survival

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We all focus most of our attention on breeding pairs and their chicks. Why not? Breeders are the loons we get to know — day after day, year after year — as they struggle to hold their territories, choose nest sites safe from raccoons, incubate their eggs for 4 long weeks, and then protect helpless offspring from all manner of environmental threats. We admire the toil and turmoil they face each year and are downcast when they lose their breeding position, nest, or chick. And we grieve when they die. I am probably unusual in this regard, but I am also inspired by observing the challenges that breeding pairs routinely confront and overcome.

In our obsession with breeding individuals, though, we forget about the many loons living on the margins. These are “floaters” — mostly 2 to 7-year olds who spend the entire summer without a fixed home. Floaters are the individuals that forage alone on small lakes or skulk along the outskirts of defended territories, occasionally socializing with or accosting territory holders. Unlike territorial loons, they drift about.

Although their lives might seem simpler and less stressful than those of territorial loons, floaters — even young ones — face challenges of their own. Our work has shown that 2- to 4-year olds are much lighter than 5- to 7-year olds, are more submissive to territory holders during territorial intrusions, and almost never initiate battles for territorial ownership. Yet these youngsters do intrude into breeding territories. We presume, therefore, that even as they mature, young floaters collect information about owners. Our data show that young floaters intrude strategically into territories within a focused area (usually about 10km in diameter, see figure below from our recent paper) so as to meet and interact with owners of their own sex that they might

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evict down the road.

Having reached optimal adult condition, floaters of 5+ years of age begin to size up owners with greater urgency, choosing to battle those that appear weak or are noticeably weaker than they were on a previous visit. Male floaters probably also listen to the quality of a male owner’s yodel, because certain acoustic elements of the yodel convey information about the yodeller’s body size and condition. As we have seen repeatedly, intrusions by floaters of 5+ years of age are not welcomed by territory holders — and can be dangerous for both parties.

Considering that 2 to 4 year-olds are still reaching optimal body condition and 5 to 7 year olds are putting themselves at risk by actively seeking territories, it is surprising that floaters of both age groups survive at a rate just as high (about 90% annually) as established pair members (see figure below). Apparently the risks of probing and competing for a territory among young loons are roughly equivalent to those that come with

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territory defense and chick-rearing among older individuals. (Note from the figure that only older age-classes, and only males, show lower survival.)

We are used to the invisibility of floaters. That is, we see and study them as intruders into defended territories, but we seldom consider where they come from or how they live. So I always get a jolt when a dead floater turns up, like the tame 5 year-old male in Linda’s photo from the Lake Nokomis area. These rare unpleasant finds are a good reminder that gaining a territory is a long and difficult slog.

 

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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.

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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.

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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!

 

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Science is a cumulative pursuit. That is, the thirst for knowledge is never fully quenched. Rather, we answer one question, only to reveal another puzzle or two more. And thus begins another search for answers. That is certainly how my 24-year-old loon project has gone. But sometimes we reach a point where a vexing question is finally laid to rest, and it feels as though we have made real progress. I am at such a point now.

Let me back up. If you have been following this blog, you know that senescence in old loons is a phenomenon we have recently discovered. Senescence, loss of body condition and decline in survival rate in aging individuals within a species, is all too familiar to me and other humans. During the past twenty years, many studies have reported senescence in birds, mammals, fish, and reptiles. So what? Well, we expect that animals that lose condition as they grow old will change their behavior in response. In other words, scientists have long predicted that senescing individuals should start to behave so as to leave more to their offspring and care less for themselves. To put it another way, old individuals should be willing to take a hit to their survival if it allows them to pour more resources into their young and help their young survive. This makes sense, of course, because old individuals reach a point where they stand little chance of surviving longer, so they would do well to give whatever they can to their offspring, which DO have a bright future. Animals that behave this way should leave more and healthier offspring, and thus this behavior should spread in populations. This very logical idea is termed “terminal investment”. Again we can all probably think of human parallels.

