As of today, 32 of our territorial pairs have hatched chicks. We are on pace with last year, despite the three-week delay in nesting resulting from the cold winter. I am encouraged; 2018 looks to be at least an average year for chick production.

My optimism about the breeding season has been tempered of late, as we have gotten fresh evidence of the frailty of newly-hatched chicks. In the past two weeks, four pairs with tiny chicks have lost them — a higher than average rate of loss. Linda first reported that the chick on her lake suddenly disappeared; her observations suggest that a snapping turtle might be the culprit. Yesterday, the chick on Crystal Lake (Lincoln County) fell victim to the attack of an intruding loon, as reported by a lake resident. And two northerly pairs — on Blue-Southeast and Carrol — also completed four weeks of incubation only to lose their chicks in the first few days after hatching. The causes of chick loss are unknown in these two cases.

Loss of chicks in the first two weeks of life is not terribly surprising. Young chicks must confront a great many challenges, including simply keeping themselves warm and avoiding physical injury as they learn to swim and move about. But the greatest hazards to hatchlings, we have learned, are strictly biological. Being tiny, having limited mobility, and with only a vague sense of the dangers posed by much larger organisms in their habitat, young chicks can be attacked and killed by a wide variety of animals — intruding loons, snapping turtles, muskies, and eagles, to name a few. In contrast, adult loons are wary, agile, and large enough that the list of potential attackers is short. Adults have simply outgrown much of the danger from other living things in their environment.

As discouraging as it is, I am convinced that this recent spate of chick deaths is a statistical blip. There has been no sudden change in the loons’ habitat, or explosion in the population of any predator, that could signal the beginning of a worrisome trend. Rather, this is just an unfortunate negative swing that will be washed out by later swings, negative and positive, and ultimately forgotten. Perhaps we can hurry the process along by focusing on Linda’s recent photo of the female (“Honey”) and chick on Muskellunge Lake.

What is better than finding out that your just-published article has been featured by an online science media outlet? Finding out from your dean! An hour ago this happened to me as I strolled out of our new science building.

We were excited to learn this article has excited some attention. It was a bit of a sleeper. Published in a good — but not spectacular — journal, our investigation of the flies’ impacts and loons’ logical responses to them caught the eye of the journal’s media department. I will not bore you by rehashing our findings, which I have discussed before. By the way, a related media blurb included Linda Grenzer’s cool photo of the male on her lake sticking on the nest in 2017 despite flies biting him mercilessly. (Another of Linda’s related photos appears above.)

Fortunately, this year has been a mild one for black flies. So while pondering the harsh negative impacts that black flies often have on loon nesting behavior and breeding success, we can all relish their absence.


Most of us have been there: determined to take the next step in life but thwarted in our efforts to do so. More often than not, another individual occupies the position we seek. That is the situation in which nine year-old W/G,B/S (hereafter “White-Green”), finds herself on Blue Lake.

Blue seems a good fit for White-Green. She grew up on Franklin Lake in Forest County, another large, clear-water lake 35 miles to the northeast. Since young males and females try to settle on breeding lakes similar to their natal ones, it is natural that White-Green should try to find a place on Blue.

But setting your sights on a goal and achieving it are two different things. Back in 2014, when she was only five years old, White-Green battled with the 15 year-old female from the Blue-West territory and lost. Since then, she has made sporadic attempts to evict her decade-older rival, failing each time. In 2016, she observed the violent overthrow of the male at Blue-Southeast by a younger rival. However, the carnage that ensued offered White-Green no opening at a breeding position at Blue-Southeast, although she paired briefly with the male evicted from that territory. Since then, we have so often seen White-Green on Blue Lake – and never on adjacent lakes that we also monitor — that she must live there, hiding out in the swath of unoccupied space between the two breeding pairs. And waiting.

