By now, most of you are aware that the loon population in northern Wisconsin is falling. Since my last report on this topic, we have made two separate formal calculations of λ (“lambda”), which estimates the number of adults in the population in year 2 divided by the number in year 1. Lambda is convenient and intuitive; if λ equals one, there are as many loons in the population this year as there were last year, and we are okay. λ greater than one tells us that the population is growing; λ less than one tells us that it is in decline. Our two separate calculations generated λ values of 0.96 and 0.94, which indicate that the loon population in Oneida County is currently falling at a rate of 4% to 6% per year. The picture is somewhat worse, it seems, than we had thought a few months ago.

This rate of decline — if it is correct, and if it persists — is grave news for humans who love loons. If these numbers are accurate, we will notice the effects of the decline within the next several years. Territory vacancies will go unfilled. Pair members that lose their mates will struggle to re-pair with new ones. Still fewer surviving young will fledge than do now. And our loons will have entered the dizzying downward vortex of a dwindling population.

In the short term, though, one cohort of the loon population benefits from falling floater numbers. The sharp downturn in floater abundance has territorial pairs breathing a sigh of relief. For breeding males and females, you see, fewer intruders — fewer scenes like that depicted in Linda Grenzer’s photo above — means fewer young upstarts seeking to evict them from their territories and a higher rate of territory tenure. How much better off are breeders? As the plot below shows, they are a good deal better off.

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The threat of being evicted from a territory in a given year is now only 1/4 to 1/5 what it was only two decades ago. Small and/or old loons that were lucky to hold a good territory for a year or two in 1998 can kick back and relax nowadays, because the eviction rate is trivial. The decreasing floater population is making the prospect of lifelong breeding on a single territory look like a reasonable expectation for both sexes. People who have become familiar with the breeding pair on their lake might feel better off in the short term. They can be much more confident now that the birds they greet each April are the same two from the previous year.

Though I feel that I know several dozen of my study animals reasonably well and look forward to seeing them each spring, I cannot celebrate the fact that I now stand an even better chance than before of doing so. To me, the dynamism of the system — the likelihood that a breeding female or male might have to accept eviction, lick its wounds, and find a new territory with a new mate nearby — was part of its beauty. Knowing what I do now, each reunion with a familiar breeder for me will be a reminder of the new normal: unnaturally long breeding tenure made possible by the drastic decrease in territorial challengers.

Many of you have e-mailed me to ask, “What became of the duckling reared by loons?” It is a reasonable question. Each passing day during the summer revealed startling new behavioral quirks in the peculiar, touching relationship between these inseparable misfits. Having witnessed well over a thousand loon families — and by this I mean those consisting entirely of loons — I found each of my visits to the Long Lake pair a revelation. Each time I watched male and female loons feed their precious adoptee a fish or warn it about a passing eagle, I involuntarily shook my head. How could two species separated by 70 millions of years of evolution come together into such a tight and successful makeshift family? Every day the family remained together seemed to defy logic.

Yet their familial bond persisted. Following my most recent post on the loon-duckling family, the duckling grew and grew some more. By the end of July (as Linda Grenzer’s photo shows), the duckling was close to adult size, and the only uncertainty was whether or not it would sink its parents by continuing to ride about on their backs. By mid-August, the pair and duckling were spending more time apart. On multiple occasions, we saw the duckling take off and fly around the lake a few times before landing near its anxious guardians. By now fully capable of feeding itself and weeks beyond the normal fledging date for mallards reared by their own species, the duckling seemed to cling to its parents more for their sake than for its own.

By September 4th, the duckling and its loon parents were gone from the lake. We will not ever know where the duckling went or how it lived after leaving Long Lake. Although we could have attempted to mark it in July, as we do loon chicks, I could not bring myself to do so. Even as a scientist fascinated by the behavioral outcome, I was too transfixed by the beauty of the family to capture them and risk disrupting it.

