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I am a nervous traveller. The day before I am scheduled to leave, I start to worry what could go wrong. Could I miss my flight? What personal items will I forget to pack? Which tasks on my to-do list will I leave unfinished?

So it was two days ago as I drove from the house where I had been staying to meet up with my Minnesota field team before flying home to California. I had spent the morning collecting data on territorial loon pairs — six on Ossawinnamakee, and one each on Fawn and Pig Lake. I relish every moment spent with loons, especially when I am on my own. But anxiety about getting my field work done, entering my data, and tidying up the place before my departure gnawed at me all day.

I tried to work backwards. Arrive at Brainerd Airport at 5:15, so leave from storage box at 4:30. Be at storage box by 4:00 to pack up canoes and check banding supplies for next month. Arrive at tech’s lodging by 2:30 to review field procedures and check in before my trip. Finish entering data in online database by 1:30. Tidy up lodging by 1pm. Leave my last study lake by noon.

When I set off to visit my techs on Ossie, I was still on schedule. As I began to round the hairpin curve on County Road 39 next to the Ossie boat landing, I thought: I just might make my flight. In a brain-staggering moment, though, I spotted an adult loon sitting on the shoulder on the east side of the highway displaying a clear intention to cross. “Oh no!”, I screamed, as I pulled to the side of the road and flicked on my emergency flashers. I ran across the highway and placed myself in the middle of the northbound lane, intending to block any traffic from passing close to the loon. As I crept cautiously toward this adult, I noticed two newly-hatched chicks huddling against it, trying to shield themselves from my view. “Oh no!”, I repeated.

Despite my shock at the loons’ predicament, I understood immediately what was happening. Six hours earlier Keith and Dawn Kellen had given me a tour of the six breeding pairs on Ossie. The Ossie-Muskie Bay pair had stumped us all spring. The Kellens had seen them together early in the year, had seen only one out on the water on multiple occasions thereafter, and yet neither they in their pontoon nor my team in our canoe could find a nest in the far east bay of the lake, adjacent to County 39. The pair had simply vanished. The sudden appearance of an adult and two small chicks told me that they had not nested on Ossie, where we had been looking for them, but on Rat Lake,

Location on County Road 39 where I found the adult male and two small chicks.

across the highway from Ossie’s eastern end. Thus, the Muskie Bay pair was in the awkward situation of seeking to nest on one lake and raise their chicks on another. That ambitious plan set them up for a difficult land crossing.

I had stumbled upon the loon family at the most dangerous point of their overland journey. The adult wailed and tremoloed as I stood in the highway 30 feet away. A southbound car and truck slowed down to rubberneck but continued by despite my frantic waving for help. My mind raced. I could not handle all three loons. If I picked up the adult, its flailing might injure the tiny chicks. Furthermore, the chicks might decide to strike out on their own across the road without their parent to guard them. I was not sure that I could discourage them from putting themselves in harm’s way while holding the adult.

Knowing that the field techs were a few minutes away, I pulled out my phone. “Call Owen”, I demanded of Siri. Owen answered in his calm baritone. But I screeched, “Drop everything and come to the Ossie boat landing. There is a loon here in the road, and I need your help!”. “On my way”, he responded.

While I waited for Owen, more southbound vehicles came by, each carrying a driver wearing a puzzled expression. But no one stopped. As I was debating the odds of getting help from a stranger, the panicked adult abruptly turned, lined himself up with the roadway, and began to run down the highway with wings flapping, leaving his chicks with me. I watched and listened in horror as his feet repeatedly thwacked against the hard pavement during this takeoff attempt and was relieved when he aborted it and skidded to a stop about 40 yards away in the southbound lane.

At that desperate moment, Mitch Carlson arrived in his pickup with his friend, Leo, and stopped in front of the grounded adult. Sensing that the window to save the loon family was closing, I scooped up the tiny chicks and marched hastily in Mitch’s direction (see photo below). He opened his door and looked at me questioningly. “Can you take the chicks?” I asked. “Okay”, he replied quickly, sensing my urgency and smoothly accepting them. He volunteered, “My wife raises chickens!”. I turned my attention to the adult in the road.

After his aborted takeoff attempt, the male loon sits in the southbound lane of County 39 while I approach carrying his chicks. Photo by Mindy Schenck.

