Few loons have endured the frustrations that the current Mildred female (“Taupe Stripe”) has. Initially captured and banded on Soo Lake in 2004, she reared two healthy chicks with her mate in that year. But each year since has yielded no offspring for this bird, despite consistent effort.

Taupe Stripe’s struggles started when she was evicted from Soo by a stronger female in 2006. Thus began an itinerant lifestyle: temporary settlement as a loner on Goodyear Lake and frequent intrusion into other lakes in the area, probing for an opening. In 2010, she finally secured and defended a breeding position on Maud Lake. Like other small, shallow lakes, though, Maud suffers from a limited prey base. Efforts by the loon pair there in the three years before her arrival were excruciating — hatched eggs followed by starvation of chicks in the 2nd week of life, the first week, and then the fourth week. Taupe Stripe and her two mates fared no better, failing to produce young in 2010, 2011, 2012, and 2013. She fell off our radar in late 2013 and 2014, but resurfaced in 2015 and 2016 — again, as a floater.

When day to day survival is a challenge, as it is for loons, you focus on the present. Taupe Stripe ultimately settled on Mildred Lake in early 2017. Unlike Maud, Mildred is a large, clear lake with a strong record of fledging chicks that hatch. Although she and her unbanded mate lost a small chick on Mildred last year, they have turned things around. Last week we caught Taupe Stripe, her mate (now banded), and their strapping six-week-old chick. Things were still looking good for the family upon my visit there today. And thirteen years of pointless wandering, frustration, and disappointment are forgotten.

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.

I have just completed my paper on black flies. The paper presents evidence that black flies cause nest abandonment, which was lacking in the literature before. The evidence is pretty convincing, I believe. (We shall see what my scientific colleagues think when I submit the work for publication in the next week.)

In the course of looking at black fly impacts on nesting, I stumbled into two  interesting findings. These findings were serendipitous, like much of what scientists report. That is, I was keenly focused on one topic — black flies and nest abandonment — when I made a finding related to another topic — other causes of abandonment. In fact, I analyzed statistically a whole set of factors, some seemingly unrelated to black flies, that might have predicted nest abandonment. Among these were age of the male, age of the female, duration of the pair bond between them, exposure to wind (which might have kept the flies at bay), size of breeding lake, and distance from the nest to the nearest flowing water (from which black flies emerge as adults).

I was excited, but also baffled, to discover two new predictors of nest abandonment. First, pairs on large lakes are less prone to nest abandonment than pairs on small lakes. Second, pairs containing an old female are far more likely to abandon a nest owing to black flies than are pairs containing young females.

Now, I like to think that I know everything about loons. When I am visiting a study lake and someone asks an easy one like, “Do loons mate for life?”, I puff myself up, lower my voice an octave, affect a mild British accent, and pontificate on the serially monogamous breeding system of Gavia immer. But I was wholly wrong-footed by these two new findings. I had been so laser-focused on black flies as the prime movers in nest abandonment that I had included age and lake size in the analysis almost as an afterthought. I had not even considered what it would mean to learn that age and lake size were significant predictors.

The statistical significance of lake size as a predictor of abandonment forced me to confront a complex variable. If numbers of black flies are correlated with nest abandonment (as they are), then it requires no great conceptual leap to infer that black fly harassment is causing loons to abandon their nests. But the fact that lake size predicts abandonment opens up a much broader range of explanations, because lake size is correlated with degree of human recreation, pH, wind exposure, wave action, available food, and numerous other factors. Having picked through the possibilities, an energetic explanation seems most likely to explain the lake size pattern. That is, large lakes provide more food than small lakes, so loon pairs on large lakes should be in better health and condition than those on small lakes. Well-fed, healthy adults with strong immune systems should be better able to cope with the blood loss and exposure to blood-borne pathogens (like Leucocytozoon protozoans, which cause a malaria-like disease in birds) than under-nourished individuals with weaker immune systems.

What about the higher abandonment rate of pairs that contain an old female? Here again, energetics might be the key. Old females senesce — they experience much lower survival and slightly higher vulnerability to eviction than young females. So it stands to reason that old females are in poorer body condition and are more likely to abandon nests when attacked viciously by black flies. Reproductive decline among old females is widespread in animals, and the tendency of old female loons to abandon nests more readily seems consistent with that pattern.