She waits still. Two weeks ago, White-Green again challenged the Blue-West female, in what has become an annual ritual. I have begun to feel frustrated on White-Green’s behalf. Her many fruitless attempts at usurping a space recall times when I myself have been baffled in a crucial life pursuit. It would seem that the writing is on the wall: White-Green is not strong enough to subdue the breeding female at either end of the lake and seize their breeding position. Shouldn’t she move on? Isn’t she wasting valuable time in the prime of her life? As a biologist, I come at this from another angle, asking, “Could White-Green’s obsession with acquiring a territory on Blue Lake be evolutionarily advantageous?”

A precise answer to this question would require a calculation of evolutionary fitness benefits of fighting for a known resource versus turning her attention to a new target — a neighboring territory on Bobcat, Bolger, or Kawaguesaga. We do not have sufficient data to make such a quantitative comparison. However, White-Green’s “siege” of the Blue-West territory does highlight two quirky features of the loon breeding system that might help us understand her odd behavior.

Whether male or female, nonbreeding loons in search of a territory set their sights on a handful of them that they visit often, rather than casting a wide net that includes dozens of potential territories. We infer from the narrow scope of their search that young nonbreeders might use a strategy of sizing up territory owners, monitoring their condition regularly, and challenging them for ownership when they seem most vulnerable. (Of course, nonbreeders would prefer the low stress alternative of replacing a breeder that has died.) The tradeoffs of focusing on a small number of territories are clear. By getting to know the behavior of a few breeders well, young nonbreeders might be able to pick up subtle changes in breeder behavior that signal weakness and allow them to time their eviction attempts effectively. And conducting a narrow search might also permit a nonbreeder to learn about the illness or death of a territory owner rapidly, so that they can quickly mount a bid for the territory and claim it before others learn of the opportunity.

Another quirk of the loon breeding system is a female-biased sex ratio caused by greater longevity among females. That is, there are always more breeding females than breeding males in the population, since many males die young. The longer lives of females is a double-edged sword from their standpoint. On the one hand, there is vigorous competition for any female breeding vacancy that becomes available. On the other hand, females live long enough that what at first appears to be an unhealthy obsession with one territory or two might ultimately be rewarded.

Breeding prospects for loons in northern Wisconsin seemed dim only three weeks ago. Not only had a frigid April delayed the start of nesting, but Simulium annulus was doing its best to keep loons from warming the eggs that had taken so long to appear. A statistical correlation between cold spring temperatures and black fly harassment had me fearing that the long-awaited nests would be abandoned in short order – delaying the season still further. My hopes for a bounce-back year of breeding, after 2017’s disappointment, seemed distant.

As I keep learning in life, unfathomably horrid situations often improve. So it was this spring. To be sure, loons were forced to abandon a few early nests – those at Langley, Fox, and Wind Pudding-East, for example – owing to fly harassment. But loon pairs that had been reluctant incubators in mid-May suddenly bent to the task late in the month. Even after accounting for the inevitable wolfing down of eggs in exposed nests – such as those at Two Sisters-Far East, Long, and Little Bearskin — by raccoons and their ilk, the vast majority of our breeders are sitting on eggs (like the male on Linda’s lake; see photo). At last count, 79 of 123 pairs we cover are on nests that have survived the crucial first ten days. Two weeks or more of incubation remain for most of these territories. But barring some unforeseen disaster, 2018 might be one of the most productive years for northern Wisconsin loons in the last quarter century. Who would have guessed that a breeding season that started so inauspiciously would gain such momentum?

The Nose Lake male I observed today had a conspicuous scar on his head. This particular scar, which I dutifully sketched on my datasheet, was located on the right side of his head, behind and beneath the eye. In comparison, the head of the Nose Lake female was sleek and without blemish. Scarred males paired with pristinely-plumaged females are a common sight. In fact, the scar I recorded today was the 72nd of the study – and the 63rd seen on a male. Moreover, this scar has persisted for a month; Linda photographed this bird on May 6th, and the scar was obvious then.

