banding

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My mom died ten nights ago. She was 94 and had struggled with Alzheimer’s for the past several years. So her passing was not a surprise. Still, her death came with jolting finality. As we sat at her bedside helplessly watching her draw her last breaths, I wondered desperately and a bit selfishly, “Is this what’s left?”. “Is this all of Mom we can take with us?”

But in the hours after Mom left us, warm memories of her returned from decades past. Most of these had to do with our common interest in birds. You see, Mom and I did not merely share an engaging hobby. We shared a love of the outdoors and many passionate and quirky friends we had met during our birding adventures over a half century. We shared the excitement of finding a rare bird and the exquisite joy of watching a beautiful one. We shared a culture.

Mom spotted my nascent interest in birds very early on. When I was six years old and we were living in Cleveland Heights, the local Audubon Society sponsored an outing to Shaker Lakes in May. Mom signed us up for a 7am trip. Initially I hung back with her watching diffidently as enthusiastic adults received help in ID’ing the colorful and active migrants that were foraging in the trees that lined the lakeshore. At one point, my attention was captured by a bird that others in the group had not yet spotted. Mom saw me struggling to identify this small, active bird. She said, “Now, Watty, you go ask the nice man what bird that is you are seeing!” I cannot recall what species I had spotted or whether I got the leader’s attention in time to identify it, but I learned from Mom that I needn’t be afraid to ask for help from an experienced birder. And I learned that some people could teach me a great deal about birds.

Two years later my family was vacationing on massive Lake Temagami in central Ontario. As my brother Henry and I lay beneath our thick woolen blankets after nightfall, we heard tremolos and wails echo across the great expanse of water that — during storms — lapped at the base of our primitive cabin. “Do you hear the cries of the loons, Watty?”, Mom asked. “Aren’t they wonderful?”. I had difficulty connecting the eerie, maniacal calls I was hearing with the large, mysterious black and white diving birds I saw from afar the next morning, but I never forgot them. In fact, loons became the treasured avian spectacle that I looked forward to each time we ventured north to Temagami.

When I was ten, my family moved to Houston. Hoping to sustain my interest in birds in this new part of the world, Mom offered to drive me to the monthly meeting of the Houston Audubon Society. The highlight of the event was a few bird slides that an Audubon member would show after the club’s business was conducted. Mom asked me several times after our first few meetings whether I thought our attendance was worthwhile. I was really a field person and had little interest in what seemed pointless blather about the club’s finances and installation of new officers. Even the slide show seemed too brief and removed from nature to provide much entertainment. Yet I always insisted on going. I soon realized, sheepishly, that what I cherished about this event was not the meeting itself, but those few hours spent with Mom during the meeting and driving to and from it. Like the birding trips we took together, those hours were my special time alone with her — time when she was not distracted by Dad or my three siblings. I became dimly aware then that my love of birds was intertwined with my love for my fiercely devoted Mom.

One of Mom’s and my favorite field trips in Houston was the Freeport Christmas Count, which took place south of Houston. In most years, we birded with Margaret Anderson’s party of eight or so. Mom was well known in the group for bringing along and sharing a delicious sweet milky tea. Her concoction was especially refreshing after we had spent a long chilly morning counting yellow-rumped warblers, ruby-crowned kinglets, and Carolina wrens.

Despite our annual participation in the Freeport Count, my interest in birds waned after a few years in Houston. Looking for a means to rekindle my passion, Mom found me a mentor. Fred Collins had done graduate work in ornithology at Texas A&M. He is a great birder who taught me an immense amount about bird identification. But he is also a bird bander. One April when I was fifteen, Fred took me along when he set up mist nets to capture and band trans-Gulf migrants on the Galveston coast. The experience was transformative. Once I had held a male painted bunting in my hand, I was utterly hooked. I could no longer see myself pursuing a career that did not involve extensive observation of wild birds.

