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.



Ending a short run of bad luck, we just had our paper accepted that describes impacts of black fly infestations on loon nesting behavior. As I have explained in many previous posts, Simulium annulus wreaks havoc with loons’ reproductive efforts. The biological relationship between the fly and the bird is of substantial scientific interest, and we are pleased to have finally brought our low-level data collection on this relationship to fruition.

On the other hand, our celebration of this achievement has been cut short by the cold weather still gripping northern Wisconsin. Why? Because one of our findings was that unseasonably cool springs often bring extended periods of fly abundance. So we face the prospect that the breeding season of 2018 will illustrate the threats to loon breeding we just described so vividly in our article.

There is also reason for hope. As the above figure shows, early ice-outs resulting from warm spring weather ensure that flies will be only a minor nuisance to loons. Late ice-outs pose a problem, but the results vary from a severe rate of nest abandonment (as in 2014, the worst year ever for fly-caused abandonments) to modest impacts. Let’s all hope that 2018 is one of those years when the correlation between cool spring temperatures and severe fly infestations breaks down.

It is a bit unseemly, I suppose, to pile on Russia now. Having been caught meddling with our election and cheating during past Olympics, their reputation could hardly get worse. Yet the metaphor of the Russian judge — meaning a person who brings a strong bias to a process that is supposed to be marked by disinterested fairness and good judgment – is almost irresistible to me at this juncture. Indeed, the metaphor has been throbbing in my brain these past weeks as I have marveled at the scores awarded to figure skaters and Big Air snowboarders.

Let me explain. I recently completed a revision of our paper on terminal investment by male loons: the most remarkable finding we have made in 25 years of research. (This is the paper showing that males become highly aggressive and territorial at the same time that their health, survival, and territory defense is declining.) Praised by three reviewers at a prestigious journal, our paper was blocked from acceptance by a fourth reviewer who insisted that we complete a complex statistical analysis to check our results. Review of scientific articles is almost always anonymous, as in this case, so we cannot know the reviewer’s identity or the reason for his/her objection. But my study of his/her statistical point convinced me that it was mistaken. Yet, the editor disregarded my carefully-crafted refutation and chose to support the reviewer. Of course, it is immensely frustrating for an author when an editor sides with a stubborn reviewer. This outcome forced us into a difficult decision: 1) kowtow to the reviewer by reworking our statistical analysis needlessly, which would have entailed a lengthy delay in publication and cost us perhaps $2000 to hire a statistical consultant, or 2) pull the plug on the submission that seemed on the brink of acceptance, pending completion of that difficult statistical revision. I hope I made the right call by withdrawing the paper and sending it to a new journal.

Two factors played a role in my decision to withdraw the paper that, perhaps, should not have. First, I have spent many months polishing this paper and am reaching the end of my rope with it. I am certain that it is sound statistically and likely to be impactful in my field, if I can just navigate the stormy seas of reviewer opinion. Second, I must soon turn my attention to acquiring new research funding and must have this paper in print in order to demonstrate to funding agencies that the past funds they have sent to me have been well spent. Thus, I have chosen to send the paper to a solid – but not highly prestigious – journal in my field, hoping to find a fast track to publication.

I am not the first person to make a decision to publish a great paper in a low-impact journal in order to keep the wheels of research turning. Each paper, in my experience, follows its own journey. A pedestrian paper sometimes catches a wave and ends up in a lofty journal, only to be scoffed at and forgotten in short order. And cool papers sometimes fall into low‑impact journals, are discovered by many scientists, and become classics. Let’s hope the terminal investment paper falls into the latter category.

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!

A lot of science is scut work. While I do ponder my findings, develop new hypotheses, and publish papers that might (slightly) change the way that others view the natural world, these activities are, in fact, only the most glamorous ones in the scientific profession. I spend far more time worrying that I am mistaken about a result. You see, scientists are nit-pickers who know from personal experience the difficulty of proving something is true. Scientists are skeptical of their own findings as well as those of their colleagues. We are always on the lookout for false assumptions, biased data samples, misleading correlations, and experimental results that are artifacts (false outcomes) of our methods. Thus, we spend a good deal of time poking and prodding our data, turning it this way and that, and making certain it is bullet-proof, before we try to publish or present it to colleagues. Scientists run many tedious and seemingly repetitive statistical tests aimed at testing a single hypothesis and ruling out alternative explanations for patterns we find in our data. If a flaw in our reasoning, an untested assumption, or a problem in experimental design weakens or invalidates our findings, we want to discover it ourselves in the solitude of our office — not have a listener at a talk or a reviewer of a grant proposal do so.