Scars on heads of males, which occur when they grasp each others’ heads and necks in a territorial battle, bring to mind the short, violent lives that many males lead. Slowly and surely, we are beginning to understand why male battles are fiercer than female battles. Part of the explanation for this pattern has to do with nesting behavior. We know from analysis of nesting behavior among color-marked breeding pairs that male loons control the placement of the nest. While we do not know why males control nestsite placement, we can see that male control of nest placement cranks up the stakes for male territorial battles. Why? Because male loons learn by trial and error where to place the nest. Once a male has nested successfully on a territory, he reuses that good nest location again and again, boosting his hatching success. Therefore, once established on a territory where he has nested successfully, a male has a large stake in holding that familiar territory. If evicted from there, the male must relearn where to nest and where not to nest on a new territory, which costs him precious time and energy. In contrast, females, which do not control nest placement, can freely move from one territory to another without paying a penalty in lost familiarity and, hence, breeding success. Since one territory is, in effect, as good as another to them, females should fight less hard than males to remain on a territory – and they behave as predicted.

A second part of the explanation for violent male battles is rapid senescence. Again, while we do not yet understand why males should age so badly, compared to females, the contrast in senescence has strong implications for male behavior. A male reaches a point – in his mid-teens typically —  where he is in rapid decline. That is, he is losing body condition and is at great risk for losing his territory. With the future offering little reproductive promise, many males in their mid-teens increase their aggressiveness and territory defense so that they can squeeze another year or two of breeding out of their territory. This, of course, is the terminal investment finding that I have been blogging about for the past months. (By the way, that paper has just been published online.)

With two factors – male nestsite selection and senescence – at play, we can begin to understand why males might be so violent. The factors are additive. A fifteen year-old male on a familiar territory is both falling into decline and facing a steep loss in breeding success, if evicted. So he has two good reasons to fight like hell to hang on.



Last week was a tense one. Dozens of pairs had laid one or two eggs, but black flies descended on them, making incubation impossible for most. Of the fifteen or so pairs with nests last week, only two incubated at all, and one of these pairs sat only during the first twenty minutes of our observations. (The other was Linda Grenzer’s notorious overachievers, Clune and Honey.) All other pairs spent their time in the general vicinity of the nest — but diving frantically, shaking and tossing their heads, even snapping their bills fruitlessly at the relentless biting insects.

Already frazzled by the grading of 131 all-essay final exams, calculation of final grades, and strident pleas of disappointed students — I fielded another while writing this post — I feared another dreadful year of nest abandonments, like 2017.

What a difference a week makes! While not altogether gone, the flies are dwindling rapidly. Breeders that could only view their eggs from afar 7 days ago are back on them. I caught the male in the photo — from Two Sisters Lake-Far East Territory — about to hop cheerfully onto his nest, after an incubation switch. He and his unbanded mate still have 27 days of incubation remaining. But, like all of our focal pairs, they have overcome the first major hurdle.

Spring is on its way. As I twiddled with my phone just now to check conditions in the study area, the temperature was nine degrees warmer in northern Wisconsin than in southern California — the result of an unseasonably warm day in the study area and an unseasonably chilly one here in SoCal. At long last, the ice is melting, and loons will soon be back on their lakes. Meanwhile, as Linda’s photo shows, they gather in droves on open water. Being Linda, she also checked out their bands, yesterday and today, to see how many she could identify. We are all the beneficiaries of her tireless efforts, because her IDs provide a window onto the lives of returning breeders that are, for the moment, baffled in their efforts to reclaim their territories.

Who are these birds, and where are their territories? Are they males or females? Are they, in fact, breeders or young floaters, who lack territories and will spend the year challenging territorial residents for ownership? Are they migrants hundreds of miles from their breeding area or neighbors stopping by until their nearby lake becomes ice-free? We cannot answer all of these questions, but we can answer most of them based on Linda’s meticulous observations.

First of all, the loons in these aggregations are almost all males. Of the 12 birds positively ID’d by Linda, 10 are known males, one is a female, and one is of unknown sex. Linda suspected this herself: she reported numerous territorial yodels, sometimes by multiple males at once, as the birds rafted about in ice-free portions of the lake. Females must be only a few days behind; in fact, as I was writing this, Linda reported seeing a breeding pair near last year’s territory on Nokomis.