I have many more recollections of birding trips taken with Mom — trips that Mom arranged so that I could learn things about birds from Fred and other experts or trips where she drove me all over the Upper Texas Coast to join other birders. I am not sure how she found the energy to supervise my ornithological education and also be a responsive, loving mother to her other three children. But I know one thing with absolute certainty: Mom’s tireless efforts to nurture my interest in birds made me an ornithologist.

Mom’s passing has left me in shock. As the school semester draws to a close, I sleepwalk from office to classroom and back. I try to find solace in everyday activities. But I feel a vast emptiness. The academic routine and the passage of time are inadequate to fill the void left by Mom’s passing. My only hope now is to find peace and acceptance in her most precious gift.

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The two-year olds have done it again. At an age when most loons are loafing, feeding, staying out of trouble, and just trying to survive, a second two-year-old has shown territorial pretensions. This time, the loon is a female. This time, the territory is in our Minnesota Study Area.

The discovery occurred three days ago on Pig Lake. Although I always smile at its undignified name, I was a bit sad to visit Pig, because neither pair member from 2022 had returned this spring. This fact reminded me of the generally poor return rate in Crow Wing County and my growing concern for loons in Minnesota. So as I gazed through binoculars at the whitecaps on Pig, I braced myself for what more bad news the lake might have to offer.

But among the four loon heads bobbing about in the surf, I was thrilled to spot a banded loon. This bird was one of a pair that dived in close synchrony off of Black Pine Resort. “One of the missing pair members is back!”, I whispered to myself, hopefully. Further observation dispelled that notion. The loon’s right leg showed two colored leg bands. Since all loons banded as adults get a metal band on the right leg, two plastic bands on the right leg meant that I was not watching one of the missing pair members, but instead observing an “ABJ” (adult banded as juvenile). That is, we had banded this loon as a chick.

Two possibilities leapt to mind. This bird might have been a one-in-a-million, 200-mile disperser of undetermined age from the Wisconsin Study Area, where we have been banding adult loons and chicks since time immemorial. Almost equally unlikely, the ABJ might have been one of our first crop of Minnesota chicks banded in 2021. The plot thickened as I compared the size of the ABJ and its mate. The banded bird was clearly smaller. I was looking at a rare female ABJ!*

My efforts to nail the ABJ’s color bands from my solo canoe were not immediately rewarded. I loosely followed the foraging pair, bobbing and spinning about comically amidst the churning waves and boat wakes. Eventually a moment came — forty minutes into my chaotic paddle — when the ABJ and I were carried to the crests of adjacent waves and the bird raised its legs clear of the water. I confirmed that the bird was blue over auric red on the right and red over silver on the left. “B/Ar,R/S”, my notes revealed, was marked as a chick on Ossawinnamakee – Muskie Bay territory on 18 July 2021. So this was indeed a two-year-old female hatched a short distance from Pig.

Like the two-year-old male who is trying to settle on his natal lake in Wisconsin (pictured above in Linda Grenzer’s photo), B/Ar,R/S is special in two ways. She is not only the first chick we banded in Minnesota and have now reobserved as an adult. She is also less than half the age of the previous youngest female ever observed to settle (even for a day) on a territory. (That female was a Wisconsin five-year-old.) Since females settle at older ages than males, her pairing up is even more surprising than settlement of the two-year-old male in Wisconsin in the photo.

What are we to make of this astonishingly early territorial behavior by separate individuals in Wisconsin and Minnesota this year? Nothing at the moment, I think. Two rare events do not constitute a pattern. But those who follow the blog closely might recall that a decline in the population of floaters — mostly young adults not yet settled on territories — is one of the hallmarks of the current downward turn in the Wisconsin population. If we continue to see two- and three-year olds compete for territories in ways they did not 15 years ago, we will have to regard it as another indication of a limited pool of nonbreeders in Minnesota and Wisconsin** — and, hence, further evidence of a broad decline in the Upper Midwest loon population.

*most loons banded as chicks return at three or four years of age. Among those few that return at age two, very few are female. Indeed, about 3/4 of all ABJs we see are males, because males do not disperse far from their natal lakes to breed.

