Despite 31 years of field research, I have seen very few dead loons. The scientist within me should know better, but I think my rather limited exposure to loon mortality has led some part of me to presume that adult loons die on migration or on the wintering grounds, not during summer months. Spring and summer, after all, are times of renewal, of bountiful food and comfortable living conditions. It seems inconceivable that loons could perish in the warm, friendly environs of the Northwoods.

But this is an anthropocentric view. While most humans that we encounter on the lakes are relaxed and smiling, loons — and all other non-human species for that matter — are in a constant struggle to ward off predators, parasites, and pathogens and keep themselves and their young alive. Loons are not on vacation from April to October; they have merely traded one set of hazards for another.

Four members of the Wisconsin loon team were reminded of the incessant fragility of loons’ lives during a visit to Katherine Lake in late May. Split into teams of two in separate canoes for training of the new field team, we first paddled to the traditional nesting site on a small island towards the southern end of the lake’s main bay. In case nesting was under way, we circled at a distance. As we completed our brief circumnavigation, our brains struggled to make sense of a visual anomaly on the west side of the island. It was Ethan who first pieced things together. “There is a dead bird,” he remarked.

After approaching to check on Ethan’s assertion, we were greeted with a macabre spectacle. Amidst a vast mound of loon feathers lay remnants of the Katherine male, a well-traveled individual with a fascinating life history. A few feet away from his carcass was a nest containing a single intact egg.

There was no need to round up the usual suspects. An eagle, it seemed, had surprised the incubating male, ended his life, and closed the curtain on Katherine’s chances for breeding success for the year. The telltale plucking of the avian carcass after the kill clinched it.

Yet this is not the end of the story. Blithely uninformed about the recent horror that had taken place on the lake, two young loons — an eight-year-old female and a seven-year-old male — had quickly paired up and made their own plans. Even as we mourned the violent passing of the old resident male, these two individuals foraged and preened calmly about the lake, apparently savoring the prize they had inherited.

Young settlers carefully choose the lake on which they wish to breed on the basis of its overall size relative to their natal lake. I was cheered to see that the new settlers on Katherine were well-suited to the vast size of their new territory. The eight-year-old female was from Two Sisters-East, a good-sized lake not far south of Katherine; the seven-year-old male was from massive Lake Tomahawk, a short distance northwards. Still, there seemed little chance that this confident new couple would attempt to nest in 2023.

When Emily sent me the photo above, I was doubly surprised. With the disturbing sight we had observed on Katherine still etched in my mind, I had crossed the lake off the list of territories where chicks might be produced. Moreover, I had never dreamed that the new pair would choose to nest on the precise spot where an eagle had ended the life of and then feasted upon the old male. From Emily’s photo, you can see vestiges of the attack. The incubating bird (the eight-year-old female in this case) sits placidly on a new set of eggs, oblivious to the smattering of her predecessor’s feathers that surround her.

There is something exhilarating about unbridled and heedless optimism. Stuck as we often are in the past and present, it is often difficult to see what good might come down the road. And I have to say that the brazen breeding attempt of the new young Katherine pair has changed my outlook. If an inexperienced loon couple can dare an eagle to attack them — and even more so if they can pull off a hatch — perhaps a breeding season that began wretchedly can end on an up note.

Today brought more bad news. As I reviewed yesterday’s lake visits, I saw that Bear and Woodcock had been whittled down from two chicks to one. I objected briefly. “Brian”, I asked, “are you sure Woodcock has lost its second chick?” He was certain.

In the old days (the 90s and early 00s), about half of all loon broods in Oneida County had two chicks, like the 9-day-olds in Linda’s photo. I recall that we used this as a rule of thumb, when gauging how many chicks we would eventually capture and mark. Okay, we thought, half of all broods will have two chicks, and half will have one, so multiply the number of broods by 1.5 to get the total number of chicks. But it has been some years since half of all broods contained two chicks. In fact, we have to go back to 2005 to find a year of parity between one- and two-chick broods. Since then, 68.5% of all broods have been singletons. From 2017 to 2019, 78% of all families had only one chick in them.