Terminal investment, which I have mentioned before, has become a central theme of the loon project, ever since we published a paper 9 years ago on fatal fighting of males. Terminal investment became interesting to us because it was the most plausible explanation for such lethal contests. Our reasoning was as follows. If males are willing to die to defend their territories, then they must reach an age at which they have little to lose. And if males have little to lose, this must mean that senescence hits males (but not females, which seldom battle to the death) very hard to the point where old males have little future to look forward to. In this case, it might make sense for them to fight like crazy to hold a territory for another year or two, rather than give it up easily and leave themselves nowhere to breed during their last year or two of life. So we have two clear predictions here: 1) males, but not females, must start to die off at a certain age, and 2) males beyond this age must still fight like hell for their territories. It is this clash of body condition and behavior among old males that might cause fatal fighting.

At the time we started to consider the terminal investment hypothesis as a means to explain reckless battling by males, we had almost no solid information on the ages of males in our population. With patience and tireless field work by dozens of us, we have now turned things around. Analysis of loons of varying age has shown us that many males hit the wall at age 15. First, and most important, they start to die at a high rate. You can see from the figure below that males (blue bars) are suffering higher mortality than females (red bars), whether they are on territory (Terr) or without one (floaters: “Float”).

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But males also lose mass at age 15, indicating loss in body condition, as shown here:

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Finally (and predictably), males get evicted from their territories at a high rate at age 15:

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Wow, males are really getting slammed after they pass the age of 15 years!

So all of these data tell us that the first prediction of the terminal investment hypothesis, abrupt senescence at a certain age in males but not females, is clearly met in loons. That age, surprisingly, is only fifteen. Females clearly remain strong, healthy, and vigorous well past age fifteen.

As hard as the first prediction of terminal investment was to test, the second prediction is even harder. You see, fights are common in loons if you take the perspective of a loon’s lifetime, but they are quite uncommon if viewed from the standpoint of human observers in canoes. In other words, most individual loons have engaged in several major battles during their long lives, but territorial battles are not common during day to day observations and often occur so quickly that we are not present to witness them.

Patience pays, however. Since we can draw upon 24 years’ worth of field observations, we now have a trove of observations that we can search for any evidence of aggression and territorial behavior. I made this search, looking for two kinds of evidence: 1) territorial yodels, which serve to communicate a male’s aggressive tendencies and willingness to battle, and 2) out and out aggression, in the form of battling, lunging, chasing and underwater attacks launched by territorial loons on intruders to their territories. I was simply asking “Do old male loons (above age 15) tend to maintain a high level of yodeling and aggressiveness towards intruders?”.  The answer is a resounding “Yes”:

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As you can see from the figure above, old males actually increase their tendency to yodel (yodels per intruder), compared to young males. Similarly, old males step up their aggression (see below) and contrast in this way with females, who show no increase:

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By the way, all of these patterns I have shown are “statistically significant” via tests that I have performed.

You cannot be as excited as I am about this set of results. No one is. But, as I mentioned, this is one of those rare cases where we have finally managed to answer a burning question to our satisfaction. Even better, the question is one that had been the foundation of my research funding from the National Science Foundation. So I can now report to them that I have found the holy grail! What makes this clear finding even more significant is that terminal investment is quite rare in vertebrates. Of the hundreds of species studied thus far, the only other one to show such a clear pattern of terminal investment is the California Gull. Appropriate, don’t you think?

(Photo by Woody Hagge.)

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Most of us think of adult females as the main care-givers and protectors of the offspring. I am reminded of this constantly during my work. Several times a year, when I chat with a lake resident about their loons, I hear them say “She was on the nest today” or “The mom was feeding them down at the south end” or “She hollered like crazy when the eagle flew near the chicks”. It is natural for humans to infer that the female takes the lead in breeding activities; after all, we are mammals. In almost all mammals, females protect the young within their bodies for many weeks or months before they are born and continue to care for the young by themselves after they are born. Lengthy gestation makes male parental assistance superfluous, so mating systems have evolved in which males occupy themselves in other ways. Most mammals are either polygynous (one male mated with multiple females) or promiscuous (rapid mating and the lack of a pair bond). Females, in such cases, are left to provide most or all of the parental care, because males are either engaged in seeking out new mates or are not around at all.

