As I mentioned a few posts ago, the Loon Project is expanding into Minnesota, the state that contains more breeding loons than any other. Of course, our plan to establish a second study area 200 miles west of the current one in Wisconsin is ambitious. So I have enlisted the help of five LP veterans to help us cover our sprawling study area. These sturdy souls include Gabby and Linda, who are keeping track of our Wisconsin birds until the bulk of the team members arrive in a week, and Kristin, who, joined by new team member Katy, is taking our first look at the Minnesota study population. All of these folks have really stepped up for the Project.

Early-season work is both arduous and exciting. Arduous because we have so many loon pairs to visit. Arduous because these now hundreds of pairs must be visited one at a time and each pair member observed until we are confident we know its identity. But also exciting because we have not seen these birds since the previous summer, if at all. During the fall, winter, and spring periods, many of our loons have died or been evicted by younger rivals. And many of these young upstarts are birds we banded as chicks five to ten years ago on adjacent lakes.

Minnesota is a whole different ballgame. When we decided to take on the task of starting a new study population on the lakes in and around Crosslake, we knew that we were making a pledge to cover brand new lakes whose loons were abundant but little known. We also understood that, unlike our breeding pairs in Wisconsin, most of the Minnesota loons defended territories on the massive Whitefish Chain, where our protocol of dropping solo canoes in at boat landings and paddling to the birds was unworkable. In short, we were pledging to take on a new study population that required a completely different mode of research.

I couldn’t wait to get started. Though tethered to my instructional responsibilities in California, I gazed at these unknown Minnesota lakes on Google Earth and felt my excitement build. I collected what information I could about the lakes and loons from folks in the area. I studied maps of loon activity and banding logs provided by Kevin Kenow of USGS, who captured and marked a few dozen birds on the Chain five to six years ago and generously shared his knowledge and data. And I scratched my head.

Since I was out of commission, I needed to find someone with great knowledge of loons and a willingness to confront the daunting challenge of making our first visit to the Chain. I told Kristin that I needed her to: 1) visit an unknown study area, 2) census dozens of unknown pairs, most of which would be unmarked, 3) travel by large motorboat on an unfamiliar lake with tricky wave and wind conditions, 4) work out all of the logistics of this work with a group of unfamiliar (but enthusiastic) Minnesotans, and 5) get permission from her advisor to suspend her Ph.D. preparation and take on the project at all. I am not sure how I managed to ask her with a straight face. Predictably, though, Kristin’s response was: “Oh – that would be a blast!”. And so Kristin has begun this crucial reconnaissance. Joined

Kristin and Katy study a map of the Chain before setting out to find loons.
One of the ten nests found by Kristin and Katy on the Whitefish Chain.

by Katy, a new LP team member who is fluent in the local dialect and has turned out to be a quick study, Kristin has now covered all but a few nooks and crannies of the Chain. As of this writing, K and K have found 45 breeding pairs on the Chain and ten active nests, like the one shown above. Most of the pairs are unmarked, but they report 14 of Kevin’s banded adults are still on territory. (These marked individuals will be most valuable, as they will permit us to make preliminary estimates of territory eviction and survival for the new study population.) K and K will wrap up their coverage of the big water today, they say, and spend the next few days visiting small lakes adjacent to Whitefish. These small

Katy attempting to ID a loon.

lake visits will no doubt bring a tear to Kristin’s eye, as they will recall the work she used to do back in the Wisconsin study area.

By starting before sunrise, Kristin and Katy made the most of windless conditions.

Kristin and Katy’s effort to establish a foundation for our Minnesota work epitomizes the work of the Loon Project. We pride ourselves in carrying out research that is uncomfortable and physically-demanding, yet also exacting and painstaking. We tackle research questions that most others deem inaccessible. The work just seems too difficult, our study animals too recalcitrant. How can one accumulate sufficient data to test hypotheses about animal behavior and ecology under these conditions?

One of the 14 banded loons found on the Chain.

I was on pins and needles. Gabby had moved steadily northward and westward in her censusing of our study lakes. She started in Rhinelander. This from her datasheet Thursday:


  1. O/Ts, W/S (O & left leg double confirmed)
  2. Unb, Unb (both legs double confirmed)


  1. P/S, G/G (P & left leg double confirmed)
  2. Unb, Unb (both legs double confirmed)


  1. Ronly, Bs/S (both legs double confirmed)
  2. Unb, Unb (almost positive it’s unbanded – never saw its legs out of water, but had many chances to see bands in good light underwater if there were any present)
  3. Intruder = Y/Y, Bs/S (both legs double confirmed). Interacted with pair for 10 minutes.

