Loon headquarters has been abuzz this week. “Clara has a chick”, Annie announced yesterday. “Bobcat hatched….and Baker’s chick is getting big!”, exclaimed Allison. Martha remarked, “Two Sisters-West has a chick, and the male was really aggressive in defending it from intruders”. Lyn’s report was the most impressive. “All three pairs on Pickerel have chicks,” she declared in her characteristically understated way. Although the featured photo is, as usual, one of Linda Grenzer’s from her lake, Lyn saw a similar picture on the Pickerel-West territory.

In short, loon chicks have been bursting from their shells at a rapid rate in the past week. What’s more, many pairs without chicks are sitting on eggs that have survived for two weeks or more and thus are likely to hatch soon. So the pall that hung in the air just two weeks ago has lifted. As a person who looks obsessively for the negative in any circumstance, I am somewhat at a loss.

The new field observers’ responses to the recent flurry of hatching — and my own — has exposed a telling contrast. All of my teammates are observing loon breeding behavior for the first time. Since everything is new to them, they view the hatching explosion as the norm. Having studied the loons of Oneida County for 27 prior years, though, I see the recent burst of hatches as unusual. And having documented declining breeding success in our population over the past two decades, I was expecting more of the same in 2020. My shoulders, already drooping from carrying too many canoes since the end of May, had been drooping even more than usual in anticipation of another dismal breeding year. Although my teammates have been getting almost blasé about the popping out of many chicks across the study area, the mass emergence has got me standing a little straighter.

Let’s take a quick look, again, at how 2020 compares with 2014. In both years, over 70% of all first nests were abandoned because of black flies, so this should be an apples to apples comparison. As of July 4th, 2014, 14 pairs had chicks — 18 chicks in all — and 40 pairs were still sitting on eggs. After many recent hatches this year, there are now 22 pairs rearing 31 chicks; 25 nests are still active. If we project the likely rate of chick production from the remaining nests this year, 2020 will produce about the same number of chicks (52) that 2014 did (51). Now 2014 was a weak year, so producing the same number of chicks as 2014 is no great shakes. But 2020 looks to have about 20% more chicks reaching five weeks of age than last year. In a swoon of optimism, I am going to view the considerable improvement in loon breeding success from last to this year as the start of a promising trend.


By now, readers of the blog are aware that 2020 has been a devastating year for black flies in northern Wisconsin. The data are not all in yet, but a rough comparison between 2014, the worst black fly year on record, and this year shows that only five breeding pairs had hatched chicks in by 27 June 2014 — the same number of pairs that have hatched chicks so far this year. So this crude comparison suggests that 2020 is about on par with our worst year ever in terms of breeding activity being hindered and delayed by Simulium annulus.

Of course, 2020 is far from over. Most pairs, having failed once from black fly-related abandonment, have renested or may yet do so. But now I need to refer back to an earlier post, where I pointed out the record-setting rate of territorial turnovers this season. If many birds are newcomers to their territory, it makes sense that they are not fully familiar with the territory and how best to use it for breeding. In fact, since males choose the nest location, the responsibility for picking a raccoon-proof nesting spot — the major challenge that a nesting loon pair faces — falls to the male on each territory. The fact that 23 of 98 marked males in the study area are nesting for the first time on a new territory (twice the normal rate of turnover) means that — from a population perspective — we should expect a higher rate of predation in 2020 than in years past and fewer chicks.

Crunching the numbers again (crudely) in an attempt to predict chick production, we had 54 pairs incubating eggs as of 27 June 2014, compared to 49 pairs still incubating as of today. Although many 2020 nests are looking good because they have been underway for at least two weeks and/or are in proven successful locations, others are new and at untested nest sites selected by inexperienced males. So we should expect a poorer rate of hatch this year, overall, than the 76% rate that occurred among active nests on this date in 2014. If the hatch rate is 65% in 2020, then we will end up with 37 hatched broods, and an estimated 35 fledglings. In short, it is still looking like a weak year for chick production, but not quite the worst year ever. Times are such that we must take solace in that fact!

The good news is that loons learn. Few will ever be as savvy as Linda’s breeding pair, which kept incubating through the black fly period and already has three-week-old chicks (see Linda’s photo). But if return rates come back to normal after a crazy 2020, few territories in 2021 will be occupied by newcomers. Having lost a nest or two or three to raccoons in 2020, when they were learning their way around the territory, the greenhorn males of 2020 will improve their nesting decisions next year and hatch more chicks. So, as snake-bit as I am feeling owing to the double whammy of oppressive black flies and a bunch of new males blundering about in search of nest sites, I look forward to a better 2021.