Birds are different. Laying of eggs “frees” females, in the sense that they are not physically connected to the eggs and are no better equipped to care for eggs or young than are males. In birds, therefore, monogamy and biparental care are the rule. Most male birds  mate with a single female and provide substantial assistance to her in rearing the young. Male loons, as I have noted in the past, incubate the eggs equally with females and actually provide somewhat more parental care for chicks. Thus, more often than not, when folks tell me that the female hollered at a menacing eagle, or the female was feeding the chick lots of minnows this morning, they have mistaken the male for the female. (This puts me in the awkward position of either correcting the mistake, at the risk of embarrassing my friend, or grinning good-naturedly and leaving the error unchallenged.)

I got one more reminder of male loons’ central role in reproduction during a statistical analysis this past week. I asked whether males or females show age-related changes in fledgling production as they mature from young territory holders to middle-aged to senescent adults. (Note that one bar is missing for each sex in the figure below: too few females settle by age 5 and too few males survive to age 24 to produce reliable estimates of reproduction for those age-classes.) Both sexes show an increase in fledgling production after their first few years on territory, a pattern seen in many animals. Females showsenescence-paper-figure-3

“reproductive senescence”, another widespread pattern, in that fledgling production declines near the end of life. What is surprising here is that males do not show a decline in fledgling production as they reach old age.

What is odd about the male pattern? We have growing evidence that male loons decline at a younger age and more severely than females do. Recent analyses have shown that males lose body weight as they age, and that males suffer a high rate of mortality, especially as they reach their late teens. And, of course, males engage in dangerous battles. So the capacity of old males to produce lots of chicks into their 20s runs counter to what we would expect based on male survival and body condition. How do they do it? We are still puzzling over the pattern, but the most likely explanation is that old males invest heavily in chick production — perhaps through extra feedings of chicks or an extended period of care — to crank out a few more chicks before the wheels come off completely. Hence, old male loons appear to make a “terminal investment” in breeding success. Of course, nothing is free. Terminal investment is a deal with the devil; high chick-rearing success comes at the cost of earlier death.

 

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It’s like deja vu all over again at Muskellunge Lake this week. Thanks to Linda Grenzer’s vigilance, we have learned that the productive and photogenic pair on Muskellunge came back together this week — just as they did about this time in 2014! As Linda’s photo shows, “Clune” and “Honey” (Linda’s names for the banded pair) were a bit wary of each other at first. This shyness should not be surprising, as they have both lost their breeding plumage and donned winter attire. According to Linda, though, they rather quickly recognized each other and paddled off contentedly together. Apparently after 6 years of being together, and rearing of 10 chicks to fledging, familiarity with your partner involves more than just feathers!

We have very poor information on the behavior of territorial loons in the fall, so we can only speculate about what it means that an established pair seems to come together routinely just before fall migration. As a behavioral ecologist, I am inclined to interpret such meetings as more calculating than romantic. I cannot resist the temptation to view such a meeting as a final patrol of this precious breeding lake by its owners to ensure that no intruders have tried to put down roots in hopes of claiming Muskellunge in 2017. To any such pretenders, the presence of a tight pair late in the fall would signal that the territory was not available without a costly battle. But that is just speculation.

