winter range

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I have started to call it “the Great Void”. It is the period between a chick’s first autumn and the point — at 2 to 4 years of age — when it has matured, molted into adult plumage, and returned to the breeding ground to look for a territory. Why “void”? Because we know almost nothing about loons during this period.

The Great Void used to be a nuisance. It was frustrating to think that our birds were passing through so many critical life stages without us knowing where they were or whether they were alive. But we have now pinpointed high mortality of young adult loons as the greatest threat to the loon population of Wisconsin and, more recently, Minnesota as well. “Nuisance” no longer captures the depth of our frustration. We now have to admit that we know least about our loons during the time when it matters most. So I think we need to begin to describe the Great Void as a grave concern.

Yet we are not completely in the dark. We get a glimpse into the Great Void now and then. Here is the story of one glimpse we got in March of 2024 from the wintering grounds.

As soon as he spotted it, Jim “Crater” Anderson could see the bird was in trouble. Seabirds in Panama City, Florida do not lounge on the beach in late afternoon sun like tourists from Ohio. And this one was looking especially out of sorts. It was well above the high tide point, sitting in dry sand. Crater did not think twice about interrupting his daily 10,000 steps to come to its aid.

“That is not how a duck should sit”, Crater thought, looking at the bird. Indeed, with legs splayed right and left of its body and belly in the sand, it was a curious sight. The animal skootched awkwardly across the beach and flapped frantically as he approached to within five yards, making him wonder if its legs were broken. At that moment, he felt strongly that he must capture the bird and take it to someone who could help. He removed his grey hoodie and, crouching low to the ground to appear less threatening, crept still closer. “It’s okay, I am going to get you to someone who can fix you up”, he murmurred reassuringly.

The bird was not mollified by Crater’s soothing words. Now that he was within six feet, it whipped its head around and eyed him suspiciously. He steeled himself and grabbed it, enduring its painful nipping at his arms and hands. As quickly as he could, he swaddled the bird in his hoodie to calm it and walked briskly to Rick and Sheila Harper’s house. “They have parrots”, he reasoned. “They’ll know what to do.”

The bird he was carrying was bigger and heavier than he had thought it would be – much larger than any duck he had handled. Its bill was thick and dagger-like. Its legs were not broken, just connected at the very end of its body. And – this was the biggest surprise of all — someone had placed four brightly‑colored bands on the bird’s legs. “What is that all about?” he thought.

When he arrived at Rick and Sheila’s, Kim Youngbeck was also there. The four friends placed the bird in a cat carrier that was snug but secure and set about trying to learn what kind of bird it was and how they could help it. Sheila’s parents are birdwatchers who live in Park Falls, Minnesota. She sent them some photos in hopes that they could help with the ID. “That’s a loon!”, they announced with equal parts excitement and concern.

The Florida Fish and Game contact they spoke to informed them that a loon would not do well in captivity and that they should return the bird quickly to where they had found it. Dutifully, the friends walked back to the beach. Night had fallen in the hour or so since Crater had first captured the loon. Knowing that coyotes and raccoons prowled the beach at night, they decided to place it higher in the dunes than it had been at first. That seemed safer.   

Still, they worried about the loon sitting exposed in the darkness. The bird had not tried to get away from them after they placed it back on the sand. And when they went back to check an hour later, it had not budged. At that point, Kimberly volunteered to take the bird for the night.

Back at home, Kimberly wracked her brain to think what was wrong with the animal. Was it weak from hunger? Knowing that its diet was mainly fish, she offered it the only fish she could – some tilapia filets from the fridge — on a small plate. The loon showed no interest. She looked at the clock and realized that it was 10 p.m. Whatever they were going to do for this loon would have to wait until the next day. She turned the lights out, draped a sheet over the carrier, and hoped it would get some rest.  

The next morning Crater and Kimberly strategized again about the bird. It looked pretty healthy and fiesty, they agreed. They could see no reason to hold onto it any longer. Together they decided to return it to the ocean.

The two friends took the carrier to the beach and removed the loon. This time, though, they let it go at the water’s edge, where the waves were breaking on shore. With furrowed brows and hands on hips, Crater and Kimberly watched as the bird bravely faced the waves and began to crawl towards the ocean. It was not pretty. On five occasions, a wave caught the loon and hurled it backwards several yards towards the beach. Kimberly was reminded of videos she had seen of tiny sea turtles heroicly battling the surf to reach the sea after hatching. The bird did not give up, however. Eventually it was able to take advantage of a lull between waves, reach water deep enough for a dive, and plunge beneath the crashing surf. Kimberly and Crater cheered to see its head pop up thirty yards from shore, well beyond the surf zone.

