To those of us accustomed to looking at loons during the summer, the sight of an adult caring for three chicks — as in Laura Unfried’s photos from two days ago — is peculiar. Loons, of course, almost always lay only two eggs. If they are lucky, two chicks hatch. It is by no means certain that those two chicks will survive to fledging age. In fact, 47 of 61 breeding pairs we study have one chick, not two. So the spectacle of two adults caring assiduously for three young was startling.

Close inspection of Laura’s photo from Hasbrook Lake reveals another peculiarity: the central chick is much larger — perhaps 10 days older — than the other two chicks. (Note that the left-hand chick is entirely downy with a small bill, whereas the center one has the anterior part of its head coming into adult feather and has a bill nearly as thick as the parent’s.) The obvious size disparity told Eileen Lonsdorf, who reported the third chick three days ago, that her nicely balanced family of two parents and two chicks had been joined by an interloper.

How could a huge, healthy chick somehow get separated from its biological parents and join another family? Territorial behavior among loons guarantees that each breeding pair will nest and rear its young far from other pairs. The likelihood of a chick straying from its own family to join another — fortuitously or by design —

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seems remote.

One lesson that you learn if you do something for a long time is that rare events do occur. Chicks do very occasionally leave their parents and territory to join other families. We have noted two causes for such chick dispersal. First, starving chicks, especially beta chicks on small food-limited lakes that are being physically beaten by their alpha siblings, sometimes attempt to escape the abuse and find an alternate loon family nearby that will feed and protect them. Second, chicks that lose one or both parents to territorial eviction are forced to flee their natal territory and seek parental care elsewhere, if the adult that evicted a parent physically attacks them.

Solitary journeys by displaced chicks seeking new homes are desperate enterprises. One reason for this is that many lakes with loon chicks simply have no neighboring pairs with their own chicks that might be joined. Even if a displaced chick is fortunate enough to find a nearby pair with chicks, they are likely to be much older or younger than itself. If so, it is unlikely to be accepted by the new family. I vividly recall a case in 1999, when an abused beta chick undertook an astounding 1/2-mile trip across woods and roads from Benedict to Bug Lake in Vilas County, only to land with a foster sibling three times its size that beat it mercilessly until it perished.

Since the monster chick that joined the Hasbrook pair is a robust, well-fed individual, we could rule out that it fled to Hasbrook because of sibling abuse or lack of food. So we were left to conclude tentatively that a nearby territorial eviction forced this young loon to relocate. We pulled out a map to assess the possibilities.

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Immediately, we pinpointed Cunard Lake, which is separated from Hasbrook by a quarter mile of woods and bog, as the likely source of the wandering chick. Cunard, a regular study lake of ours, had two large, healthy, 5-week-old chicks at our last visit on July 25th. Yesterday, however, I found the lake empty of loons, except a single floater adult. The steward of the campground reported that loons had been chasing each other repeatedly across the water on July 30th and 31st, which indicated a protracted territorial battle. The absence of the territorial pair suggested strongly that the breeding male had lost the battle to a usurper and either died or been forced to abandon his territory and chicks. This tragic event, in turn, would have scattered the rest of the family and subjected the chicks to attacks by the new male owner.

Last night we captured the peculiar but close-knit family of two adults and three chicks on Hasbrook. It will require genetic analysis to be certain that the huge new chick on Hasbrook is a refugee from Cunard and the offspring of the displaced Cunard pair, as we surmise. But we have strong reason to believe that he is a most fortunate survivor of a desperate overland journey.

For the past several years, I have begun to turn my attention to the effect of lake size on breeding success of common loons. Clearly loons on large lakes produce more and healthier chicks than those on small lakes. We showed that on our paper from six years ago. This raises the question of why loons ever attempt to breed on small lakes. They are doomed to failure — or at least to greatly reduced likelihood of success. The water is muddied further by the fact that loons reared on small lakes prefer to breed on small lakes themselves. That’s right: chicks fortunate enough to avoid starvation on small, food-limited lakes replay the whole scenario as adults, subjecting their young to the same travail they themselves faced.

The puzzle of loons breeding on small lakes was thrown into start relief again yesterday, when I visited the Wind Pudding-West territory on a scouting trip for nocturnal capture. After not finding the chick and parents in the shallow bay on the lake’s western side, where we had seen them on previous visits, I headed towards the channel that connects that bay with the main lake. I was crestfallen when I reached the channel, as it was choked with lily pads and grasses to the point where it was difficult for me to find a passage through — even in a canoe. This discovery led me to doubt whether the pair might lead their chick through the channel and into the main lake as a means of finding more food for it. I began to fear that — walled off from an abundant source of food — the chick had probably starved to death on the shallow western bay since our last visit.

I had underestimated the determination of the pair to provide for their chick. As I paddled to the end of the navigable portion of the channel, I heard a chick’s desperate cries to its parents. I spotted the chick about half way across the marshy isthmus that now separates the shallow western bay from the main lake. The isthmus is no more than 20 meters wide perhaps, but it is densely overgrown with marsh grass to the point where the chick — equipped only with legs at the very posterior of its body — was forced to lunge awkwardly forward in order to make headway towards the main lake. To make matters worse, the chick had no clear idea of where it was going. I caught the chick’s initial confusion on video, as it sits within the marsh grass, uncertain how to extricate itself.