This year will only strengthen that trend. After loss of one of two chicks on Woodcock and Bear, 28 of 36 focal pairs with chicks this year (78%) are caring for only one. By the way, chick loss is not just the whittling down of two chick broods to singletons. Indeed, eight of our focal pairs that hatched one or two chicks initially are now without chicks. So the massive increase in chick mortality that began during the past decade or so has wiped out entire broods as well as cutting many down by half. Since the trend of increased chick mortality long ago reached statistical significance, I have begun to fixate on it. What is killing loon chicks?

We cannot blame my favorite scapegoat, black flies, for chick loss. True, the flies had a devastating impact on nesting behavior in May and have reduced breeding more than any other single factor this year. Poor overall loon breeding success in the past five years can also be laid at least partly the tiny feet of Simulium annulus. That is, the flies suppress overall breeding success by wiping out many early nests. But it is late July now. The flies are a distant memory, and chicks are still dying.

Naturally, we look at what has changed in loons’ habitat during the period when chick mortality has been increasing. There are myriad possibilities. (1) Bald eagles are undoubtedly the most despised of all loon enemies. The eagle population has soared over the past four decades, and their impact on loon breeding success has been documented already. We have observed and have had reported numerous cases of loon chicks being taken by eagles — and loons seem to spend most of their waking hours on the lookout for eagles — so we must consider bald eagles a likely cause of increased chick loss. This year we have added eagle counts to our observation protocol. We will soon know whether eagles can be blamed for the increased mortality of chicks. (2) Declining small fish populations are another likely culprit. Small panfish, unfortunately, are not monitored as closely as are large gamefish, but the possibility that less food might be available now than before for loon chicks dovetails nicely with the fact that they are now 10% lighter than they were 25 years ago. We will explore the “decline in small fish” hypothesis in coming years. (3) There are far more humans on Oneida County lakes than there were 25 years ago. Indeed, a collaborator at Michigan State University has already documented that human population density is a strong correlate of adult mortality in our study area. It is quite plausible that human impacts — chiefly boat strikes, accidental hookings, and line entanglements — are the root cause of the decline in chick survival too. Our lakes vary enormously in the amount of human activity they support; this will make it straightforward to test the “human impacts” hypothesis.

Of course, multiple factors might have conspired to reduce the survival rate of loon chicks, including those just mentioned and others. If so, the task of detecting those that are most significant — and devising some means of mitigating them in an effort to restore loon breeding success to what it once was — will be daunting. Naturally, I am hoping that there is a single discrete cause. For example, if we learn that bald eagles are starting to have an unacceptably high impact on loon chick mortality, we would simply have to…….. well….okay…… Let’s hope eagles are not the cause!

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!

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.


If you have been floundering lately, as I have, let’s gain some perspective by considering the plight of the Silver Lake loons. The pair’s struggles began in mid-May, as black flies thwarted their efforts at incubating a first clutch of eggs. According to Pat Schmidt, who watches the pair carefully throughout the breeding season, incubation proceeded normally during the nighttime — cool temperatures kept the relentless pests at bay. But the marked female and male were unable to stay on the eggs during daylight hours, when black flies were active and biting. On again, off again incubation finally gave way to abandonment during the last week of May, but the pair reset themselves quickly, adding two additional eggs to the two they had earlier tried and failed to hatch. Despite the cumbersome task of warming four large eggs simultaneously, the birds produced a chick at the very end of June. Their fortunes seemed to have turned.

