Are Late Chicks Doomed?

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I must confess that I had mixed feelings to learn this week from Nelson that the North Nokomis pair had hatched two chicks. Despite having seen scores of newly hatched chicks, I still enjoy watching the tiny fuzzballs bob up and down next to their huge parents while the adults, in turn, move gingerly around their tiny young to avoid injuring or drowning them.

So it was, in one respect, nice to learn that the North Nokomis pair had hatched the eggs from the conspicuous nest I had inspected on 25 July, after following the simple, clear instructions from my research team. But I recall thinking, “Oh geez!” on that date, because only two other breeding pairs of the 120 that we follow were still sitting on eggs. (Both of those, we had determined, were cases of infertile eggs that the pair had incubated for six weeks or more.) I have always presumed that chicks hatching in late July or August have too little time to mature physically, develop foraging skills, and learn to fly in time to make the fall migration.

Now we have the data to look at this question robustly. In other words, having captured and marked 983 chicks since 1991, we can determine whether hatching date is a predictor of survival to adulthood. Logically, there must come a date in late summer beyond which chicks run out of time. However, pairs might face a gradual decline in the likelihood of their chicks surviving migration, or there might be a rather sudden threshold date past which chicks that hatch cannot survive.

If we look at all chicks banded from 1991 on, and calculate how many have made it back to the study area as adults, we learn what the figure

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shows. In short, hatching date does not appear to influence survival to adulthood strongly. At the very least, we can say that chicks hatching in mid-July survive at a rate no lower than those that hatch a month earlier. There is a hint of a decrease in survival from early to late hatches, but it is only a hint.

As usual, our data are not perfect. In fact, we have too few cases of very late hatches to gauge the likelihood of the two North Nokomis fuzzballs (which hatched on about 28 July) making it off the lake this November. On the plus side, 470-acre North Nokomis Lake has one of the highest rates of survival to adulthood in the study area. (The territorial males on Gilmore and Cunard were hatched there.) I would like to think that the gutsy North Nokomis pair will be rewarded this fall with two healthy fledglings. So I am keeping fingers crossed for them.

Still Feeling the Bite of Black Flies

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A few months ago I wrote a post about the impact of black flies on nesting of loons. Some might recall that, after abandoning their first nesting attempt, pairs sometimes reuse the nest, leaving the two original eggs in place. This situation produces supernumerary eggs: two addled ones, two still alive. Despite some odd-looking clutches, though, the impact on reproduction seems minimal. That is, the presence of extra eggs in a new nest does not appear to impair incubation of live eggs. Chicks still hatch normally.

In fact, I had all but forgotten about black flies by the time it came to the loon capture season this year. You see, capture is an inherently cheery process. First of all, capture is only possible on lakes with chicks, so we only visit such lakes. Second we work at night and become so absorbed in the demands of creeping up on protective adults and their awkward, fuzzy offspring that the travails of the population at large do not enter our sleep-deprived brains. Between the adrenaline rush following a challenging capture and the warmth of feeling that accompanies the release of parents and their adorable young, nothing else matters.

One issue nagged me even during capture this year though. The great majority of chick broods were singleton chicks (like the one on Muskellunge Lake in Linda’s photo). So few two-chick broods did we encounter that each one seemed an oddity — an almost inconceivable reproductive bounty. 2017 was a surprise, because, based on many previous years of capture, I had come to expect roughly equal numbers of two-chick and one-chick broods.

In the days following my nocturnal boating adventures, I mulled over the abundance of singletons in 2017. It was then when black flies entered my mind. Was it possible that black flies had disrupted incubation to such a degree that many pairs had lost one of their two embryos early and hatched only one chick? This might happen if fly-bitten pairs spent enough time off of their nests that one, but not both, of their eggs became inviable. If so, years with many nest abandonments owing to black flies should also be those with many singleton chicks. In fact, this is the case, as the figure below shows.

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Thus, it seems that black flies inflict a double whammy: they cause widespread abandonment of nests, and nests not abandoned suffer from reduced hatching rate. To make matters worse, cold spring weather, which prolongs the lives of black flies, also causes hypothermia of loon embryos, endangering their survival.

Now I have somewhat simplified the factors that cause singleton chicks in loons. I certainly have to explore additional factors, looking, for example, to see if loons are more prone to laying one-egg clutches during severe black fly outbreaks (although a quick check of the data revealed no such pattern). But it seems that we have yet one more reason to hope for rapid and sustained spring warmup in the Northwoods.