Quick, decisive action yields the best results when capturing animals, I have found. When I drew close enough, I lunged at the rearing adult and managed to grasp it. I then folded its wings against its body, held it to my side, and did my best to fend off its bill. Meanwhile, Owen had arrived. I struggled towards the boat landing with him guiding me. Mitch followed with the chicks, while Leo walked alongside, gawking and snapping photos.

The chicks were so small that I was afraid the adult might leave them behind in its haste to put distance between us and himself after release. So I asked Mitch to let the chicks go, waited a moment, and gently

Mitch holds the two newly-hatched chicks moments before we release them at the Ossie boat landing. Photo by Leo Carner.

lowered the adult — which felt like a male based on size and ornery demeanor — into the water at the end of the boat landing. Fortunately, he dove, surfaced quickly, spotted the chicks, and promptly resumed his parenting responsibilities. It was an ample reward for Mitch and me to see them all together so quickly again in the middle of the lake.

The male and chicks reunited quickly after we let them go off of the Ossie boat landing. Photo by Leo Carner.

I will always be a nervous traveler. I do not think one outgrows that. And I need to put a schedule together to convince myself that I can meet a deadline. But perhaps on my next trip I will remember to include 30 minutes of wiggle room for unforeseen events.

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We face many difficulties in studying loons. They are aquatic. They dive and resurface far away when we approach them. They are gone for half the year. We can capture and mark adults only during a brief window when chicks are small. We cannot keep them in captivity, which limits what we can learn about their biology. Finally, loons are long-lived, so it requires decades to understand their life histories fully.

Back in 1993, when I informed her that I was about to begin a loon study, my postdoctoral advisor at Indiana University made a face. “Are you sure?”, she said. She was well aware of the difficulty of studying species like whales, eagles, tigers, and loons. These are beautiful, charismatic animals. But they are challenging to learn about scientifically. Was it wise for me, a young untenured academic, to embark upon a long-term investigation of a notoriously recalcitrant species?

No, it was not wise. But wisdom does not always guide our decisions. I felt drawn to loons. I also believed that the training I had received at Indiana, at Purdue, and especially from Haven Wiley, my PhD advisor at the University of North Carolina, had equipped me to ask rigorous, meaningful questions about the behavior of any animal.

When I first began my work in 1993, I recognized immediately that my greatest obstacle was going to be telling loons apart. This problem is familiar to behavioral ecologists. I had confronted it myself when studying wintering white-throated sparrows in North Carolina in the 1980s. But treadle traps allowed Haven and me to band hundreds of white-throats and recapture them at will. Moreover, we could see the bands on sparrows’ legs at all times.

Not so for loons. In most cases, we cannot identify an individual when it is resting on the water. Even when we have nailed the bands on both members of a breeding pair, we must reidentify each bird when it dives and resurfaces. (Every so often a loon has an oddity in its plumage or on its bill that sets it apart from other adults.)

Loons themselves must be far better at identifying others of their species than humans are. After all, if humans lose track of which loon is which during an observation session, we curse and make a few erasures on our datasheet. But a loon that mistakes an intruder for its mate might pay for the error with its life.

So it was with more than casual interest that Anna Alber and I entered the second phase of our analysis of loon appearance by computer. Could a computer learn to tell a large sample of loons apart visually? If so, then surely loons themselves can tell each other apart. A loon, of course, can base its identification not merely on appearance, but also on behavior and vocalizations.

Anna ran two trials. First, I identified 10 loons from Wisconsin and Minnesota for which we had at least 24 photos from a range of angles. Anna chose a set of “test” images of each loon in the sample and set them aside. She then “trained” the program to identify all 10 loons, using the remaining images. Upon testing, the computer correctly assigned 85% of Anna’s test images to the proper individual. Considering that pure chance would have resulted in a success rate of 10%, 85% seemed pretty good. In the next trial, we used 35 banded loons. This time I picked one test image for each loon, trying hard to select ones that closely resembled no other in the sample. In this go round, the program correctly identified loons at a 68% rate. Since random guesses would have resulted in a 2.8% success rate (1/35), Anna and I have begun to think that the computer knows what it is doing.

