It is often said of field biologists that we resemble our study animals. I guess it is true. No, I am not aquatic. Nor do I subsist on a diet of fish, crustaceans, insect larvae, and the occasional mollusk. I did not even engage in a dangerous battle to secure my mate and territory. But, like loons, I enjoy being alone.
One of the joys of my profession is the time that I spend alone in a canoe, watching loons and taking in the beauty and simplicity of their lives. When your world is distilled down to watching the sky for other loons and bald eagles, chasing fish under water, and preening from time to time to take care of your feathers, life seems pretty straightforward. During those moments when I am with loons, their few concerns are all that matters. At such times, the headaches of keeping a major research project afloat, supporting a young field staff, repairing or replacing broken equipment, publishing scientific papers, and sharing engaging stories, photos, and video via social media vanish.
Loons would seem to gain even more than I do from avoiding crowds, especially at this moment. As a migratory species that winters along oceanic coasts, summers on northern lakes, and uses a variety of lakes and rivers in between, common loons appear at great risk from the current outbreak of highly pathogenic avian influenza. After all, waterfowl like ducks and geese, which share these waterbodies with loons, are known to be important hosts for the virus. Yet to date, loons seem to have avoided the epidemic of HPAI that has decimated other aquatic birds in the United Kingdom and eastern North America. How have loons dodged this juggernaut? Mostly by breeding solitarily, instead of gathering in dense breeding colonies on oceanic islands, where the virus spreads quickly via saliva, respiratory droplets, and feces.
Loons’ ability to avoid massive mortality events from HPAI is welcome news. After all, they already have had to contend this year with a late ice-out that has delayed their reproductive efforts and a higher-than-usual population of Simulium annulus, the black fly that singlehandedly makes May a miserable month. Yet some pairs have remained steadfast. At long last this week, several breeding pairs in Minnesota and Wisconsin Study Areas have hatched chicks, like the ones in the photo above from Ossawinnamakee Lake (photo by Keith Kellen). Maybe things are beginning to turn around!
I’ll just admit it: I have started to root for the elderly. While I used to support one contestant or the other based solely on geography, I now rejoice when an old individual surprises us by winning a battle against a younger opponent. Recently, for example, I have found myself more than normally excited that Justin Verlander, who at 39 is far older than most Major Leaguers, is still a dominant fireballer for my Houston Astros. Despite my lingering dislike for the Patriots, at times I catch myself admiring Tom Brady, who has continued to be an effective NFL quarterback at 44, defying the usual bounds of age.
Attuned as I am to learning of female loons’ age-defying exploits, I was blind-sided by Sarah Slayton’s report from Pickerel a few days back. Upon her arrival, Sarah witnessed a nasty battle between two adults on the Pickerel-North territory. She nailed bands on the participants and was able to ascertain that this contest was between males. The contestants, she told me, were Green/Mint-Right and Blue/Red-Left. Blue/Red-Left, I thought???. Blue/Red-Left is the ancient male from Pickerel-West who was evicted from his own territory last July by a young male from Pickerel-South. That defeat was especially painful; Blue/Red and his mate were rearing two chicks at the time which were certainly killed by the new male as he solidified his hold on the territory. Lacking the strength to re-engage with the 8-year-old opponent that had recently bested him, Blue/Red evidently set his sights on a more achievable prospect — evicting the 17-year-old male a short distance up the lake whose territory has been a consistent chick producer.
We have limited information on territorial contests between old loons. Quite frankly, male contests usually involve a very predictable pair of opponents: a male (15 or older) that is past his prime and a young male (5 to 8 years of age) that has suddenly realized he is capable of defeating an older male and seizing his territory. I have to confess that I have begun to give up on old, defeated males. A few of these washed-up individuals are able to recover from eviction by settling peacefully on a vacant lake near their original territory. Some have even bounced back and reared multiple chicks on their new stomping grounds. But most males that are evicted after age 15 disappear from the study area quickly and quietly, as if stoically bowing out to make way for the younger generation.
So it was thrilling to see Blue/Red, who at 24+ years of age is well into his dotage, put himself in harm’s way, challenge the 17-year-old Pickerel-North male for his territory…and actually win the contest. To be clear, this was a battle between one of the handful of really old males in our Wisconsin Study Area and a male, Green/Mint, that is not ancient but certainly well past his prime.
