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.

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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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.