We found two additional patterns that shed light on the use of AI to identify loons from photos. First, in the cases wherein the computer correctly ID’d the loon in the test photo, it had 18.7 images to practice on beforehand, whereas the mean number of photos for misidentified loons was 11.5. In other words, when the computer had developed a good sense of what a bird looked like, it was better able to identify that loon later. Second, the computer was good at predicting its errors. In the 24 cases where it had ID’d a loon correctly, the computer’s average certainty of its guess was 81%. In contrast, the mean certainty of the computer for photos where it misfired was only 53%. And if we narrow the sample to instances when the computer had 90% certainty or more, it was right 12 of 12 times.

There is more work to be done in identifying loons from their photos. Phase Two, happening this year, will be to take photos of as many loons photographed last year as we can to see if the computer can use photos of a loon in one year to identify it in another year. This, of course, recreates the problem that male and female breeders across the Upper Midwest faced a few weeks ago when they returned to their territories and encountered an individual of the opposite sex. “Is that you?”

The photo above is by Hayden Walkush and shows the long-time male breeder on North Two Lake, near Lake Tomahawk, Wisconsin. Hatched and reared on Hodstradt Lake in 2007, this male settled on North Two in 2014 and has fledged four chicks on the territory since then. The Wisconsin Team found him back on North Two this past week, so he is back for another go!

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I love southern California. I truly do. Although it is disconcerting to look outside — or even step outside — and never really know what the season is, the weather is always beautiful here. The beauty of the region pales for me a little this time of year though. Why? Because we get curious, muted springs. True, Orange-crowned Warblers, House Wrens, and Bell’s Vireos have exploded into song. But it is only slightly warmer now than it was a month ago — and barely greener. The spring that I read so much about in the paper each day must be going on elsewhere.

Indeed it is. With ice off of our study lakes in Wisconsin and Minnesota, loons have returned to their territories. Most are reacquainting themselves with their mates of the previous year after eight months apart, foraging to recoup energetic losses from migration, and checking out potential nest sites.

But rest and recovery are not the only orders of the day for territory holders. The few weeks after iceout are a time of great peril. Young loons without territories probe those in their neighborhood for vacancies and weakness. These young adults try especially hard to seize territories where they observed chicks the year before. (Chicks on a territory are like a badge signalling its quality.) Breeders intent on holding their territories must invest considerable effort convincing young pretenders that an attempt to evict them would be costly and futile. Providing ocean conditions on the wintering grounds a few months before allowed them to prepare well for the breeding season, most territory holders do ultimately hold off all competitors and turn their attention to breeding.

Loons are not the only ones scrambling. With classes still in session until May 16th, I am stuck in California for two more weeks. While my Wisconsin and Minnesota teams are prepping for fieldwork, I am completing an endless stream of forms, contracts, online trainings, and other paperwork to help bring that about. On weekends, my wife and I ride our bikes toward the ocean and take in the mild greening and hint of warm weather that mark springtime in this part of the world. Yet a big part of me hungers to be on northern lakes, where spring arrives with a vengeance and loons fight tooth and nail for the privilege of rearing young for another year.

Sheila Johnston’s cool photo from this spring shows her favorite loon, Lena. Lena was a victim of an early-season eviction last May and spent weeks recuperating. We are delighted to see her back this year and re-paired on her old territory. With some luck, she and her mate will raise chicks on Upper Gull in 2025, just like the old days.

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In recent blog posts, I made the point that the course of a young loon’s life is more affected by its early experiences in Wisconsin or Minnesota than by conditions during its first winter in Florida. Winter happenings along Florida’s Gulf Coast do affect youngsters, but the amount of food they receive in their first several weeks of life makes an indelible imprint on their well-being.

One might have expected established breeders to show even greater immunity to winter conditions. Once an adult has claimed a territory, reared chicks to fledging, and survived several trips from the Midwest to Florida and back, what challenge is left that can threaten it? Can’t adult loons begin to “coast” a bit after these achievements? And if so, might the four months spent along Florida’s shoreline simply be a period of rest and recovery from the stresses of territoriality?

To some degree, established adults can coast. Having settled on a breeding lake at the age of 6 years or so, they have surmounted life’s greatest obstacle. Since senescence does not take hold until they are in their mid teens or 20s and since annual survival of loons in their prime is 94%, newly-settled breeders stand a good chance of holding their territories for a decade or more. But long-term ownership is never certain. The simple act of raising chicks exposes an adult loon to territorial challenges, because nonbreeders bent on claiming a territory use the presence of chicks there as a badge indicating its quality. So proud parents in one year pay the steep cost of increased territorial defense — and the risk of eviction — the next.

