mortality

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It is easy to forget that research on the loons of Crow Wing County, Minnesota has been underway for over a decade. To be sure, this work has been spotty. From 2011 to 2014, Kevin Kenow and his USGS team placed geotags on a few dozen adults on four medium-sized lakes in the county. From 2015 through 2017, he shifted his efforts to the Whitefish Chain, where he captured 68 individuals, including 36 territorial adults.

Kevin’s goal was to determine migration and wintering routes of Minnesota loons, which he did after recovering many of the geotags placed on loons’ legs. Although his study was short-term, Kevin’s loons lived on. Each summer and fall they nested and reared young, foraged to build up their reserves for migration, staged on the Great Lakes, and made long overland flights to the Gulf of Mexico. Each spring they molted their feathers and made return trips back to the Whitefish Chain to restart the cycle.

When our Minnesota Loon Project began in 2021, we relocated many of the loons Kevin had banded 4 to 6 years before. We were quite thorough — obsessive, even — in our efforts to do so. At the time I regarded the USGS banding effort as fortunate for us, since it gave us a head start in our efforts to mark all territorial pairs on the Chain.

But Kevin’s marked loons have not merely reduced our loon marking workload. Kevin’s birds are charter members of the Minnesota Loon Project. The survival of these inaugural adults since the years Kevin’s team marked them provides our first multi-year snapshot of adult loon survival in Crow Wing County.

The data provide an unconventional snapshot. When one conducts a mark-recapture study, one normally searches diligently for all marked individuals during the years immediately after marking. This strategy produces data on annual return rate, which provides an estimate of annual survival. But we lack data on return rates from 2018, 2019, and 2020. So we must do the best we can to extract information from Kevin’s birds despite multiple years with missing data.

Fortunately, this is not rocket science. If “r” is the annual rate of return, then r2 is the probability of being on territory two years after banding, r3 is the probability of still being present three years later, and so on. Recognizing this, we can easily project how many of the 36 territorial adults that Kevin banded in 2015, 2016, and 2017 should have still been on territory in 2021. If annual rate of return were 90%, we would have expected to see 20.5 of Kevin’s loons in 2021. At 85%, the expectation is 15.1. If the annual rate of return were 80%, then we should have seen 11.0 loons. In fact, our exhaustive search turned up 13 of Kevin’s loons. So this places our rough estimate of annual loon survival for the Whitefish Chain at 82.5%.

To my knowledge, ours is is the first long-term estimate of adult loon survival from Minnesota based on a marked population. This is rather shocking; loons are well studied in the U.S., have been marked in at least ten states….and are the state bird, for goodness sake! In any event, this preliminary estimate gives us a ballpark figure for adult survival that we can compare with more robust estimates from other states.

A figure of 82.5% for Minnesota survival is lower than we would like. This long-term number based on Kevin’s birds, though, is slightly higher than the separate return rate of 51 Crow Wing County adults we banded in 2021 and looked hard for in 2022: 80%. For comparison, we have robust estimates of survival from a study done 15 years ago that included data from New England (88%; data from 1994-2001) and Wisconsin (87%; data from 1991-2001). We can also compare with longer-term survival rates from our well-known Wisconsin Study Area, which, again, were 86 to 87% for both males and females. In short, early data from the Minnesota Study Area indicate a percentage of adult survival in the low 80s, which is below the rates in the upper 80s we have grown accustomed to seeing in Wisconsin and New England.

The data from Minnesota so far only provide a glimmer about the loon population in Crow Wing County. However, these low survival estimates do bring to mind a worrisome downward trend in loon numbers for the region that can be seen in the 2021 Minnesota Loon Monitoring Report. But, really, it is early days. We need more data. Furthermore, the status of a loon population is not dependent upon adult survival alone. Low adult survival can be offset by a high reproductive rate. So we will have to spend at least two more years tracking return rates of marked loons and measuring breeding success before we can pull them together into a model that will tell us (preliminarily) how Crow Wing loons are doing. Still, if I am being honest, I wish the survival numbers were a bit higher.

Thanks to Katy Dahl, who photographed the Cross Lake-Arrowhead Point loon pair after we banded them in 2021. The male in the foreground with his bands out of water was spotted a few days ago just north of Minneapolis.

If, like us, you are concerned about the persistence of loons in Minnesota, consider a donation to support our field efforts. We run a lean program. Funds donated to the Loon Project do not pay overhead, administrative costs, or salaries for staff or senior personnel. They pay only field costs like: 1) stipends to keep student field workers alive, 2) travel costs to, from, and within our study areas, and 3) supply costs such as for colored leg bands and canoe paddles. Thanks!

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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.

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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.)

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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!

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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.

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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.