But what about males? As I have emphasized in recent blog posts, males senesce even more dramatically than females do. How is it possible that old males can continue to incubate eggs when being bitten mercilessly by black flies when old females cannot? Terminal investment appears to be the answer. Terminal investment — efforts to increase breeding output as death approaches — occurs only among male loons, even though both sexes senesce. As the months have passed, we have learned that male loons not only become hyper-aggressive when they reach old age (15 years) in an apparent attempt to hold their territory for another year or two of breeding, they also seem to show a more subtle willingness to try harder to hatch eggs and rear young to fledging. The new finding showing that old males do not abandon nests as readily as old females when beset by black flies is thus part of a growing pattern.

My tentative explanations for the impacts of lake size and sex on nest abandonment are not the end of the story, of course. Rather, they raise more vexing questions. Why on earth would a loon settle to breed on a small lake, when small lakes doom loons to poorer body condition, a higher rate of abandonment, and the likelihood of losing one or both chicks in the event they can hatch the eggs? And even if the higher rate abandonment of nests by old females fits a growing pattern, why do males and females differ so much in their life-history strategy? We do not know….and this is why I love my work!

I have often sung the praises of female loons. Females, you will recall, have much greater staying power than males do. Adults of both sexes face the constant threat of eviction, by younger, fitter individuals. Males fight desperately for their territory, retaining it at great cost and sometimes dying in its defense. Females, on the other hand, seem to keep defeat in perspective, retreating to a nearby lake after losing their territory and then going about the arduous process of reestablishing themselves on a new territory.

Even among females, the Upper Kaubashine female stands apart for her tenacity. One distinction is simply her age. Having been banded in the first year of my study, 1993, she is most likely at least 31 years old. She is, therefore, the oldest loon ever in our study area. What seems even more remarkable about the Upper Kaubashine female is her breeding success, which spans a quarter century, five different territories scattered across Oneida and Vilas Counties, and at least six mates. No other loon, male or female, can match the breadth of her breeding record.

The Upper Kaubashine female epitomizes the relentless efforts of female loons to reproduce. However, her story is not one of unbridled success, like that of the Townline male (pictured during capture from a few nights ago). The Townline male has been a success through holding his territory for 24-plus years and cranking out chicks there. The Upper Kaubashine female has achieved genetic immortality by a nomadic path — tirelessly relocating and re-pairing following repeated losses of territory and mate. After all, to achieve the lofty distinction of having bred on five different territories requires the ignominious distinction of having been evicted from four.

What is it about this female that set her on this reproductive odyssey? We do not have a complete answer, but size likely plays a role. Throughout her life she has weighed in at about 200 grams lighter than average, which puts her in the lowest quartile of female size. Most of the female intruders that have visited her various territories to challenge the Upper Kaubashine female for ownership have outweighed her. It stands to reason that she has lost more than her share of battles. Only her uncanny ability to establish herself as a breeder on one high-quality territory after another has allowed her to overcome her physical limitations and become a productive breeder.

We always celebrate when someone identifies a new banded adult. “You got an exclusive!”, I say to one of my students, if they nail all bands on a loon that we banded as a juvenile in the study area and have not seen since. In fact, Melanie reported an exclusive ABJ (for Adult Banded as Juvenile) just yesterday; this one happened to be a four-year-old male hatched on Samway Lake that she ID’d on Elna. (Linda’s photo shows an exclusive that she nailed bands on, this one from Soo Lake.)

Sightings of young ABJs are valuable. These loons are all “floaters” — nonbreeding individuals that live on small lakes or parts of large lakes that are not used by breeding pairs — so they live a marginal existence. Still, they provide us with data on juvenile rates of survival and return to the study area, which contribute to mathematical models that tell us whether our population is stable, increasing, or decreasing. Young ABJs are also the future, because these green, reticent individuals — they are notably subordinate when interacting with territorial residents, have low fighting ability, and are well below optimum adult body weight — will ultimately replace our established and well-loved territorial breeders.

I spend most of my research time asking behavioral questions about our long-term territorial residents, which is regrettable, because it leaves young ABJs out. In fact, a vexing question concerning young ABJs has been lurking in the back of my brain for some years now: where do they all go? From the countless small celebrations the students and I have had over the years at new ABJ sightings, an expectation has formed that we would see a vast wave of new territory settlements by this youthful cohort. But it has not happened. Each year only a handful of young ABJs claim new territories by evicting a living territorial resident, replacing a resident that has died, or carving out a new territory where there was not one previously.