The greatest risk faced by a breeding loon pair with a chick is our national bird. Bald eagles nest on tall white pines along lake shores and are a frequent sight over lakes. Indeed, eagles are such a routine part of the scenery on the lakes that loons often deign to wail at them as they pass overhead. Eagle fanciers might try to convince us that these raptors even purposely lull loons into a false sense of security with their constant, mostly innocuous flights nearby so that they can occasionally strike at loons suddenly with deadly purpose. An opportunity for such a surprise attack might occur when an eagle appears just above the tall trees at the lake’s edge as a week-old chick’s parents both happen to be underwater diving for food. Perhaps it was such happenstance that allowed an eagle to carry off the Silver Lake chick on July 2nd. In any event, eagle predation brought the breeding efforts of the pair to an unsuccessful close this year.

The sting felt by lake residents at the loss of the chick had begun to abate by July 18, at which point the territorial female, “Copper” (named for one of her plastic leg bands), found herself in a desperate battle. She was beaten badly, chased across the water, attacked from below as she rested on the lake surface, and finally forced to take refuge on land to escape further damage. By the time the violence had ceased, Copper had to be carried, helpless, to the Northwoods Wildlife Center. She died there a few days later.

As I have made clear in numerous posts, males are the ones that battle dangerously (apparently because of senescence) in most cases. So how do we explain the latest Silver debacle? An oddity concerning contestants might offer a clue in this case. Copper, who had reared chicks on Silver in 2014 and 2015, had battled repeatedly for ownership over the past several years with her bitter rival, “Mint”, the previous Silver female and mother of the chicks in 2010 and 2012. Even after losing the territory to Copper in early 2013, Mint was a frequent intruder into Silver Lake. Hence, both females had raised chicks in multiple years with the male, and both were highly motivated to vie for control of the territory. In addition, banding records indicate that Copper and Mint were of very similar size.

Now to game theory. If an animal encounters a long-lived opponent with which it is very closely matched in fighting ability but happens to get the upper hand at some point, it might then pay for that first animal to press its advantage and even kill the opponent. Why? Because our research has shown us that closely-matched pairs of females, like Copper and Mint, often give each other fits. Two females on Heiress and two others on Oscar-Jenny were so close in fighting ability that they traded off ownership of those territories over many years, each female hindered in her breeding efforts because of the constant interruptions of the other. The result was poor reproductive success for both rivals. Although there is enormous risk involved, it might occasionally pay for females to exhibit the vicious battling we associate with males. Specifically, a lightning strike to finish off your archrival might sometimes be worthwhile to avoid a chronic, destructive feud.



“Wow”, Lainey said, “that band number is right next to the female we caught last night on Sherry”. She was right; the adult male from Skunk, which we had just netted and whose band number I was reading aloud to Lainey for data entry during banding, had a number imprinted on his aluminum USGS band that followed immediately after that of the Sherry female from the previous night. The reason for consecutive bands is that the Sherry female is the mother of the Skunk male and was caught and banded with him a decade ago (less two days) on Sherry Lake. I remember July 31st, 2005 on Sherry vividly, because I was equipped with a video recorder on top of a helmet with which we recorded the capture process for research presentations. But the recapture of mother and son on back to back nights ten years after we had first marked them has also caused me to reflect upon several key features of loon biology that have become familiar to me through my work.

First, loons live a long time. In this twenty-third year of my work, I still encounter birds in the study area that were on territory, as adults, when I first started covering them. Females, in particular, are survivors. While males have rather high mortality –partly owing to their proclivity for battling dangerously — females linger. When their mate dies, females find another; when a female is evicted unceremoniously from her territory, she stoically moves to a new lake nearby and awaits a chance to re-insert herself back into the breeding population. So it goes with the Sherry female whose worn-out band from 2005 is pictured on the bottom in the photo. She was “widowed” suddenly in 2009 (a possible eagle kill) but hung onto her territory and was joined by a new male in short order, who has been her mate since.