Recently we have learned an incredible thing. Ocean conditions that loons face during winter — whether they are 8, 11, or 15 years old — can reduce their body condition subtly such that they are prone to eviction from their territories several months later, when they return to the breeding grounds. Specifically, loons that have spent the winter in cold, dilute ocean water are much more likely to get booted from their summer territories than those that spent the off-season in warm, salty water. Here is what those patterns look like.

Fig. 1. Territory holders that experienced cold ocean water during the previous winter are more likely to lose their territory in a battle than those that spent the winter in warm water.
Figure 2. Breeders that encountered ocean water of low salinity were more likely to be evicted from their territories than breeders that had wintered in salty water.

An obvious question is this. Why is warm salty water beneficial to loons? Sadly, the answer is not obvious, although loss of salinity can be linked to increased runoff from rivers into the Gulf of Mexico, which reduces water clarity and can spawn phytoplankton blooms. (Both low clarity and increased phytoplankton are harmful to loons.) The negative impact of cold ocean water is also hard to interpret, but cold water forces loons (and other warm-blooded aquatic creatures) to expend energy just to maintain a high and stable body temperature. Perhaps the energetic hit that loons face in keeping warm in a cold ocean puts them at a long-term disadvantage.

We are not the first to discover that environmental factors in one season can impact animals in another. In fact, such “carry-over effects” are now known in several species of songbirds. Understanding carry-over effects is crucial to conservation, because they reveal the interconnectedness of the seasons. If the quality of a bird’s winter habitat limits when it can migrate in the spring, how successful it is at finding a territory on the breeding grounds, and the number of offspring it raises, then clearly we must take a holistic view to understand avian conservation.

From a territorial loon’s standpoint, poor ocean conditions in winter pose yet another challenge. It is bad enough that raising chicks puts a great big target on your back. We now realize that loons that encounter cold, dilute ocean water during a winter after rearing chicks will face a double whammy in holding their territory the following spring.

Our discovery of carry-over effects in loons might help us understand how the species’ odd system of territory eviction evolved in the first place. Perhaps natural and inevitable fluctuations in the quality of the winter habitat guarantee that some adult breeders will be vulnerable to takeover each year. If so, winter-weakening sets the stage for the evolution of territorial eviction as an effective behavioral strategy for claiming a territory.

We eagerly await the 2025 field season and have a very strong team in both states. However, field costs have mushroomed unexpectedly by a whopping $28,000. As it stands, we are $1,800 short of our goal of raising $20,000 to earn an additional $20,000 in matching funds from the Walter Alexander Foundation. If you are able, please consider helping us cross this threshold so that we can defray most of our field costs. Thanks so much to those who have already given!

The beautiful photo of the male is one of Linda Grenzer’s. It shows the Deer Lake male (B/S,P/R) becoming airborne during a takeoff run. Love that pink band!

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A few years ago, a team from Canada learned about the declines in loon populations that have been found by researchers in Ontario and Quebec and by us in Wisconsin and decided that it was time for a documentary. It took the company a few years to make the film available in the U.S., but now it is streaming on Peacock. The title is “Loons: A Cry from the Mist”.

One never knows how these pieces will turn out. The producer tells you that they want to interview you on such and such a date against this background and have you talk about this, that, and the other thing. Of course, you try to steer the interview towards topics that you deem most important. In the end, the producer and editor (I think) stitch together some of your comments and some comments of others to create the best possible story. You can only sigh to learn that your best quips ended up on the cutting room floor.

I cringed at a few aspects of the film. Like many others before them, these filmmakers could not resist the patently false idea that loons are ancient. Mercury, which has been studied for decades yet still has not been shown to have more than weak negative impacts on loons, is portrayed as a likely cause of the decline. The age at which loon chicks reach independence is stated incorrectly. And, of course, I wish I had worn a nicer shirt!

On the other hand, I was proud of how well the 2022 Wisconsin Team handled loon capture. Because of scheduling, filming could only occur on our very first night of capture. Yet Molly, Chris, Sarah, and Claudia shrugged off my nervousness and looked like seasoned professionals. The crew got some dazzling footage from Canada and our Wisconsin Study Area. Their profile of Linda Grenzer and her loon pair, Clune and Honey, is sweet and uplifting. I did not sound like a complete idiot during my bits. Most important, I was able to highlight the high rate of young adult mortality that we are seeing in Wisconsin and the need to understand that recent pattern.*

In short, Yap Films produced colorful, entertaining, and largely accurate loon documentary describing the concerns that conservation scientists have about the species. If you have 50 minutes free, it is worth a look!