Scientists have a much higher threshold for accepting statements as fact than does the public at large. Indeed, flawed and misleading conclusions — which would bring harsh criticism to a scientist uttering them — are rampant in public discourse. The biased sample problem leads to many misleading conclusions. Following a political debate, TV commentators always tell us who won, based upon a sample of viewers. Unless one is very careful to control the political makeup of an audience, however, the outcome of such a poll is certain to be biased. Naturally, Fox News and CNN have audiences that differ greatly in their political leanings; in addition, people who watch debates on television or in person represent a biased sample of voters, not the population at large. Finally, viewers are more likely to see the candidate they favor as the winner of a debate, so favoritism towards one candidate will make that candidate more likely to be seen as the winner, even if their performance was worse that their opponent’s. That is, if 65% of all voters favor Ms. Sims over Mr. Peach ahead of the debate, and 55% of all voters say afterwards that Ms. Sims won the debate, Mr. Peach almost certainly performed better, because he beat his poll numbers.

I face the biased sample problem constantly in my analysis of loon behavior. For example, we have observed that loons shifting from a first to a second breeding territory tend to move a very short distance, often settling to breed on a new lake right next to their old one. It is tempting to surmise that loons that move between territories cover only a short distance in order to take advantage of their knowledge of the local area and ease their transition to the new breeding space. This sounds plausible but ignores the fact that shifters are not a random cross-section of the population. Instead, these loons are almost all old individuals with low fighting ability that have been evicted from first territories. Moreover, the new territories they shift into are not average breeding territories but new, untested ones with limited nesting habitat that seldom yield offspring. So old, worn out loons do not seem to be carefully choosing to settle in a new breeding space that they know well; rather, they are desperately setting up a new territory near their original one — and in a place that no other loon wishes to use — because it is not worthwhile trying to compete for a proven territory anywhere else.

mentions correlation

At the moment, I have turned a critical eye towards black flies and nest abandonment. I have “known” for decades that black flies cause high rates of nest abandonment in certain years, as they did in 2017. But it is one thing to know something is true, and quite another to convince other scientists of what you know. So I have gone back to field records from 1994 to 2017 and tallied occasions when field observers reported severe infestations of black flies on loons or around their nests during the early nesting period. Then I looked at the correlation between reports of severe black flies and rates of nest abandonment across years. The result, as shown in the figure above, is unsurprising. In years when black flies were reported to be abundant, nest abandonments were very common.  (By the way, that data point in the upper right corner is 2014.)

While I was certainly not on pins and needles during this latest analysis of black flies, it is a crucial piece of the puzzle. Lacking any direct data showing that black flies caused loons to abandon nests, my best evidence to support this conclusion was that cool springs lead to a high rate of nest abandonment. The strong correlation pictured above now implies a direct causal connection between flies and abandonments.

I breathed a sigh of relief at this finding. I am not sure how I would have responded if I had found that years of severe black flies were NOT correlated with rates of nest abandonment. Yet I cannot rest. I can imagine a scientific reviewer complaining that the correlation might have resulted from observer bias. For example, once an observer starts to notice that black fly population is high early in the year and possibly related to nest abandonment, he or she might be more likely to report severe black fly infestations on subsequent days. Such behavior by field observers might explain the correlation I found, at least in part.

In short, I am still uneasy about my analysis of black fly impacts on loon nesting. I am looking for additional statistical analyses that could help convince a skeptical audience of the link between flies and abandonments. That is what life is like for a scientist.


A few months ago, a loon naturalist and photographer from New England told me I was wrong when I said that males choose the nesting site for pairs. For 15 straight years, he said, he had watched a female look at potential nest sites that her mates had selected during the pre-nesting phase and then choose to lay the eggs in one of her own favorite sites, ignoring her mates’ suggestions. Thus, he claimed to have an exception to the rule that males choose the nest location.

Now let me say right off the bat that he might be correct. The paper we published showing that males choose the site where eggs are laid demonstrates an overwhelming statistical impact of male identity on nest location. That is, male identity is clearly far more important to selection of nest location than is female identity, but we cannot exclude the possibility that an occasional female might turn the tables on her mate and lay the eggs in a site that only she prefers.

Let’s look more broadly at avian breeding behavior to examine the possibility that a female might buck the usual trend in nest-site selection. Hundreds of studies have shown us that reproduction in birds requires tight behavioral synchrony in mated pairs. Coordination in behavior, in turn, leads to harmonious hormonal profiles of males and females. In other words, mates must be on the same page — both behaviorally and physiologically — throughout courtship, copulation, nest-searching, egg-laying, incubation, hatching, and rearing of young. (Linda Grenzer’s beautiful photo from a few years back illustrates this coordination nicely.) If one pair member is out of phase with its mate — say, not ready to incubate the eggs after they are laid, or unprepared to rear the young — breeding fails.