What now? According to Sarah, who heroically paddled up and down the main bay of 581-acre Pickerel Lake to get the skinny on all loons on the lake, the evicted Green/Mint is now living alone on the former Pickerel-South territory, where he lived from 2010 to 2013 and fledged three chicks. With luck, he will re-pair with a new female there and possibly even nest again this year.
The burning question on Pickerel Lake is this. What happens to the Pickerel-North nesting attempt, which is within a week of hatching? Blue/Red, the ancient male that has just won this territory in battle, might decide to join the female, Copper/Yellow, and incubate the eggs as if they were his own. (We have seen evicting males do this four times in the past.) It is more likely that he will make the evolutionarily-sound decision to ignore the nest until Copper/Yellow finally abandons it. Fortunately, there is still plenty of time to nest. So we hope that Blue/Red will do what he has done in 8 previous years on the lake during an 18-year breeding career: find a good nest site, incubate the eggs patiently for 28 days with his mate, and raise two big, fat, sassy chicks. If he does so, he will have completed a rare and improbable comeback by a very old male.
Each spring I feel my adrenaline level rise as we carry out the annual census of returning loons. This practice seems mundane, at first glance. During the census, we simply visit all loon territories and identify each territorial loon we find from its colored leg bands. But since I have gotten to know many of my study animals quite well, I wait with bated breath to learn whether Clune (the famously tame male on Linda Grenzer’s lake, whom I have known since he was a chick) comes back. I feel almost as strongly about Clune’s son, who settled 6 km away, on tiny Virgin Lake. I even have a soft spot for the comically skittish female on Silverbass Lake. She routinely appears down at one end of this long skinny lake, seems to wait for us to paddle in her direction from the other end, and then races by us underwater and reappears at the end of the lake we just vacated. She is so notoriously hard to approach that her very skittishness has become a useful identifying trait. In Minnesota, I was anxious to see whether the young male of unknown identity on Lower Whitefish — who nested rather recklessly on a water-logged artificial nesting platform exposed to the powerful west wind and waves — would return from the winter and try that move again or learn from his mistake and seek a more protected location. (I am happy to report that all four of these loons are back this year.)
Apart from the relief or dejection we feel when we spot our familiar study animals — or don’t — loons’ tendency to return provides critical scientific information. A tally of the proportion of all adult breeders that returned from the wintering grounds in the spring tells us about survival between late summer of the previous year and early spring of the current one. Of course, territorial eviction muddies the water. That is, a loon can either fail to return to its previous territory because it is dead or because a competitor has driven it off of its territory and forced it to move elsewhere. So we must be cautious in interpreting return rates. Still, they provide us with a crude metric of survival.
Let’s look at return rates throughout the study. What is clear from a quick inspection of the graph below is that loons in the Wisconsin Study Area have fluctuated in their tendency to return, coming back at a rate of over 90% in great years and just above 70% in dismal ones. (Minnesota study loons returning in 2022 also fell within this window, as the graph shows.)
Perhaps the most striking pattern is the lack of concordance between return rates of each sex. In other words, knowing that it is a bad year for male survival tells us nothing about female survival. True, there are some years in which male and female survival seem to go hand in hand — look at 2005-2009, for example. But male and female rates seem to run in opposite directions between 2010 and 2017. Overall, there is no statistical tendency for male survival to be correlated with female survival.
We can draw an important — though tentative — conclusion from the fact that male and female survival do not vary in concert. Major loon mortality events outside of the breeding season do not seem to drive annual loon survival strongly. If major die-offs during the non-breeding period (i.e. winter and migration) were a major cause of loon mortality, then male and female numbers should be correlated, because the sexes use similar migratory routes and winter quarters and should suffer in parallel each year.
The most interesting and potentially worrisome pattern we could spot in the annual return rate data would be a decline in survival of either males or females. As you can see from the color-coded dotted lines, female return rate has actually shown a slight rise over the past 29 years. On the other hand, male return rate has declined slightly, though not significantly, during this period. Still, since we already know that males are struggling to maintain optimal body mass in the Upper Midwest, it is disconcerting to see male survival decrease in a way that seems consistent with the mass loss.