 

Juvenile loons are in a race against time. While their parents seem to relax following the breeding season — wandering from lake to lake as if on a goodwill tour — juveniles, like the three-month-old in Linda Grenzer’s photo, face a ticking clock. After hatching in June or July, juvies must reach near-adult size by ten weeks of age, practice takeoffs and landings, and become strong enough to make flights of hundreds of miles on their southward migration in early November.

They are racing the ice. Temperatures cool in September, become unpleasantly chilly in October, and truly plummet in November — and lake temperatures follow suit. Ice-up can occur anytime between mid-November and mid-December in northern Wisconsin, and ice-up is the end of the line for juveniles. Opportunistic bald eagles await juveniles that are not prepared to migrate and become trapped in the ice. Apparently sensing the desperate task that will confront their offspring in the fall, parents stuff them with fish for eight long weeks in July and August. Chicks grow explosively during mid-summer. But they face their most challenging task in autumn, when parental support wanes and they must learn to feed themselves, improve their body condition, and prepare for their southward journey.

In general, scientists have paid little attention to the juvenile period in birds. Our neglect is natural enough. The breeding season is chock full of interesting behavioral and ecological events: pairing of mates, defense of breeding territories, selection of nest sites, and relentless territorial intrusions by nonbreeding adults seeking to settle. Perhaps ecologists can be forgiven for focusing their attention on breeding behavior and trusting that juveniles will take care of themselves.

But we wondered. If young adults settle on breeding lakes that closely resemble their natal lakes, might juveniles — which must fight for their lives just to become adults — also exhibit clear preferences for certain kinds of lakes over others? Constrained by flightlessness to forage only within the lake where they hatched, we might expect juveniles to become highly specialized to hunt and consume the species of prey found on the natal lake. So once they become capable of flight, we might expect them to visit and forage on other lakes very similar to their natal one. That is, juveniles reared on a diet of bluegill sunfish and used to hunting that species should spend most of the pre-migratory period visiting lakes full of bluegill that they can catch and consume efficiently. And juveniles accustomed to eating snails and leeches should find lakes full of those invertebrates on which they can feast.

Our interest in lake visitation patterns of juveniles during fall inspired us to plot the local movements of youngsters between lakes in the fall of 2012, 2013, and 2014. Kristin, Gabby, and Nathan used their band-spotting skills to locate juvies in September and October of these years. They found close to 200 cases where a juvenile we had marked had flown to forage on a lake other than its own. Using these data, Brian, who joined us this summer, asked, “Do juveniles forage on lakes at random, or do they prefer to forage on lakes like the one that hatched them?”. As the figure below shows, the mean difference in pH between a juvenile’s natal lake and the lake where we spotted it foraging (red vertical line) was far less than the distribution of differences we would have expected, if juvies had foraged randomly (grey bell-shaped curve).

Z_pH_Randomization

Although Brian has a few statistical checks to complete, the pattern seems clear. Juveniles exhibit strong preference for lakes that resemble their natal one in two respects: 1) pH and 2) water clarity (data not shown). Brian’s analysis is ongoing, and he is trying to learn how closely these chemical and physical attributes predict the food available to loons in a lake. But we are betting that the stark preference of three-month-old juveniles for lakes that remind them of home occurs for a simple reason. Juvies try to spend their time hunting prey in familiar conditions to build themselves up for their most dangerous first southward journey.

I have put off writing those words for some weeks now. The patterns in my data were clear; every measure of breeding success was pointing downwards. If you have been following the blog, you might recall that number of chicks per pair has fallen sharply since I began studying loons in 1993. Although I had not reported it yet, loss of chicks after hatching has also increased significantly since I began my work. That is, many pairs hatch two young but lose one or both of them nowadays. Furthermore, even chicks that survive to five weeks of age are now in poorer condition (as measured by body mass) than in 1998 or 2006 or 2013. In short, breeding pairs in northern Wisconsin now raise fewer and less robust chicks than they did 25 years ago.