Our Fragile Identification System

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In a sense, our ability to identify loons as individuals hangs by a thread. As most of you know, we rely upon a unique combination of three colored leg bands — together with the mandatory numbered USGS metal band — to ID our study animals. The Upper Kaubashine female, for example, is “silver over yellow on right leg, red over green on left leg”, while the Lee Lake male is “blue with white stripe over taupe with white stripe on right, red with white stripe over silver on left”. (He is nicknamed “Stripe Hell” by my staff.)

The system seems simple enough on its face. Together with the DNR, however, we have banded over four thousand adults and chicks in northern Wisconsin since 1991. Thus, we have used a lot of color combinations over that span. Inevitably, certain individuals differ only slightly from other individuals in their band combination. While we make every effort to use contrasting band combos on mated pairs, loons move around between lakes because of natal dispersal (movement from natal lake to breeding lake) and eviction. Sometimes birds with similar band combos end up close together. For instance, the male on the southeastern end of Squash Lake, which we caught last night, is “yellow over taupe stripe, green over silver”, while the female at the northwest end of the same lake is “red over taupe stripe, green over silver”. A single band is crucial to distinguishing one bird from the other on Squash.

I describe our identification system as fragile, because the loss of only one of its four bands by a loon can throw its identity into question. In several cases, a loon with one or more missing bands could only be ID’d when it was captured and we read the number on its USGS metal band. In most years, there is at least one such “mystery loon” in our study area.

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Our mystery loon of late has been the female on Bear Lake (pictured above in Linda’s photo). She has lost one band and is now “orange over mint burgundy, silver only”. A check of our banding records finds four birds that could match that combo, if they lost a single band. All are “ABJs”: adults banded as juveniles. In other words, all were marked as chicks: one in 2004, one in 2005, and two in 2007. I was excited to see that Bear Lake had a chick this year, because this gave us a reasonable chance of being able to capture Mystery Female and learning her age and natal origin from her metal band. But she is a skittish bird, and we failed to catch her.

So we left it to Linda. Linda is a great photographer and a very patient naturalist. Many times she has taken photos so crisp that one can read the numbers stamped into the metal band on birds legs. Below is an example of a photo by Linda in which one can make out several numbers on the metal band on the right leg, above the “auric with red stripe” band. I thought that Linda might pull off the same magic with

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the Mystery Female, which would permit us to discover her age and natal lake. Thus far, she has been able to make out three separate digits on the bird’s metal band. That information has allowed us to eliminate two of four possibilities; we now know that the Mystery Female was hatched on either North Nokomis Lake in 2005 or on Buck Lake in the same year. The tendency of young adults to settle on breeding lakes similar in size to their natal lakes makes us favor North Nokomis as the more likely natal lake. If we are lucky, Linda might get a chance to nail the numbers well enough for a certain ID.

Now you might wonder why we are so obsessed with the identity of a single loon. After all, we have identified scores of other lake settlers who held onto all four of their bands. We have come to feel that each data point is precious, because each one allows us to refine our population models and survival estimates. Females are particularly valuable to us, because most of them disperse so far from their natal lake that we cannot relocate them as breeders. (Males, in contrast, often settle within a few kilometers of their natal lake, so we have far more data on male settlement.) So please send positive vibes Linda’s way, as she hunts the skittish Mystery Female of Bear Lake.

Loons Hide Their Chicks from Strangers….Most of the Time

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It is July and time to hide the chicks! That’s right; while human parents show off their progeny — perhaps partly to solicit help in caring for them — loons do the opposite. You see, intruders looking to evict territorial residents scour lakes for chicks, because the presence of chicks indicates that the lake contains good nesting habitat and abundant food. So by producing young, a breeding pair has put a giant target on their backs, providing an incentive for any intruder that discovers the chicks (like one of the six intruders shown in Linda’s photo) to return the following year and make an eviction attempt. We should expect, therefore, that parents would hide their chicks from intruders whenever possible.

Of course, breeding pairs are fighting a losing battle. On the one hand, they must feed and protect their chicks, which includes vocalizing often to warn their mate and chicks of passing eagles and other dangers. On the other hand, when intruders fly over or land, parents need to ignore the chicks altogether. Toggling between these two behavioral modes is no small task. Furthermore, while it is desirable to protect your long-term ownership of the territory by hiding your chicks from intruders, you do not want to lose them in the process!

Although chick-hiding is a tricky business, loon families do have a strategy for coping with the sudden appearance of intruders overhead, which fly over at a speed of about 70 miles per hour. We call it “dive and scatter”. At the appearance of a flying intruder in the distance, a loon pair and their chicks quickly slip under water. The chicks swim toward shore and, once there, are hidden by their brown plumage, which makes them resemble rocks or logs. Meanwhile parents swim under water to the middle of the lake, which draws the intruders to them and not the chicks. The aim of this coordinated behavior pattern by chicks and their parents seems clear: keep intruders from seeing the chicks. On its face, dive and scatter behavior clearly seems a means of helping parents’ maintain possession of their territory.

