It is usually no fun to be wrong, but maybe this is an exception. In my blog post yesterday, I surmised that the sudden appearance in flight of the male from Little Bearskin meant that he and his mate had failed in their second nesting attempt. This seemed a safe presumption; I knew from many years of experience that males do not often leave females alone with small chicks. Yet I was mistaken. A lake resident (thanks, Nancy!) corrected me by pointing out that at least one chick had hatched on Little Bearskin this year, and Martha found two chicks on the lake during her early-morning visit today.

As we have explained in an earlier publication, there are three reasons why males tend not to leave their breeding lakes when their chicks are in their first two weeks of life. First, females cannot yodel, and therefore they are unable to discourage intruders from landing in the lake and approaching chicks by means of this aggressive vocal signal. Second, by virtue of their greater size, males are better equipped to intimidate and drive away intruders that do approach chicks. Third, having two parents guarding chicks when they are small permits breeding pairs to cover two bases — they can send one parent out to engage intruders and leave the other to protect the chicks, in case an intruder should come close.

In fact, years ago on Langley Lake we witnessed the danger that parents face if one of them ventures off territory when their chicks are small. In this case, two intruders landed when the male was off the lake, forcing the female to choose between: 1) staying beside its week-old chick, and 2) leaving its chick to interact with the intruders. She chose the latter course, but that strategy backfired when the intruders dove and split up. At this most inopportune moment, the chick happened to give an alarm call that one of the intruders heard. The intruder quickly found the calling chick and, with no parent nearby to intervene, killed the chick in a matter of seconds.

With that horrid incident seared into my brain (and a good deal of quantitative data on chick attendance to back it up), I was fairly confident that the appearance of a breeding male on a lake not his own meant that he had failed in his breeding attempt at home. In fact, I am still scratching my head over the Little Bearskin male’s decision to leave his mate, his two helpless chicks, and his home lake with its abundant food supply, in order to visit a neighboring lake that held nothing but failed and displaced conspecifics. I guess I will have to continue my research for a few more years to make sense of that odd bit of behavior.

At first glance, Bearskin Lake does not strike one as unique. It is rather round in shape, and, at 163 hectares, is much larger than our average study lake. But we cover many lakes rounder than Bearskin and several — including Two Sisters, Clear, and Minocqua — that are much larger. Likewise, Bearskin falls into the middle of the pack in terms of average and maximum depth. True, the lake bottom fairly seethes with rusty crayfish, but that nasty invasive species is also abundant in Oneida, Crescent, and Lower Kaubashine. What sets Bearskin Lake apart is not its shape, size, or biology, but the sort of loons that visit and live on it. 

I was reminded of the unusual status of Bearskin among loon lakes two days ago when I made our first visit of the year there. I was not greeted by the adorable sight of a loon parent capturing tiny minnows and gently leaning downwards to present them gingerly to its 3-day-old chick, as one might see on Silver, Hodstradt, or Bear. Nor did I encounter a male and female that had tried and failed to hatch chicks and were looking forward to next year, when they could renew their breeding efforts. Instead, I observed a nervous loon that immediately raised its head high upon surfacing to scan for a territorial pair that might take exception to its visit. (Linda’s picture above shows the alert posture characteristic of anxious loons.) This bird, “green over silver, white-blue over orange”, was a former breeding female on Seventeen Lake in Hazelhurst that we had seen only once since 2012. We have no idea what this loon has been doing since we last saw it, but its presence on Bearskin and without a mate suggests that it has been marking time and has not reacquired a breeding position. 

Three hundred meters southwest of the displaced Seventeen female was another forager that was far more relaxed on the lake. Like the first loon, though, she was alone. To my surprise, this bird — “silver only, white over yellow” — was the former breeding female from West Horsehead Lake. One of the most prolific breeders ever in our study area, this female has reared 19 chicks since her initial capture in 1996 and, at 29+ years, is our second oldest bird. Her residence on Bearskin solved the puzzle of her disappearance from West Horsehead, which Al Schwoegler (a West Horsehead resident) and I had been mourning all spring long. “Silver only, white over yellow” had finally met a young opponent this spring willing to fight harder than her for the territory. She had thus accepted defeat, left West Horsehead, and taken refuge on the lake where evicted adults have always gone — Bearskin Lake. 

I continued my paddle south from the boat landing, feeling that my effort to visit Bearskin had already been repaid. A lone loon foraging just west off the huge island diverted me briefly; I was deflated to find this bird unbanded. As I veered southeast, following the arc of the island, I scanned eastwards and spotted an apparent pair synch diving (i.e. diving and surfacing together repeatedly). These two loons seemed to know me and were no trouble to identify. “Red-stripe over copper, silver over orange” was a vaguely familiar band combination, but I knew his mate, “red-stripe over silver, red over white”, very well indeed. Initially banded on 2001, this female has raised 10 young on Little Bearskin Lake and on Currie, where she had settled in 2015 after her eviction from Little Bearskin. The male with her, I now realized, was her new mate from Currie. 

