minnesota’s loon population remains stable with an average of 2 loons per 100 acres of lake across all six Index Areas.” It would be pleasing to conclude, as this statement does, that: 1) there is one statewide population pattern and 2) that this overarching pattern could be encapsulated so simply. But the DNR’s summary seems to gloss over some worrisome trends in the data.

What Do the Data Show for the Past Ten Years?

In light of the brevity of the DNR’s summary, it seems worthwhile to take a deeper dive into the MLMP. One oddity of the 2020 DNR report is that it uses 1994 to anchor the trend line. Why 1994? Simply because this was the inaugural year of data collection. But we are most interested in the trend over the past decade, because that gives us a better sense of what is happening now. Over the past ten years, Crow Wing/Aitken and Itasca regions both appear to have suffered sharp declines in loon density; Cook/Lake has declined slightly; and Becker and Otter Tail regions have been more or less stable. Only Kandiyohi County provides good news, as it appears to have greatly increased in loon density in the past decade. But since loon density in Kandiyohi remains far below that in Crow Wing/Aitken and Itasca, the good news from Kandiyohi does not even begin to offset the disappointing findings from Crow Wing/Aitken and Itasca.

What is the Real Take-Home about Minnesota Loons?

We cannot reach any firm conclusion about the status of Minnesota loons based on the Minnesota Loon Monitoring Report. There is simply too much scatter in the data for that. However, careful inspection of recent findings reveals worrisome downward trends in two vital loon population hubs. I take these troubling signs seriously. With support from the National Loon Center in Crosslake, I am accelerating my effort (begun in 2021) to establish a large marked study population in one of these two hubs — Crow Wing County. In the next few years, we will produce estimates of adult survival, reproductive success, and other demographic parameters to construct a new population model for the region. Our fine-grained analysis will indicate whether the downward trend suggested by the MLMP data is real and sustained or whether those of us who wish to conserve loons in Minnesota can breathe a great, collective sigh of relief.

As we motored around the Whitefish Chain in late May, the thought crossed my mind. As I looked over Katy and Jordana’s field notes from Minnesota in June, it occurred to me again. And by the time we banded five tightly-packed loon pairs on Ossawinnamakee Lake in a single night in July, I had become utterly convinced: there are more loons per lake, on average, in our new Minnesota study area than in our long-time study area in northern Wisconsin.

Of course, it is one thing to have a gut feeling that a natural pattern is out there and quite another to demonstrate that the pattern is real. Indeed, having enough self-discipline to wait and test a hypothesis instead of blurting it out and selling it as fact is what separates science from…..well, something less than science.

So I examined our data from both study areas. If there are more breeding loons per acre of lake in Minnesota, the difference should be evident from a statistical analysis. I looked at all lakes between 165 and 740 acres in both study areas for which we have reliable data, divided lake area by number of breeding pairs, and ran a test. The result: In our Wisconsin study area, a loon pair’s average territory size is 282 acres, while in Minnesota an average pair occupies a territory of only 180 acres. This is a highly “significant” statistical difference, which means that the huge disparity seems to represent a real pattern, not just a chance result.

What does it mean? Having done the easy part — finding a difference — we are now faced with the thorny task of explaining it. Innumerable hypotheses leap to mind. (1) The slightly different climate of central Minnesota might support a denser breeding population than the northern Wisconsin climate. (2) Lake chemistry might be more favorable in Minnesota and thus explain the difference in density. (3) Minnesotans are somewhat more apt to put out artificial nesting platforms for loons (21 of 105 territories; 20%) than are Wisconsinites (23 of 216; 11%), which might support more loon pairs. (4) Predators might be more abundant in Wisconsin and/or food scarcer. (5) Minnesota lakes might be more convoluted in shape and thus contain more natural boundaries that allow coexistence of more loon pairs on the same area of water. (However, a quick glance at lake shapes suggests the opposite — that our Minnesota lakes are more round.) (6) Human harassment of loons might be more intense in Wisconsin. (I have not noticed any such pattern, however.) In short, we have lots of questions and no answers, at present!

Now, it is important to take a step back. We have under active investigation only about 10% of all Wisconsin loons. In this beginning phase of Minnesota research, we have only 1.4% of all Minnesota loons in our study. (The nice loon photo by Katy Dahl above shows only one of about 14,000 loons in the North Star State.) So our two study areas — especially the one in Minnesota — capture only a snapshot of a small subsample of each population. The overall statewide loon densities might be quite different. Still, the two study populations are similar in numerous ways, including latitude, degree of human lake usage, and deep affection of almost all lake residents for the species. The ability of Minnesota loons to live “shoulder-to-shoulder” tells us something profound, I think, if we can only ferret it out.

In a recent post, I described how the popularity of loons and the willingness of many folks to pontificate about them without solid data or thoughtful scientific analysis makes loons unique. I tried to point out that this practice can be harmful, if we make misleading statements about loon conservation at a time when some loon populations are declining.

Now, let me give an example. Millions of state and federal dollars have been spent in recent decades in attempting to measure the effect of methylmercury (the toxic form of mercury) on wild animals, especially birds. Without a doubt, more funds have been spent analyzing mercury impacts on loons than on any other aspect of loon biology. What have we learned from this body of work? The major take-homes are that: 1) mercury certainly can affect behavior and survival of adult loons and chicks if it occurs in a high enough concentration in their tissues, 2) high mercury levels tend to occur mainly in loons living on small, acidic lakes, which have negative effects on loons that have nothing to do with mercury, and 3) harmful concentrations of mercury do not occur in most geographic areas within the breeding range. In short, despite an abundance of research and the expenditure of millions of research dollars across three decades, we have no direct evidence that mercury negatively impacts loon populations. In fact, the consensus among loon scientists is that mercury probably has little or no negative impact on most populations.

The situation is dramatically different with lead. Careful analysis of loon carcasses in New England has shown us that lead is quite deadly and affects a great many loons. (The featured photo above shows a deadly lead sinker in the stomach of a loon that died a few days ago in Wisconsin. Photo by Wild Instincts.) In a 2017 study, Grade et al. determined that a whopping 48.6% of the loons they examined had been killed by lead sinkers and lures. The authors estimated that this mortality rate had reduced the New Hampshire loon population by 43%.

The contrast between mercury and lead is stark. Mercury might affect loon survival and breeding success slightly in a few isolated populations. Lead has been shown to cause half of all loon deaths in one state and to make an enormous dent in the loon population of that state.

The contrast between these two toxins goes further. Mercury exposure is pushed to high levels mainly through burning of fossil fuels like coal and oil, which contain mercury. So reducing loons’ exposure to mercury requires a long-term effort to reduce burning of fossil fuels over a large geographic area. In contrast, loons are exposed to lead through our use of lead sinkers and fishing lures. The remedy for lead-related loon deaths is simply to implement use of lead-free fishing tackle in lakes where loons breed. (Steel, tin, and tungsten are common alternatives). Indeed, lead bans are now in place across New England.

Here is the problem. Despite the lack of evidence that mercury affects loons in nature, mercury has become the “go-to” environmental toxin mentioned by many loon researchers. Mercury has become such a prevalent scapegoat in grants, reports, and even published papers that many of us are not keeping its limited impact on loons in proper perspective. A clear-headed, candid, objective review by a loon researcher with a strong background in mercury toxicity would do wonders for loon conservation. At a time when studies have just reported long-term declines in two loon populations, those of us trying to conserve loons would do well to focus our attention on the real enemy.