A combination of scientific caution and denial caused me to delay describing the implication of these trends — and others that I have detected more recently. As a scientist, I am used to finding one pattern, drawing a tentative conclusion based on that single finding, and then being proven wrong by the next finding. Having had an initial conclusion reversed many times during my career, I was unwilling to sound the alarm without a stronger, more consistent set of findings. But the data I now have are consistent and come from multiple independent analyses. Furthermore, the data are fundamentally simple. My conclusions are not derived from complex models based on measurements of invisible particles detected by finicky high-tech devices. We are just counting and weighing loons here!

Still, you might wonder why my earlier caution has turned so suddenly to alarm. Let me explain. I followed a simple line of reasoning. If loon pairs are producing fewer and weaker chicks, then fewer chicks must be able to migrate to the wintering ground. And if fewer juveniles make it to Florida, then fewer should survive long enough to return to northern Wisconsin (which happens at 2 to 4 years of age) and look for a breeding territory of their own. So, declining chick production should result in a reduced population of nonbreeders (or floaters) in our study area, which are young adults looking to settle on their first territory with a mate. Since we mark chicks and obsessively reobserve them as young adults, we can test the idea that lower chick production has resulted in fewer floaters. The results are stark. After one adjusts for number of observer-hours spent looking for floaters each year, a dramatic pattern

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emerges. The population of floaters has plummeted. Look at the scale of the graph carefully. This is not a small decline. Between 1998 and 2006 the number of floaters seen per observer hour fell from 0.020 to about 0.010. From 2006 to 2015, that number has fallen still farther — to about 0.006. In other words, we have seen roughly 1/3 as many floaters from the 2015 year class (which are 4 years old now) as we saw from the 1998 year class. In terms of percentages, we reobserved about 45% of all chicks banded in 1998 and 1999 much later as adults; we see only about 14% of banded chicks as adults these days.

So what? Floaters are nonbreeders. They contribute no offspring to the population. Do they really matter? There are not even enough territories to hold them. They are surplus individuals, in a sense. You might view the presence of any floaters at all as a positive sign that the population is bursting at the seams. Yes….but floaters are also the future. That is, floaters are loons not yet old enough to claim territories but waiting to fill in for dead breeders (or evict them forcefully). Without floaters, a breeding population cannot sustain itself, because, inevitably, breeders die and must be replaced.

Even now that I have a set of strongly suggestive patterns, I cannot be absolutely certain that loons are in trouble in Wisconsin. Perhaps the steep decline in floater survival simply means that the weak floaters now die off long before settlement, leaving the strong ones to replace dead breeders. Perhaps something very odd is happening in the north-central part of the state (more intense human recreational activity?) that is not happening elsewhere. So, let’s keep fingers crossed that this is a fluke of some kind. But I am convinced that we are seeing a worrisome pattern that is unlikely to be confined to my study area.

What does the future look like, if the floater population truly is declining markedly, as I suggest? Despite the strength of the pattern, the short-term effects might be subtle, because loons are long-lived. Imagine that families in your town or city suddenly began to have only 1/2 or 1/3 as many children as in years past. When would you notice a marked change in the community? You might — if you were very sharp — notice fewer large families at local playgrounds. Sometime later, you might notice the closing of a school here or there. But decades would pass before you would discern a loss of occupied homes in your neighborhood (presuming that kids in your town grow up to inhabit local homes).

So it will be with loons. On some lakes, the death of a pair member — especially a male, because males are in short supply — will leave a vacancy that is not filled by a floater. Some lakes that always supported a breeding pair will lose that pair and instead only see loons that come and go to forage. Large lakes with six perennial breeding pairs will, over time, see some territories “wink out”, leaving only three or four. In a few decades perhaps, even those territories will vanish. If I am correct, and unless this long-term pattern in the survival of young loons reverses itself, loons will ultimately disappear altogether from northern Wisconsin.

The Audubon report put me on notice. Loons are not immune from climate change. While I have wondered at times whether their aquatic habitat might somehow buffer them from the warming of the Earth and increased moisture in the atmosphere, this was a false musing. Recent changes in temperature and precipitation have myriad and complex effects on lakes and their inhabitants. Loons will have to confront the changing conditions just like all other organisms must.