Second, young males do not disperse far from their natal lakes to breed. The Skunk male, from whom we removed the top band in the photo last night, moved about 15 miles from his natal haunt, Sherry. That dispersal is, actually, a bit longer than average for males, many of whom settle to breed on a lake adjacent to where they hatched years earlier. Short-distance male dispersal is essential to my work; without it, I would not have a large marked cohort of 2 to 5 year-olds of known age and natal origin in the study area at all times whose territory settlement strategies could be investigated. (At last count, we had seen 295 adult loons in the study area that were marked originally as chicks.)

Third, loons vary tremendously in their behavior towards humans. My assistants and I dread the Sherry female, because she is the most skittish individual we know. She cannot be approached easily within 100 meters on the water; she tremolos (i.e. alarm calls) incessantly when a chick is present and a canoe appears on the water. In fact, my assistants tell me that she begins to tremolo in anticipation of a canoe being placed on the water and that they have begun a strategy of hiding behind bushes and trees along the shoreline in order to make observations of her when she is with the chick. (Fortunately, Sherry Lake is tiny, so this observation strategy is workable.) I joked that we should wear camouflaged clothing when visiting Sherry; my assistants did not find this funny. Oddly, the Sherry female’s mate is among the tamest loons we study and never tremolos at us when we collect data there.

The great variety in loon tameness is a topic of great interest to us, as I have mentioned. It amazes me that an adult such as the Sherry female could react so strongly (and, it would seem, maladaptively) to humans, which she encounters constantly. Doesn’t she waste energy with her fruitless calls? Shouldn’t skittish birds like her leave fewer offspring and live shorter lives than other adults who tolerate humans without constant complaint? If so, she is not a good example of the pattern, as she has behaved this way for the ten years we have known her while cranking out chicks. Indeed, the Sherry female and the Oneida-East male, another vociferous but fecund individual with whom my staff has to cope, make me wonder if I have got it backwards. Maybe loud-mouthed loons warn humans away, lessening the likelihood of injury to themselves and their brood, and are rewarded with high evolutionary fitness.

Although we were sad eight days ago, when we lost the male to an eagle on Tomahawk-Sunflower Bay, his sudden demise gave us an opportunity to observe what happens when an established breeder disappears. In this case, the unbanded mate of the dead male was on her own for a day or so and then was joined by a banded male that we know well. He is blue over orange (right leg), blue over silver (left leg) or “B/O,B/S”. B/O,B/S is the former breeder on Mud Lake, just next door. In late May of 2011, B/O,B/S picked up an orange fishing bobber on his right leg that slowed him down a little and affected his diving. We were very worried about him, as we thought that the bobber and associated monofilament line might cut off his circulation and cause him to lose his leg. We visited the territory often to check on him. He lost the Mud territory that year but remained in good health, it seemed. He was sometimes spotted on Bird Lake, just next door, so clearly he was able to fly. Now he has come full circle, as he has lost the bobber on his leg, recovered from that injury, and established himself again on a breeding territory. By the way, B/O,B/S is a male ABJ (Adult loon that was Banded as a Juvenile) that has a special place in my heart, because he is a “third-generation” loon to our study. He is the son of a female ABJ from Shallow Lake that was hatched and banded in 1993, my first year of research on loons. (This female is still around. After many years as the breeder on Fawn Lake, she is now a pair member on Lumen Lake.)

This morning Kristin found the banded male on Tomahawk – Sunflower Bay freshly killed and being consumed by eagles. This is a sad discovery for us, because he was a sweet, tame bird with a rich history of rearing chicks — on two separate territories. We cannot be certain that an eagle killed the male, but he was healthy on our last visit, and the pair had recently nested. So we strongly suspect our national bird!

This is a reminder that, while they usually seem to be merely a nuisance, eagles DO have the potential to kill adult loons. Our best-documented example of an adult kill was a female attacked and dispatched by an eagle on a nest on Alva Lake back in 2005. Of course, eagles are a constant threat to chicks.

Funny, but I have struggled to love our national symbol recently. I hope that does not sound unpatriotic!