No loons


  1. M/S, W/B (both legs double confirmed)
  2. Bs/M, Mb/S (right leg and Mb double confirmed)

At the rate she was covering lakes, I gauged that Gabby would get to Upper Kaubashine on the 3rd, 4th, or 5th. I almost asked her to jump ahead to Upper Kaubashine, but I did not want to kill her momentum. But it was hard to wait and see whether the oldest known loon in Wisconsin, thirty-three-year-old “Red-Green”, had returned to her breeding territory.

When Gabby’s report came, it was not what I had expected:

Upper Kaubashine
Sooo the good news is I found the male (Cc&S, G/G – all confirmed) and that old female (S/Y, R/G – all confirmed). The bad news is the old female may have met the end of her tenure and potentially her demise at the hands (wings??) of an Unb, Unb (confirmed) intruder who was on the lake interacting with the pair when I arrived. I witnessed a VICIOUS 12 minute battle between the female and the UNB where they were latched onto each other’s throats and beating each other with their wings (both were covered in blood) for about 8 minutes, until the old female started fleeing underwater. But the UNB was relentless and pursued her, beating her the whole way. Then the old female finally made it to little islet and looked like she was trying to find a place to go on shore, but ended up being trapped against the islet while the UNB continued to stab her with her beak and beat her. The old female finally gave out a two note wail and then the UNB finally stopped and left to go preen elsewhere. I thought the old female could be dead already, but when I left her at the shoreline she was still turning her head. I hope she can hide long enough to recover to get off the lake, but the way she was being attacked, it did not look good.

Although we have studied them for decades and know their behavior well, we find it freshly shocking to watch loons battle. The brawl that Gabby describes was more violent than any of the few dozen or so that I have seen over the years. Despite the whipping of wings and jabbing of bills that these fights entail, one almost never sees blood. However, what began as a stereotypical head-grasping and wing-beating contest, she reports, quickly morphed into an all-out struggle for survival — once resident Red-Green recognized that she was overmatched and her goal changed to self-preservation.

Physical features of a lake can play a role in territorial battles. In fact, a lake’s shape, size, clarity, and peninsulas and islands often determine whether a fleeing bird eludes its victorious opponent and flies off to a nearby lake to lick its wounds or fails to do so, suffers repeated pummeling, and ultimately dies on the lake it used to own. After the Upper Kaubashine battle, the clarity of the lake water made it simpler for Red-Green’s pursuer to track her underwater, complicating her efforts to reach safety. Thoroughly defeated but unable to elude her opponent, Red-Green was ultimately pinned against the long peninsula near the southern end of the lake, as Gabby describes.

We have no idea how Red-Green managed to escape the unbanded female’s grasp. What we do know, thanks to Linda’s visit to Upper Kaubashine today, is that, despite her dire circumstances two days ago, Red-Green is still alive. Linda was relieved to find her hugging the shoreline — as her photo shows — and skulking about under piers at the north end, while the male and his new mate cavorted far to the southwest in the protected nesting bay. Though clearly beaten up, Red-Green seems safe for the time being. Indeed, maybe she will emulate thirty-one year-old White-Yellow, a long-time breeder on West Horsehead. Evicted in 2019 after breeding on one lake for a quarter century, White-Yellow resurfaced this spring as the new breeding female on productive Little Bearskin Lake. In their tireless efforts to cope with defeat, bounce back, and resume productive lives, Red-Green and White-Yellow exemplify the dogged tenacity of female loons.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Inevitably the news comes in the form of an excited text message from Linda. This year it came on March 30: “Yippee! Clune is back”. “Clune”, a tame 23-year-old territorial male on Muskellunge Lake, got his name as a result of an autocorrect/typing error of mine a decade or so ago. He has been one of our most successful male breeders, having fledged 17 chicks on two different territories with at least four different females since 2003. Last year he gave us a scare when he showed up a week after ice-out and had to drive the neighboring male from Deer Lake off of Muskellunge in order to reclaim it for himself. This year Clune left no doubt: he arrived as soon as the water opened up on Muskellunge. He is alone at the moment. This is not unusual; males commonly arrive on the breeding grounds a few days ahead of females. Linda says that he spent some of his alone time giving soft-wails, as if calling for his missing mate. “Honey”, as Linda calls Clune’s equally-accomplished breeding partner, should be along shortly.

