longevity

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Linda began to worry on April 18th when “Lucy” — the female from Muskellunge Lake whom we banded last year — showed up in a patch of open water with two other loons from the neighborhood. Male loons usually arrive a few days before females. Clune, the most famous loon in our study area, resident on Muskellunge since 2008, and Lucy’s mate, should have been back. Linda’s careful records show that Clune has appeared on Muskellunge before his mate in every year during the past 10 years except 2020, when his mate showed up two days before him.

It’s funny how, even as a scientist, I became attached to Clune. I remember encountering him back on Manson Lake in 1998. As his parents fished together in one cove near the boat landing, 4-week-old Clune and his sister dove together in a nearby cove. I tried to stay in contact with adults and chicks without approaching either pair too closely, but the chicks kept surfacing near my canoe and on the opposite side from their parents. On each such occasion, I paddled rapidly away and towards the lake’s center to restore the parent-offspring sightline. But neither parents nor chicks panicked, as I did, when my canoe split them. My canoe and I inspired the same degree of alarm as boulders, piers, and patches of vegetation.

Clune was precocious. He first appeared back in the study area as a two-year-old intruder on Hancock Lake. He wandered around for the next few years, as nonterritorial adults do. In 2003, he settled on Deer Lake, only 3 miles from Manson, where he had been raised. He and his mate produced chicks in 2003, 2004, and 2005 on Deer. Two of his sons from this period have followed in his illustrious webbed footsteps: one is the long-time breeder on tiny Virgin Lake; the other has cranked out offspring since 2014 as the territorial male on Squash Lake-Southeast.

Although we did not know it at the time, Clune’s breeding success on Deer was merely a prelude. Indeed, Clune and his second mate hit a slump on Deer from 2006 to 2008, failing to hatch a single egg. And so, as loons often do in the prime of life, Clune turned his attention to nearby alternatives. Muskellunge Lake was a chick-producer during the three years of Clune’s slump. Thus, in mid-June of 2008, Clune intruded into Muskellunge, battled the male territory owner, drove him off the lake, and settled on Muskellunge with the resident female.

Yet Clune seemed ambivalent about leaving Deer, where he had produced several chicks, and occupying his valuable new territory on Muskellunge. He faced an embarrassment of riches, it seemed. For three years, Clune and his mate bounced between Deer and Muskellunge. And Clune’s breeding slump stretched to five years.

At long last in 2011, Clune and a new female (“Honey”, as Linda came to call her) reared two chicks on Muskellunge. It was no fluke. The chicks of 2011 began one of the most impressive runs of breeding success we have ever seen in northern Wisconsin. Between 2011 and 2021, Clune and Honey hatched chicks in every single year and raised 13 chicks to adulthood. (Clune added a 14th chick in 2022 with a new mate, Lucy.)

What set Clune and Honey apart from other pairs was their dogged determination as incubators. 2011, 2014, 2017, 2019, and 2020 were years during which 27% to 90% of all loon pairs in northern Wisconsin abandoned their May nests owing to severe black fly infestations. Clune and Honey sat tight throughout these dreadful years, tolerating hours of motionless incubation while flies sucked their blood at will. They did not abandon a single nest. Consider this feat for a moment. Both pair members must be committed to warm the eggs for several hours at a stretch in order for a nesting attempt to succeed. While loon pairs throughout the study area abandoned their nests and hatched few chicks for a decade, Clune and Honey thrived.

Despite his sterling breeding record, it is Clune’s affability that I will miss the most. He seemed to sense that humans in canoes and kayaks meant him no harm. Perhaps he even got to know Linda and me, since he had seen us so often throughout his life. It certainly seemed so at night when he hardly budged as we gently threw a net beneath him each year, lifted him out of the water, weighed him, and replaced his worn bands.