I wondered whether my long-term data on loons might show climate-induced changes. I am not a climate scientist — nor even a hard-core ecologist who might routinely measure fish populations, water temperatures, or lake chemistry. But we do weigh all loons that we capture and band. Perhaps masses of adult loons or chicks have fluctuated in response to the changing climate.

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My findings are quite striking. Chicks have decreased in mass consistently since my team began capturing and marking loons. This finding alone is worthy of concern, but it is not the only one. Breeding males (see below) too show a decline in mass during our study. Breeding females, on the other hand, show no steady loss in mass.

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What are we to make of these patterns? Are populations of small fish down in the past few decades such that chicks and their male parents struggle to put on or maintain body mass? Or are lakes changing in ways (e.g. clarity) that might make fish more difficult to catch? Whatever the cause of these decreases in mass, why are female loons not affected similarly? These questions must remain unanswered for the time being. In fact, these results are so new that I must run some more double-checks before I fully trust them. Even if they are real effects, as it appears, it is much too early to attribute them to global warming. My worrying self, though, fears that these significant declines in body condition might be the leading edge of a changing climate’s impacts on Wisconsin loons.

On its face, it seems absurd. Why would loons ever communicate with eagles? Apart from raccoons, bald eagles pose a greater threat to loons than any other species. Eagles are opportunistic feeders, always looking for an easy meal. And they are large and well-armed enough to seize almost anything edible they find. Nesting loons provide a tempting stationary target for eagle attack. We have had two eagle kills of nesting loons during our study. The eggs themselves are vulnerable to eagles, because they do not flee and provide a nourishing snack. Loon chicks, whose diving skills are more limited than adults’, also draw unwanted attention from eagles. According to our own observations and those of others on our study lakes, eagles are a major cause of mortality among loon chicks older than two weeks. No doubt this explains why chicks learn to track the movements of nearby eagles obsessively, like the three Bass Lake chicks in Linda Grenzer’s photo.

Why would loons, which seem to spend most of their waking hours scanning the skies for eagles, ever speak to them? Could it ever be profitable to speak to your arch enemy? According to a number of studies by behavioral ecologists, it could, providing the information you pass along to your enemy increases your likelihood of surviving.

Deer and antelope engage in a behavior termed stotting in the presence of predators. Stotting means jumping upwards (often while flashing the tail upwards) in a way that makes the animal more conspicuous to its predator. But data collection and analysis on the occurrence and timing of stotting by gazelles has shown that they chiefly practice this behavior when they spot the predator at a distance and can easily outrun it. This and subsequent research suggests that prey often signal to predators to inform them of the unprofitability of an attack. That is, a prey species is saying to its predator, “I see you and am faster than you; save us both a lot of time and energy by looking elsewhere for food.” In fact, honest signals between prey and predators are not uncommon in nature. Many animals have evolved bright warning coloration to signal to potential predators that they are poisonous or dangerous to the predator in some other way that makes attacking them a bad idea. Colorful prey are, in effect, doing predators a favor by informing them that they should not attack! (Again, though, the prey are acting in their own best interests, not the predator’s.)

Could the mournful sounding wail that we often hear from loons be a signal to eagles that they have been spotted and that an attack would be fruitless?  If so, wails should: 1) occur often when eagles are passing overhead, but only when they are at a safe distance, and 2) be emitted by loons regardless of the presence or absence of other loons (like mates and chicks). The second prediction is crucial; if loons give wails to eagles only in the presence of their mates and chicks, it would seem as though they are simply warning their family about the eagle and not talking to the eagle itself. Our data clearly show that the wail is a long-distance signal given by loons when eagles are overhead. And loons wail to eagles whether they are alone or with mates and offspring. So loons certainly look as though they are speaking to eagles with their wails.

Strange to think that telling your arch-enemy anything could ever be a good idea!

I will admit it: I am flabbergasted. When the Bass Lake pair hatched three chicks in the first week of July, I never gave them a chance. I suppose my pessimism was, in part, an attempt to protect myself from further disappointment. This year, as I have mentioned, has been a forgettable year in our study area. The dust has not yet settled completely, but 2019 will certainly go down as the worst year for chick productivity since I began the study in 1993. And we have had some dreadful breeding years!

