eviction

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The saying “success breeds success” was not coined with loons in mind. But we humans know from experience that an initial success can increase the likelihood of a second one. Indeed, I relearn the value of accumulated experience each spring during the period when I train field observers. With no background in the technique, new observers are utterly astounded when we locate the first nest of the year. After five more nest discoveries, though, they begin to develop a “search image” for nests. It is a thrill to see them learn quickly over a period of a few days to the point where they begin to point out loon nests to me!

Loons are not complete strangers to the benefits of learning. Males often place nests in poor locations when they first attempt to nest on new territories. After a bit of blundering about and some poor decisions, males typically find a nesting spot that results in a successful hatch. Afterwards, they reuse that good spot again and again, enjoying much greater success than during their first attempts. Thus, nesting success following an initial period of failure leads to further nesting success.

The impact of a loon pair’s nesting success on territory defense is another matter. The loon territorial system differs in a crucial respect from those described in other species. In many birds, most notably colonial seabirds, young adults prospect for good breeding sites by looking to see where other adults have produced chicks. When these young seabirds settle to breed, their settlement has little or no negative impact on adults already breeding at the huge colony. Not so in loons. Young adult loons prospecting for territories use chicks they spot on a specific territory as a badge indicating quality of that territory alone. Young prospectors must battle the current residents for ownership of such high-quality territories. That is, chicks seen in one year induce prospectors to return the next seeking to evict the owner of their sex and claim the territory for themselves. So adults that produce chicks experience the joy of parenthood…..but have also placed their future territory ownership in jeopardy.

The mixed blessing brought about by successful chick-rearing is nowhere more obvious than on the Pelican Lake-Mousseau Bay territory in the Minnesota Study Area. Online observers watching via the live nest cam were treated to a lengthy battle between two adult loons a few days ago. While the battle was shocking in its brutality, it was not surprising. We have long known that the successful rearing of chicks leads to a surge in interest in the territory and, hence, the likelihood of territory loss by one or both breeders. After raising two strapping chicks last summer, the male and female of Mousseau Bay must have braced themselves for a litany of territorial intruders and challenges. Indeed, the banded 2022 male apparently lost his position this spring; last year’s marked female is now paired with an unmarked male.

And yet there is hope. Yesterday, the old female laid an egg. She and her new mate both seem anxious to sit on it. If they can weather the blitz of black flies currently dogging their incubation efforts, they stand a good chance of repeating last year’s success.

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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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Each spring I feel my adrenaline level rise as we carry out the annual census of returning loons. This practice seems mundane, at first glance. During the census, we simply visit all loon territories and identify each territorial loon we find from its colored leg bands. But since I have gotten to know many of my study animals quite well, I wait with bated breath to learn whether Clune (the famously tame male on Linda Grenzer’s lake, whom I have known since he was a chick) comes back. I feel almost as strongly about Clune’s son, who settled 6 km away, on tiny Virgin Lake. I even have a soft spot for the comically skittish female on Silverbass Lake. She routinely appears down at one end of this long skinny lake, seems to wait for us to paddle in her direction from the other end, and then races by us underwater and reappears at the end of the lake we just vacated. She is so notoriously hard to approach that her very skittishness has become a useful identifying trait. In Minnesota, I was anxious to see whether the young male of unknown identity on Lower Whitefish — who nested rather recklessly on a water-logged artificial nesting platform exposed to the powerful west wind and waves — would return from the winter and try that move again or learn from his mistake and seek a more protected location. (I am happy to report that all four of these loons are back this year.)

Apart from the relief or dejection we feel when we spot our familiar study animals — or don’t — loons’ tendency to return provides critical scientific information. A tally of the proportion of all adult breeders that returned from the wintering grounds in the spring tells us about survival between late summer of the previous year and early spring of the current one. Of course, territorial eviction muddies the water. That is, a loon can either fail to return to its previous territory because it is dead or because a competitor has driven it off of its territory and forced it to move elsewhere. So we must be cautious in interpreting return rates. Still, they provide us with a crude metric of survival.

Let’s look at return rates throughout the study. What is clear from a quick inspection of the graph below is that loons in the Wisconsin Study Area have fluctuated in their tendency to return, coming back at a rate of over 90% in great years and just above 70% in dismal ones. (Minnesota study loons returning in 2022 also fell within this window, as the graph shows.)