As pleased as I was to encounter the tame pair from Currie, their presence on Bearskin was very bad news. They had hatched two chicks on about June 25th, and had lost one of those by the time Lyn observed them on July 2nd. Since parents attend and protect young chicks assiduously and since we have never observed both pair members to leave chicks unattended until they reach four weeks, the Currie pair’s presence on Bearskin signaled that they had lost the second chick not long after the first and were done breeding for the year. “What are you guys doing here?” I said with a mixture of sadness and disapproval. Bearskin is not a lake where loons go to celebrate their achievements. 

My visit to Bearskin ended with an oddity. As I was lamenting the Currie pair’s disappointment, they wheeled around and began tooting to signal the arrival of a flying intruder. The intruder obliged me by arcing towards the Currie pair and skittering to a landing only 50 meters west. The morning sunlight allowed me to read most of its “red-stripe over blue, white over silver” band combination before it hit the water. This male, I knew, was the current breeder from Little Bearskin. His arrival here was more bad news, because males rarely leave their territories during a breeding attempt. “Red-stripe over blue” circled tensely with the pair and then became aggressive, sending both Currie birds fleeing in different directions as he stalked them underwater. Maybe he was stung by his own breeding disappointment. A later check of the database showed that he and his mate had been sitting for at least 32 days on four eggs on Little Bearskin without a hatch. We can reasonably surmise that the pair abandoned a first clutch of two eggs in early or mid May, reused that nest by laying two more eggs with the abandoned ones still present, and now have failed in a second attempt — either because of black flies again or perhaps infertility of the eggs. So this has been a year of frustration on Little Bearskin, as well. 

I found two more unmarked loons along the west shore of Bearskin on my visit and no hint of a resident pair or breeding activity. In fact, most pairings on Bearskin are fleeting, and nests are scarce. The last successful breeding on Bearskin occurred in 1997, when a pair fledged two healthy, crayfish-loving chicks, repeating their feat from the year before. Since then there has been a smattering of breeding attempts, but none — to our knowledge — has produced a hatch. Moreover, no pair has ever formed a breeding partnership that lasted more than three years on Bearskin. Loons seem to sense something about the lake that humans do not. Bearskin is not a lake where you go to raise a family; it is a lake where you go when you have nowhere else to go. 

In many ways, I was dreading the call. After three weeks of frantic training and two more of new team members beginning to find their way around the study area and become fully comfortable with our techniques, we were finally in a groove. But it was an early morning groove — the kind where you get up at four, hit your first lake at five, and finish eight hours later, dragging yourself home bleary-eyed, overheated, and definitely not stoked about entering your day’s observations in the database.

When Linda called to ask for my help in capturing a loon that was thoroughly entangled in monofilament line, I felt strongly that I should go. The loon was certain to die without our help. Even if it continued to elude the constant harassment and attacks of the territorial pair, the bird would suffer damage to its wing muscles over time. Furthermore, it was bound to have serious injuries that were not evident from the grainy photo we had seen. But Linda’s plan was to try to net the bird at night. I had not seen a sunset in six weeks!

“Okay, I’ll be there in 45 minutes”, I told her. “Will I fall asleep at the wheel?”, I wondered. I cranked up Coldplay’s Viva La Vida and sang along too loudly as I drove north to Mercer Lake.

Feeling only slightly gauzy, I reached the landing and set out with Linda and Kevin on the lake’s northwest end. Luckily they had done the heavy lifting by finding the bird and tracking it as darkness fell. The entangled individual sat almost motionless where the lake meets a dense marsh.

Had I been a bit more on the ball, we would have caught the bird in a flash, as it did not start to dive until our boat was within a meter or two. But I missed….twice. “Not used to the boat….net is awfully heavy and shallow….the electric motor is in my way”, I grumbled, half to myself. Linda and Kevin were patient, though, and the bird fortunately returned to the fringe of the marsh, following my misses. Given a third chance, I was finally able to net the impacted loon, and we proceeded to shore.

An inspection on shore revealed that the monofilament was wound tightly around its tail and wing and had damaged those feathers badly. A later x-ray showed a hook buried deeply in the loon’s chest, which we had known nothing about.

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Despite its injuries, the prognosis seems pretty good for this bird. First of all, it is still physically strong, as we learned during capture. It is now being cared for at Raptor Education Group and will be held another day or so until the hook can be removed and its feathers recover their normal shape. I have banded it so that we can track it after release and monitor its recovery. 

Coldplay got me home safely at about midnight. My body was not sure what tricks I was playing on it, but I eventually fell asleep and slept in — until 6:30. Ughh, I thought. I have lost my early-morning groove. But I smiled to think that I had helped give a doomed loon a new lease on life.

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.