Of course, while making the rounds of territorial pairs, we also notice if a territory is vacant or occupied by a lone adult after having supported a breeding pair the previous year. And therein lies a bit more troubling news. Ten of 118 Wisconsin territories that were occupied in 2021 are now vacant or inhabited by loners. We have also recorded two new territories in lakes not used for breeding last year, so the net loss in territories is only eight. Still, this was not the picture we wished to see in a population that has been on a downturn. (Though we are only learning about the Minnesota Study Population, it appears that only one territory among seventy or so that we have visited so far fell into disuse this year after having been occupied last year.)
Let’s put aside worrisome population patterns and turn to news of the moment. It is early June in the North. This is a time of great hope for loons. A few breeding pairs in our Minnesota and Wisconsin study areas — like the Lower Hay pair in the photo — were fortunate enough to dodge both black flies and raccoons and are on the brink of hatching young. Many more have rebounded from early setbacks and renested. If we are lucky, we still have the potential for a good crop of chicks in both regions. Lacking any more effectual means of bringing this about, I will keep my fingers crossed.
One of the pleasing sights of spring in the Northwoods is that of a territorial pair of loons, foraging side by side. No doubt the myth of lifetime fidelity of loons to their mates arises, at least in part, from the tight association of female and male loons at this time. Their apparent devotion to each other, their compulsion to remain together at all times, the touching plaintive wails that keep them in contact when they chance to become separated for a brief period all recall young human couples with limitless possibilities before them.
During the past three weeks in Minnesota and Wisconsin, I have seen many loon pairs foraging, resting, and preening together. It is truly heart-warming — to a degree. You see, once the territory resettlement period — the first three weeks after ice-out, roughly — has come to a close, loon pairs should be nesting, which means that humans watching out for “their loon pair” should see only one pair member or the other on the water.
Egg-laying marks the start of the nerve-wracking 28-day period of incubation where innumerable things could go wrong. A raccoon could wander by; an eagle could flush the incubating bird and feast on the eggs; a sudden downpour could turn a nest that seemed safely above water level into egg soup, cooling the eggs and killing the embryos. But one single cause of incubation failure has emerged as the single greatest threat to loon breeding success in Wisconsin and Minnesota in the past decade. The agent, a single species of black fly with a peculiar taste for loon blood, has recently surpassed even egg predation by raccoons and their ilk as a cause of nesting failure. When hundreds of black flies surround incubating loons and bite them mercilessly on the head and nape, the agony can become too awful to bear, causing the pair to abandon the nest. In recent years, black fly survival and persistence dictate how productive an entire loon population will be. It is that simple.
Yesterday, five of us — four members of the loon research team and a reporter for Minnesota Public Radio — ventured out onto the Whitefish Chain to mop up the few territorial pairs that we had not yet been able to visit this year. The trip was memorable for more than loons. An unexpectedly stiff west wind turned Middle Whitefish into a seething Lake Superior, forcing us to beach our motorboat prematurely at Boyd Lodge. (It took four Blizzards at DQ in Crosslake to help us move on after that hair-raising experience!)
Despite sketchy conditions, we visited nine new territorial pairs. We were thrilled when Kate spotted an incubating loon in a protected cove of Pig Lake. But that was the only territorial pair we scouted that was sitting on eggs. All others behaved as if the ice had just come off: they preened, rested, and foraged side by side. What would have been a cheerful sight in mid-May causes consternation now. Sixty to seventy percent of all pairs should be incubating eggs at this point in the season. Sadly, the featured image from Sibley-South depicts the situation in many of these lakes at present: two perfect golden-brown eggs — and loons nowhere nearby.
The nest in the featured photo has that forlorn, unloved look that many do at the beginning. It seems, at first glance, that the female just crept up on shore and dropped an egg there — as if she had to put it somewhere. Closer scrutiny reveals that the pair had gathered a substantial bed of pine needles from the surrounding area and formed a crude bowl shape around the lone egg. Still, it does not inspire confidence that a portion of rotted oak leaf is draped over the egg. Yet the male approached me as I quickly snapped a few photos, registered the nest’s GPS coordinates, and skedaddled to see if he would incubate. He did not.