There was no good reason for the Crystal female to defend her nest. I had confirmed the colored leg bands on her mate, and he was no longer the male with whom she had mated and laid eggs on the platform. Instead, he was the neighboring male from Halfmoon, who had left there under mysterious circumstances. Lake residents had reported a “ruckus” early this morning, and that ruckus had turned the 14-year-old male who had been her steady partner for 5+ years (lake residents had nicknamed him “Walter” — not after me but after the largemouth bass in “On Golden Pond”, which features loons) from an expectant father into a displaced, childless nonbreeder. Walter’s eviction meant that any ongoing reproductive attempt was over, as evicting males and females have no interest in incubating eggs or feeding young that are not their own. Yet the Crystal female — lake residents named her “Katherine” because of Katherine Hepburn in “On Golden Pond” — felt an inescapable attraction to the nest. As I approached to inspect the four defunct eggs on the platform, Katherine showed classic nest defense, swimming twice under my canoe. The evicting male from Halfmoon preened indifferently 100 meters away, as if willing to indulge his new mate’s obsession with her past nest but hoping she would get over it soon.

I witnessed a related behavior pattern on Swanson Lake just yesterday. There a mammalian predator (probably a raccoon, according to a camera study conducted some years ago by the Wisconsin DNR) had taken the two eggs that the Swanson lake female had laid in a second nest on the west end of the lake to replace those abandoned during the black fly period (see photo). When I arrived at first light, the female was alone, wailing intermittently, as loons do when their partner is not present. Forty minutes after I arrived, the male flew in, and he swam purposefully over to the newly-failed nest and climbed onto it. For three minutes he sat contentedly on the nest, as if all was good in the world. Then, he stood up on his legs and reached his bill downwards to turn the eggs, as loons habitually do. He seemed to put two and two together when he found no eggs to turn; afterwards, he sat only a few moments more before climbing down off of the empty nest and joining his mate in the water.

Despite 28 years of observation, I had never witnessed loon behavior that reflected slowness or inability to adjust to a new, stark reality — or perhaps I had simply not seen such behavior twice in so short a time, which made it impossible to ignore. As humans, of course, we have all behaved in such a way. That is, we have forgotten for a moment that some abrupt, fundamental change has occurred in our lives and mistakenly acted as we had before the change. Over a longer timescale, I find myself behaving so now. On each visit I make to a study lake in mid-June I expect to see young loon chicks or a pair late in the four-week incubation stage and on the brink of a hatch. But like the Crystal female and Swanson male, I find myself slow to adapt to a new reality — almost universal abandonment of first nests, many pairs without chicks or nests, and a great big dent in the breeding success of the population.

I think I have made it clear already that loons’ allegiance is to their territory, not their mate. That is, when offered a choice between abandoning a territory and following their mate after their mate has lost a territorial battle, loons always choose to remain on the territory and form a new pair bond with the winner of the battle. This behavior seems heartless, but it makes perfect sense, because loss of a breeding territory is a crushing blow that makes it impossible to breed. Mates, in contrast, are easy to find.

While loons routinely say farewell to breeding partners, 2020 has seen more of our breeding pair members change mates than ever before. The graph below shows the proportion of adult loons on a breeding territory in one year that were not on that territory a year later. As the graph indicates, some years have very stable pairs (like 2008 and 2019), while other years see lots of turnover among pair members. In 2020, one quarter of all breeding pairs experienced a loss of at least one pair member, and a sixth of these — 6 pairs of the 145 we follow — saw both members of the pair

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replaced by a new adult.

Of course, eviction is not the only factor that causes a loon that is on a territory in May of one year to be gone from that territory a year later. In fact, there are two main causes: 1) eviction and 2) death. Both of these biological processes contribute greatly — and about equally — to the failure of breeders to return.

Looking closely at the graph, you can see that annual return rate jumps around a good deal. Last year, for example, was a year when a very high proportion of all adult breeders came back to their territories of the previous year. (We can only speculate here, but these jumps are probably caused by occasional “die-offs” during migration or winter.) If you were looking at the return rate as a proxy for adult mortality, you might breathe a sigh of relief at this point; the graph does not seem to show an increasing trend in failure to return to territory that might mean increasing adult mortality over the years.