I need to pause here for a second to consider an alternative explanation for dive and scatter. In fact, the most obvious reason why a pair and chicks would dive and scatter is to protect the chicks themselves. Intruders do kill chicks commonly, so this is a viable hypothesis at first blush. But chicks are most vulnerable to being killed by intruders in their first two weeks, so dive and scatter as chick defense — if it is a viable explanation — should occur mainly among small chicks. Yet dive and scatter occurs rarely in small chicks and very commonly in those four weeks and older. So the hypothesis that dive and scatter is a behavior to protect small chicks from intruder attacks can be easily rejected by its timing.

We have known about dive and scatter behavior for some years, but yesterday on Woodcock Lake I learned that loon parents know when to call off the ruse. While feeding their single chick along the lake shore, the Woodcock pair spotted two intruders in flight. The family dove and scattered, the chick hiding near shore and parents making for the lake’s center, in stereotyped fashion. Following the script, the two intruders landed by the parents (and far from the chick), the four adults circling and diving together for several minutes. The charade abruptly fell apart when an eagle flew over the part of the lake where the chick was hiding. Both parents immediately ceased interacting with the intruders, wheeled towards the eagle, and wailed desperately for several minutes, while swimming in that direction. In a half-second, the breeding pair had morphed from cool, detached individuals with nothing to hide into into frantic worry-warts!

Some might view such a loss of composure by a breeding pair to be quite costly. If intruders are able to learn about the presence of chicks by detecting chick defense behavior such as that shown by the Woodcock pair, then the pair exposed themselves to the threat of future eviction by wailing to defend their chick in the presence of two intruders. A clear blunder….until you consider that the alternative was to lose the priceless product of their summer’s breeding efforts.

 

The Indefatigable Female of Upper Kaubashine

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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.

Bad News from Science… but Perspective from Langley¬†

I had been obsessively checking email in the past week, waiting to hear from Science about our terminal investment paper. Since it was a cool set of findings, I held out some hope that they would accept it. 

When I felt my phone vibrate, I had just found the Langley pair with their chick. Watching them was bittersweet. On the one hand, they had hatched a chick in a tough breeding year and both male and female were feeding it rapidly. But what they were feeding it were tiny minnows, and it takes hundreds of them to satisfy a voracious chick. No sooner did a parent feed a minnow to the chick than the chick vigorously nibbled at the adult’s chest and neck, soliciting another feeding. I admire the perseverance of the parents but wonder whether they can find enough food on this small lake to keep their chick alive to fledging age. 

The e-mail was bad news; Science had rejected the paper without review, simply meaning that the panel of people had not found it exciting enough to warrant detailed review. So it usually goes at Science. 

Don’t cry for me! My chief battle with this paper is over, because I have now gotten it written up in a form that can easily be reconfigured for another high-impact journal like Proceedings of the Royal Society B, where it will be read widely. A paper in Science would have been a feather in my cap, without a doubt, but it would not have had much of an impact professionally. It is hard for me to wring my hands much over this minor setback when, day after day, I see the life and death struggles of my study animals, like the hard-working Langley pair!

Cold, Blue Pragmatism

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Though it sounds odd to say, people put loons on a pedestal. Their love for loons causes many people to want them to be a bit better than us. Of course, this is the origin of the popular myth that loons mate for life. Such a handsome animal, it seems, should have behavior to match. Besides, loons certainly appear to work so well together in foraging, defending their territory, and rearing young that one can easily imagine that male and female are committed to each other deeply.

Having studied several other species of animals before turning to loons, I did not share the expectation that loons would be good role models for humans. I had seen too many cases of nature red in tooth and claw. In fact, I suppose I expected to learn ways in which loons might not fit the mold of traditional monogamy. What has surprised me the most of all my findings is the degree to which loons have broken that mold. Rather than aiming to remain paired with a single mate throughout their lives, loons seem pursue a far different but straightforward goal. They seek to produce as many chicks as possible by remaining on a breeding territory whenever possible. This strategy requires them to turn a blind eye when their mate is evicted by another loon. Their allegiance is to the breeding territory, not the mate.

No territory illustrates the cold pragmatism of loons better than Blue Lake-Southeast. Recent years have been turbulent on Blue-Southeast. In 2015, the male was evicted by an unmarked male after producing two chicks with his mate. The displaced male hung around on the lake and later regained his position, but last year was a repeat performance; this time a four-year-old male from Bolger Lake evicted the long-term male after hatching and killed the single chick. In a scene worthy of Greek mythology, the Bolger bird actually picked up the lifeless two-week-old chick while chasing its mother across the water’s surface.