I can understand the Thunder Lake pair’s inability to adjust to changing conditions. Only an hour before seeing them, I had stumbled out of my guest room (a wonderful, secluded home by a small lake where our friends permit us to lodge in May and June). My trip to Rhinelander on the previous day had not been the relaxing, sumptuous journey I had hoped for. After a last-minute cancellation of our flight, I buddied up with two other shell-shocked passengers near the gate — one a sales director for a pharmaceutical company from Minocqua, the other a Colombian fellow from Tomahawk who sells farm machinery for a Finnish company — and we rented a car for the 3 1/2 hour drive instead of waiting overnight to be rescheduled. (In truth, Steve rented the car, since his company would cover the cost.) By the time our rental rolled into Rhinelander, it was 2 a.m. Luckily, the engine turned over in the 2007 Toyota Corolla that we leave for nine months in our storage box (the “Loonmobile”). I was able to grab three hours of shut-eye before some passing Canada Geese awakened me. Two — okay, three — donuts and a cup of coffee later, I had seen my first loon pair on Thunder.
We have learned over the years that loon pairs take a day or more to “accept” that they have laid an egg and must incubate it. On these initial days, pairs sometimes wander far from their new nest, leaving the egg dreadfully exposed. I find this curious. The egg is, of course, in danger of being found and eaten from the moment it is laid. The embryo inside it cannot begin developing rapidly until it becomes optimally warmed by the parents. Every moment spent off the eggs seems time wasted and needless risk taken. I suppose, though, that I must defer to my study animals, who have a pretty good record of turning eggs into chicks.
The Thunder pair can be forgiven more easily than most for their reluctance to incubate. The male is new to the territory and unmarked. Probably a 5- or 6-year-old, this is likely the first egg that a mate of his has ever laid. One hopes that he and his well-seasoned mate — whom we banded as a chick on Currie Lake in 2003 — can restore Thunder Lake to productivity, after a six-year chickless slump. To do so, they will have to shake off this egg-denial and get serious about breeding!
I love the painting because it is not about loons. John Seerey-Lester’s artwork*, pictured above, is about rain. The painting recalls those moments when you were out on a lake — taking in the vast expanse of its surface; gazing at an eagle circling high above; or watching a loon pair drift by with their four-day-old chick — and a rogue cloud emptied upon you. Most of us who have ventured out onto lakes can recall such an experience. In the moment, there is panic: a hastily zipped jacket, a vain attempt to find some form of shelter to thwart the impending deluge. But there is wonder and beauty in the storm itself. As Seerey-Lester’s painting shows, raindrops transform a lake’s monotonous surface into an astonishing palette of dancing splashes. Accompanied by a soothing whisper, the spectacle of a rainstorm on a north-country lake is one of nature’s wonders.
Loons cope well with rain, of course. What harm is more water, after all, when you live in water? Like most birds, loons assiduously preen their feathers, coating them with oil from a gland at the base of their tail, so water beads up on their heads and backs, but ultimately rolls harmlessly off them — like water off a loon’s back. A downpour might necessitate a few shakes of the head, inspire a few extra wing flaps, and prevent foraging for a time, owing to reduced visibility. But loons greet rainstorms with little more than a shrug.
Considering the grace with which rain appears in loons’ lakes — and, of course, its fundamental importance in supporting all life — I was unpleasantly surprised to learn this week that rainfall has likely contributed to the reproductive decline of loons in northern Wisconsin. You see, rain does not merely stimulate plant growth, raise water levels, and rinse car windows. Rainfall also washes all sorts of matter into lakes. This includes visible organic matter such as sticks, leaves, and soil but also invisible nutrients and chemicals. Many substances that reach lakes via rainstorms reside naturally in soils or on the forest floor. Others, like fertilizers and sewage, have been added by humans to the environment. Human-added materials that contribute nitrogen and phosphorous to lakes can cause populations of phytoplankton to surge, which reduces water clarity.
And this brings us back to loons. Loons rely strongly upon their vision to catch fish and other prey underwater. As our recent investigations have shown, reduced water clarity hinders loon foraging. We now know that reduced water clarity leads to poorer body condition both in breeding males with chicks and in chicks themselves. The decline in chick body condition and accompanying rise in chick mortality are essential components of the breeding decline now underway in northern Wisconsin.