*Of course, we now know that the decline results in large part because of poor feeding conditions early in life, which ruin a loon’s chances at a long, fruitful life. Too bad the film was not made a few years later!

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If you have been following my blog, you are aware of a worrisome set of circumstances. Survival of Wisconsin adults is as high now as ever, but breeding success has fallen sharply. And the negative silver spoon effect I detected this fall compounds the reproductive downturn. Underfed chicks are unlikely to survive to adulthood. Those that do survive are unlikely to claim a territory and raise chicks themselves. In other words, Wisconsin breeders produce fewer and poorer quality young than before, which contributes to population decline.

And matters are worse in Minnesota. Our data from northcentral Minnesota show: 1) consistently lower adult survival than in Wisconsin, 2) breeding success on a par with Wisconsin, and 3) a more severe silver spoon effect. That’s right, adult loons in Crow Wing and Cass counties experience lower overwinter survival than their Wisconsin counterparts and have been rearing young of poorer quality in recent years. Here is a figure showing the latter pattern.

As you can see, Wisconsin breeders have actually bounced back to raise healthier young in the past few seasons! This is excellent news, and we hope the pattern persists. But Minnesota breeders have gone the opposite direction. Why is this a concern? As the figure below shows, the probability that a loon reaches adulthood depends upon its mass as a chick.

Thirty two years’ of data in Wisconsin have shown that loon chicks with a mass/age value above 80 have about a 50/50 chance of returning to the study area as adults. Roughly 42% of those with mass/age values of 70 to 80 come back as adults. Chicks in mass/age classes of 60 to 70, 50 to 60, 40 to 50, and below 40 return at rates of 36%, 28%, 18%, and 14%, respectively. Now look at the mass/age data from Minnesota for the past two years:

The future looks bright for the Big Trout-West chick we banded in 2023, the larger Cross-South of Happy Bay chick from 2023, and the Fawn-E chick from this past summer. Things look fairly rosy for both Island-Channel chicks from last year, the Goodrich-SE chick from 2023, the Kimball-West chick from 2023, last year’s Little Star/Star chick, two of three Lower Hay chicks from 2024, the alpha Margaret-North chick from 2024, the chick on North Roosevelt, the Lower Cullen-SW chick from 2024, the larger of two 2024 chicks from Cross-Arrowhead, this year’s Roy-South chick, the alpha chick from Ossie-Island, and the Little Pelican-South chick from 2023. The remaining 51 Minnesota chicks were below average size (56 grams/day). Hence, 75% of 2023 and 2024 chicks from Crow Wing and Cass counties stand very little chance of reaching adulthood. Even if they beat the odds and do so, they are unlikely to produce a single chick.

In light of these patterns, I am getting a sinking feeling about Minnesota loons. Of course, the worrisome data come from only the past two years and one part of the state. Perhaps these years were atypical, and Minnesota loons will bounce back this summer. I hope so!

The featured photo shows the female from Rush Lake-Channel in 2024 as she alertly approaches an intruder. Photo by Isaac Pavalon.

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The Silver Spoon Effect occurs when individual animals that experience favorable circumstances early in life — like abundant food — enjoy long lives and produce many offspring when they reach adulthood. In essence, growing up well-fed places a young animal on a track to become successful as an adult.

The Silver Spoon Effect is strong in loons of the Upper Midwest. How do I know this? I have just done a massive analysis of factors associated with return to the breeding grounds among loons banded as chicks. I learned that chick mass (adjusted for age) is the single strongest predictor of both survival to breeding age and breeding success. That’s right: a loon’s mass as a chick accurately predicts how long it will live and how many young it will raise.

This does not mean that a loon chick that grows up without adequate food is guaranteed to die young and raise no chicks. Nor does it mean that a fat, healthy chick is certain to survive to adulthood and have many offspring. After all, it is a statistical pattern. But body mass in chicks is a very strong predictor of lifelong success. The graph below shows the effect.

Loons that did not survive to breeding age tended to be those with low mass as chicks (top row). Loons that survived to return to the breeding ground but never raised young (middle row) tended to be of intermediate mass as chicks. Loons that became successful breeders were mainly those that had been heavy as chicks.