There is a new male on Muskellunge this year. (See Linda’s featured photo of him yodeling, above.) He is “Yellow over Copper, Red-stripe over Silver”, a 12-year-old hatched on Prairie Lake who has lived and attempted to breed on nearby Halfmoon and Clear Lakes for the past three years. Like all males on new territories, he will probably struggle on Muskellunge to find a nest site where he and his new mate can hatch eggs. Maybe Yellow over Copper will beat the odds, take advantage of the plentiful breeding habitat on the lake, and raise a chick or two in his first year. I am keeping my fingers crossed for him. He is a fairly tame loon and a vigorous defender of his new territory. I knew his parents for many years on Prairie and have a good feeling about him. But he is not Clune.

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I have often trumpeted the high survival rate and steadfastness of adult females. Female breeders are masters at perceiving when the tide of battle is turning against them, fleeing from their stronger opponents, and living to breed another day on another territory. Females are survivors.

Male loons, it seems, are not so clever. Perhaps because males control nest placement and, therefore, gain critical familiarity with territories that females do not, males value their knowledge and ownership of a territory highly and seem to fight too hard to hold familiar territories. They often lose their lives as a result.

Against this backdrop of pragmatic, long-lived females and reckless, short-lived males, our capture of a certain male a few nights ago was particularly striking. “Silver over White, Blue over Blue-stripe” first settled on clear, 221-acre South Two Lake in 2002 — when my current field interns were infants or toddlers. The next year, however, Silver over White was booted off of South Two. He settled ultimately on the the Lake Tomahawk-Thoroughfare territory. Thus began one of the most productive runs of chick production we have seen in the history of the Loon Project. Silver over White and two different females reared at least 12 chicks over seventeen years. Moreover, we could hardly help loving this affable male, who year after year nested in plain view and within a stone’s throw of the busy channel that connects Lakes Tomahawk and Minocqua. Dodging indifferent motor-boaters, the Tomahawk-Thoroughfare pair each year led their tiny chicks out of this dangerous channel to the relative safety of the big water of northwestern Lake Tomahawk.

This spring, Silver over White’s second mate apparently did not return. Not missing a beat, he paired with the former female breeder on tiny Schlect Lake — whose mate was also missing — and again nested in his favorite spot along the thoroughfare. Fortune did not smile upon the pair this year, and they did not hatch chicks. When it became too late to nest, both Silver over White and his new mate seemed destined to ride out the year loafing and foraging on Lake Tomahawk.

But Silver over White, who at 25 years of age was well past the time in life that most males look to take a territory by force from another male, was not satisfied with that laidback plan. Instead, he returned to South Two Lake — where we had not seen him since 2003 — and apparently evicted its young owner. (We caught Silver over White a few nights ago, as the featured photo shows.) Silver over White’s feat was especially impressive, because his territorial opponent had two three-week-old chicks and no doubt fought viciously to protect his territory and young.

I returned to South Two today, in daylight, to confirm the territorial situation there. (Marge and Gerry Perner were kind enough to take me out in their pontoon boat.) The scene was chaotic: seven loons socialized distractedly, coming together, splitting apart, and converging again. One fact seemed clear though; Silver over White and a new female — a seven-year-old hatched on Silver Lake, near Minocqua — are the new territorial pair. The freshly-evicted male was nowhere to be seen; we hope he is still alive somewhere. The old female, who was rearing two healthy chicks with the evicted male a few days ago, appears also to have lost her breeding position. As she did two years ago, when she settled on South Two after losing her mate on Little Carr Lake, this female will have to bounce back and find a new place to breed.

Silver over White’s remarkable ability to win a battle against another territorial male at 25 raises two exciting questions. First, how can this male defy the odds and make an aggressive, risky play for a new territory, when most males his age are merely hoping to hang onto their territory for another year or two? Second, it is astonishing and unprecedented to have an adult breeder return to a lake that s/he had been away from for more nineteen years. (The longest stretch of time that a loon had been a breeder on a territory and then had returned to it after eviction had previously been six years.) Did Silver over White try to take over South Two because he still remembers safe nesting sites there and thus knows that he can quickly resume a successful breeding career on the lake? If so, his seizing of his old territory suggests that loons have impressive long-term spatial memory.

I wonder why I have been rooting so hard for Silver over White. I suppose it is because — at a time when I have turned rather silver over white myself — I find it quite inspiring to see his dogged determination to be productive despite the passage of years.