The dependency of reproductive success on behavioral and hormonal coordination between mates puts enormous evolutionary pressure on pair members to conform to the normal breeding roles and patterns of the species. In general, a male or female that behaves differently from others of the species will not find a mate, or if it finds a mate, will not nest. Weirdos generally do not leave offspring, so weird traits — to the extent that they are genetically based — do not persist in populations. For this reason, I am skeptical that the naturalist has found a female loon that flouts the “males choose nest sites” rule. Based on previous research findings across many species, I would expect a female that laid her eggs in a spot not selected by her mate would be faced with a mate unwilling to share incubation duties.

The naturalist’s claim of an exception to the rule has a more fundamental flaw. It is based solely on observations of a single female and her mates. As someone whose data consists mainly of behavioral observations, I am keenly aware of the limitations of  behavioral data that are not analyzed rigorously, especially observations from one or a handful of animals. Countless times I have thought that loons were behaving one way, only to find, on closer scrutiny and with a larger sample, that they were behaving another. If your sole evidence for a conclusion is “I looked closely at an individual and it looks as though she is doing this”, as in this case, you are on thin ice.

The story of how we learned that males choose the nest site illustrates well the pitfall of trusting limited observation to reveal true behavioral patterns, so it is worth saying a bit about how that analysis unfolded. On the face of it, we thought, how could males choose the site where a mated pair lays their eggs? After all, females, not males, lay the eggs. In a very basic sense, females must always control where the eggs are laid. Therefore, I expected my analysis to show that females controlled nest site selection. However, egg-laying in loons occurs only after many days of nest-searching within the territory. So it was conceivable that males might somehow influence their mates to lay the eggs in one spot or another. In fact, our statistical analysis showed that males take the lead in nest-searching and spend much more time than females in looking for a nest location. And an additional set of statistical tests showed unambiguously that males control where the nest goes. Here is the essence of our finding. Nesting pairs comprising a male that bred previously on the territory and a new female unfamiliar with the territory tend to reuse the successful nesting site from the previous year. Indeed, pairs composed of an experienced male and a new female select nest sites identically to pairs wherein both pair members are experienced on the territory. In contrast, pairs made up of a female with previous breeding experience on the territory and a male without experience there ignore the successful nesting location from the previous year and instead select entirely new, untested sites for nesting. Such pairs show no more knowledge of good nesting sites than do pairs in which both pair members are new and unfamiliar with the territory.

I was — and still am — puzzled by these findings. It seems absurd that a veteran female breeder permits her novice mate to choose an untested nest site, when she “knows” the best place to nest, based on her past experience. As the egg-layer, moreover, the seasoned female would seem to have absolute control over where the eggs are placed. But loon behavior defies common sense in this case. The data are very clear.

One more point about “knowing”. The naturalist who insists that he saw a female choose nesting sites is quite confident in his report. That is, he contacted me to inform me of his finding, not to try and reconcile his interpretation with mine. He “knows” that he saw a female select the nest site in the territory he observed. As humans, we often make observations, puzzle over their meaning, and then settle on an explanation of what we have observed. Then we get stuck. We become so invested in our explanation that we are unwilling or unable to give it up. In fact, reluctance to admit errors is a great problem in science, as we often make findings, build our reputations on those findings, and are unwilling to admit — even in the face of overwhelming evidence to the contrary — that we were wrong. I made a great error of this kind a few years ago and took many months to admit my mistake.

Human stubbornness of this kind makes sense….to a degree. In a world where we encounter many people who try to fool us or influence us to serve their own interests, we should show a strong tendency to “stick to our guns”. In the age of information, though, we also have access to useful knowledge from skilled practitioners — people who have rigorously and critically tested ideas and considered alternatives before settling on a conclusion. If we can see no reason why they would benefit from misleading us, we would do well to listen.


It is hard being successful. I don’t know this from personal experience, of course, but I have studied the topic in some detail. In fact, I spend a disproportionate amount of my time analyzing the behavior and ecology of highly accomplished loons.

You see, the individuals that I talk about in my blog and focus on in my scientific papers are the crème de la crème among loons. These animals have passed myriad biological milestones. They have hatched from eggs, survived the cold and dangerous first few weeks of life, dodged eagles and loon intruders to reach adult size at four months of age, completed energetically-costly molts, and navigated through thousand-mile migrations to and from the ocean. Above all, though, the subjects of my research effort have won battles to claim and defend breeding lakes, found safe nesting locations, and reared healthy chicks. Those chicks — their life’s work — permit my team to capture and mark them for study.

Don’t get me wrong; I did not set out 24 years ago to study this elite class of loons. In fact, I have always been most interested to learn how young adults without territories collect information about potential breeding sites and decide where to settle. But it is difficult to study such “floaters”, because, being floaters, they bounce around. Moreover, floaters cannot be captured easily, because they do not have chicks to protect. Only two years ago did we accumulate enough information to assemble a scientific paper that describes the goals and strategies of this itinerant cohort of individuals.