It is hard to know how to feel about the Silver Spoon Effect. On the one hand, it seems cruel. One would love to think that a loon chick could overcome a rough start and turn its life around. But such a turnabout rarely happens. A juvenile that struggles to get enough food in its first month might make its first migratory flight to Florida. However our data show that such a loon has very low odds of surviving beyond its first few years.

On the other hand, loons reared with a silver spoon become the reproductive pillars on which the population’s persistence depends. Take the Pickerel-West male pictured in Hayden Walkush’s photo above. This male — “yellow over white-blue, auric red over silver” (Y/Wb,S/Ar in the table below) — was 8% heavier than average when we captured him on Tom Doyle Lake on August 3rd, 2013 with his parents and younger sister. He was then five weeks old. The momentum that his parents built for him gave him good odds of surviving to adulthood, settling on a productive territory, and rearing young himself. Indeed, he has already fledged six chicks on Pickerel with two different females despite being only eleven years old.

“Yellow over white-blue” is not exceptional. In the table below, you can see the list of all of our recent Wisconsin breeders that were marked as chicks. (Most are males because of the much shorter range of natal dispersal by males.) Pay particular attention to the right-hand column (“% above avg”). A “0” in this column indicates that this loon was of average mass for its age as a chick. If this were a random set of loons, the red numbers would all fall around zero; some a bit negative, some a bit positive. In fact, the table looks like something from Lake Wobegon: almost all territorial breeders in our study area were well above average mass at the chick stage. Sixty-five percent were absolute whoppers — 20% or more above average mass. This is a good illustration of the strength of the Silver Spoon Effect. (The pink-shaded cells show the few current breeders that were of below-average mass as chicks.)

Breeding lake, natal lake, band combination, sex, Chick Mass Index, and % difference from population average for current breeders in the Wisconsin Study Area.

The table shows something clearly. Territory settlers are the cream of the crop. Yes, there are a few overachievers — Harrison Flowage, Manson, Nose, Sherry, Silverbass and Soo. But their small number speaks to the strength of the pattern.

Leaving aside the fascinating and often brutal nature of silver spoons, let’s look at the implications of the pattern for loon conservation in the Upper Midwest. If you recall, the young adult “die-off” that we have found there is the most troubling aspect of the current population decline. Put simply, we are losing the vast majority of all young adults between the time they leave the breeding grounds as juveniles and return to it as adults 2 to 4 years later. This mortality must occur at some stage(s) of the life history of young loons — like migration or winter — that we have not studied well.

Average +/- standard deviation for Chick Mass Index from 1998 to 2020.

Here is the critical point. I have been suggesting that a decline in habitat quality along the migration route or on the wintering ground in Florida might be responsible for the die-off of young adults. But look at the graph above. Chick Mass Index has slid downwards steadily during the past quarter century. This means that the number of loons “fit” enough to survive to adulthood, claim territories, and rear chicks has also declined steadily. So loons are likely not dying because of environmental degradation on the migratory path or in Florida. Rather, loons themselves are of poorer quality than they were 15-20 years ago owing to limited food they received as chicks and can no longer survive the same challenges as well they used to.

Thus, the Silver Spoon Effect forces us to confront an uncomfortable reality: factors on the breeding grounds — during the chick-rearing period — are almost certainly contributing strongly to population decline. We cannot blame Florida.

But the silver spoon has a silver lining. Why? If we can improve lake conditions in Wisconsin and Minnesota so that loon parents can feed their chicks amply each July and August, we can help them raise fit chicks. And those fit chicks will grow up to become robust, successful breeders and strengthen the population.

So the answer, after all, lies in the lakes of the Upper Midwest. And my current push to discover the exact cause of water clarity decline in Minnesota and Wisconsin lakes suddenly takes on even greater importance.

$20,000 Match from a Wisconsin Foundation

If you have already donated to support our work, thank you! If have not yet done so recently, this would be a great time. Earlier this week we learned that a northern Wisconsin foundation will match every dollar raised from other sources up to $20,000. So every dollar that folks are able to donate will add $2 to our 2025 research fund.

DONATE HERE

We would dearly love to take advantage of this opportunity and field a strong research team next year. Thanks in advance, if you can help!

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This seems a dark time for loons in the Upper Midwest.