I must apologize for taking so long for this post; I have been busy exploring loon survival patterns. Indeed, I have been able to sharpen our view of senescence considerably. Some of you will remember that I announced several months ago that males senesce, while females do not. While I was excited about the apparent finding, it seemed to defy logic and begged for elaboration. With the return rate data from 2016 in hand, I was able to reanalyze survival patterns of both males and females banded as adults on territory. As is becoming all too common, I must eat crow. It is still clear that males senesce — those between 5

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and 19 years of age survive at a rate of 94% annually, while those 20 years and older survive at an estimated rate of only 71% (see graph, above). That is a steep drop-off in survival rate, indicating clear senescence. But the newer, more robust dataset has shown that females are not immune to the march of time. Indeed, 5 to 19 year old females survive at about 94%, like males; 20+ year old females fall off to 79% survival (see above graph). It is a tad deflating to realize that the world was more complicated than I had reported before, but also a relief to know that — and don’t take this wrong — females are not immortal!

One more tidbit relating to senescence. I have been able recently to complete a survival analysis of loons that were banded as chicks in the study area or nearby. (We call these birds “ABJs”, or “adults banded as juveniles”.) The most striking outcome of the ABJ survival analysis is, again, a difference between females and males. In this case, male survival plummets from 94% at ages 4 to 14 to 78% at ages 15 to 18 among both territory holders and floaters (adults without a

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territory; see graph above). In contrast, females show steady survival of about 92%, regardless of age or territorial status (see above graph). Males, in addition, suddenly begin to lose their territories to eviction at the rate of 38% when they turn 15 years old, while females only suffer eviction at a rate of 12% from 4 to 18 years of age. So here we have evidence that males not only die at a higher rate once they turn 15, but that they also become vulnerable to being booted off of their territory.

If you have paid attention closely through the litany of data I have dumped on you, you have probably noticed one final pattern: the ABJ analysis showed senescence occurring in a younger age class than did the analysis of territory holders! That is, male ABJs senesce at age 15, while male and female territory holders show no senescence until age 20. This is a brand new finding that I am still puzzling over, but there is an obvious explanation. Territory holders are likely to comprise a fitter class of adult loons that have shown their ability to fight for and defend territories and also rear chicks. In contrast, ABJs are only chicks that have survived to adulthood and returned to the study area. They are not “battle-tested” by having claimed a territory and bred there. Much later senescence among the evolutionarily fittest set of loons in the study area should not surprise us.

I am not ready to stake my reputation on this latest finding, but if it holds up, it dovetails nicely with one of the long-standing debates among ecologists concerning territorial breeders and floaters. We have long wondered whether territory holders should be regarded as floaters who got lucky and found a territory, or whether the two groups are, in fact, distinct classes in terms of fitness. The steep drop off in survival of male floaters in loons, compared to male territory holders, would strongly support the latter interpretation.

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He doesn’t look it, but this male from Townline Lake, just outside of Rhinelander, is at least twenty-seven years old. He is among a dwindling few males from among those we banded in the mid 90s. This bird was banded in 1994, at which point he was certainly at least five years old, which means that he was hatched in 1989 or before. Thus, twenty-seven is a minimum estimate for his age.

The age of “Silver over Red, Orange over Green” (as I call him affectionately) is not his only remarkable attribute. What sets this individual apart from most others is his ability to hold onto his territory year after year while fledging healthy chicks. (Below, he relaxes near his mate and two strapping chicks from 2016.) A successful common loon is not only good at locating safe nest sites and defending and feeding young. A breeder that wishes to

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reproduce successfully must confront intruders that land in the territory without warning throughout the breeding period.

Intrusions are especially frequent during the chick-rearing period. A common scenario plays out as follows. Early in the morning, a male is diving for food, while his two chicks track his progress from the surface. Each time he surfaces, the chicks rush over to him, snatch food from his grasp, and nibble relentlessly at his bill, neck and chest, signaling their unquenchable appetites. On one occasion, he surfaces holding a small yellow perch, only to find five adult loons in flight above his lake. He drops the fish, gives a short barking call, and the chicks dive and head to the nearest shore. The male too dives but surfaces near the middle of the lake, drawing the now-descending intruders to himself. Three quarters of an hour later he has driven off the intruders, thanks in part to a lunge and point yodel that caused his five visitors to scatter and tremolo. Shortly afterwards his mate returns, and both parents forage for the chicks. The family suffers no further disruptions until the evening, when another group of three nonbreeders circle and land, causing yet another brief skirmish.