The Bass Lake Miracle — hatching and rearing of three vigorous chicks on a tiny lake — is so far a welcome exception to the dreary pattern. As I noted in my previous post, however, the Bass Lake pair are fighting more than the negative tide of 2019. Lakes that you could throw a baseball across — well, lakes that Trevor Bauer could throw a baseball across — generally do not contain enough food to allow two chicks to reach fledging size, let alone three. Fawn Lake is a case in point. Slightly larger than Bass, Fawn hatched two chicks, which weighed 2.1 and 1.2 kilograms at capture ten days ago. So the smaller chick is just over half the weight of its sibling, and its survival prospects appear grim. Moreover, Evelyn reported that the beta chick was begging fruitlessly for feedings from the male today, while its fat and sassy sibling rested nearby. Such is the normal state of affairs for families that try to raise more than one chick on small lakes.

But don’t tell all of this to the over-sized Bass Lake family. As Linda’s recent photo shows, the trio of chicks there are beating the odds so far. During my visit to the lake today, the three-week-old chicks swam along in a tight group, tracking their foraging parents and getting fed constantly. The food items brought up by the parents were not tiny minnows and leeches, such as one often sees on smaller, food-stressed lakes, but crappies and yellow perch large enough that the chicks had to work a bit to swallow them. There was no desperate begging, no pecking of the small chick by its larger siblings. Most important, the size disparity among the chicks, quite evident a week ago, is less so now, which suggests that all chicks are receiving ample feedings.

I retain some healthy pessimism about the loon family on Bass. I have seen too many starved chicks on small lakes to feel otherwise. But if a pair of loons can adopt a mallard duckling, raise the duckling on fish they catch and feed to it, and teach it to dive as they do, I suppose anything is possible.

The loon pair and mallard duckling remain a close-knit family, if a non-traditional one. This fact became clear on Linda’s recent visit to Long Lake, as the pair remained fiercely protective of their charge (as her photo shows), and the male permitted it to preen while standing on his back. But Linda’s observations also suggested that the duckling is not helping its foster parents’ in their efforts to safeguard their territory ownership.

Let me provide some context. During July and August, loons that do not have territories  look hard for them. Why? Well, because (with apologies to Jane Austen), “….it is a truth universally acknowledged that a single loon in good physical condition, must be in want of a territory.” Indeed, single loons search ceaselessly, and at times desperately, for territories and mates. They do not search blindly but instead heed a signal. The presence of chicks with a breeding loon pair is a shining beacon to unpaired loons that announces, “This is a good breeding territory; remember this lake, return to it next year, and claim it for your own!”

In order to counter the prying eyes and evil intentions of such nonbreeders, loon pairs play hide-and-seek with their chicks. This is not the kind of light-hearted hide-and-seek that we humans play with our offspring. Instead, loon pairs with chicks play a high‑stakes hide-and-seek game to keep nonbreeding loons from spotting their young.  And if pairs (or their young) play the game poorly, they place their future territory ownership at risk.

Hiding of loon chicks by parents often seems a difficult task. Loon chicks are chocolate brown in color and can hide near shore among rocks and logs — if they wish to do so. Nonbreeders, for their part, do not call ahead to warn of their visits. Instead, nonbreeders appear suddenly over a lake, flying at 70 miles an hour, and scan the lake’s surface for loon chicks. Often they land in the lake as well. Under these circumstances, it is a daunting task to keep chicks out of sight. Yet, if pairs with chicks are fortunate enough to spot flying intruders early and to be in a part of a lake from which their chicks can easily swim to shore, they sometimes hide their chicks successfully by means of an odd “dive and scatter” strategy.

Hiding of a fostered duckling from snooping intruders has turned out to be an even greater challenge, Linda reports. While keeping a fostered duckling well fed is easy, preventing intruders from spotting the duckling is comically difficult. Picture the scene from a few days ago. An intruder suddenly appeared overhead, emerging out of the early morning fog while the loon pair and duckling were resting. Both adults immediately dove and swam underwater towards the center of the lake to engage the intruder. Instead of diving itself and racing underwater to hide near shore, as a loon chick would have, the duckling freaked. When it spotted its foster parents far away and next to nonbreeders that had landed, the duckling raced towards middle of the lake, while peeping loudly, making itself very obvious. Needless to say, efforts by the loon parents to hide their youngster were at an end.