Wisconsin breeding pairs fledge 26% fewer chicks now than they did 25 years ago. Our more limited data from Minnesota indicate low breeding success there as well. (A long-term study by Minnesota DNR confirms that chick production is decreasing in the state.) The decline in breeding success across the Upper Midwest concerns me. Do enough chicks still reach adulthood so that they can sustain the population of breeders?

But, as I have discussed in previous posts, loss of chicks while under their parents’ care is less of an issue than the escalating die-off of young adult loons after they leave the breeding grounds. Survival in this later stage of the life history is down over 80%. Of 99 chicks that we banded in 1998, 1999, and 2000, we had resighted 38 (38%) as adults by 2004. In contrast, we have reobserved as adults only 9 of 155 chicks (6%) banded between 2018 and 2020.*

Of course, these young adult returnees are troublemakers. They loaf on undefended parts of large lakes or on vacant small lakes. They intrude into breeding territories. Their visits force pair members to confront them physically and steer them clear of chicks. If the pair’s hints are not sufficient to drive the youngsters off, they are attacked. Naturally, the more of these 2- to 6-year-olds there are in the study area, the greater the chance that one of them evicts a member of the pair.

But these young loons are also the future. From their ranks come replacements for breeders that die each year. So young adults — warts and all — are essential to population stability.

The huge drop in the young adult population has turned our annual spring census into a stressful experience. In early May our Wisconsin and Minnesota teams race from territory to territory to see which of our marked breeders have returned and which territories from previous years are still occupied. Each year I fear that breeding lakes will be lost because the dwindling young adult population will be unable to fill breeding vacancies.

In truth, we have lost several of our traditional territories in Wisconsin during the past few years. We did not find breeding pairs on Bridge, East Horsehead, Hildebrand, Miller, Oneida-East, Pickerel-North, Tom Doyle, Swamp, or Muskellunge (Lincoln Co.) in 2024. We seem to have lost one of our breeding pairs on Bertha Lake and another on Butterfield Lake in the Minnesota Study Area as well, although our data do not extend as far back there. Still, there has not been a wholesale loss of territorial pairs in the Upper Midwest, which one might have expected from the high mortality of young adults. So while we have far fewer young nonbreeders milling around, the decline in the territorial loon population is, as yet, small.

Thus, the loon population might be more resilient than we had feared. We have long known that the majority of young loons that return to the breeding grounds never settle on a territory. Perhaps the die-off of young adults merely reduces their number to those few that would normally claim territories anyway. It is a hopeful thought!

Meanwhile, my work continues in both states. I am connecting with water quality specialists in Wisconsin and Minnesota in hopes of learning why we are losing water clarity in July, which harms loon chicks. And I am searching feverishly — both on the breeding grounds and in Florida, where most of our birds winter — for the cause of the high mortality in young adults. These are not quixotic quests. I feel that people who love loons in the Upper Midwest will step up and help them if we can pinpoint the factors that endanger their population.

If you would like to support my efforts to conserve loons in Wisconsin and Minnesota, please consider a donation to our 2025 field effort. We squeeze all we can out of every dollar we receive.

* People sometimes ask me, ”Could these missing loons have simply gone somewhere else? Have they gone to Canada?” It is a reasonable question. Ecologists have marked and tracked movements of thousands of bird species as well as many other vertebrates. With the exception of nomadic species, though, territorial animals like loons stick to a rigid set of guidelines with respect to settlement. If it is still alive, a loon will return to the near vicinity of its natal lake as a young adult to look for a breeding spot. (This is especially true of males.)

The featured photo is by Hayden Walkush of the territorial female on Two Sisters-East. This photo is among the 1906 taken by the team this year as part of our study of whether or not loons can be distinguished using artificial intelligence.

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Almost four years ago, I wrote a blog post about the importance of Florida’s Gulf Coast as a wintering area for loons breeding in the Upper Midwest. I pointed out that 75% of loons breeding in Wisconsin and Minnesota winter along the Gulf Coast of Florida from Pensacola to Fort Myers. And I suggested that conditions in Florida were likely to have substantial impact on the loons we see on our lakes in the north.

My thoughts have returned to Florida of late. Why? Because recent findings suggest that the answer to our greatest riddle might be found there.

Followers of the blog may recall that the single most worrisome pattern related to the Upper Midwest loon decline is the mysterious disappearance of juvenile loons before they reach adulthood. In Wisconsin, the survival rate of juveniles to adulthood plummeted from above 50% to less than 20% between 1993 and 2016, as the graph from our statistical test shows.