One final point. While it is true that failure to return to the territory does not obviously shift upwards or downwards over the past quarter century, careful readers of the blog might remember that the eviction rate has fallen dramatically in our population in the past two decades, because there are now far fewer nonbreeders seeking territories than there were 20 years ago. If evictions have declined over the years, then deaths must have begun to account for a growing proportion of all cases of non-return shown in the graph. Thus, it might actually be the case that adult breeders die at a higher rate now than they did a few decades ago, but that the graph does not show us the data cleanly enough to tell. In short, whether adult survival is trending downwards or not will not be clear until we do a more detailed quantitative analysis.

Oblivious to the territorial chaos swirling around them in 2020 — I mean loon-related, not human-related chaos — loons have been going about their business. Whether members of a growing or declining population, and whether their mate is new or old, most of our study animals have picked up the pieces after a devastating black fly season and renested. We still hope that these late nests will allow the population to generate enough chicks so that 2020 will not be our worst year ever for chick production. There is some comfort in the fact that chicks are produced one brood at a time. Perhaps the stalwart seven-year-old Pickerel-South male in the video below and his mate will contribute a chick or two to the total.




Most scientific research comprises snapshots of a biological system. That is, we usually study the behavior or ecology of an animal for a year or two in a forest, on a coral reef, or in a desert. On the basis of such a short term study, we pontificate about what constitutes a good territory and what constitutes a bad territory for the animal we are studying. Then, feeling that we have described the system accurately, we fold our tents and move on to the next study and habitat.

But time changes things. My team and I got a demonstration of the impact that time can have yesterday when we visited two lakes located towards the northern part of our study area. Life has always been hard for loons on Dorothy and Hodstradt lakes. They are both rather clear lakes and full of fish. But they have been disasters reproductively, because they lack the islands, marsh, and bog that loons seek out to keep their eggs safe from raccoons.

The gradual but now-dramatic rising of lake levels in the Northwoods has produced a spectacular reversal of fortune for loons on Dorothy and Hodstradt. What had been an unremarkable spit of land on Dorothy has become an island several meters offshore, reachable only by water (see photo below). What once was a long curving peninsula on Hodstradt has been transformed into an island, accessible only after a lengthy swim. In short, two lakes for which chick production was a freak occurrence have now become prime real estate, because they offer offshore nest sites inaccessible to all but the most ambitious raccoon.

Of course, the rising waters have not been kind to all lakes. Heiress Lake had a handy island that saw regular chick hatches in the late nineties and early 2000s. But no more. That raccoon-proof site is now four feet underwater, and Heiress no longer supports a breeding pair.

The take-home message is clear: territory quality is not fixed and unchanging. Instead, changing climatic patterns transform the landscape in surprising ways. A goldfinch’s lifespan is short enough that habitat transformations probably matter little. But loons live long enough to see poor nesting habitat become good nesting habitat and vice-versa; this species should be able to detect and respond adaptively to fluctuations in territory quality.

In fact, loons do exhibit some ability to respond to changing landscapes. We see this ability in the willingness of breeding pairs to explore vacant lakes near their original one and sometimes nest at sites different from those they have used to hatch chicks. And, of course, young nonbreeders use the presence of chicks on a territory as a measure of current reproductive quality so that they can target lakes for eviction attempts that will reward them with many offspring. On the other hand, many adults settle on a productive territory during the prime of their lives only to see its quality decline along with their own body condition. Lacking the fitness to defeat an opponent in a battle for a new territory, such birds are stuck breeding on a failing territory. These old codgers could tell ecologists a few things about territory quality and the passage of time. 

What has been most striking about the dozens of loon territories we have visited in the past week has been how similar they seem to be to loon territories in early May. At that time of year, pairs have mostly recovered from the energetic stress of migration and have shifted their focus to breeding. With ice gone from the lake surface and perhaps a territorial challenger or two repelled, breeding pairs can search for a nest site, build a nest, lay eggs, and — if lucky enough to have a safe nest site or to avoid attracting egg predators to a risky one — jointly incubate them for four weeks until hatching.