We are mostly stuck investigating the lives of life’s winners, like “Honey”, the breeding female on Muskellunge Lake whom Linda Grenzer has immortalized in countless photos (see the recent one above). I am not really complaining. We have learned a good deal about the lives of loons in general, despite focusing on the loon elite. Even winners face adversity and evolve interesting strategies to cope with it.

Jeremy Spool, a Ph.D. student at U.W.-Madison who works with Lauren Riters, developed an interesting research question aimed at the coping mechanisms of winners in our study population. Jeremy asked an intuitive, reasonable question about territorial breeders. Territorial pairs, Jeremy thought, should defend their lakes in a way that reflected their recent success. Pairs that had produced chicks in the past few years should be aggressive in territorial defense, because they were defending a resource whose value was clear and which would be costly to lose. Pairs that had not been successful rearing chicks recently might be expected to be a bit more lackadaisical about territory defense. Jeremy tested his hypothesis by exposing some of our territorial pairs to a loon decoy, which simulated a territorial intruder, and measuring their behavioral responses.

Jeremy’s results were unexpected. Pairs with recent breeding success did not behave more aggressively toward the decoy than unsuccessful pairs. In fact, they showed less aggressiveness towards intruders than did failed pairs. But successful pairs were clever about their defense; they became aggressive towards intruders in the few days leading up to egg-laying, a period when territories become vulnerable to intruders owing to incubation. In contrast, pairs without chicks the previous year showed no change in level of aggressiveness during the season. Jeremy concluded that successful pairs save energy by becoming aggressive only when they need to.

What Jeremy’s findings appear to show is that long-term pairs get into a groove with respect to territorial defense, targeting their defense towards times when it is most crucial. As with all good research findings, his raise a number of new questions. One obvious one is “Why should failed pairs be so inefficient about their territorial defense?”.    Another is “Must loons learn to defend their territories efficiently instead of doing so instinctively?”. These are exciting questions for the future that we look forward to tackling. For now, we are celebrating that Jeremy has just had his findings accepted for publication in the Journal of Avian Biology, a flagship scientific journal for avian research.



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!


LMG_9628 Manson Lake Male Yodeling

Loons do not settle on territories as we think they should. Traditional models in long-lived animals maintain that hopeful young individuals should be systematic in settling on territories. By current theory, a young loon should explore a certain region within proper habitat, find several territories that might be suitable for breeding, and then routinely monitor those potential breeding spots, waiting for a vacancy to occur. During this exploratory period, it is thought, the young loon gains familiarity with this small cohort of territories that will lead to a competitive advantage in territorial battles with other would-be settlers once a territorial slot opens up. The “foothold hypothesis”, as I call this model, is quite pleasing and logical. What’s more, there is evidence that many territorial animals gain territories in this manner. Loons do not.

We got another reminder of the quirky territorial settlement pattern of loons this past week, when Linda and Kristin scoured the study area and ID’d the pairs that had taken possession of the lakes we monitor. Among these settlers were many familiar faces — including a male on Townline Lake that has been in possession of the territory since 1994 and a female on West Horsehead who has bred there with a series of different males since 1995. One of the surprises was a 9 year-old female hatched on Rock Lake in Vilas County who settled on Manson, replacing a female that had bred on Manson for a dozen years. Owing to Linda’s careful observations, we know this Rock Lake female as a frequent intruder during 2014 and 2015. But she did not intrude into Manson Lake, where she eventually settled; instead she intruded repeated onto nearby Muskellunge Lake! Thus, our expectation that the Rock female was laying the groundwork for settlement on Muskellunge was not fulfilled.

There are several possible reasons why loons often do not settle on lakes that they seem to prefer. One of the most obvious is that settlement is not merely a matter of finding a desirable territory.  A loon bent on settling must also contend with the current resident on a territory where it hopes to settle. So a young nonbreeder that visits Territories A, B, and C might prefer Territory A but be prevented from settling there by a healthy and aggressive territorial resident of the same sex. In that case, the nonbreeder might end up settling on Territory B or Territory C. The Rock female is fortunate; Manson Lake, where she has settled, is one of the most productive territories in the study area. So even if she could not take possession of the territory she seemed to prefer, her future breeding prospects are bright.

You can read more about our testing of the “foothold model” for territory settlement in this blog post, which is based on a paper published in Animal Behavior. E-mail me if you would like a pdf of the paper.

The crisp photo above is by Linda Grenzer. It shows the Rock female performing a wing flap on Manson, her new breeding lake, while her mate, an 18 year-old male, yodels in the foreground.