The pattern is stark. As you can see from the graph below, loon pairs using artificial nesting platforms have produced a much higher rate of fledged chicks in the Wisconsin Study Area than in the Minnesota Study Area. The pattern was especially dramatic in 2021, when Wisconsin platform pairs reared twice as many chicks per platform as Minnesota pairs. But to compare study areas on the basis of a single year is unwise. Moreover, 2021 was a dreadful year for black flies in north-central Minnesota; most Minnesota nests started in May of last year were abandoned because of the blood-sucking pests. The current year provides a better comparison because flies were not severe in either state. Yet even when we carry out this “apples to apples” comparison by looking only at 2022 data, Wisconsin platforms look far more productive than their Minnesota counterparts. How can this be?

Let’s be very clear on one point. Lake residents in both Minnesota and Wisconsin are moving heaven and earth to help loons. Indeed, folks in both states who float platforms for loons commonly shift them from a first spot to a second and even a third, if doing so keeps nests safe from mammalian egg predators, eagles, waves, and curious humans. It makes no sense to suppose that Wisconsinites are better or more committed platform monitors than Minnesotans.

How then might we explain this curious cross-state disparity in platform success? Perhaps the difference can be attributed to lake size. Since more of the platforms that we study in Minnesota are found on large lakes, the lower rate of fledged chick production from platforms in Minnesota might simply result from higher wind and boat exposure on large lakes, not any state-to-state difference. Lake size, however, cannot explain better platform outcomes in Wisconsin. As the graph below illustrates, the proportion of hatched chicks that actually survives to fledging age is higher in Wisconsin both on large and small lakes. Furthermore, survival of hatchlings is, in general, a bit higher on large than small lakes. So having more large lakes in a sample should increase fledging success, not decrease it.

The new graph does shed some light on the platform pattern. Chicks seem to fledge better in Wisconsin at least in part because more hatched chicks make it to adult size. That is, part of the reason for greater fledging success at Wisconsin platform nests is high chick survival, not necessarily high nest survival.

Could it be that platforms are somewhat overused in Minnesota? In the past two years, 67 of 141 Minnesota nests (48%) but only 43 of 195 Wisconsin nests (22%) have been placed on platforms. Maybe in their zeal to support the state bird, some Minnesotans have lured loons to nest on lakes or parts of lakes that are unsuitable for rearing chicks. At present, this is only one speculative hypothesis to explain the rather low fledged chick production of Minnesota platforms. But it is certainly worthy of investigation. *

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Featured photo by Woody Hagge

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*I must quickly note that most platforms in Minnesota seem well-placed. Some clearly provide loons an opportunity to nest in locations that lack nesting habitat but where food is plentiful. Such locations are perfect for platforms and must help the loon population produce more chicks than it would otherwise.

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.

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.

On May 27th, the Little Pine-Dream Island pair was in dire straits. Hounded by black flies, they could not stand to incubate their eggs for more than a few seconds. At the time of our visit, the female foraged a hundred meters north of the nest, having been relieved of incubation duties for the time being. It was the male’s turn to cover the eggs. We watched helplessly as he mounted the nest, settled on the eggs for a few seconds, and then retreated back into the lake, his nape thoroughly inflamed with bites of flies that still savaged him.

Yet even the short dives he made after leaving the nest did not help. Whether it was because the flies’ mouthparts were inserted too securely into his flesh or their six legs grasped too firmly to his feathers, the male failed to dislodge his tormentors as we looked on.

We did not linger on the ill-named Dream Island territory. Although both pair members are exceptionally tame, we did not wish to be an additional distraction to them during their struggles. As soon as we had freed our prop from a stubborn underwater snag, we departed.

Plagued by boat problems and poor weather, it was a full five weeks before we were able to return to the Dream Island territory. Kate and Emily were thrilled to locate the pair with two healthy 10-day-old chicks bobbing about in the light chop of Little Pine. Evidently this sweet pair had the toughness and determination to achieve an outcome that, five weeks ago, seemed a dream indeed.

Video by Katherine Marthens.