**The logic is simple here. If there are few young adult floaters (usually 4-, 5- and 6-year olds) in a population competing for territories, then even very young floaters (2- and 3-year olds) might be able to acquire one, despite their generally lower competitive ability and aggressiveness.

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I have had a lot to say about male loons and their experience. Indeed, the fact that the male decides where to place the nest means that he develops a tight bond to his familiar territory and fights hard — harder than his mate — to keep it.

But females too play a vital role in breeding success (like the pictured female photographed by Linda Grenzer on Bear Lake). How might female experience affect the outcome of a nesting attempt? Now that I have begun a detailed analysis of causes of breeding success and failure, I have started to ferret out the difference that female experience makes. I am only halfway done, but I can already see that the number of years a female has spent on her territory strongly affects the date her chicks hatch. As the graph below shows, females that have just arrived on a new territory — because they have evicted the previous female owner or replaced a dead one — have an average hatching

date of 22 June. In contrast, 4-year veterans on territories hatch their eggs, on average, 5 days earlier — June 17th. Now this might not sound like much of a difference in hatching date. But when you are tasked with stuffing your voracious chicks with fish, watching them grow rapidly to adult size, and hoping they get proficient enough at foraging, flying, and avoiding trouble to eke out a successful migratory flight to Florida, you take every extra day you can get!

You might ask: “Does this delay occur because of female inexperience with breeding in general or does it come about because of lack of experience on a specific territory?” The delay seems to be associated with lack of familiarity with a specific territory, because females that pick up stakes and move to new territories show delays in hatching date just like the ones they suffered on their first territories.

The cause of the improvement in nesting schedule with experience is likely to be energetic. That is, a female that knows how and where to find food on a lake is able to recover from spring migration quickly and begin the lengthy and arduous process of raising chicks. A female that is still learning where to find food on her new lake spends extra time before she reaches a suitable body condition to commence breeding.

Don’t male loons have just as big a problem restoring their body condition and thus readying themselves for a nesting attempt? Perhaps. But males experience minimal breeding costs until they begin joint incubation duties with females. Apparently males’ energetic deficit from migration does not hinder the breeding schedule.

You probably noticed that the graph depicts a curve, not a line. Older age-classes of females — those that have spent 5 or more years on a territory — actually begin to nest later than females that have spent 4 or fewer years there. What on Earth could explain this peculiar pattern?

Since it makes little sense that a female’s experience on a territory could begin to work against her after several years, we must look beyond experience for an explanation. The later hatching dates of more experienced females probably arise from reproductive senescence — a decline in reproductive performance that occurs with advancing age. Senescence is well-known in mammals and also many birds. We should not be surprised to see such a pattern in loons.

It is exciting to discover and ponder the reproductive quirks of female loons. Like many of our findings, this one only became visible because we studied thousands of nests, by hundreds of marked loons, across decades of their breeding lives. That, of course, is our bread and butter.

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The fact that all loons look alike is so widely known in the North that it scarcely bears mentioning. But this fact has impacts on our understanding of loons that range from annoying to devastating. From the public’s point of view, the difficulty of distinguishing one adult loon from another is simply confusing. No doubt it contributes to the enduring myth that breeding loon pairs mate for life. After all, the loons that showed up on your lake this year looked and acted pretty much like those from the year before — and ten years before — right?

A minor source of confusion for the casual observer is a massive obstacle to the scientist. Our inability to tell one individual from another means that we can catch only glimmers of knowledge about territory defense and settlement, aging, survival, nesting ecology, and mate fidelity without marking loons individually. To view the situation more positively, the individual marking of loons has produced huge breakthroughs in our understanding of their behavior and ecology.

Yet even the marking of loons for study has severe limitations. Consider our situation in Minnesota. Yes, we banded dozens of loons in 2021 and they seem, if anything, a bit easier to approach and study than the 120 marked Wisconsin pairs we have been observing for almost three decades. But we are, in a sense, starting from scratch in the North Star State. Why? Because, well, loons all look alike! The breeding pair we marked on Rush-Northeast consists of a male that we can only estimate as being 5+ years old and a female that we can estimate as being 7+ years old. (Females settle about two years later than males do, on average, leading to these estimated ages of newly-banded adults.) The same estimated ages apply to the Rush-Boyd pair, the Ossie-Island pair, the Roosevelt-Southwest pair, the pair on Big Pine, and the twenty-odd other pairs we marked in July. In fact, many of these Minnesota loons are in their teens and twenties; a few are likely to be in their early thirties, like the female in Linda Grenzer’s photo, above.