Perhaps the most striking pattern is the lack of concordance between return rates of each sex. In other words, knowing that it is a bad year for male survival tells us nothing about female survival. True, there are some years in which male and female survival seem to go hand in hand — look at 2005-2009, for example. But male and female rates seem to run in opposite directions between 2010 and 2017. Overall, there is no statistical tendency for male survival to be correlated with female survival.

We can draw an important — though tentative — conclusion from the fact that male and female survival do not vary in concert. Major loon mortality events outside of the breeding season do not seem to drive annual loon survival strongly. If major die-offs during the non-breeding period (i.e. winter and migration) were a major cause of loon mortality, then male and female numbers should be correlated, because the sexes use similar migratory routes and winter quarters and should suffer in parallel each year.

The most interesting and potentially worrisome pattern we could spot in the annual return rate data would be a decline in survival of either males or females. As you can see from the color-coded dotted lines, female return rate has actually shown a slight rise over the past 29 years. On the other hand, male return rate has declined slightly, though not significantly, during this period. Still, since we already know that males are struggling to maintain optimal body mass in the Upper Midwest, it is disconcerting to see male survival decrease in a way that seems consistent with the mass loss.

Of course, while making the rounds of territorial pairs, we also notice if a territory is vacant or occupied by a lone adult after having supported a breeding pair the previous year. And therein lies a bit more troubling news. Ten of 118 Wisconsin territories that were occupied in 2021 are now vacant or inhabited by loners. We have also recorded two new territories in lakes not used for breeding last year, so the net loss in territories is only eight. Still, this was not the picture we wished to see in a population that has been on a downturn. (Though we are only learning about the Minnesota Study Population, it appears that only one territory among seventy or so that we have visited so far fell into disuse this year after having been occupied last year.)

Let’s put aside worrisome population patterns and turn to news of the moment. It is early June in the North. This is a time of great hope for loons. A few breeding pairs in our Minnesota and Wisconsin study areas — like the Lower Hay pair in the photo — were fortunate enough to dodge both black flies and raccoons and are on the brink of hatching young. Many more have rebounded from early setbacks and renested. If we are lucky, we still have the potential for a good crop of chicks in both regions. Lacking any more effectual means of bringing this about, I will keep my fingers crossed.

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Since we band hundreds of loon pairs, we get used to losing pair members here and there. The female on Sunday Lake, newly-banded in 2020, did not return in 2021. Likewise there is a new male on Clear2-Seven Islands, a new female on Towanda, a new male on Harrison Flowage. Some losses of old pair members are gut-shots. The absence of both pair members at Arrowhead reminds us of the tragic close to that lake’s 2020 breeding season. The Baker male’s disappearance is bittersweet; it brings back the recollection of his having reared a mallard duckling in 2019 with his mate. But after many years of watching breeders vanish, I now greet most such losses with only a sigh.

A bit more unsettling than mere disappearances of single birds — and far more interesting to a behavioral ecologist — are cases where breeder loss on one lake has ripple effects on lakes nearby. Since such domino effects seem to occur shortly after ice-out, when our lake coverage is spotty, we must usually guess at what transpired. In 1998 for example, the McGrath and North Two males, which defended adjacent lakes, seemed to switch places for no obvious reason. We inferred at the time that the huge North Two male flew over and evicted the smaller McGrath male, while the McGrath male assuaged his loss by settling on North Two, which his conqueror had just vacated. But we will never know for certain. A similar mystery occurred last year on Upper and Lower Kaubashine, whose males swapped lakes early in the year, before we were there to see how it happened. Again, we surmise that one male evicted the other, and the loser merely filled the victor’s breeding slot.

This year, we had enough observers present at critical moments to read the ripples more precisely. Following the eviction of his mate on May 3rd (Linda’s photo shows that evicted female), the Upper Kaubashine male — yes, the same male that had swapped territories in 2020 — must have decided that his breeding prospects were dim on Upper Kaubashine. So he looked nearby for an alternative. He found it on Silver, a small lake with an artificial nesting platform and a resident, Pat, who misses nothing. On May 9th, the Upper Kaubashine male intruded onto Silver, where the pair was incubating eggs, beat the resident male severely, and forced him to take refuge in a swampy area. The defeated male has not been seen since.

There is a ray of sunshine to share. The Upper Kaubashine male had no interest in sitting on the eggs of his predecessor at Silver, so the lake’s first nest was abandoned. But the usurper wasted little time renesting with the old female at the opposite end of the lake. Boosted in part by the earliness of ice-out this year, the Upper Kaubashine male might actually survive the loss of his mate and a vicious territorial battle of his own and still hatch chicks in June!