This morning I got fed up with waiting around for all of the young ABJs to settle — and looked at the numbers. They are pretty shocking. We have been able to celebrate sightings of 348 young ABJ floaters over the years. That is a lot of loons. Of these, though, only 124 settled on breeding territories and paired with a mate for at least 60 days. And an even smaller number — 94 — nested and hatched chicks. Since most of these individuals were last seen years ago, most died long ago. So only slightly over one-fourth of all young ABJs that returned the breeding grounds ever produced young. Even this rather low fraction is too high, because it presumes that we actually ID all young ABJs that come back to the study area. Clearly a typical young ABJ deals with many challenges — lengthy migrations between breeding and wintering grounds, bouncing around in the study area, probing here and there for territory openings, absorbing attacks and chases at the hands of territory owners — only to fall short in that last, most crucial test: territory settlement.

Why? Why would the rate of failure to settle be 75%, when vacant lakes with a successful record of chick production abound in the study area? If I were a loon (I know….but don’t say it!), I would look around for a prime breeding territory, pick a few fights to try and get one, and then settle for a less-than-perfect but adequate territory, if it came to that. Because failure to settle leads to evolutionary oblivion. That is, we expect that natural selection has acted on behavior in such a way as to maximize breeding success, and breeding success would appear to be maximized not by failing to settle but by settling wherever you can and cranking out as many chicks as possible there.

Of course, it is hubris to think that humans know how loons should behave. Loons have been molded by natural selection and other evolutionary processes for countless generations in a way that virtually guarantees that their behavior leads to high evolutionary fitness. However, as my students in Animal Behavior class know well, there are a few caveats to the expectation of sensible, adaptive behavior by animals. The main one is that rapid environmental change can sometimes outpace the capacity of animals to adapt, causing animals to behave in a way that does not maximize their reproductive success. In other words, if the environment that an animal faces — its predators, competitors, physical environment, etc. — changes so rapidly that the species cannot evolve suitable behavioral adaptations, then we might see animals behaving “foolishly”. So we might surmise that ABJs fail to settle on vacant territories because the availability of vacant territories has only recently increased, and loon settlement behavior evolved during a period when vacant territories were scarce. In effect, then, ABJs would be practicing behavior not suited to the territorial situation that now exists.

While we cannot reject the hypothesis that rapid environmental change has made loons look stupid, it is a bit hard to stomach. The hypothesis posits that young floaters are poor settlers because they are not used to territories being readily available. But whether territories are scarce or abundant, young floaters should have evolved to be able to occupy any available one readily. That is, the capacity to snap up a vacant territory is so fundamental that it is a trait that should be possessed by all young loons, regardless of the territorial environment in which they evolved. There must be a better explanation for the failure of so many young ABJs to settle on territories.

The reason for lackadaisical territory settlement by floaters is probably habitat preference. Some of you may recall that young loons show a peculiar but very strong preference for natal-like habitat. Specifically, young floaters from small, acidic lakes strongly prefer to breed on small, acidic lakes, and those from large lakes of neutral pH try to establish themselves as breeders on large, neutral-pH lakes. Strong habitat preference creates a situation where a young floater reared on one kind of lake does not see vacant territories on another kind of lake as a viable breeding option. If young ABJs are being finicky about the territories they choose to settle on, we should expect to see some “perfectly good” territories go unsettled, as we do. More to the point, we should not be surprised that many floaters fail to settle.

Natal habitat preference might help us understand the seemingly inefficient territory settlement of young floaters, but, if so, it merely shines a spotlight on another vexing question: why do loons strongly prefer to breed on lakes that resemble their natal one? I have speculated about this before, but no satisfactory answer has yet emerged. As we collect more and more survival data, we might find that loons have evolved to take into consideration more than just the potential of a breeding lake to produce chicks. Indeed, settling on a territory like your natal one might mean that you were prepared since day one for that kind of environment and might be able to survive well there. If so, natal habitat preference might allow you to offset with longevity any loss you suffer from settling on a territory that is less-than-stellar for producing chicks. The slow but steady approach of rearing a chick here and a chick there but surviving to a ripe old age might be the one that maximizes lifetime breeding success.

A few years ago, my daughter and I were talking about her high school homework. I cannot recall precisely what class we were discussing, but a moment occurred when I became concerned that she was unprepared for an upcoming test. Anxiety hung in the air for a second before she reassured me. “Dad”, she said with a twinge of impatience, “I am a nerd”. It was her way of telling me that she was studious, exacting, and did not need to be told to get her work done.