Knowing loon ages is not trivial. Some of the most valuable findings we have made in recent years have emerged from our knowledge of loon ages in our Wisconsin study population. Most crucially, information about age helps us refine our population models so that they yield more precise predictions about population trends. So we would very much like to know the ages of our new Minnesota study animals.

How might we learn the ages of freshly-banded loons in Minnesota? Alas, there is no obvious aspect of loon appearance (like wrinkles or grey hair) that can clue us in. However, one exciting possibility is telomeres.

Telomeres are simple segments of DNA that sit at the ends of chromosomes. They are not genes, nor do they contain genes. Instead, telomeres serve as protective “end caps” on chromosomes. Unlike genes, which reside on chromosomes and are always replicated in their entirety when a chromosome is copied, telomeres become shorter each time a chromosome is replicated. Why? Because the process of DNA replication is imperfect and can never quite replicate the entire ends of a chromosome. Since telomeres reside at the ends of chromosomes, a portion of each telomere is shaved off each time a chromosome is replicated. In effect, by allowing themselves to be shortened, telomeres sacrifice a portion of their length to prevent genes from suffering the same fate.

If telomeres get shorter each time a cell replicates, then they might serve as a clock within the bodies of animals. Young animals should have long telomeres, while old animals — whose cells have undergone many rounds of division — should have short ones. Studies in many vertebrates have confirmed this broad expectation. In fact a recent study showed that telomere length is quite closely correlated with age in a wild bird.

A new collaborator at Chapman is currently measuring telomeres of Wisconsin loons using small blood samples we collected. He is at a very early stage, but his findings so far are promising.

Ys/Gs,S/Gs Townline, 6-year old T/S = 1.02
Bs/Ar,O/S Two Sisters-East, 9 years old T/S = 1.06
Ts/S,W/W Mildred, 21+ years old T/S = 0.71
S/O,O/R Arrowhead, 22+ years old T/S = 0.91

Thus, two young males known to be six and nine years old had rather long telomeres, while two females in their 20s had short ones. This difference occurs despite a pattern that we had noted earlier about loon telomeres — that females generally have longer ones than males.

So we await further telomere measurements from our Chapman collaborator with great anticipation. If Wisconsin data show that telomeres are predictive of age in loons, we will begin to be able to separate the old-timers from the young whippersnappers in Minnesota.

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One of the challenges of studying loons is that they are so well-loved. Many people have observed them, written down notes about them, and — here’s the problem — shared their speculations about all aspects of loon biology with others. Those of us who study loons are in a position of power, because the public looks to us for information. It takes some humility, when a journalist asks us a question about loons, to admit that we do not know the answer. Admitting ignorance is embarrassing. It disappoints the questioner. It makes us feel inadequate and uninformed. Yet admitting ignorance is vital. Our willingness to say we understand fully some aspect of loon biology that we do not — on websites, at conferences and in print — poses great problems for loon science and conservation.

Wait. Published material on loons should help move our understanding forward, right? Yes and no. Well-researched, robust science on loons improves our understanding; anecdotal, speculative work based on small samples of loons, inexpertly analyzed, and passed off as fact does not. In the field of loon behavior and ecology, a huge “grey literature” exists, which consists of popular loon articles, books, websites, unpublished Master’s theses, and low-brow pseudo-science that eked its way into the lower echelons of science journals. When such sketchy information makes up the majority of the material publicly available about loons, there is a real danger that speculation and pseudo-science might drown out real science.