The beginning of the tale is heart-rending. A gosling is orphaned before hatching. A loon pair fails to hatch chicks of their own and, seeking to fill the void, sits on eggs they find near their nest. When these two desperate parties converge into a single — if nontraditional — family, they produce a heart-warming story*.

To see two species coexist despite 90 million years of evolutionary time spent apart is surprising. To see them not merely tolerate each other but become thoroughly interdependent, as parent and offspring, is truly striking. Such an improbable scenario makes one hopeful. This story suggests that differences between groups — even vast ones such as between geese and loons — can be overcome.

On the other hand, the sight of a gosling nestled comfortably on a loon’s back is also strange. It is a reminder — like exploding black fly populations, loss of water clarity, devastating storms, and the sudden abundance of wake boats — that the loon’s world has changed.

*Thanks to photographer Brad Thompson, who shared his beautiful photo.

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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!

One of the pleasing sights of spring in the Northwoods is that of a territorial pair of loons, foraging side by side. No doubt the myth of lifetime fidelity of loons to their mates arises, at least in part, from the tight association of female and male loons at this time. Their apparent devotion to each other, their compulsion to remain together at all times, the touching plaintive wails that keep them in contact when they chance to become separated for a brief period all recall young human couples with limitless possibilities before them.

During the past three weeks in Minnesota and Wisconsin, I have seen many loon pairs foraging, resting, and preening together. It is truly heart-warming — to a degree. You see, once the territory resettlement period — the first three weeks after ice-out, roughly — has come to a close, loon pairs should be nesting, which means that humans watching out for “their loon pair” should see only one pair member or the other on the water.

Egg-laying marks the start of the nerve-wracking 28-day period of incubation where innumerable things could go wrong. A raccoon could wander by; an eagle could flush the incubating bird and feast on the eggs; a sudden downpour could turn a nest that seemed safely above water level into egg soup, cooling the eggs and killing the embryos. But one single cause of incubation failure has emerged as the single greatest threat to loon breeding success in Wisconsin and Minnesota in the past decade. The agent, a single species of black fly with a peculiar taste for loon blood, has recently surpassed even egg predation by raccoons and their ilk as a cause of nesting failure. When hundreds of black flies surround incubating loons and bite them mercilessly on the head and nape, the agony can become too awful to bear, causing the pair to abandon the nest. In recent years, black fly survival and persistence dictate how productive an entire loon population will be. It is that simple.

Yesterday, five of us — four members of the loon research team and a reporter for Minnesota Public Radio — ventured out onto the Whitefish Chain to mop up the few territorial pairs that we had not yet been able to visit this year. The trip was memorable for more than loons. An unexpectedly stiff west wind turned Middle Whitefish into a seething Lake Superior, forcing us to beach our motorboat prematurely at Boyd Lodge. (It took four Blizzards at DQ in Crosslake to help us move on after that hair-raising experience!)

Despite sketchy conditions, we visited nine new territorial pairs. We were thrilled when Kate spotted an incubating loon in a protected cove of Pig Lake. But that was the only territorial pair we scouted that was sitting on eggs. All others behaved as if the ice had just come off: they preened, rested, and foraged side by side. What would have been a cheerful sight in mid-May causes consternation now. Sixty to seventy percent of all pairs should be incubating eggs at this point in the season. Sadly, the featured image from Sibley-South depicts the situation in many of these lakes at present: two perfect golden-brown eggs — and loons nowhere nearby.

There was no good reason for the Crystal female to defend her nest. I had confirmed the colored leg bands on her mate, and he was no longer the male with whom she had mated and laid eggs on the platform. Instead, he was the neighboring male from Halfmoon, who had left there under mysterious circumstances. Lake residents had reported a “ruckus” early this morning, and that ruckus had turned the 14-year-old male who had been her steady partner for 5+ years (lake residents had nicknamed him “Walter” — not after me but after the largemouth bass in “On Golden Pond”, which features loons) from an expectant father into a displaced, childless nonbreeder. Walter’s eviction meant that any ongoing reproductive attempt was over, as evicting males and females have no interest in incubating eggs or feeding young that are not their own. Yet the Crystal female — lake residents named her “Katherine” because of Katherine Hepburn in “On Golden Pond” — felt an inescapable attraction to the nest. As I approached to inspect the four defunct eggs on the platform, Katherine showed classic nest defense, swimming twice under my canoe. The evicting male from Halfmoon preened indifferently 100 meters away, as if willing to indulge his new mate’s obsession with her past nest but hoping she would get over it soon.