The problem has gotten worse since 2016. Only 13 of 209 chicks (6.2%) banded in Wisconsin between 2017 and 2020 have returned as adults. That is a ghastly statistic.

What might be the cause of this massive die-off of young loons? We have good data from the breeding grounds. If juvenile mortality were high during this interval, we would have detected it. Death during migration is another possibility, of course. We do not have good data from that period. But it seems implausible that the varied array of aquatic habitats used by young loons along the migration route have suddenly become a death trap for them.

So it was with increased urgency that I turned my gaze to Florida two weeks ago with our juvenile return data in hand. My hope was to take a second, more thorough look at the likelihood of spotting loons two to four years after we marked them as chicks. I had taken a preliminary glance at this pattern 12 years ago. This time I had: 1) twice as much data, and 2) measurements of physical and biological patterns from ocean water along the Florida Gulf Coast that might help explain the decline. Among physical and biological ocean attributes that I could examine this time were water clarity, temperature, pH, salinity, and concentrations of Chlorophyll A, dissolved oxygen, nitrogen, and phosphorous.

What do the data show? After accounting for observation intensity 2-4 years after banding (which has varied during the study) and location of lake where the chick was banded (because juveniles from central lakes are spotted more often), three variables strongly predict the probability of resighting of a color-marked juvenile loon. In order of decreasing importance, they are:

  • Year — The likelihood of spotting a banded chick as an adult has decreased by an average of 8% from one year’s “crop” to the next. This is the alarming pattern that I seek to understand.
  • Body condition at banding — Chicks that are heavy for their age when banded are much more likely to be resighted as adults.
  • Chlorophyll A level in Tampa Bay in December of the first year — Chicks are much less likely to return if Chlorophyll A levels in Tampa Bay were high in December of their first year (see graph below).

Wait! Does this last finding make sense? First, it is vital to understand that Chlorophyll A is a measure of aquatic phytoplankton — the microscopic algae that can make water appear green to us. A very high concentration of Chlorophyll A can indicate an “algal bloom”, which reduces water clarity and can lead to loss of oxygen and release of toxins. Second, it is important to understand that the negative impact of Chlorophyll A on loons occurs only in December of a loon’s first winter. Return rate of juveniles is not associated with Chlorophyll A levels the month before (November) nor the month after (January). Third, we must be familiar the the migration schedule of juveniles. Juveniles reared in Wisconsin and Minnesota typically reach their Florida winter quarters in late November. Stitching all of this together, the negative impact of Chlorophyll A in December on return rate to Wisconsin suggests that many young loons perish in their very first month on the wintering grounds in Florida if algal levels are high at that time. We would expect these neophytes to be at risk during this period, because they must suddenly find new aquatic prey in wholly unfamiliar habitat. High algal levels add another layer of difficulty to foraging, likely reducing the abundance of prey as well as a loon’s ability to find them.

Of course, this is a hugely important finding. This is the first evidence — to my knowledge — where an occurrence in winter affects a demographic pattern detected on the breeding ground. The effect, moreover, is strong. And the pattern is evident despite the fact that Chlorophyll A data represent only one small part of the winter range (Tampa) that is as far as 350 miles from where some Wisconsin loons spend the winter. We can reasonably surmise that the pattern would be far stronger if we had complete data from all along Florida’s Gulf Coast and could match locations of wintering loons up with Chlorophyll A data from their exact location.

Unfortunately, this striking finding cannot explain the steep decline in juvenile survival rate over the past quarter century. Why not? First, Chlorophyll A levels have remained roughly stable in Florida — maybe even falling slightly — across the two decades or so when juvenile survival has been getting steadily worse. Second, the statistical decline in annual return rate among young adults remains strong even after we have accounted for the effect of Chlorophyll A.

In short, many of our first-year loons do appear to die in Florida, shortly after arriving there. But we are still utterly in the dark with regard to the continuing yearly decline in young adult survival. Young adult loons are future breeders — essential to the stability of the Upper Midwest loon population. It is urgent to learn what is killing them. I will keep looking.

The featured map is from Google Earth. It shows lines drawn between where a loon was banded in summer and where it was recovered or spotted during winter months. Green end points indicate Wisconsin breeders and red indicate Minnesota birds.