There is good news, however. Our understanding of loon biology is better now than ever before. Across the continent, loon researchers have started to mark individual loons, examine many aspects of their ecology and behavior, use powerful statistical tests, and publish their findings regarding loons in peer-reviewed scientific journals. This last step is critical, because peer review means that three or more scientists are criticizing a paper submitted for publication anonymously and candidly before publication. In most cases, scientists who review loon research do not themselves study loons, so they can bring an important bit of objectivity to the process and read what a loon scientist writes without preconceived notions about the species. Reviewers who are not loon researchers, in effect, are helping pull the study of loons into the mainstream of scientific research. If scientific studies on loons are treated with the same level of rigor as those on fruit flies, downy woodpeckers, wolves, elephant seals, and angelfish, loon science will eventually become as robust and reliable as science carried out on other species.

Such rigor in loon study is long overdue. Now that we see multiple populations of loons declining in number or reproductively, we must do better. We need to advance from “there are still loons on my lake, so the population is stable” to careful, longitudinal quantification of adult survival, juvenile survival, breeding success, and other demographic parameters that can contribute to a valid statistical population model.

Why does it matter? Because when we fall into that very human trap of expounding upon a topic without a foundation of scientific fact, people sometimes listen and use our pronouncements in ways that we did not foresee. Case in point: the Minnesota loon population. Any population ecologist who looks at the data — well, lack of data, in this case — will tell you the following. We truly have no idea whether the population of loons in Minnesota is rising, falling, or remaining steady. We simply have not marked adults, carefully recorded their rate of return to their territories, measured the number of chicks they have produced, marked those chicks, measured the rate at which those chicks return, and plugged all of these data into a statistical model. Without such a thoughtful, complete analysis of survival and reproductive success, any statements about the Minnesota loon population are simply speculation — speculation that could be seized by others to undermine conservation efforts. Indeed, one difficulty faced by the “Get the Lead Out Minnesota” campaign (which anyone who loves loons and wildlife should support strongly) is that there are many baseless statements to the effect that the Minnesota loon population is stable in the media and the grey literature.

So, a plea. Let’s emulate population ecologists in describing our knowledge of loon populations in Minnesota and elsewhere. Let’s apply rigorous techniques and wait until the research has run its course to reach any conclusions. In the meantime, let’s have the courage to utter those most honest but difficult few words: “We don’t know”.

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I am fearful of new challenges. In 1993, when I began to study the behavioral ecology of loons on a cluster of 12 Wisconsin lakes, doubt gnawed at me. How can one carry out meaningful, publishable, scientific research, if one’s study animals are large, aquatic, diving birds that range over huge territories, dive constantly, and must be followed in boats? Would my work be severely limited in scope, like that of researchers on porpoises, whales, and sea turtles? I had no training in field techniques for study of aquatic animals, only my childhood experiences paddling canoes over vast stretches of Lake Temagami in central Ontario. But my fascination with loons — which also grew during summers on Temagami — and my sense that canoes could be an effective means of tracking them without altering their behavior pushed me forward. And so, for reasons that I do not understand, I began to treat seemingly insurmountable problems with funding, logistics, and personnel as mere nuisances. And I ignored warning signals that any reasonable young scientist would have heeded. I began to study loons.

So it was in Minnesota. Although one might surmise that beginning a field project on loons in one state would be much like doing so in another, this is not so. True: loons are loons. We see many of the same behaviors, hear the same basic calls, and witness the same sorts of human-loon interactions in Minnesota that we have seen over the past 29 years in Wisconsin. But all else is new. Starting a major field study in the Crosslake area has reminded us that we have an army of friends, lake residents, and supporters in Wisconsin. These folks have housed us, fed us, carried us around in their boats at times, and — most important — provided us with a trove of information on our study animals to supplement our field data.

And our Minnesota study lakes are far larger than those in Wisconsin. Only a masochist would attempt to study loons on the massive Whitefish Chain — where about half of our Minnesota study animals reside — by canoe. So a growing list of Minnesota friends and supporters have provided us with boats — thanks, John, Mike, Mary, Keith, and Dawn! — that permit us to cover the big water. (By the way, several others have made our work possible by providing housing — thanks, Melanie, Charlie, Mary, Jim and Jon!) In fact, we have learned that we can move about far more easily on huge lakes than on the tiny lakes where most of our Wisconsin loons live. Moreover, we can hold our position in the water more effectively and work in greater comfort on the Chain, providing winds are calm.