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He was the biggest, healthiest juvenile we caught in Minnesota last year. The Rush Lake-Northeast chick was so independent on July 16th, when we first attempted to catch the family, that we could not relocate him after capturing and banding his parents. We shrugged, returned the following night, and had better luck. At 2900 grams, “Copper-White”, as he became after banding, was 300 grams heavier than the second-heaviest chick we caught last summer and almost certainly a male.

Considering the risky environment inhabited by juvenile loons, it is a mistake, I have found, to become attached to them. So, with the exception of the “Miracle Chick” — a juvenile on Squash Lake in 2012 that lost his father at three weeks, watched his mother quickly re-pair with a new male, but still got enough food and attention to fledge — we have tried to avoid this practice. Still, Copper-White became lodged in my mind. I had great hopes for him. If any juvenile had a chance to fledge, migrate, and come back in a few years as an adult, it was Copper-White.

Large size and good body condition, it seems, are not enough to protect a loon in his first few months of life. Last Friday, the National Loon Center got a report of a loon hemmed in by ice on on Cross Lake. They raced out to check the bird, and Mike Pluimer snapped the photo above.

It was alarming enough to hear of a loon still on the breeding grounds in mid-December. By this time, loons from the Minnesota population should have arrived in Florida and begun adjusting to a saltwater diet. Our hearts sank a bit further to see the bird’s plight. Resting in a tiny pool of open water surrounded by encroaching ice, this juvenile was clearly in dire straits. Why had he failed to migrate south with others of his species? Something must have gone horribly wrong.

Following heroic efforts on the part of the Crosslake Fire Department, Copper-White was caught and transported to Wild and Free Rehab Center in Garrison. Terri and Richard, who live on Rush Lake and watched the chick grow from its earliest days, reported that the captured bird was strangely docile — another worrisome sign.

Arrow points out where Copper-White’s right wing was sheared off at the metacarpal bone by a boat propeller. (Photo courtesy of Wild and Free Rehab, Garrison, MN.)

It took little time for Katie, the vet at Wild and Free, to diagnose Copper-White’s problem. The end of the loon’s right wing had been sliced off some time ago by a boat propeller, rendering him incapable of flight. Unlike many hawks and owls, loons’ size and need for open water make them impossible to keep alive in captivity. The only option was to euthanize this bird.

Alas, I have no cheerful anecdote to cushion the blow. We are disheartened to lose a healthy, strapping juvenile loon to a boat strike. But boat strikes that injure loons are a fact of life in the Upper Midwest. We lost a healthy adult male even more tragically two years ago in Wisconsin. The only comfort here is that boat strikes occur infrequently enough in the Upper Midwest that they do not contribute meaningfully to loon mortality. At the moment, that is cold comfort.

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Science, of course, is cumulative. Solving scientific riddles generally requires multiple studies by diverse authors using a broad range of scientific techniques. In fact, scientific conclusions are more compelling when they rest upon findings from many scientists using different techniques and with different backgrounds.

So I was quite anxious to learn what Kevin Kenow had found. Kevin, a scientist with the U.S. Geological Survey and also a member of the Scientific Loon Council at the National Loon Center, has studied common loons for about as long as I have. But while I have focused on the behavioral ecology of loons exclusively and established two fixed study populations for this purpose, Kevin has collected data on many species of migratory water birds, tackled questions related to human impacts and conservation, and worked across a variety of states and waterbodies in the Upper Midwest and beyond.

Kevin’s just-published article pulled together data from loons in Michigan, Wisconsin, and Minnesota. In contrast to my low-tech methods, Kevin’s team used satellite transmitters and geolocator tags to either: 1) track loons’ migratory movements in real time or 2) reconstruct their movements, following recovery of the geotags.

Kevin’s team confirmed several migratory pathways that we had known about or suspected through recoveries of dead birds. First, adult loons from the three Upper Midwest states typically “stage” on Lake Michigan in the late summer and early fall, before departing southwards to the Florida Gulf Coast. Second, juvenile loons (those only a few months of age) do not visit the Great Lakes prior to migrating south. Third, first- and second-year loons that are too young to return to the breeding grounds instead migrate northwards in the Atlantic, summering off of the Canadian Maritime provinces. The quirky patterns in loon migration and wintering behavior are important. They make it clear that a loon’s survival to the breeding stage requires that it survive and remain healthy across a period of many months, a variety of water bodies, and a number of geographic areas.

But one of the patterns that Kevin’s team identified loomed above the rest. They found a high rate of mortality among first- and second-year loons, especially in the spring. If you are following this blog and have an excellent memory, you recall that this finding appears to dove-tail with a recent one of ours. We found that “floaters” — the segment of adult loons that are two to five years old and are looking for breeding territories — have been disappearing at a high rate. Floaters alone, you might recall, account for most of the decline we have detected in the Wisconsin breeding population.