I know what you are thinking — the loon pair lost nothing from the conspicuous behavior of the duckling. The intruder might have been confused by the duckling’s presence, but it probably would not have confused the duckling with a loon chick, taken it as a sign of breeding success, and planned to challenge the pair for territory ownership next year. That is probably true, unless, of course, nonbreeders cue in not only on loon chicks themselves but also on protective and aggressive behavior exhibited by loon parents. Let’s hope the duckling’s misbehavior had no long-term impacts. It would be a shame if the loon pair suffered doubly — by rearing a youngster of the wrong species and losing their territory the following year.

This is a frantic time of year for wildlife and wildlife rehabbers. Why? Because while you are ditching Weird Aunt Beatrice at your family reunion, loon pairs and their chicks must dodge your crazy nephew Lucas on his Jetski. Needless to say, loons have considerably more on the line.

The tranquility of May did not prepare the Tomahawk-Kemp pair — or me — for the life and death struggle they would face in July. On May 11th I ran across the super tame male and female from Tomahawk-Kemp when they were preparing to nest in the long channel between Minocqua and Tomahawk. On that visit, they seemed almost to welcome my presence, and it was a simple matter to scribble down all of their colored leg bands as they rested and made short dives near my canoe. I experienced one of those moments when you are alone with nature and feel a sudden, ineffable connection with a wild animal. I wondered: “Does the male remember me from 17 years ago, when I first encountered him as a settler on South Two Lake?”

The Tomahawk-Kemp pair’s recent experiences with humans have been considerably less pleasant than those in May. We do not know the whole story, but on about June 17th, the pair hatched two chicks. (Judith Bloom, whose June 20th photo appears above, helped us narrow the dates with her routine checks.) Having survived black flies, raccoons, eagles, and curious humans to hatch both eggs, the Kemp pair headed out into the main body of Tomahawk to locate small fish suitable for their ravenous youngsters. There they began the daunting task of diving to catch food for the chicks, while at the same time helping the tiny fuzzballs steer clear of boat traffic. Most boaters adhere to local ordinances with respect to speed, distance from shore, and respect for wildlife; some do not. We suspect that a boater in the latter category ran down – either purposely or not – the Kemp hatchlings on the 1st or 2nd of July. The parents were unscathed; adult loons can dive rapidly and deeply, and those living on Lake Tomahawk have ample experience avoiding motorboats. Young chicks, however, have neither the diving capacity nor the familiarity with speeding watercraft to help them escape collisions.

Both chicks were hit by the boat. Linda Grenzer snapped the photo below of the less severely injured chick; it showed a healed wound towards the tail end, near the base of the left leg.

LMG 26251 Lake Tomahawk Kemp Injured Chick

The second chick looked better externally but had internal damage from the boat strike — a ruptured air sac — which prevented it from floating upright in the water. (Bird’s air sacs are thin membranes that connect to the lungs and are part of the respiratory system.)  So Linda, Elaina, and Kevin decided to catch this listing chick and take it to REGI for treatment. Fortunately, REGI repaired the damage, fed the chick well, and prepared it for successful release three days later. As you can see from Linda’s photos at the release, both pair members quickly accepted their missing youngster.

LMG 26337 Lake Tomahawk Kemp Rehab Chick Release

On the other hand, its sibling had apparently enjoyed being an only and had mixed feelings about the reunion!

LMG 26278 Lake Tomahawk Kemp Rehab Chick Release

According to recent reports, all is now well with all four members of the Kemp family. Life will continue to be a wild ride, because boat traffic will not wane for several more weeks, and the siblings will no doubt bicker over food from time to time. Since chicks rapidly improve their diving skills, though, we can hope that these two have had their last close encounter with fast-moving watercraft.