However, loon capture is another matter. Having caught rather few loons on huge lakes in Wisconsin, I was concerned that my team would waste many hours each night scanning the dark water before our spotlight came to rest upon a tiny light smudge that would become, on approach, a loon parent and a chick that we could capture. In truth, we do spend somewhat more time searching for Minnesota loon pairs that we are accustomed to. Furthermore, locating loon families acoustically is more difficult in Minnesota, because Minnesota loons seem less vocal at night than their small-lake brethren in Wisconsin. But once located, loons in Crow Wing County have proved easier to capture. So my irrational fear that loon capture would be slower and more difficult in our new western study area was unfounded.

What progress have we made in Minnesota so far? Despite the ill-timed failure of an outboard motor that forced us to cut short our night and limp back to our boat landing using only a single canoe paddle and three tote box lids, we have marked 37

adults and chicks in four nights. We banded sixteen loons on Ossawinamakee alone last night. In a few hours’ time, five anonymous territorial loon pairs on Ossie have become a valuable set of individuals whose behaviors, life histories, and survival rates we can track to enrich our understanding of loon breeding behavior and population dynamics. Moreover, our experience in Wisconsin tells us that the brief capture and marking process leaves little or no imprint on loon behavior. Loons caught and marked one night act the next day as if the event never happened. They display the same casual indifference towards us and other humans that they showed on the day before.

On the other hand, we ourselves are greatly changed after we capture and mark loons. Marked loons are individuals to whom we are committed forever afterwards. Yes, we get scientific data from them. But marking creates a lifetime bond between observer and loon. We know these birds. We cheer as chicks we marked return as adults to the study area and claim territories. We mourn when marked parents lose a chick or abandon a nest. And we move heaven and earth to guard these individuals and come to their rescue, if they need it. It has proved impossible to maintain pure scientific indifference to our study animals.

In short, Minnesota loons are excellent study subjects. They ignore our visits to their territories and forgive us immediately after capture and marking. My initial fears and doubts about marking and observing Minnesota loons have subsided. We can now see that we will learn an immense amount about territorial behavior, breeding ecology, and population dynamics of Minnesota loons — if we are willing to shoulder the burden of an intensive field project in a new state on these most engaging birds.

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Our work in Minnesota is just beginning. Although we have great support from the National Loon Center and seem to be getting lots of folks from across the state interested in our work, there is much left to do. At present, we are scouting lakes in the Crosslake area and hoping to find chicks so that we can band the chicks and their parents. Only through this arduous process can we establish a large study population, measure survival rates, and construct a population model for Minnesota loons. So far we have only fifteen banded birds in our entire Minnesota study area.

Make that sixteen. On Wednesday, Katy and Jordana found a new nesting pair on Lower Whitefish. This duo — the nesting loons, not Jordana and Katy — has the distinction of using the oldest, most sunken, washed-out nesting platform that we have yet seen in Minnesota. (Most nesting platforms that we have found in our new study area are quite bouyant and well maintained.) The platform location is also exposed to a substantial wind fetch, not to mention endless wakes from passing boats. And yet, drawn to this location by the predator-resistant nesting opportunity, a pair of loons has made this site their home.

Jordana shared the news of this new nesting pair with me in the most thrilling possible way. She told me there was a nest and sent me a video of one of the pair members swimming underwater and behaving protectively towards it. I immediately ran the video and caught an unmistakable sparkle on the bird’s left leg. (Note the bright white spot on the left leg of the loon in the featured photo and the video below.) The sparkle told me that the bird had a silver band on its leg that was catching the sunlight; the fact that the left leg was banded told me that this loon was an “ABJ” (adult banded as a juvenile) and not an “ABA” (adult banded as an adult). Hence, this loon, when we capture it and confirm its age and natal origin from the number on its USGS metal band, will be the first known-age individual in our Minnesota study area.