After a late March sojourn with beach-going humans, the loon, which we had banded the previous summer on West Twin Lake in north-central Minnesota, was back where it belonged — and looking none the worse for wear. We have no idea what brought this nine-month-old to shore.

We got a second, more sobering glimpse into the Great Void in late August 2025.

Battered by stiff winds and high waves from Hurricane Erin, the loon sat within the surf zone on Rockaway Beach in Queens, New York, twelve miles southeast of the Statue of Liberty. Waves crashed over it — even submerging it entirely on occasion. Susan Garman and her ten-year-old son Justin had made a quick trip to the shore to gawk at the surging whitecaps. But when they spotted a large bird that was being pummeled by waves and seemed unable to help itself, their light-hearted jaunt to marvel at nature’s fury took a serious turn.

They hurriedly shed their shoes, waded into the surf, and approached the bird. It looked as bad as Susan had feared it would: dazed, bedraggled, and water-logged. Worse still, the bird showed little fear of Susan and her son when they approached it. “You’re hurt, aren’t you?” she said to the animal, a comforting, motherly tone in her voice. “We are going to help you”.

Yet after she had gathered the bird up, Susan’s concern deepened. She had hoped to feel a smooth, reassuring mass of pectoral muscle when her fingers reached around its chest and belly, but instead, she encountered the sharp protruding keel of its sternum. So it was also emaciated. “Oh, buddy, I am so sorry!”, she whispered. It lifted Susan’s spirits slightly to see that the bird had four bright color bands on its legs. Her mind now racing, she reasoned that the person who had marked this bird would surely wish to help them save it.

She and Justin carried the bird to their home to do what they could. They nestled it in some blankets in the kitchen; it made no objection. Susan Googled “injured bird”, and found some local rehabbers and veterinarians, but no one that she reached could or would help. Justin submitted a photo of the bird to Google Lens to try and identify it. Lens came back with: “The bird in the image is a Common Loon.” “A loon!”, Susan repeated, trying to square her recollection of that glamorous northern species with the unsightly mass of soaked, tousled feathers on her kitchen floor. She and Justin were cheered by their ability to identify the bird they had rescued. They finally seemed to be getting somewhere.

But the loon was very weak and slipping away. “We are here with you”, was all she could muster, her voice softer and breaking from sadness and frustration. Finally, the loon stretched its head forward for a moment, pulled it back again to rest on its chest, and let out its last breath. Crushed by the loss herself, Susan looked for a positive to share with her distraught son. “At least it did not die alone”, she offered.1

We will have to record many more encounters of our young marked loons before we can shed much light on the alarmingly high mortality of loons during their first few years of life. Meanwhile, I am keeping my fingers crossed that other loons of ours who are in need of aid find such generous, compassionate people as these two youngsters did.

1 – We had banded the loon that Susan and Justin found as a chick on Upper Hay Lake, near Pequot Lakes, Minnesota, in July of 2024. So it was just over a year old when it perished. From the work of Kevin Kenow and his team, we know that loons from the Upper Midwest that winter off of Florida make their way up the Atlantic coast to spend the summers of their first and second years of life as far north as the Gulf of St. Lawrence. Thus, this young bird was probably on its way back to the wintering grounds in Florida.

Our paper on the Silver Spoon effect in loons has just been published online. You can read it at:

https://link.springer.com/article/10.1007/s00442-025-05836-8?utm_source=rct_congratemailt&utm_medium=email&utm_campaign=oa_20251124&utm_content=10.1007/s00442-025-05836-8

The top photo is of the loon from Panama City Beach, Florida. Photo by Jim Anderson.

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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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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.

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I did my graduate work at the University of North Carolina-Chapel Hill. My advisor and I spent tooth-chattering mornings from November to April sitting in blinds and watching 300+ color-marked white-throated sparrows compete for seeds at feeding stations. We learned a good deal from this work. We now understand how aggressive behavior affects the survival and local movements of this species.