Second, loons present on the breeding grounds at the cusp of the seasons are mostly breeders that have come to reoccupy territories, rather than young floaters bent on evicting them. Only one ID’d loon from Linda’s list is a possible floater; all others are known breeders.

Third, loons that aggregate on ice-free water in early spring are a geographical smattering — many from neighboring lakes but a good many from farther north, whose lakes might not be open for a week or more. Linda’s sightings show this clearly, as her list includes breeding males from:

1) the adjacent Nokomis-East Central territory,

2) Indian Lake, which is 6 miles to the NE,

3) Soo Lake, 11 miles to the NE,

4) Silver Lake (Lincoln County), 8 miles S,

5) South Blue Lake, 16 miles to the N,

6) Miller Lake, 18 miles N,

7) Blue Lake-West Territory, 20 miles N,

8) Forest Lake (Vilas County), 40 miles NE,

9) Rock Lake (Vilas County), 50 miles N, and

10) Crab Lake (Vilas County), 50 miles N.

and a lone female from Burrows Lake, 10 miles NW.

What can we learn from these sightings? The preponderance of males confirms that males precede females on migration by at least a few days, and shows that males are the main ones bottlenecking on rivers and open lakes near their ice-locked breeding territories. Returning males push hard to return very close to the date that their lake becomes ice-free; females dawdle by a few days. Why it is so crucial for males to return as close to ice-out as possible is unclear, especially since the paucity of young, non-territorial birds present suggests that breeders are not likely to be challenged for territorial ownership in the first few days after settlement. Perhaps males, because they select the nesting site, return as early as possible to take note of any changes in the lake or shoreline over the winter that might require them to move the nest from the prior year’s site.

We can also discern that these early spring aggregations do not comprise neighbors reacquainting themselves after a winter apart, but individuals from far-flung lakes that do not know each other at all and are likely not to encounter each other again. While we should not be surprised by some tense moments between such unfamiliar individuals — it is, after all, spring and hormone levels are high — we should expect mostly peaceful loafing and feeding. These males simply have nothing to gain from battling unfamiliar loons.

In short, the rafts of loons in Linda’s photo are playing a waiting game. Since territory settlement is a time during which owners must defend their lakes vigorously — even if they do get a brief hiatus after settlement, owing the late return of young challengers — we would expect these males to do next to nothing until their lakes open up. They should feed, rest, and expend as little energy as possible before the onerous task of breeding begins.


I have always loved working in the field. While others remain indoors, chained to their desks and computers, much of my work requires paddling canoes on beautiful lakes to record behavior of loons. It is a dream job. Recent findings, though, are forcing us back into the laboratory.

Why must we return to the lab? Most of you know already from recent posts that male loons senesce dramatically in their mid teens and that they also become aggressive at that age. But the fact that males decline, whereas females do not, raises vexing questions about underlying physiological causes of male decline. Does male health hit the skids because of the cumulative impact of blood parasites? Does the greater body size of males make it more difficult for them to maintain good health throughout their lives? Is male decline linked in some fashion to conditions faced during the chick phase? As always happens in science, one finding, even a very clear one, raises a legion of related questions.

Fortunately, we can answer many such questions by taking small blood samples from our loons at the time of capture. Jeremy Spool, a soon-to-be-Ph.D. from University of Wisconsin-Madison, supervised the taking of these samples, which can tell us about hormone levels, parasites, and genetic patterns. Jeremy also completed a preliminary wave of analyses and has made an interesting discovery with regards to telomeres.

First some background. Telomeres are “end caps” on chromosomes — composed of many repeated DNA sequences — that protect chromosomes when they are replicated during cell division. In both humans and loons, the sequence of repeated DNA building blocks (nucleotides) that comprise telomeres is the same: TTAGGG. Telomeres grow shorter with age and with illness in humans and many other animals. Human babies have chromosomes capped with about 2,500 repeats of TTAGGG; older humans have only about 800 such repeats. A number of researchers have found that shortening of telomeres is related to stressful conditions faced by non-human animals. For example, one study reported that cormorants and albatrosses hatched late in the breeding season showed greater shortening of telomeres — possibly indicating more rapid aging — than did individuals born early in the breeding season. A good deal of work remains to be done on telomeres to determine if they can predict patterns of aging and body condition, but there are some promising signs that they can do so.