So this is not just any pair of loons. No, this Minnesota loon pair represents a first for the new Minnesota study area, because one of the two pair members is an individual whose age can be known precisely. Kevin Kenow of the USGS captured and marked this silver-banded loon as a chick four to six years ago on a different part of the Whitefish Chain. At present we must say “four to six years ago” because Kevin placed only a single band on the left leg of this bird, and he banded six other loon chicks similarly. Until we capture it, we will not know which of those seven chicks grew into this breeder. However, we can be virtually certain that the banded loon is a male, because most females settle to breed many miles from their natal lake.

Why am I so excited to see this young adult settle in our study area? Because one very important demographic parameter we seek to measure in Minnesota loons is the survival rate of juveniles and young adults. This, you may recall, is the cohort of the Wisconsin loon population that has suffered a high rate of mortality in recent years and thrown that population into decline. While we will be able to estimate the survival rate of breeding Minnesota loons — a crucial parameter in its own right — after another year or two of work, it will take five years or so before we have seen enough settlements of ABJs like this male to produce a good estimate of young adult survival in Minnesota. But the sight of this first young settler shows that we are on the road.

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In many recent posts, I have emphasized a certain theme: male loons begin to die off at a rapid rate after age twenty, while females linger on. Part of the reason for this contrast is the nature of territorial contests in each sex. Territorial males fight hard in attempting to hold their breeding position on a lake and commonly die in territorial battles. With rare exceptions, territorial females survive eviction from a territory, move to an unoccupied lake nearby, and resettle on a new territory when opportunity permits.

While the escalation of male territorial battles is interesting in itself, it also impacts the composition of the breeding population. Specifically, adult male loons’ propensity to die frequently in battle skews the sex ratio towards females in the breeding population.

These excess females are “floaters” — adults capable of breeding but prevented from so doing by the lack of a mate and/or a territory. Floaters are the loons that one sees living alone on small lakes, drifting about aimlessly on large lakes, and intruding into territories from time to time to confront breeders. A large proportion of the loons that gather in flotillas of five adults or more during July and August are floaters. Floaters can be thought of as “hopeful breeders”; that is, they are always ready to settle and breed with a mate and territory, if they can find one. The excess of female floaters means that there are always far more of them looking to settle and breed than there are male floaters able to pair with them. In effect, males are snapped up by females as soon as they become available for breeding.

In May of this year, we re-encountered one of our veteran breeders, “Silver over Blue, Green over Orange” (or “S/B,G/O”), whose breeding history illustrates the striking contrast between males and females brought about by male-biased mortality. S/B,G/O was first captured and marked as an adult in 1997 on Dorothy Lake, where she raised two chicks with her mate. Her mate was evicted in 2001 and died either during eviction or shortly afterwards. But she lingered on. When an opening became available in 2002, she settled and nested with a different male on Hasbrook Lake, just a few miles to the northwest. Having failed to raise chicks on Hasbrook, S/B,G/O (now at least 14 years old) evicted the female breeder on Hodstradt in 2004, paired with a third male, a six year-old, and reared four chicks there during the next three years. She followed this young male to Horsehead Lake in 2008, when he was driven off of Hodstradt, and the pair fledged 3 more chicks over the next four years on their new lake. When the male was evicted yet again in 2013, S/B,G/O traded experience for youth and found a new six year-old male as a breeding partner. We breathed a sigh of relief when she broke up with this youngster after a year together, as he was unfortunately her son from Hodstradt! Then 23+ years old, S/B,G/O again became a floater, forced to return to the breeding grounds in 2014 and 2015 with no clear prospects for breeding.

I have become attached to the birds in the study area, so I was delighted to find S/B,G/O back at Hodstradt in May of this year with her fifth recorded mate. At 26+ years of age, she is perhaps fortunate to be paired again. Her mate this time: a four year-old hatched on Clear Lake. We observed no breeding attempt by this new pair – only a small percentage of four- year-old males that settle on territories actually nest – but it is likely they will nest in 2017.