As you all know by now, I too am a nerd. I wear that label — like my daughter does — as a badge of honor. The nerds I know are thoughtful, bookish folks who enjoy making fine distinctions and extracting subtle patterns from scientific data. Nerdiness of this kind is essential to a scientist, of course. Publishing our work and being taken seriously by our colleagues requires that we navigate a mine field of biased samples, uncontrolled variables, and specious correlations to arrive at valid conclusions to our questions.

Nerds are different. Most people, while chatting with a stranger in a supermarket line, can get away with saying, “Aaron Rodgers killed the Packers last year with his erratic passing in big games”. A nerd, however, would want to look at the data. S/he would examine Rodger’s passing statistics against teams with winning records and division rivals to see if, truly, he played worse in those games than in less important contests. While nerds can be annoying nit-pickers in society — the kind of people you want to avoid sitting next to at a party — we are quite valuable as scientists. We have the patience and passion to discover true causes of patterns in nature.

I was able to bring this patience to bear on a recent question about loon behavior. In my ongoing investigation of senescence in male loons, I faced a puzzle. The territorial yodel of males serves two purposes. It is, most obviously, a territorial call that males emit when a competitor is flying overhead or sitting nearby in the water. At such times, the yodel announces the willingness of a male to fight for territory ownership. But the yodel also serves to protect the young (see Linda’s photo, above); that is, male parents often yodel to prevent landings of flying intruders, which sometimes attack and kill chicks. Why does it matter that the yodel serves two purposes? Because I am trying to make a nerdy distinction: Do old male loons yodel more than young males because they are defending their territories, or do old-timers yodel more simply to defend their chicks?

This distinction is important. If you have been following this blog, you know that old male loons make a terminal investment in reproduction. The most obvious evidence of terminal investment by old males is their tendency to yodel more often than young males. But since yodels occur both in territory defense and in chick defense, it was not immediately obvious whether old males were yodeling their heads off at intruders simply to protect their chicks or to maintain ownership of their territories. Fortunately, we have enough yodel data from periods with and without chicks to see if the increased yodeling of old males occurs at both times. It does! Hence it seems that old males are employing the yodel call to defend their territories as well as to defend their offspring.

To a nerd, the ramifications of this finding are profound. An old male who yodels simply to protect his chicks is investing extra energy to rear his offspring to adulthood at the possible expense of his own survival. This is rather a short-term strategy, as it is aimed at rearing young to 11 weeks of age, after which young are out of the woods, and the investment has been successful. An old male without chicks that yodels, however, is taking a long-term view. Chickless males are months away from producing young. Their yodeling is aimed at guaranteeing territory ownership for many future months, even years. Although terminal investment in offspring is rare in animals, terminal investment in territory ownership is virtually unknown. So the stepped-up yodeling by old, chickless male loons is an exciting finding. As you might imagine, this result has set off quite a nerd celebration!

I do not know why I am still surprised by it. Again and again we see territorial females vanish, only to reappear as intruders in their former territory or another in the same neighborhood. The theme has been consistent throughout my quarter-century-long research project on loons. In fact, it is about a 50-50 proposition that a female who disappears from her territory will be resighted nearby in the next year or two.

I suppose the reason why I am always wrong-footed by female reappearances is that I am calibrated to human social conditions. Unlike loons, humans are highly social and benefit from a vast network of family ties and friendships. Humans have evolved to cultivate those bonds — leaning upon family and friends when necessary; providing support, in turn, when called upon to do so. Humans, therefore, rarely vanish without a trace from an area where they have lived for many years. We typically maintain most or all of our social connections even when we shift from one location to another.

Loons, in contrast, are quite alone. To be sure, an adult male or female has the companionship of its mate for several months each year. But this companionship is ephemeral and conditional. When a loon’s mate is evicted by an intruder, the loon faces a stark choice: remain with its mate of many years but move to a new territory, or stay on its territory and accept the evicting intruder as its new mate. Adult loons always spurn their long-term partner and make the coolly pragmatic choice.

Knowing loons as I now do, I should not have been surprised when Linda sent me this crisp photo of an intruder departing from Muskellunge Lake. Although the bird is missing a colored leg band from its right leg, it was not difficult to determine that this intruder is the former female from Manson Lake, who has not been seen since fall 2015. Since loons almost never desert a territory, we can surmise that “Silver over Red, Mint Burgundy over White” (as we affectionately call her) was evicted by the 9-year-old female from Rock Lake in Vilas County who was first seen on Manson in April 2016 and still owns that territory. The eviction forced “Silver over Red” into an itinerant existence. Though you might think that a veteran of 12 years of breeding and mother of 11 fledged chicks had earned better treatment, this 20+ year old now spends her time drifting from one inhabited lake to another as an intruder, searching for a new mate and territory so that she can resume breeding.