Though the ice is long gone and challengers long since defeated, most loon pairs (over 90%, by our preliminary estimate) now face the same long slog of incubation they encountered a month ago. Having had their first nesting effort obliterated by black flies, these pairs now must start over from scratch. Thus, the video below depicts a common sight: a pair that has chosen a new nest site, started to lay eggs, and must work together to hatch chicks. These two birds, a 7 year-old male from Hasbrook Lake (background) and a 10 year-old female from Day Lake in Vilas County, seemed to contemplate this task with a degree of circumspection.

As nasty and harmful as black flies are, they are not as bad as egg predators. Flies are only really abundant for three weeks or so, whereas egg predators are always present. Loons behave as if they understand the time-limited threat that black flies pose. How? They commonly reuse nest sites that contain eggs from an attempt ruined by black flies, whereas they almost never reuse nest sites in the wake of egg predation by a raccoon or another predator. (Our recent paper describes this logical response to black fly abandonments.) Sometimes a males’ love of a nest site is so strong that he chooses it even though it still contains two eggs from the previous nesting attempt. In such cases, a loon nest contains two viable eggs from the renesting attempt and two duds from the abandoned effort weeks earlier (see the photo at the top, from Little Bearskin Lake this year). We often wonder how the sitting birds manage to cover and warm the eggs such that the good ones hatch.

In short, there is a new round of nests in the Northwoods of Wisconsin. During the past several days, as we have found pair after pair laying a second round of eggs and forging ahead in the hopes of raising chicks, it has raised my spirits. We will never look back at 2020 as a banner year for chick production, but the loons are not giving up.








My new team and I are racing around the study area, still catching up to our banded breeding population. At each lake, we record the bands of the female and male, look quickly for any active or failed nests — only in obvious places — and race to the next lake to repeat the process: (“Ok…the female has a yellow band on right and is red over green on left? Good enough….let’s go!”.) The work is frantic and exhausting, and we are only halfway through. We are all so busy covering lakes that there is little time to reflect on what we have seen. I have trouble remembering what lakes we have even visited at the end of each day, so anxious am I to eat a meal and hit the hay for the next 5am wakeup.

Yet some patterns have emerged from our lake visits that remain lodged in my brain. It has been a dreadful first round of nests for most breeding pairs. Typical pairs in the study area abandoned their first nesting attempt three to four weeks ago because of the clouds of flies that descended upon them and have only just begun to renest or think about doing so. Based on what we have seen, it appears that 70 to 80% of all pairs could not stand to incubate the first clutch of eggs they laid in early to mid-May, making 2020 even slightly more devastating a black fly year than 2014, the previous worst year on record. Our study population has seen a steady slide in chick production over the past quarter century; 2020 will only strengthen that demoralizing pattern.

So you can imagine how it warmed my heart to hear about Linda’s loon pair (“Clune” and “Honey”), who managed to buck the trend and stick it out through all four weeks of incubation. At a time when the population as a whole is reeling, the assiduous parenting on display in Linda’s video below took my mind off of the population’s struggles for a moment and reminded me that good things can still happen.

There was something distinctly wrong with the Buck male. He had never been tame. Indeed, he was one of those loons that made you work to see his leg bands on each hourlong visit. So, a few days ago, as I hefted my canoe down the steep paved road to the public beach that we use as our access to the lake, I knew I would face a challenge to get enough good looks at his legs to produce a convincing ID. But the male that foraged all around the lake with the usual female was well beyond a challenging ID. He was somewhere between highly vexing and impossible to identify. While the female gave me occasional good looks at her leg bands as I tracked her loosely during her foraging routine and seemed indifferent to my presence, her mate clearly avoided me and gave me no close looks at all. This was a reversal from two decades of past observations on the lake during which the female, not the male, had always been the tougher ID on Buck.

I paused at intervals to consider a change in tactics. But there is not much flexibility and creativity involved in IDing loons from colored leg bands. One simply approaches a breeding pair closely enough to see any bands on the loons’ legs but not so close as to upset the birds — and hopes for the best. This undertaking takes great patience and some luck, especially at times when black flies are out in numbers, as they are now, because loons shorten their above-surface time and seldom preen when hounded by flies. In an attempt to rally my spirits through distraction, I stopped tracking the pair after about an hour and circled the small island in the southeastern corner of the lake. Denying what was clearly a move borne of frustration, I told myself that taking my eye off of the foraging pair for a moment would allow me to search for a possible abandoned nest on the island. After all, I was weeks behind schedule in this first visit to Buck, and an experienced pair like the Buck pair should have long since started incubation.