As a human, I like to think of S/B,G/O’s life as a lesson in resilience – the dogged refusal of an animal to forsake breeding despite repeated setbacks and advancing age. But, as a behavioral ecologist, I think of this female more as a striking example of how animals adapt to maximize their breeding capacity regardless of the breeding environment they face. By the way, S/B,G/O is not the only female in our study area who has continued to breed despite frequent changes of partner. S/R,O/O, another 26+ year-old from Swamp Lake that we recaptured a few nights ago (see photo with Eric), has gone through at least 5 younger mates during her 20 years of breeding there. Clearly the pairing of tough, old females with much younger males is – as my daughter says – a thing.

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2016-07-31 01.32.29

Loon capture is a blur. We set out from our house at 8:45 pm, launch our small motorboat on the first lake, wait for nearly complete darkness, and catch any loon chicks and parents that we can net easily. By the time we have repeated the process four more times, we are rubbing our eyes, our weariness justified somehow by the presence of the sun lurking just below the horizon.

As an essentially negative person, what I often recall after a night of capture and banding are the physical demands of the process and my complete exhaustion. But there are dimensions of the work that are exciting and rewarding. Each loon is unique, and one never knows whether an individual will permit itself to be approached closely and netted or will be wary and elude us. So we experience many disappointments, but they are tempered by the occasional thrill of capturing an individual that, at first glance, appeared too skittish to catch.

The fruits of loon capture are obvious. By marking individuals and resighting them year after year, we learn about survival rates of adults and juveniles, territory fidelity, natal dispersal, and habitat preference. We glean a good deal of important information from these data. For example, survival rates of young and adults allow us to learn whether the  local population is increasing, decreasing, or remaining stable. And tracking of young loons from egg to first territory has revealed that loons develop strong preferences for breeding lakes that closely resemble their natal lake. Finally, capture is essential as a means to disentangle loons that have been run afoul of angler’s lines or lures.

This year’s capture exposed another distinctive pattern in loon ecology: the presence of ecological traps. An ecological trap is a breeding habitat that appears at first glance to be a good one but ends up being poor for reproduction. For example, a field might experience a burst of insect activity during early spring, enticing songbirds to settle there for breeding, but a crash in insect levels after eggs hatch might occur that suppresses the number of young birds produced. Two nights ago, we captured two chicks from two different lakes back to back. The first territory was a shallow 11-hectare portion of Wind Pudding Lake (my favorite lake name). The chick captured there was a five-week-old that weighed a scant 0.92 kg — less than half what we would expect from a chick of that age. Our daytime observations show that the chick’s parents are no slouches; they respond to its constant begging by making frequent dives and retrieving what food they can to feed it. Moreover, the chick itself dives often to forage. But this shallow lake, covered almost entirely by lily pads (which impair loon foraging), offers scant sustenance. I am afraid that the emaciated Wind Pudding chick will ultimately starve to death, as did the chick on nearby Liege Lake, another shallow lake choked by vegetation. Loon parents on small, acidic lakes struggle to rear even a single chick, whereas those on large lakes of neutral pH often raise two. This stark contrast was highlighted for us, as the lake we visited following Wind Pudding was 1373-hectare Lake Tomahawk. To be sure, loon parents on Tomahawk must steer their chicks through countless jet skis, water-skiers, anglers, and speed boats at all times of day. But vigilant parents are rewarded with abundant food for themselves and their chicks. The Tomahawk-Sunflower Bay chick held by Mina in the photo weighed 3.02 kg, yet it was only a few days older than the chick on Wind Pudding. Clearly the strapping youngster in the photo is heading for a healthy future and likely fledging.

Why on Earth would loons settle to breed on lakes that often provide too little food for their chicks? The answer might relate to the disconnect between nesting and foraging requirements. Alas, large lakes that contain many fish for loons often lack the islands, emergent marshy bays, and bogs that allow loons to avoid egg predators like raccoons. So loons looking to breed seem to be lured onto small, marshy lakes that yield successful hatches but doom their offspring to starvation.