The second installment shows the chick after it has blundered around in the grass for a time but finally gotten a sense of where its parent wants it to go. The chick stops to give a distress call, then hears its parent call to it, which seems to give the chick the strength to complete its journey. (Apologies for the nervous narration and grainy video!)

The fact that the parents can entice this year’s chick to cross the isthmus and take advantage of food in both the western bay and main lake means that they are better off than they were here in 2016, when a chick wasted away and finally died of starvation. However, we caught the chick and female in the video last night. They are both severely underweight. The female, in fact, has the lowest mass we have ever measured for an adult loon. So even if the pair can find enough food to fledge the chick, chick-rearing seems to have taken a toll on the parents. Add yet one more item to the growing list of reasons to avoid breeding on small lakes with limited food.

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.

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.

 

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.

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

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

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

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

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

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

As we expected from the early ice-out, nesting has begun a bit ahead of schedule. Linda’s photo shows “Clune”, a male hatched on Manson Lake in 1998, on a substantial nest mound in a marshy part of Muskellunge Lake. If all goes well for them, Clune and his mate (“Honey”) will alternate incubation duties for four weeks. Their reward will be 1 or 2 needy hatchlings that they will have to shield from the elements, protect from eagles and other loons, and feed tirelessly for three months. With luck, their efforts will yield two big, fat, sassy chicks, like those pictured here.

But they have a long way to go. May is the month when black flies emerge, bite loons mercilessly on the nest, and generally make them wish they had hands instead of wings. Al from West Horsehead reported today that the flies have driven the pair off of their egg for the time being. Since we know from experience that loons are loathe to abandon a nesting attempt, we hope that they will resume incubation shortly. (Surprisingly, eggs can hatch despite loons spending considerable time off the nest.)

I will return to Wisconsin in a few days myself to race around the study area and find what nests I can. I hope to find those nests by observing loons sitting peacefully on them, rather than thrashing about in the water nearby in a vain effort to rid themselves of their winged tormentors.

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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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Loon capture is a blur. We set out from our house at 8:45 pm, launch our small motorboat on the first lake, wait for nearly complete darkness, and catch any loon chicks and parents that we can net easily. By the time we have repeated the process four more times, we are rubbing our eyes, our weariness justified somehow by the presence of the sun lurking just below the horizon.

As an essentially negative person, what I often recall after a night of capture and banding are the physical demands of the process and my complete exhaustion. But there are dimensions of the work that are exciting and rewarding. Each loon is unique, and one never knows whether an individual will permit itself to be approached closely and netted or will be wary and elude us. So we experience many disappointments, but they are tempered by the occasional thrill of capturing an individual that, at first glance, appeared too skittish to catch.

The fruits of loon capture are obvious. By marking individuals and resighting them year after year, we learn about survival rates of adults and juveniles, territory fidelity, natal dispersal, and habitat preference. We glean a good deal of important information from these data. For example, survival rates of young and adults allow us to learn whether the  local population is increasing, decreasing, or remaining stable. And tracking of young loons from egg to first territory has revealed that loons develop strong preferences for breeding lakes that closely resemble their natal lake. Finally, capture is essential as a means to disentangle loons that have been run afoul of angler’s lines or lures.

This year’s capture exposed another distinctive pattern in loon ecology: the presence of ecological traps. An ecological trap is a breeding habitat that appears at first glance to be a good one but ends up being poor for reproduction. For example, a field might experience a burst of insect activity during early spring, enticing songbirds to settle there for breeding, but a crash in insect levels after eggs hatch might occur that suppresses the number of young birds produced. Two nights ago, we captured two chicks from two different lakes back to back. The first territory was a shallow 11-hectare portion of Wind Pudding Lake (my favorite lake name). The chick captured there was a five-week-old that weighed a scant 0.92 kg — less than half what we would expect from a chick of that age. Our daytime observations show that the chick’s parents are no slouches; they respond to its constant begging by making frequent dives and retrieving what food they can to feed it. Moreover, the chick itself dives often to forage. But this shallow lake, covered almost entirely by lily pads (which impair loon foraging), offers scant sustenance. I am afraid that the emaciated Wind Pudding chick will ultimately starve to death, as did the chick on nearby Liege Lake, another shallow lake choked by vegetation. Loon parents on small, acidic lakes struggle to rear even a single chick, whereas those on large lakes of neutral pH often raise two. This stark contrast was highlighted for us, as the lake we visited following Wind Pudding was 1373-hectare Lake Tomahawk. To be sure, loon parents on Tomahawk must steer their chicks through countless jet skis, water-skiers, anglers, and speed boats at all times of day. But vigilant parents are rewarded with abundant food for themselves and their chicks. The Tomahawk-Sunflower Bay chick held by Mina in the photo weighed 3.02 kg, yet it was only a few days older than the chick on Wind Pudding. Clearly the strapping youngster in the photo is heading for a healthy future and likely fledging.

Why on Earth would loons settle to breed on lakes that often provide too little food for their chicks? The answer might relate to the disconnect between nesting and foraging requirements. Alas, large lakes that contain many fish for loons often lack the islands, emergent marshy bays, and bogs that allow loons to avoid egg predators like raccoons. So loons looking to breed seem to be lured onto small, marshy lakes that yield successful hatches but doom their offspring to starvation.