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I’ll just admit it: I have started to root for the elderly. While I used to support one contestant or the other based solely on geography, I now rejoice when an old individual surprises us by winning a battle against a younger opponent. Recently, for example, I have found myself more than normally excited that Justin Verlander, who at 39 is far older than most Major Leaguers, is still a dominant fireballer for my Houston Astros. Despite my lingering dislike for the Patriots, at times I catch myself admiring Tom Brady, who has continued to be an effective NFL quarterback at 44, defying the usual bounds of age.

Among loons, it is females that normally show the ability to perform well at advanced ages. The most impressive old female, without question, is Red/Green of Upper Kaubashine. After raising chicks with at least three different partners on three different lakes, Red/Green produced two chicks with a fourth male on a lake that had not seen chicks before. A few years later, she survived a bloody and violent battle that cost her the Upper Kaubashine territory, but not her life. (She is pictured above in Linda Grenzer’s photo, a few days after that battle.) The current Little Bearskin female, White/Yellow, is another example of steadfastness by a thirty-something bird. After producing 18 fledglings during a 23-year breeding career on West Horsehead Lake, she was severely injured by a fishing line last summer during her first year on Little Bearskin. White/Yellow has bounced back and is now the mother of one of our first chicks of 2022. Banded as an adult in 1996, she is at least 33 years old.

Attuned as I am to learning of female loons’ age-defying exploits, I was blind-sided by Sarah Slayton’s report from Pickerel a few days back. Upon her arrival, Sarah witnessed a nasty battle between two adults on the Pickerel-North territory. She nailed bands on the participants and was able to ascertain that this contest was between males. The contestants, she told me, were Green/Mint-Right and Blue/Red-Left. Blue/Red-Left, I thought???. Blue/Red-Left is the ancient male from Pickerel-West who was evicted from his own territory last July by a young male from Pickerel-South. That defeat was especially painful; Blue/Red and his mate were rearing two chicks at the time which were certainly killed by the new male as he solidified his hold on the territory. Lacking the strength to re-engage with the 8-year-old opponent that had recently bested him, Blue/Red evidently set his sights on a more achievable prospect — evicting the 17-year-old male a short distance up the lake whose territory has been a consistent chick producer.

We have limited information on territorial contests between old loons. Quite frankly, male contests usually involve a very predictable pair of opponents: a male (15 or older) that is past his prime and a young male (5 to 8 years of age) that has suddenly realized he is capable of defeating an older male and seizing his territory. I have to confess that I have begun to give up on old, defeated males. A few of these washed-up individuals are able to recover from eviction by settling peacefully on a vacant lake near their original territory. Some have even bounced back and reared multiple chicks on their new stomping grounds. But most males that are evicted after age 15 disappear from the study area quickly and quietly, as if stoically bowing out to make way for the younger generation.

So it was thrilling to see Blue/Red, who at 24+ years of age is well into his dotage, put himself in harm’s way, challenge the 17-year-old Pickerel-North male for his territory…and actually win the contest. To be clear, this was a battle between one of the handful of really old males in our Wisconsin Study Area and a male, Green/Mint, that is not ancient but certainly well past his prime.

What now? According to Sarah, who heroically paddled up and down the main bay of 581-acre Pickerel Lake to get the skinny on all loons on the lake, the evicted Green/Mint is now living alone on the former Pickerel-South territory, where he lived from 2010 to 2013 and fledged three chicks. With luck, he will re-pair with a new female there and possibly even nest again this year.

The burning question on Pickerel Lake is this. What happens to the Pickerel-North nesting attempt, which is within a week of hatching? Blue/Red, the ancient male that has just won this territory in battle, might decide to join the female, Copper/Yellow, and incubate the eggs as if they were his own. (We have seen evicting males do this four times in the past.) It is more likely that he will make the evolutionarily-sound decision to ignore the nest until Copper/Yellow finally abandons it. Fortunately, there is still plenty of time to nest. So we hope that Blue/Red will do what he has done in 8 previous years on the lake during an 18-year breeding career: find a good nest site, incubate the eggs patiently for 28 days with his mate, and raise two big, fat, sassy chicks. If he does so, he will have completed a rare and improbable comeback by a very old male.