It is tempting to pity Silver over Red. These past two years have been difficult and dangerous for her, no doubt. But rather than viewing her and others like her as individuals whose best years are behind them, I always feel an intense admiration for displaced female loons. While many of us humans respond to setbacks with a shrug of acceptance, female loons never stop hunting for a new opportunity.

LMG2693 Loon Between the Ice

I always dread ice-out. While I am excited to know that I am scant weeks away from seeing the loons, ice-out now tends to occur during the high-stress period of the Chapman spring semester — and I am seldom ready for the event. As Linda’s photo from the Wisconsin River shows, loons are coming back, accumulating on the river, waiting for their breeding lake to open up enough to permit landing there. Meanwhile, my Animal Behavior students are sweating their behavioral experiments and write-ups.

Let’s focus on the positive of early ice-out for data collection. Rain and warming temperatures mean that ice-out is only days away. Soon we will begin to log the identities of returning veterans anxious to attempt another year of breeding. Since the lakes will be habitable two or more weeks before the historic mean date of ice-out, while many returning birds are still en route from the wintering grounds, we have an opportunity. In theory, adult loons that are in good physical condition generally should be those that can complete the breeding molt early and also migrate early. So the loons that show up first on breeding lakes should be those in good condition. Recent findings have shown us that this group comprises males and females about 8 to 15 years old — the prime of life for a loon. Thus, we predict that the early arrivals are in this age-class. The laggards should be breeders that are either very young — 5 to 7 years old — or very old — 20 years and older. We might expect the territories of such individuals to remain vacant for a week or more after the ice has come off of them.

If age does turnout to be a good predictor of date of territory occupation, then late return from migration could be another source of trouble for an old established breeder. That is, an old territorial bird whose body condition has begun to decline might not only need to worry about being evicted by a young, fit nonbreeder in the midst of breeding; danger might also come from the tardy return of the old bird to its territory in the spring, which could open the door for a youngster to seize the territory, pair with the old bird’s mate, and hold off the former owner when it returns.

I have painted a dire picture. We will have to use the increasingly early ice-outs like this year’s to measure date of return accurately and see if early ice-outs truly destabilize territory ownership. At the moment, I will tantalize you by reporting that breeding success across the population is higher when ice-out comes late. It is speculative at this point, but this pattern might indicate that early ice-outs lead to ousting of old, experienced breeders from their territories, which in turn suppresses chick production of the entire population. If so, I have one more reason to rue early ice-outs!

 

Our paper that describes basic features of senescence has been accepted for publication Journal of Avian Biology. With the lightning-fast turnarounds and early views that the public is now granted to scientific articles, you can search for the paper and read an advance copy…months before copy-editing and proofing of the final version is done. Let me know if you find any typos!Screen Shot 2017-03-10 at 12.47.06 PM

The paper describes findings that I have been blogging about for some months now. First, both sexes of loons senesce (begin to die at a high rate) once they reach their mid-20s. Second, at first blush it seems that the sexes do not differ substantially in the senescence pattern. Third, this paper looks only at territory holders, which are the creme de la creme of adult loons, because they have not only survived to adulthood, but also claimed a territory and produced chicks there. Thus, this group of birds analyzed does not include the many adults who tried but failed to settle on a territory or settled briefly but did not reproduce. Fourth, old males (but not females) suffer a decline in territory resettlement after being evicted from a territory. Finally, we present in the paper preliminary evidence that suggests male might increase or at least maintain high breeding success at advanced age, while it seems that females fall into reproductive decline. So there is a glimmer of possible terminal investment by males (increased investment by animals near death) at which this paper hints. If you have followed my blog, you know that we have data from a separate analysis that deals more directly with the possibility of terminal investment by males.

That is all I have for now. I have just finished hiring the four field staff members for this year. They are a strong bunch and include one of our seasoned hands from 2016. Since we are on the verge of ice-out already, I have gotten the crew hired none too soon. By the time most of us arrive in May, nesting will be well underway. No matter. We are accustomed to scrambling to keep up with the loons.

See you out on the lakes!