Now, if a human mother had witnessed such a grisly spectacle, I doubt if she would have been able to forgive and forget. But loons are not humans; the female whose chick had been killed by the usurper quickly paired with him and remained so this spring. The unlikely pair weathered the black fly emergence in May, hatched a chick in early June, and are now raising that chick on the east lobe of Blue Lake. As the triptych of photos above shows, I caught up with this very tame family yesterday afternoon. At the time, “Chick-Killer” (as my field team affectionately calls the male) was enthusiastically diving for food for the thriving chick, while the female looked on. The dutiful, coordinated parenting of the two adults suggested that they constitute an indivisible unit — that their pair bond would withstand the test of time. But looks are deceiving.

Courage from My Daughter

There is a long tradition of failure — or, more accurately, the feeling of unfulfilled potential — in my family. We all feel that we have the capacity for greatness, but we have not gotten there. There are a variety of reasons why we have failed: bad luck, poor timing, others conspiring against us. But more than anything, we blame ourselves. Through a series of missteps, we feel, we have doomed ourselves to obscurity. We are just getting by, when we should be basking in the spotlight. 

It all started with my grandfather. As the family story goes, Lewis Piper was a late bloomer. Dismissed as weak-minded by his older sisters, he struggled in school. In fact, he had a brilliant mind, great patience, and enormous compassion. Eventually people recognized his abilities. He became an inspiring teacher, a successful administrator, and ultimately worked with local benefactors to build a thriving small college in central Kentucky, where he served as president. This might seem like a modest achievement, but Grandad was one of 12 children of a traveling salesman. He far exceeded expectations.

In a curious twist, Grandad’s rise to prominence cast a pall over the family of his eldest son. Dad, who became a college professor, has always felt himself a disappointment: a son who inherited much of his father’s intelligence but could not continue the family’s upward trajectory. All of life’s setbacks have confirmed for Dad what he always suspected: that he was just not living up to expectations. He was unable to celebrate his achievements, greeting tenure and promotion with a yawn and feeling that each paper could have been better written or accepted in a more prestigious journal. Despite publishing countless books and articles, earning teaching accolades, and retiring as a full professor from Rice University, he knows beyond all doubt that he has let his father and his family down.

Dad’s feeling of inadequacy lives on, because he has looked to his children to turn things around. This is not conscious. Dad loves us and means no harm. But his blindness to the monkey on our family’s back — and how it impacts his children — has been costly. My older brother and I felt the burden of his expectations most acutely. Even now, on the brink of our 60s, we labor to bring honor and renown to the family. An academic like my father, my reactions to life’s ups and downs mirror his. Successes inspire only regret; failures confirm our pitiable lot in life. 

My family’s past served as an inevitable backdrop as I contemplated a journal where I might publish our findings of terminal investment in male loons. Readers of the blog might recall this finding. Briefly, male loons fall into poor condition and suffer increased mortality beginning at age fifteen. In response to this abrupt senescence, older males become highly aggressive and territorial, an effort to hold onto their territory and eke out another year or so of breeding success. The strategy of an animal to increase its efforts to breed in the current year or two — at the risk of hastening its demise — is aptly termed a “terminal investment”. This is a beautiful result, truly. No other finding that I have made in my career is so stunning and clear. What’s more, the finding could and should become a landmark in my field. Though life history theory predicts it, no other study has demonstrated that terminal investment can take the form of aggressive territorial behavior. 

I have known of the finding for many months, yet fear of rejection paralyzed me until a few weeks ago. “I must send it to Science“, I thought. Science is the flagship journal for scientists, of course. Publication of a paper there confirms that numerous eminent reviewers found a paper highly significant and worthy of wide dissemination. Yet with my exciting data fully analyzed, my literature search completed, the context and background for the finding etched in my mind, I could not move forward and complete the manuscript.

My daughter broke the impasse. One morning I mentioned to her the difficulty I was having in getting the paper submitted to Science. She was on her way to a summer internship, but she paused for a moment, sensing my inner struggle. “Well, Dad, there is probably only a ten to fifteen percent chance that they’ll accept it, but you might as well try.” It was a powerful statement of unblinking, youthful optimism and also acceptance of life’s vagaries.

Allison’s statement was not merely thoughtful advice. Her words showed that the family curse has been lifted. It seems, somehow, that a diffident, underachieving father can — perhaps largely through marriage to a smart, positive, hard-working spouse — raise kids not afraid to tackle life’s challenges.

On Nesting and Knowing

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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.

 

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Many Return….Few Settle….But Why?

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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.