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I do not think of myself as a cheerful bearer of bad news. Yet I repeatedly bring it. Each time I meet a new lake resident and secure permission to cross their land and observe their loons, I brace myself for the inevitable question: “Is it true that loons mate for life?”. I gently share the truth with them. “No, they don’t; but they really have a strong allegiance to their territories!” The idea that loons love their homes, not their breeding partners, provides scant solace to most folks.

Having spent a quarter century disappointing loon lovers in Wisconsin and Minnesota, I have been searching for scientific news to share about breeding pairs that sheds a warm, wholesome light on loon mating behavior. My quest is not inspired by guilt alone. As a scientist, it makes sense to me that adults should become acquainted with their mates and benefit from doing so. How could complex, long-lived animals like loons jointly defend a territory, build a nest, divvy up incubation duties, and raise young together — as seen in Linda’s photo above — without benefitting in some way from their association?

At last, my current study of predictors of breeding success has revealed one way in which loon pairs do benefit from a long-term association. The graph below shows two patterns. First, there is a gradual improvement in hatching success over time as a pair remains together on a territory. These numbers jump around a lot owing to limited samples of pairs that have been together ten or more years.

Second and more clear cut is the improvement in hatching success between a pair’s first year together (Year 0) and their second (Year 1). As you can see, loon pairs improve their chances of hatching eggs by almost 10% between these first two years.

Now we can only speculate about the cause of this dramatic improvement in breeding ability among young pairs. Perhaps pair members synchronize their breeding behavior better in their second year together than in their first. Maybe pair members rotate incubation duties more crisply in year two, thus seldom leaving the eggs uncovered and unguarded.

Of course, the challenge that romantic couples face of living and working harmoniously, following an awkward adjustment period, has a familiar ring to it. That challenge is depicted in “Period of Adjustment“, a 1962 comedy-drama film based on a play by Tennessee Williams. It is heart-warming to see that loons — like actors Jane Fonda, Jim Hutton, Lois Nettleton, and Tony Franciosa — bounce back strongly after a rough first year.

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

Mildred:

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

Maud:

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

Coon:

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

Ole:
No loons

Soo:

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

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

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

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

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

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

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

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At first glance, Bearskin Lake does not strike one as unique. It is rather round in shape, and, at 163 hectares, is much larger than our average study lake. But we cover many lakes rounder than Bearskin and several — including Two Sisters, Clear, and Minocqua — that are much larger. Likewise, Bearskin falls into the middle of the pack in terms of average and maximum depth. True, the lake bottom fairly seethes with rusty crayfish, but that nasty invasive species is also abundant in Oneida, Crescent, and Lower Kaubashine. What sets Bearskin Lake apart is not its shape, size, or biology, but the sort of loons that visit and live on it. 

I was reminded of the unusual status of Bearskin among loon lakes two days ago when I made our first visit of the year there. I was not greeted by the adorable sight of a loon parent capturing tiny minnows and gently leaning downwards to present them gingerly to its 3-day-old chick, as one might see on Silver, Hodstradt, or Bear. Nor did I encounter a male and female that had tried and failed to hatch chicks and were looking forward to next year, when they could renew their breeding efforts. Instead, I observed a nervous loon that immediately raised its head high upon surfacing to scan for a territorial pair that might take exception to its visit. (Linda’s picture above shows the alert posture characteristic of anxious loons.) This bird, “green over silver, white-blue over orange”, was a former breeding female on Seventeen Lake in Hazelhurst that we had seen only once since 2012. We have no idea what this loon has been doing since we last saw it, but its presence on Bearskin and without a mate suggests that it has been marking time and has not reacquired a breeding position. 