Why am I so determined to blame it on the rain? Because a few days ago I examined water clarity estimates from my collaborators — Kevin Rose and Max Glines of Rensselaer Polytechnic Institute — and found that water clarity in July, the best predictor of adult male and chick mass, is, in turn, strongly dependent the amount of rainfall in June and July. Just as April showers bring May flowers, June and July showers bring July algal blooms in Wisconsin lakes that make it more difficult for loons to find their prey.
Of course, rain itself is not the true villain. Rather it seems to be fertilizers, leaky septic tanks, and maybe even pet waste that human lake residents have added to the ecosystem that are contributing to the loss in lake clarity.
You might wonder if there is truly a sustained, irreversible downward trend in water clarity or whether water clarity fluctuates according to natural cycles and is merely on a downward trend at the moment. If we are simply on a temporary downward trend, then it is a decade-long trend, according to Max and Kevin’s measures of water clarity (see graph just below).
Moreover, as I reported recently (see graph below), loon males have been losing body mass for the past 30 years. So the data we currently have indicates that we are on a prolonged downward slide with respect to both water clarity and loon mass.
So what do we do? All hope is not lost, I think. But if our data and interpretation are correct, then we must immediately begin to monitor — and curb — chemical runoff from shorelines into lakes from sources such as fertilizers and septic systems. In the long-term, we need to understand that summer rainfall will only increase as the Earth continues to warm and cloud formation accelerates. In short, it is a bit harsh to blame the rain for loons’ current reproductive woes, but increasing rainfall in coming decades will probably push us more rapidly in the wrong direction.
*”Sudden Rain”, copyrighted by Sir John Seerey-Lester
The Upper Midwest remains — for the moment — in winter’s clutches. This fact is oddly comforting to me, stuck as I am in the pleasant but seasonless climate of southern California. In one sense, I dread the coming of spring in Wisconsin and Minnesota. Each year I find myself weeks behind schedule. While my study animals in the Upper Midwest spend April facing real problems like migrating safely, settling on their territories, contending with hopeful usurpers, and beginning their breeding effort, my Aprils are more mundane. I prepare study guides, conduct review sessions, and quiz my students about evolution and ecology in preparation for the final exam.
Despite the bland Mediterranean climate and muted seasonality of southern California, I am not entirely in the dark about the coming of spring. When I hear house finches, orange-crowned warblers, and the impossibly loud and bubbly song of the tiny house wren out my front door, I understand that loons are on the move. Last Wednesday’s birdwatching trip to the Newport Pier provided the most stark reminder yet. As I stood next to my spotting scope, scanning the ocean for pelagic rarities like jaegers and shearwaters, a familiar dark silhouette appeared several hundred yards offshore.
His crisp breeding plumage gave him away. But just to drive home the point, this adult-plumaged Common Loon uttered several awkward, truncated yodels — to the befuddlement of many Western Grebes rafting nearby. No doubt this male will improve upon his sputtering vocal performance by the time he reaches his breeding territory in British Columbia or Alaska. For the time being, his voice reminded me that I have much work to do in the coming weeks.
My tardiness reaching the Upper Midwest each year guarantees that I spend the first two weeks of every field season in a tizzy. I race frantically to a boat landing, drop my canoe into a lake, and make a beeline for the breeding pair. After ID’ing them from their leg bands, I throw the canoe back up on my roof rack, drive to the next lake, and repeat the process. It is not the way one might choose to take in the wonders of early spring!
But enough of my problems. Loons are the ones most impacted by late spring thaws. As Linda Grenzer’s above photo from northern Wisconsin shows, lakes are only beginning to open up in the Northwoods. This means that, for now, breeding loons must be content feeding and resting on rivers and dodging ice floes, like the bird below from Linda’s video:
Perhaps today’s warmth will melt enough ice for breeding pairs to begin to land and stake out their territories for the year. They must rue each day that passes before settlement. A recent statistical analysis showed that each four days that pass before loons can take possession of their territories pushes back nesting one day. On the one hand, this is good news, because it means that breeders bounce back from late ice-outs by being more thoroughly recovered from migration and ready to nest when they finally do settle. On the other hand, like me, they must be pretty anxious to get their summer’s toil under way.
What if we had an early warning system in loons that could alert us to population decline, like the proverbial canary in a coalmine?