The events of the past few weeks on Upper Kaubashine and Silver reveal that chaos on one lake can spill over to others nearby. So if loons are capable of hope, they should hope for peace and tranquility for their neighbors as well as themselves.

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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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I often thank my lucky stars that I am a field biologist. Being outdoors, especially in Wisconsin, is a huge perk of my profession. There is something thrilling about being in a situation where nothing is planned and anything can happen. Yet as glorious as it is to be outdoors, field work is perilous. Although I might tell the National Science Foundation, or Chapman, or the U. S. Geological Survey (who provide leg bands) that I have much of loon behavior figured out — that I have systematically tested all hypotheses and eliminated all plausible alternatives — I never feel confident when I am watching loons. They invariably surprise you by doing something that defies explanation. “What does that adult have to gain from wailing so often and so loudly when there is no other loon nearby to hear it?” or “Why is that loon wasting time alarm calling at the harmless muskrat?”. Rarely does a day in the field go by when I do not scratch my head at least once at inexplicable loon behavior.

Paradoxically, the best place to be when you are trying to figure out why animals behave as they do might be in your office, crunching the numbers, without any animals in sight. Free of distractions and laser-focused on the data, sometimes you discover a pattern that gives you a clear answer to a central question.

That happened to me yesterday. I was puzzling over a weird finding. In the midst of analyzing patterns in territorial intrusion, I was surprised to learn that territorial loons intrude more often into neighboring territories with chicks than do young, non-territorial floaters that are looking to settle on a territory. How on Earth could this be so? Floaters are young adults that are on the prowl. They search widely for territories with chicks, use those chicks as a badge indicating a good territory, and then return to try and evict a pair member in order to seize the territory for themselves. So it is floaters, not territory holders, that should be obsessed with finding, visiting, and competing for territories with chicks. Territory holders should have as their priority simply holding onto the territory they already own.

I must point out here that intrusions into territories with chicks, regardless of which loons make them, are generally a bad idea. As many of you have seen, territorial loons do not appreciate landings or close approach by intruders when they have chicks to protect and are much more apt to attack intruders at such times. This fact only thickens the plot. Now we must try to understand why a territory owner — a loon with something valuable to lose — would take a chance at being injured by visiting a nearby territory with a super-aggressive owner!

Lacking any other obvious path forward, I dove even more deeply into the curious tendency of territorial loons to seek out neighbors with chicks. Late in the breeding season, territory owners can be partitioned into two groups: those with chicks and those without. So I could look to see if, as one might predict, territory owners that had failed to raise chicks — and who therefore might be looking to trade up to a better territory — were those most likely to intrude. But quite the opposite was true. Territory owners rearing chicks of their own were much more likely to intrude at neighboring lakes with chicks than were territory owners that had no chicks.

As it happened, I discovered this last vexing pattern late in the day and could not dwell upon it. At 2:32 a.m. — during that inevitable hourlong period of sleeplessness that comes each night — I figured it out. While successful rearing of chicks is the ultimate goal of an adult loon’s life, chicks pose a great hazard too. To a floater, a territory owner’s chicks signify a high-quality territory, and so chicks raised in one year guarantee the owner will spend the next year fending off eviction attempts from floaters. It follows that owners should take any and all steps they can to keep floaters from learning about their chicks. Simply decamping and leaving your chicks alone during early morning is a good strategy, because floaters learn about chicks chiefly after spotting their conspicuous parents on the water and landing near them. If you are not on your territory, then no floater is likely to find your hidden chicks. But being away from your own territory and also intruding into your neighbor’s territory is doubly beneficial for a loon with chicks, because your presence will draw other adults to the neighbor’s territory (and away from your own territory nearby) and increase the likelihood that your neighbor’s chicks will be the ones that are spotted. That is to say, neighboring pairs with chicks seem to be locked in a desperate, reciprocal effort to expose each other’s chicks to floaters in order to protect their own territory ownership.

As I write this, I am listening to the hideous whine of a circular saw next door. Our own neighbors have contracted with the loudest and most inefficient construction crew west of the Mississippi to renovate their home. I find the noise, the clutter, the truck traffic, and the ceaseless cursing and shouting tiresome, to say the least. But I am fairly confident that our neighbors are not conspiring with outside forces to get us evicted. So I guess we have it pretty good.

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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.