Three hundred meters southwest of the displaced Seventeen female was another forager that was far more relaxed on the lake. Like the first loon, though, she was alone. To my surprise, this bird — “silver only, white over yellow” — was the former breeding female from West Horsehead Lake. One of the most prolific breeders ever in our study area, this female has reared 19 chicks since her initial capture in 1996 and, at 29+ years, is our second oldest bird. Her residence on Bearskin solved the puzzle of her disappearance from West Horsehead, which Al Schwoegler (a West Horsehead resident) and I had been mourning all spring long. “Silver only, white over yellow” had finally met a young opponent this spring willing to fight harder than her for the territory. She had thus accepted defeat, left West Horsehead, and taken refuge on the lake where evicted adults have always gone — Bearskin Lake. 

I continued my paddle south from the boat landing, feeling that my effort to visit Bearskin had already been repaid. A lone loon foraging just west off the huge island diverted me briefly; I was deflated to find this bird unbanded. As I veered southeast, following the arc of the island, I scanned eastwards and spotted an apparent pair synch diving (i.e. diving and surfacing together repeatedly). These two loons seemed to know me and were no trouble to identify. “Red-stripe over copper, silver over orange” was a vaguely familiar band combination, but I knew his mate, “red-stripe over silver, red over white”, very well indeed. Initially banded on 2001, this female has raised 10 young on Little Bearskin Lake and on Currie, where she had settled in 2015 after her eviction from Little Bearskin. The male with her, I now realized, was her new mate from Currie. 

As pleased as I was to encounter the tame pair from Currie, their presence on Bearskin was very bad news. They had hatched two chicks on about June 25th, and had lost one of those by the time Lyn observed them on July 2nd. Since parents attend and protect young chicks assiduously and since we have never observed both pair members to leave chicks unattended until they reach four weeks, the Currie pair’s presence on Bearskin signaled that they had lost the second chick not long after the first and were done breeding for the year. “What are you guys doing here?” I said with a mixture of sadness and disapproval. Bearskin is not a lake where loons go to celebrate their achievements. 

My visit to Bearskin ended with an oddity. As I was lamenting the Currie pair’s disappointment, they wheeled around and began tooting to signal the arrival of a flying intruder. The intruder obliged me by arcing towards the Currie pair and skittering to a landing only 50 meters west. The morning sunlight allowed me to read most of its “red-stripe over blue, white over silver” band combination before it hit the water. This male, I knew, was the current breeder from Little Bearskin. His arrival here was more bad news, because males rarely leave their territories during a breeding attempt. “Red-stripe over blue” circled tensely with the pair and then became aggressive, sending both Currie birds fleeing in different directions as he stalked them underwater. Maybe he was stung by his own breeding disappointment. A later check of the database showed that he and his mate had been sitting for at least 32 days on four eggs on Little Bearskin without a hatch. We can reasonably surmise that the pair abandoned a first clutch of two eggs in early or mid May, reused that nest by laying two more eggs with the abandoned ones still present, and now have failed in a second attempt — either because of black flies again or perhaps infertility of the eggs. So this has been a year of frustration on Little Bearskin, as well. 

I found two more unmarked loons along the west shore of Bearskin on my visit and no hint of a resident pair or breeding activity. In fact, most pairings on Bearskin are fleeting, and nests are scarce. The last successful breeding on Bearskin occurred in 1997, when a pair fledged two healthy, crayfish-loving chicks, repeating their feat from the year before. Since then there has been a smattering of breeding attempts, but none — to our knowledge — has produced a hatch. Moreover, no pair has ever formed a breeding partnership that lasted more than three years on Bearskin. Loons seem to sense something about the lake that humans do not. Bearskin is not a lake where you go to raise a family; it is a lake where you go when you have nowhere else to go. 

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Most scientific research comprises snapshots of a biological system. That is, we usually study the behavior or ecology of an animal for a year or two in a forest, on a coral reef, or in a desert. On the basis of such a short term study, we pontificate about what constitutes a good territory and what constitutes a bad territory for the animal we are studying. Then, feeling that we have described the system accurately, we fold our tents and move on to the next study and habitat.

But time changes things. My team and I got a demonstration of the impact that time can have yesterday when we visited two lakes located towards the northern part of our study area. Life has always been hard for loons on Dorothy and Hodstradt lakes. They are both rather clear lakes and full of fish. But they have been disasters reproductively, because they lack the islands, marsh, and bog that loons seek out to keep their eggs safe from raccoons.