I witnessed a related behavior pattern on Swanson Lake just yesterday. There a mammalian predator (probably a raccoon, according to a camera study conducted some years ago by the Wisconsin DNR) had taken the two eggs that the Swanson lake female had laid in a second nest on the west end of the lake to replace those abandoned during the black fly period (see photo). When I arrived at first light, the female was alone, wailing intermittently, as loons do when their partner is not present. Forty minutes after I arrived, the male flew in, and he swam purposefully over to the newly-failed nest and climbed onto it. For three minutes he sat contentedly on the nest, as if all was good in the world. Then, he stood up on his legs and reached his bill downwards to turn the eggs, as loons habitually do. He seemed to put two and two together when he found no eggs to turn; afterwards, he sat only a few moments more before climbing down off of the empty nest and joining his mate in the water.

Despite 28 years of observation, I had never witnessed loon behavior that reflected slowness or inability to adjust to a new, stark reality — or perhaps I had simply not seen such behavior twice in so short a time, which made it impossible to ignore. As humans, of course, we have all behaved in such a way. That is, we have forgotten for a moment that some abrupt, fundamental change has occurred in our lives and mistakenly acted as we had before the change. Over a longer timescale, I find myself behaving so now. On each visit I make to a study lake in mid-June I expect to see young loon chicks or a pair late in the four-week incubation stage and on the brink of a hatch. But like the Crystal female and Swanson male, I find myself slow to adapt to a new reality — almost universal abandonment of first nests, many pairs without chicks or nests, and a great big dent in the breeding success of the population.

What has been most striking about the dozens of loon territories we have visited in the past week has been how similar they seem to be to loon territories in early May. At that time of year, pairs have mostly recovered from the energetic stress of migration and have shifted their focus to breeding. With ice gone from the lake surface and perhaps a territorial challenger or two repelled, breeding pairs can search for a nest site, build a nest, lay eggs, and — if lucky enough to have a safe nest site or to avoid attracting egg predators to a risky one — jointly incubate them for four weeks until hatching.

Though the ice is long gone and challengers long since defeated, most loon pairs (over 90%, by our preliminary estimate) now face the same long slog of incubation they encountered a month ago. Having had their first nesting effort obliterated by black flies, these pairs now must start over from scratch. Thus, the video below depicts a common sight: a pair that has chosen a new nest site, started to lay eggs, and must work together to hatch chicks. These two birds, a 7 year-old male from Hasbrook Lake (background) and a 10 year-old female from Day Lake in Vilas County, seemed to contemplate this task with a degree of circumspection.

As nasty and harmful as black flies are, they are not as bad as egg predators. Flies are only really abundant for three weeks or so, whereas egg predators are always present. Loons behave as if they understand the time-limited threat that black flies pose. How? They commonly reuse nest sites that contain eggs from an attempt ruined by black flies, whereas they almost never reuse nest sites in the wake of egg predation by a raccoon or another predator. (Our recent paper describes this logical response to black fly abandonments.) Sometimes a males’ love of a nest site is so strong that he chooses it even though it still contains two eggs from the previous nesting attempt. In such cases, a loon nest contains two viable eggs from the renesting attempt and two duds from the abandoned effort weeks earlier (see the photo at the top, from Little Bearskin Lake this year). We often wonder how the sitting birds manage to cover and warm the eggs such that the good ones hatch.

In short, there is a new round of nests in the Northwoods of Wisconsin. During the past several days, as we have found pair after pair laying a second round of eggs and forging ahead in the hopes of raising chicks, it has raised my spirits. We will never look back at 2020 as a banner year for chick production, but the loons are not giving up.