Many lake residents and outdoorsy types in Wisconsin and Minnesota recognize white-throated sparrows from another time of year. These striking little birds sing distinctive, whistled songs in late May and June along forest edges in the Upper Midwest. Although they are more understated, the calls of white-throats typify northern boreal forests much as loons’ calls symbolize northern lakes.

White-throated sparrows live two very different lives in summer and winter. We witnessed part of the transition between these lives in North Carolina. During early May, the undisciplined hordes of sparrows we had grown accustomed to seeing broke up into smaller flocks. In mid May, they spurned the seeds we offered and fed instead on protein-rich buds they found in treetops. By late May, our sparrows had left for the north country.

The departure of our study animals left us with mixed feelings. On the one hand, it gave us a much-needed break from the daily grind of field work. On the other hand, it left a void and a puzzle. Where had our birds gone? Were they New England breeders that serenaded summer hikers in the White Mountains of New Hampshire with their plaintive calls? Or had they headed inland towards the Upper Great Lakes where they crooned to cottagers on lakes? Perhaps they had ventured to northern Ontario, Manitoba, or even the Northwest Territories. If so, they likely belted out their songs with no human around to enjoy them.

I spent many hours pondering summer destinations of our wintering sparrows. I felt — quite irrationally — that there must be some way to learn where they migrated to breed. Could some distinctive wisp of vegetation or a sticky residue from berry or insect from the breeding quarters become lodged in their feathers or stuck to the bill; survive the journey southwards; and still be detectable in North Carolina in October? Perhaps. But no researcher, to my knowledge, has ever determined the migratory origin of a small songbird by such a means. Eventually I gave up on my fanciful notion of learning where our sparrows spent the six months when they were not in our company.

Other scientists did not give up on the dream of linking breeding and wintering areas. Indeed, for a few decades now scientists have used stable isotope analysis to detect geographic movements of itinerant animals. Stable isotopes are different versions of a chemical element with different masses. For example, most hydrogen atoms (over 99.9%) occur as H-1, which has no neutron in the nucleus. But a few hydrogen atoms take the form of H-2, which possesses one neutron and weighs twice as much. Here is the key point: water droplets in rainfall in each geographic region contain a characteristic tiny percentage of H-2 (.02% in one place, .008% in another). And living things absorb water so that they too contain a ratio of H-2 to H-1 in their bodies that is distinctive to the region they inhabit.

Measurement of stable isotopes is especially useful to bird biologists because of feathers. Feathers are not living tissue. They are keratinized structures that grow from living tissue and, once formed, no longer receive a blood supply. So the stable isotope ratio within feathers does not track the current environment like that in skin, blood, or muscle. Instead, feathers are a time capsule that contains the stable isotope ratio at the time and place of their formation. When a bird grows new feathers in one place and migrates to another, its feathers retain the stable isotope signature of the molting location.

Loons grow fresh wing feathers on the wintering ground prior to migration. This means that wing feathers of breeding loons bear the isotopic signature of their winter quarters. Thus, a small wing feather we clip in July can tell us where a specific breeder spends its winters.

We have some understanding of loon migration and wintering patterns, thanks to the work of Kevin Kenow, Jim Paruk, and their co-workers. Furthermore, recoveries of banded loons have helped us sketch out the wintering range of our Wisconsin and Minnesota breeders (see map below). However, we cannot tell where any particular loon — like the territorial female on Roosevelt-Southwest — winters.

Sources and destinations of loons banded in Wisconsin and Minnesota. Light blue lines are paths of adults; dark blue lines indicate first-winter birds.

Why does it matter where a specific territorial loon spends the winter? Because we have burning questions about conservation of Wisconsin and Minnesota loons that require fine-scale understanding of migratory patterns. For example, does use of certain wintering areas lead to low survival for Upper Midwest breeders? Do poor years for adult returns in Wisconsin and Minnesota correspond to “die-offs” in specific wintering areas? Does the low annual return rate of adults in Minnesota (compared to Wisconsin) indicate unfavorable conditions in their more westerly winter range (see figure above)?

In fact, we have many more questions of this kind. To answer some, we will need ecological data from the Gulf of Mexico and Atlantic Coast. At the moment, however, subtle information locked within the feathers of our study animals and transported by them from wintering to breeding grounds is giving us hope that we will soon have a better understanding of common loon survival throughout the year.

Thanks to Linda Grenzer, who took the cool photo of the male from Halfmoon Lake coming in for a landing some years ago.