Clune is not the only loon back in the study area. I have reports of loons back on two more lakes that are completely or partially open. In short, it is early April and already the loons are returning to their breeding territories. Since I am in the midst of an extremely busy spring semester of instruction, and am two-thirds of a continent away, I can only sigh and try to remain patient. I am trying to stay positive. After all, I am only six weeks — nine quizzes, two midterms, a scientific report, two final exams, and fifty-four office hours — away from joining the loons!

Fortunately, others are stepping up in my absence. We have a large and seasoned team that will help me learn which of our banded loons have returned. Gabby will be sneaking away from her graduate work at Illinois to cover the Wisconsin study area in early May, and Kristin will dodge her major professors in Madison for a week and zip over to Crosslake, Minnesota to begin covering our brand new population on the Whitefish Chain. Three other veterans are returning from last year: Brian, a postdoc at Chapman, and Martha and Allison (my daughter). Brian will be on site in Wisconsin for most of the summer. Martha and Allison will scout lakes and help with capture in Crosslake in July.

Crosslake??? Minnesota??? That’s right! One of my responsibilities as the new National Loon Center Scientist will be to roughly double the number of breeding loon pairs under intensive study in the Upper Midwest by starting an investigation in the state that supports as many breeding loons as the remaining 47 contiguous United States combined. Our new Minnesota population, centered at what will be the National Loon Center headquarters in Crosslake, should equal the Wisconsin population in number of marked pairs under study by 2025.

Why a second study population? Our worrisome population data from Wisconsin has made it clear that we need better data across the southern fringe of the common loon’s breeding range. This will allow us to determine, for example, if the dip in the northern Wisconsin population is a local phenomenon or part of a broader pattern of decline. Strangely there are no long-term demographic data in Minnesota that permit us to construct a population model. So we simply do not know how healthy the Minnesota population is. As a worrywart, I am concerned that Minnesota’s loons might be in trouble, like those in Wisconsin. After all, Minnesota is right next door and the loons there face a similar set of environmental challenges. We shall see!

In the meantime, keep me in mind. And let me know if you see any interesting loon behaviors or any loons in trouble. I shall be mired in paperwork for the time being and connected to the loons only by Linda’s striking photos – like the one above of Clune from a few days ago — and reports I receive from folks on the lakes.

We are gearing up for another year of field work. This one is going to be a doozy, because we will be adding a new study population. That’s right, we are expanding west into Minnesota and beginning a partnership with the National Loon Center in Crosslake, Minnesota. Once we complete our capture and marking of the loons in northern Wisconsin, we will head west to mark dozens more in and around Crosslake. I will say more on this topic in the coming weeks.

Meanwhile, we face a familiar obstacle: limited housing. We have our usual Wisconsin team of 5 to 6 members this summer, and nowhere to put them between July 1st and August 10th. How did this happen? First, our funding came in later than usual. Second, we were about to close on a deal for a cottage to cover the entire period, and the owners suddenly changed their minds. So please let us know if you know of a place somewhere in the Rhinelander – Minocqua area where we might stay. We can afford to pay a reasonable rent as well.

Meanwhile, meet Katy, one of our new field interns this year. It is fitting to include Katy in this post, because she, like our new study population, is from Minnesota! In fact, she will be traveling with veteran Kristin to Crosslake in early May to help locate loon pairs that will be part of the new Minnesota study population!

We have had an exciting last few weeks. First, our paper on population decline in northern Wisconsin has been the most frequently read paper in Condor: Ornithological Applications every single day during the past three weeks. Of course, I jinxed it, and when I looked just now I found that we have fallen and are only the second-most read paper! In any event, we seem to be getting the word out about problems that loons are facing in the Upper Midwest.

Second, Brian Hoover’s paper that describes and explains lake preferences of juvenile loons — those that have just fledged and become independent of their parents — has just come out. Brian’s paper shows that juveniles tend to visit lakes that have similar pH to their natal lakes and also that they use large lakes with a variety of fish species present. In other words, if we are to preserve the Upper Midwest loon population, we must look out not only for lakes where loons nest but also those lakes nearby where juveniles fatten themselves up to prepare for migration.