No nest was evident on the island, but my effort to avoid for a moment the exasperating task of IDing the male ended up solving the puzzle of the male’s identity entirely. Draped over a fallen red pine on the south side of the island, I found the carcass of the Buck male that we had banded way back in 1999.


It was sad to see silver over blue, red-stripe over red gone forever after watching him vigorously defend his territory for 21 consecutive years and never lose it — even for a day — in all that time. But it is the ultimate fate of every territory holder to meet a fitter, stronger, younger territorial opponent and bow to them. That is the essence of terminal investment in old male loons. The death of this oldest male in our study area (26+ years) now leaves the placid 24+ year-old Bear Lake male as the most senior representative of his sex. I am hoping the day on which the Bear male meets a determined, superior opponent in a territorial battle is still several years away.

I have had a whirlwind last 24 hours. It began last night just after 10pm (Pacific), when I realized that I did not have the key to the storage unit in Rhinelander where we leave our car over the winter. No, I thought, that key is in lockdown in my office at Chapman. An hour and a half later, I had convinced campus security to let me into the science building, retrieved the key, and returned home to Irvine. At that point, I had about 4 hours of sleep to look forward to before heading to LAX and thence to Rhinelander. As I tossed and turned, trying to empty my mind for sleep, I burned more potential hours of rest. In the end, I got about two and a half hours.

But the worm turned during my trip. I polished off a troublesome article review assignment on the plane, dozed a bit afterwards, and arrived in Rhinelander before 2pm. Following an awkward and damp 2-and-a-half mile trek along Highway 8 to the storage box, I tasted sweet victory as the Toyota Corolla I had moth-balled in August instantly purred to life. The disaster of a dead car battery averted, I was suddenly ahead of schedule, so I stopped off at my first lake of the year — Townline, just west of Rhinelander.

Though observing loons on Townline Lake means putting up with the constant whizzing by of cars on County K, Townline has always been one of my favorite lakes. Most of my affection for the lake took root during the residency of a long-term breeder —a very approachable male who defended the territory for at least 24 years, 1994 to 2017. But somehow my warm feelings for S/R,O/G turned into love for the lake, and now I look forward to every visit there.

I was instantly rewarded for my short walk down to the lake’s edge today, when a foraging loon surfaced less than 10 meters from me. The bird made a series of short dives, spending — it seemed — as little time as possible on the lake’s surface. Even so, at that range I had no problem determining that it was unbanded. This surprised me, because the Townline pair, as of August 2019, consisted of a twenty-something female (banded on the lake in 2002, as an adult) and her young mate — the 7-year-old male from Anvil Lake in Vilas County that had replaced my favorite male loon when he failed to return from the winter in 2018. The presence of an unbanded loon that acted very much at home on Townline showed that at least one of these two pair members had not returned from winter or had been evicted from the territory.

I should point out that quick dives and endless foraging bouts, such as I saw today, are the rule during 2- to 3-week-long black fly outbreaks. That is, loons dispense with resting and preening during peak fly season; instead, they spend as much time as possible under the water to avoid the flies. I often wonder what they are doing during these bouts. Since the bouts consume far more hours than loons need to satisfy their energetic needs, they must spend some of this dive time simply swimming underwater, while ignoring any and all terrified fish they pass. So I guess it is not relaxing to be a bluegill during black fly season either!

The black flies that so pester loons have no taste for human blood, but even we human observers dislike them. Abundant flies complicate our efforts to ID loons from leg bands, which is easiest during preening and resting. Indeed, it took me almost 40 minutes to even locate the mate of the unbanded loon I first saw foraging near the shore this afternoon. This second bird too was dodging the relentless dipterans, diving constantly and spending only a few seconds on the surface between bouts. Luckily, this individual was tame and turned out to be the now-8-year-old male hatched on Anvil. When he began cozying up to the unbanded bird I had seen earlier, it became clear that the old female is gone from Townline.

I looked quickly for a nest, circling the little island that the Townline pair almost always uses. I found nothing and suspect that to the female turnover and the black fly abundance together have pushed back nesting at least four weeks on Townline this year. Judging from the cloud of hundreds of flies that hounded (but did not bite) me as I searched the island, several more days or a week will pass before this new couple can consider laying eggs. As thick as the flies were today, they were worse ten days ago, as this video shared by Linda shows.

So I guess we can take heart that we are moving in the right direction!