Male loons might serve as such an early warning system. That is, careful monitoring of the health of male loons might provide a good indication of the health of the loon population as a whole. How is this possible? Because the more we study the breeding ecology of loons, the more stark differences we find between the sexes. And — more to the point — male loons have some chinks in their armor that females do not.
Most fundamentally, males are 25% larger than females. Greater size places greater energetic demands on males. Males are living “closer to the edge” than females and might often fail to acquire enough food during the season to maintain good body condition. Thus, a decrease in the quality or quantity of food — which could set in motion a population decline — should strike males first and hardest. Indeed, as the graph below shows, the average mass of male loons has declined in northern Wisconsin over the past 30 years in a way that suggests they are having more time finding food now than they used to. (Note that females have not declined in mass during the same period.) The obvious conclusion: something in Wisconsin lakes has changed in the past three decades that has impaired males’ ability to feed themselves.
Long before I discovered that male masses were in decline, I had begun to worry about male loons. You see, male loons live shorter lives than females. This means that there are simply fewer adult males around. In fact, the majority of non-territorial adults (“floaters”) in the loon population are females. Since males are in short supply, the loss of an adult male breeder on a lake or territory sometimes leads to that territory becoming vacant. In fact, in 23 of 24 well-documented instances where an adult breeder’s death was associated with a territory vacancy, the dead breeder was a male. Vacant territories are, of course, a harbinger of overall population decline.
Sadly, recreational fishing does not help the situation. Possibly because males’ greater size makes them a bit more desperate to feed themselves, male loons are twice as likely as females to be hooked by anglers or become entangled in fishing line. This pattern is well-documented in New England loons, but the same scenario plays out in the Upper Midwest. Specifically, of 47 known fishing entanglements among our study animals, 33 involved males, and only 14 involved females. Angling mortality, then, exacerbates what is already a female-skewed sex ratio owing to early male senescence.
It is difficult to predict the future, but I think you can see why I am concerned. Male loons appear to be in trouble. We cannot say for certain whether mass loss by male loons will cease or continue. Furthermore, we have no evidence to date that the 4% net loss in mass by males since 1991 has negatively affected their survival. So it is too early to panic about these patterns. But it is also hard not to feel like a miner glancing anxiously at his lethargic canary.
I do not think of myself as a cheerful bearer of bad news. Yet I repeatedly bring it. Each time I meet a new lake resident and secure permission to cross their land and observe their loons, I brace myself for the inevitable question: “Is it true that loons mate for life?”. I gently share the truth with them. “No, they don’t; but they really have a strong allegiance to their territories!” The idea that loons love their homes, not their breeding partners, provides scant solace to most folks.
Having spent a quarter century disappointing loon lovers in Wisconsin and Minnesota, I have been searching for scientific news to share about breeding pairs that sheds a warm, wholesome light on loon mating behavior. My quest is not inspired by guilt alone. As a scientist, it makes sense to me that adults should become acquainted with their mates and benefit from doing so. How could complex, long-lived animals like loons jointly defend a territory, build a nest, divvy up incubation duties, and raise young together — as seen in Linda’s photo above — without benefitting in some way from their association?
At last, my current study of predictors of breeding success has revealed one way in which loon pairs do benefit from a long-term association. The graph below shows two patterns. First, there is a gradual improvement in hatching success over time as a pair remains together on a territory. These numbers jump around a lot owing to limited samples of pairs that have been together ten or more years.
Second and more clear cut is the improvement in hatching success between a pair’s first year together (Year 0) and their second (Year 1). As you can see, loon pairs improve their chances of hatching eggs by almost 10% between these first two years.
Now we can only speculate about the cause of this dramatic improvement in breeding ability among young pairs. Perhaps pair members synchronize their breeding behavior better in their second year together than in their first. Maybe pair members rotate incubation duties more crisply in year two, thus seldom leaving the eggs uncovered and unguarded.
Of course, the challenge that romantic couples face of living and working harmoniously, following an awkward adjustment period, has a familiar ring to it. That challenge is depicted in “Period of Adjustment“, a 1962 comedy-drama film based on a play by Tennessee Williams. It is heart-warming to see that loons — like actors Jane Fonda, Jim Hutton, Lois Nettleton, and Tony Franciosa — bounce back strongly after a rough first year.