The gradual but now-dramatic rising of lake levels in the Northwoods has produced a spectacular reversal of fortune for loons on Dorothy and Hodstradt. What had been an unremarkable spit of land on Dorothy has become an island several meters offshore, reachable only by water (see photo below). What once was a long curving peninsula on Hodstradt has been transformed into an island, accessible only after a lengthy swim. In short, two lakes for which chick production was a freak occurrence have now become prime real estate, because they offer offshore nest sites inaccessible to all but the most ambitious raccoon.

Of course, the rising waters have not been kind to all lakes. Heiress Lake had a handy island that saw regular chick hatches in the late nineties and early 2000s. But no more. That raccoon-proof site is now four feet underwater, and Heiress no longer supports a breeding pair.

The take-home message is clear: territory quality is not fixed and unchanging. Instead, changing climatic patterns transform the landscape in surprising ways. A goldfinch’s lifespan is short enough that habitat transformations probably matter little. But loons live long enough to see poor nesting habitat become good nesting habitat and vice-versa; this species should be able to detect and respond adaptively to fluctuations in territory quality.

In fact, loons do exhibit some ability to respond to changing landscapes. We see this ability in the willingness of breeding pairs to explore vacant lakes near their original one and sometimes nest at sites different from those they have used to hatch chicks. And, of course, young nonbreeders use the presence of chicks on a territory as a measure of current reproductive quality so that they can target lakes for eviction attempts that will reward them with many offspring. On the other hand, many adults settle on a productive territory during the prime of their lives only to see its quality decline along with their own body condition. Lacking the fitness to defeat an opponent in a battle for a new territory, such birds are stuck breeding on a failing territory. These old codgers could tell ecologists a few things about territory quality and the passage of time. 

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There was something distinctly wrong with the Buck male. He had never been tame. Indeed, he was one of those loons that made you work to see his leg bands on each hourlong visit. So, a few days ago, as I hefted my canoe down the steep paved road to the public beach that we use as our access to the lake, I knew I would face a challenge to get enough good looks at his legs to produce a convincing ID. But the male that foraged all around the lake with the usual female was well beyond a challenging ID. He was somewhere between highly vexing and impossible to identify. While the female gave me occasional good looks at her leg bands as I tracked her loosely during her foraging routine and seemed indifferent to my presence, her mate clearly avoided me and gave me no close looks at all. This was a reversal from two decades of past observations on the lake during which the female, not the male, had always been the tougher ID on Buck.

I paused at intervals to consider a change in tactics. But there is not much flexibility and creativity involved in IDing loons from colored leg bands. One simply approaches a breeding pair closely enough to see any bands on the loons’ legs but not so close as to upset the birds — and hopes for the best. This undertaking takes great patience and some luck, especially at times when black flies are out in numbers, as they are now, because loons shorten their above-surface time and seldom preen when hounded by flies. In an attempt to rally my spirits through distraction, I stopped tracking the pair after about an hour and circled the small island in the southeastern corner of the lake. Denying what was clearly a move borne of frustration, I told myself that taking my eye off of the foraging pair for a moment would allow me to search for a possible abandoned nest on the island. After all, I was weeks behind schedule in this first visit to Buck, and an experienced pair like the Buck pair should have long since started incubation.

No nest was evident on the island, but my effort to avoid for a moment the exasperating task of IDing the male ended up solving the puzzle of the male’s identity entirely. Draped over a fallen red pine on the south side of the island, I found the carcass of the Buck male that we had banded way back in 1999.

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It was sad to see silver over blue, red-stripe over red gone forever after watching him vigorously defend his territory for 21 consecutive years and never lose it — even for a day — in all that time. But it is the ultimate fate of every territory holder to meet a fitter, stronger, younger territorial opponent and bow to them. That is the essence of terminal investment in old male loons. The death of this oldest male in our study area (26+ years) now leaves the placid 24+ year-old Bear Lake male as the most senior representative of his sex. I am hoping the day on which the Bear male meets a determined, superior opponent in a territorial battle is still several years away.