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Jeremy analyzed telomere length in loon blood samples from 2017 to see if: 1) telomere length was correlated with age, and 2) males and females differed in telomere length. He noted a weak tendency for male telomeres to shorten with age. We will have to add more data to see if the pattern holds up. On the other hand, Jeremy also found that females had telomeres significantly longer than those of males (see figure, above). Since we know that female loons live longer than males and do not experience a sudden decline in condition in their mid teens, this pattern is as we might have predicted.

What does the telomere pattern tell us? While it is vaguely comforting to find a physiological correlate to confirm the difference in aging pattern between male and female loons, telomere shortening is still a mystery in animals generally — and most certainly in loons. We can draw no immediate link between short telomeres and any other aspect of physiology, like parasite load, immunological capacity, or even age. But the male/female difference gives us hope that telomeres might predict body condition, disease resistance, and/or life expectancy, within each sex. If so, then measuring of males’ telomeres might permit us to predict if and when they are near death and should begin behaving aggressively — to allow themselves one last desperate reproductive gasp. Moreover, if young loons, like cormorants, pay a price by losing some of their telomeres from the stress of being hatched late in a breeding season, then differences in hatching date might help us solve the enduring mystery of why some male loons cannot survive past their mid teens, while others thrive well into their 20s.

As many of you know, I am a worry-wart. Normally I get so stressed-out about my kids, my teaching, my research, my health — and many other matters that are going well — that I hardly have time to obsess about loons in the study area. But Linda Grenzer’s bleak photo of conditions on her lake today gave me a jolt. Could the late ice-out that we are facing in 2018 delay the season so much that it damages the breeding prospects of our loon population?

One might think that the later the ice comes off of the lakes, the later the loons nest, and the less time parents have to fatten up their chicks and prepare them for their first southward migration. Thus, a late ice-out might well lead to reduced breeding success for the population. Although there are many “if”s in this string of logic (and a preliminary analysis did not bear out the pattern), I felt concern  gnaw at me.

So I did what scientists often do to stave off despair: I looked at the data. First, I looked to see if loons nest later when the ice goes out later, which almost has to

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be true. It is true, but there is a lot of noise in the data. That is, loons are constrained to nest somewhat later in years when the ice goes out later, but the picture is not simple. The reason for the noise becomes clear when you look at the lag time between when loons settle on their territories and when they hatch their

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young. There is a very strong pattern here. When the ice goes out early (left side of graph), loons dawdle and wait weeks before nesting. But when the ice goes out late, as it will this year, pairs get down to business quickly, nesting within a week or so of territory return. So loon pairs are somehow able to catch up in years of late ice-out so that their breeding schedule does not differ greatly from other years. (Notice also that the orange line in the top graph is flatter than the blue line.)

What accounts for this pleasing pattern? We can make a pretty good guess based on findings in other migrant birds. Spring migration is an energetically costly process. In an early year, the ice is gone so quickly that loons settle on their lakes as soon as they return from the wintering grounds. In such cases, their fat levels are very low from migration when they first occupy their territories, and it takes a good deal of foraging before they return to good condition. In a late year, loons cannot settle on their territories right away but must wait on nearby rivers that have open water. There, they are able to forage and restore their bodies to good condition. As a result, loons hit their territories in prime body condition and fully recovered from the migratory flight in years of late ice-out. Thus, they can get down to breeding quickly.

Although I was heartened by the data I saw above, I had a look at the numbers that most directly addressed my concern about late ice-out and population breeding success. There is a no statistical tendency for the population to produce more loon chicks in years of early ice-out, despite the many years of data we have to look for such a pattern. Indeed, some of our best years for loon breeding (2013, for example) have occurred when the ice goes out late. So those many of you shivering in northern Wisconsin and other frigid regions can relax about one thing; the loons are no worse off in years when spring comes late than when it arrives early.