Do Kevin’s findings of high first- and second-year loon mortality solve the riddle of what is ailing the loon floater population in Wisconsin? Unfortunately not. In fact, we had long suspected that young adults would die at a higher rate than older adults, because they are less experienced. High mortality among young adults is a common feature of avian populations everywhere. But these new findings might help narrow down the “period of vulnerability” in the life history of loons. And our findings of high young adult mortality in the last decade combined with those of Kevin’s team might tell us where to look. Perhaps conditions along the Florida Gulf Coast and/or the Atlantic have deteriorated recently, causing higher than normal mortality during this trying time of life for young loons. This is only one hypothesis, and it will require rigorous testing. Thanks to Kevin’s team’s cool recent findings, though, the wheels of science are turning.

By the way, follow us on Instagram, if you like, at @loonproject. The whole LP team works together to post cool, informative “loonstagrams”!

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As my family and friends will tell you, I am judgmental. When an event happens that could be attributed to mindless error, I am inclined to view it, instead, as deliberate selfishness or irresponsibility. I derive my hypercritical worldview in part from my profession. As a behavioral ecologist, I presume that much of the behavior we see in animals (including humans) has evolved in order to promote their evolutionary fitness. Put another way, I assume that a good deal of animal behavior is selfish — evolved because it allowed the ancestors of living individuals to survive better and leave more offspring than others of their species.

The presumption of selfishness is a helpful touchstone in my field. It provides a starting point when one is interpreting a new and unexpected behavior pattern. For example, if I notice a new soft call emitted by female loons during courtship, I am apt to hypothesize that this call might help mates synchronize their breeding activities so that each will be prepared to do its share of the incubation duties, once eggs are laid. (Such synchronization, which involves rising prolactin levels in the blood, has proved crucial to successful breeding in many species of birds.) So the presumption of selfishness can  be a useful prism through which to understand animal behavior.

A week ago, the folks at REGI learned of an event that pushed even my cynical viewpoint to the limit. Following a report from a lake resident, they found an injured loon on Metonga Lake, which is just south of Crandon, Wisconsin. After Linda and Kevin Grenzer captured the loon (pictured in Linda ‘s photo above) and the REGI team examined and x-rayed it, they learned that it had been shot at close range with a shotgun and had lead shot throughout its body. Despite efforts to save the unfortunate shooting victim, it died in their care. The story might have ended there, except that the loon was banded.

Since Metonga is outside of our study area — some 20 miles east of our southeasternmost lake — we do not know the lake at all. Sleuthing by Linda and me revealed that this oval 2000-acre waterbody supported two breeding pairs in 2018. According to the loon ranger, both pairs hatched chicks this year, although only one of the pairs fledged their two hatchlings. Most important, neither pair contained a banded individual. Thus, the shooting victim was not a member of either resident pair.

Some of the circumstances surrounding the tragic shooting make sense. As many of you know, breeding loon pairs become restless in September and October, often leaving their territorial lakes. Moreover, large, clear lakes like Metonga are favorite spots for wandering adults to visit, as they forage intensively and lay down fat stores to fuel their southward migration. So it is not at all surprising that a breeding adult from a neighboring lake — as we presume the victim was — would be found on Metonga. Finally, virtually all of the loons that we band that show up that far from our study area are females, because females are the more dispersive sex. (On average, females settle 24 miles from their natal lake, while males settle 7 miles from their birthplace.)

The identity of the shooting victim allows us to speculate about its tragic end. When I looked up the band colors and partially-obscured USGS band number that Linda provided, I learned that we had banded this female nine years ago as a chick on Bear Lake in Oneida County. We have not seen her since. The father and mother of this female were among the most approachable loons in the study area. (The male still holds the territory there, as he has since 2001 or earlier.) As Chapman student Mina Ibrahim showed a year ago, tameness (the minimum distance that a resting loon will permit a canoe to approach before diving) is similar between parents and offspring. So it is almost certain that the dead female was a tame individual, like both of her parents.

If our simple inference is correct, then this incident has exposed one hazard of extreme tameness in loons. While the vast majority of humans who approach loons closely are merely curious and would never dream of harming them, an occasional human might do so. It is easy to reconstruct the chain of events that led to the shooting. In the opening week of duck season, a hunter got an easy shot at a duck-like diving bird and took full advantage.

This analysis might well be correct, but it has one hitch. Loons are so well-known across the heart of their breeding range that they can scarcely be confused with ducks. None of the species of ducks that a hunter in northern Wisconsin would be looking to bag is patterned much like a loon. Furthermore, all duck species in the area are far smaller than loons and are prone to fly, not dive, when approached by humans. And since we know that the hunter blasted this loon from very close range, it is even more difficult to believe that the incident arose from a misidentification.

Call me cynical, but I believe that the hunter who killed this loon was not foolhardy, as generous and forgiving people might believe, but rather purposely wicked. Of course, this conclusion further erodes my opinion of other humans. What kind of person deliberately shoots a loon?