Considering that a large pool of territorial intruders are constantly sizing up the resident male or female of any successful territory for an eviction attempt, it seems remarkable that residents are able to hold on to their territories for even a single year. Yet Silver over Red, Orange over Green has put together a string of 23 years of straight ownership, the only blemishes a half-year in 1996 and another in 2003, when he was briefly deposed. He has fledged 20 chicks during his breeding career with four different mates. This male is not the only resident with an impressive resume. A female on nearby Langley has fledged 17 chicks on that territory since 1995, while the O’Day female has been on territory since at least 1997 and has produced at least 16 full-grown chicks during her breeding career.

But female loons are survivors. Females enjoy a high rate of survival and no detectable senescence well into their twenties. Males, on the other hand, hit the wall abruptly at age 20; almost half of all territorial males of age 20 will perish before the subsequent year. So when we see a male who defies the odds, like this one, it is worth looking closely to see if he possesses an attribute that sets him apart. As a scientist, I am loathe to draw conclusions based on a sample of one. Colleagues in my field would dismiss any such conclusions out of hand. But today Nelson, one of my Chapman research students this year, reported that Silver over Red, Orange over Green is the tamest bird we have ever measured in the study area. So let me invite ridicule by advancing a very preliminary hypothesis. Perhaps the key to lifetime productivity in a habitat rife with human recreation is picking one’s battles carefully. Maybe by ignoring the inquisitive, well-meaning primates in their watercraft, this male has been able to conserve his metabolic resources for provisioning young and driving off pesky intruders.

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The first round of censuses in the study area each year is always bittersweet. On the one hand, it is exciting to see the crop of new young adults that have settled and to wonder how well they will defend their new territories. On the other hand, some old familiar loons are missing. This year is typical in that the disappeared veterans are mostly males. Three of 12 males of 20+ years have failed to reclaim their 2015 territory; only 1 of 12 20+ females have not resettled on their territory from the year before. Thus, male senescence lives!

Among the 2016 no-shows are the Jersey City Flowage male, who bounced back from a nasty fishing entanglement in 2014, regained his territory in 2015 and hatched a chick there. Another loss is the Soo Lake male, who was among the most aggressive in our study area. I still tremble when I recall his response when we played a few loon calls in his direction in 2000. He approached my canoe to within 2 feet, sat right next to me in the stern and glowered for the better part of two minutes. A spine-tingling experience for sure!

Yet the news is not all bad. Six young ABJs (“adults banded as juveniles”) have settled in the study area, providing us with valuable data on loons whose age is known precisely. New settlers include two females hatched in Vilas County — a 9 year-old that settled on Manson and a 6 year-old now paired with the male on Harrison Flowage. New male faces belong to an 8 year-old that took over Brandy Lake (near Woodruff) and a 7 year-old that battled and evicted the 22 year-old male from Oscar Jenny. (Thanks to Jeremy, who observed this eviction in progress.)

Perhaps the most intriguing findings from the first round of lake visits by Kristin and Linda are the serendipitous ones. Kristin relocated one of our oldest males — a bird known to be 27 years of age or older. Evicted two years ago from Muskellunge Lake, this loon licked his wounds and got himself back in the game by settling on nearby Swanson Lake, which had fallen into disuse in 2015. We had not seen this bird in two years and were almost ready to give up on him. Linda found a female with even greater resiliency. This old loon produced a dozen chicks over the years as the breeder on Buck Lake from 1998 to 2009. After her eviction from Buck in 2010, she floated, found a breeding position on Hildebrand in 2012 and produced a chick there in 2013. But she was driven off of Hildebrand last year. Her response to this second setback was typical of female loons — she bided her time and claimed that territory again when the opportunity presented itself. As I confront another season of hauling canoes from lake to lake, my back begins to ache in anticipation. I hope the examples of these two dogged old codgers gives me the strength to persevere!