Third, our collaboration with Sarah Saunders of Audubon has borne fruit; Sarah’s paper has just been accepted by Journal of Animal Ecology and should appear as an accepted article in the next week or two. Her model, which combined measures of land use, climate, and our study population, indicates that the North Atlantic Oscillation — a fluctuating climatic pattern that is projected to increase under climate change — is having a net negative impact on both adult loon survival and chick production in northern Wisconsin. The pattern is complex, but it dovetails logically with the population trends we have seen in northern Wisconsin. The simplest interpretation of her findings is that the North Atlantic Oscillation affects food levels on the loons’ wintering grounds, which, in turn, impact survival and subsequent chick production. Sarah also found that increased human development reduced adult loon survival. Most alarmingly, Sarah’s simulations of the next decade all project decline for the northern Wisconsin population, just as our Condor paper did. So, we must look for more ways to boost loon breeding success and adult survival on the breeding grounds in an effort to counter what is a most worrisome trend.

Sarah’s findings place new urgency on my efforts to understand all 12 months that constitute a year in a loon’s life. Most recently, I have batch-plotted recoveries of loons banded in northern Wisconsin that covered distances of more than about 200 miles. As you can see from the featured image above, we have a lot of these data. (You might have to click on the title in the e-mail to see the map.) Leaving aside the small number of interesting shifts westward and northward, the photo confirms the wintering pattern that I mentioned in a recent post. Our Upper Midwest loons winter in large numbers along both coasts of Florida — especially the Gulf Coast. About a quarter of our loons, however, winter off of the Carolinas, especially North Carolina. Concerned as I am with the increased rate of mortality among adults in recent years, I cannot help thinking that hazards along these coastlines are creating trouble for them. Clearly while I can use the fall, winter, and early spring to rest and recover after intense field work during May, June, July and August, my study animals do not have that luxury.

No, I am not talking about the Buccaneers. Kansas City and Tampa are both far from anywhere I have spent meaningful time. Besides, KC won last year, and Tom Brady has won countless times. Enough already!

I am talking about Tampa Bay the place — the large, protected inlet halfway down the west coast of the Florida peninsula. Loon enthusiasts should love Tampa Bay because it serves as the wintering grounds for a good many loons from the Upper Midwest. In fact, so far 33 of 53 recoveries of loons banded by the Loon Project and others in the Upper Midwest — sadly, these are mostly loons found dead on the beach or elsewhere and reported to the Bird Banding Lab in Maryland — have come from Florida’s Gulf Coast, between Pensacola and the Keys. By chance, or more likely just because it is an area of dense population, a good percentage of these birds come from the Tampa Bay area.

This is not a brand new finding. Kevin Kenow of USGS has used satellite transmitters to track loons from Minnesota, Wisconsin, and Michigan and reached the conclusion that Florida’s Gulf Coast is a vital wintering area for our birds. He puts the percentage of Upper Midwest loons that winter there at above 70%. So we have two separate lines of evidence that tell the same story about the wintering location of Upper Midwest loons. Well, okay, you must be thinking, our loons have to winter somewhere. Why does it matter where exactly? It matters because, while we only see them in the summer and tend to focus only on their trials and tribulations during summer, our loons must also survive on their southward migration, sustain themselves on the wintering grounds, and then make it through another northward migratory journey in order to get back to us each year. Of the period during which it is out of our sight, a typical loon from our area spends four to five months on Florida’s Gulf Coast.

When you learn where breeding animals are spending their winters, conditions on the wintering ground suddenly get very real. During the past two decades, ecologists have improved in the ability to track individual animals (usually birds) from breeding to wintering locations, using such tools as satellite transmitters and geolocators. They have also learned that migratory trips do not somehow “reset” an individual so that all individuals that have migrated to the breeding ground start on equal footing. Instead, a difficult (or easy) migration or wintering period leaves a lasting imprint on an animal, placing it at a disadvantage (or giving it an advantage) during the next phase of its life history. Such impacts are called “carryover effects” and have become hot topics for investigation. Surges or declines in breeding populations, we now see, can be as easily explained by events on the wintering grounds as those during the breeding season.

We are at an early stage in our analysis of breeding season impacts on wintering loons and vice-versa. In fact, we know nothing about carryover effects in loons. But now that we are zeroing in on wintering locations of loons from different breeding populations, the stage is set to look for such patterns. At the moment, I have set my sights on a less lofty goal. You might recall my post in June 2020, when I pointed out how many adult loons had failed to return to Wisconsin in spring of 2020 after leaving in fall 2019. The simplest explanation for this very low return rate of Wisconsin breeding adults is that some event occurred during the winter of 2019-2020 along the Florida Gulf Coast that killed many loons there. More broadly, I have begun to explore data that Florida wildlife officials collect annually on red tides and other environmental events that threaten ocean-dwelling animals. Could fluctuations in annual survival rates of loons in Wisconsin be explained by mortality events recorded along the Florida Gulf Coast?