When you live on a lake with loons, you grow attached to them. You feel a sense of ownership and responsibility. You share in their failures and successes. If you are a real loon aficionado, your view of the entire summer can depend upon how your loons fare. When they are sitting on eggs, you are nervous and protective. When they hatch a chick or two, you are excited and hopeful. When the chicks mature and begin to fly, you look back at a job well done. And, of course, if they should lose a nest or — worse still — a chick, you are bitterly disappointed.

Those of us who visit 100+ study lakes live in a different world. Like lake-dwellers, we mourn lost nests and chicks — and we too are devastated by adult loons that are injured or killed during the summer, especially those we have come to know well over a decade or more. But we do not have all of our hopes riding on a single lake. Our disappointment at the failure or loss of loons on one lake is tempered by the success of a different breeding pair on the next lake we visit. Even during a truly dreadful year for breeding — like 2019 or 2011 — there are always a few breeding pairs that beat the odds to produce young on lakes where we thought they never would.  

Despite being buffered somewhat from mood swings by our tendency to flit about from lake to lake, those of us who cover the study area do form attachments to certain loons. In fact, I was almost as alarmed as Linda when she told me last week that the first loon to return to her still mostly iced-up lake was not “Clune” — her beloved, 22-year-old banded male — but instead the banded male from neighboring Deer Lake. Things went from bad to worse the following day when “Honey”, the resident female, returned and quickly paired up with the interloper (as seen in Linda’s photo). 

I have known Clune since he was a chick. He and his sibling and parents were almost comically tame back on July 22, 1998, when I visited them on Manson Lake. As always, I tried to keep my distance from the family on that day, while collecting behavioral data. Once, though, the foraging parents happened to surface on one side of my canoe, while the chicks surfaced on the other and only a few meters away. While I paddled as quickly as I could to escape that unfortunate situation, neither parents nor chicks called out nor showed the slightest degree of alarm. As an adult, Clune has been every bit as tolerant of humans as he was when young. So it is easy to understand how he has long been the favorite loon of the Loon Project team.

Clune made us sweat for two more days before returning, on April 10th, to reclaim his territory and drive off the male from Deer Lake. Now, it seems, things have returned to normal.

What of the Deer Lake male, you ask? His effort to “trade up” by seizing Clune’s highly productive territory has been thwarted. After five consecutive years of breeding frustration on Deer — and at least nine consecutive nesting failures — he is in an unenviable position. Will he be desperate enough in late 2020, if his luck on Deer has not turned by then, to have another go at Clune’s territory?

As I gaze vacantly out my back window, I wonder, as all of you must, when life will return to normal.

Linda Grenzer reports that our southern study lakes are on the brink of opening. Eager to occupy their territories as soon as possible, fight off pretenders seeking to supplant them, and set about the business of nesting, our breeding birds are bottlenecking on the Wisconsin River and various dammed flowages along the river’s tortuous path, she says. Their vigil will end in the next week or so. Offered even a sliver of open water in their territory, breeding pairs — sometimes the male alone, for a few days — will take possession.

We, on the other hand, are trapped at home. Three of us, Brian, Annie, and myself, are in southern California, which has never seemed so far from Wisconsin. Lyn, another new team member (along with Annie) is homebound in Ontario, Canada. As each day of lockdown passes, and as forecasters assure us the worst is still weeks away, we wait, our uneasiness mounting. Will we be allowed to travel to the study area come May? June?

To pass the time and convince myself that the project has not stalled, I analyze loon data. At present, I am resuming an analysis that a Chapman undergrad from Minnesota began in 2012. Katie and I looked at how the behavior of young nonbreeders changes over time. Nonbreeders, we know, do not begin to evict pair members and settle on territories until they are five years old. Further, we have learned that young adults gain substantial body mass in their first 5 years. Could it be that 2-, 3-, and 4-year old nonbreeders, which are too young to compete for territories, behave differently from older nonbreeders when they intrude into breeding territories?

It seems logical that loons should take some time to develop physically and behaviorally; after all, similar maturation occurs in humans. But what is the larger importance of loon maturation to territorial behavior? That is, how should the fact that young loons are not initially a threat to the ownership of territorial pair members affect behavioral interactions between young loons and pair members?

Maturation should shape nonbreeder behavior strongly. Not being competitive for territories, 2-, 3-, and 4-year old nonbreeders must feed themselves well, learn about the lakes in the small region where they live, and get to know the local territorial loons of their sex — which they must ultimately defeat in battle in order to claim a territory. Since they are in an information-gathering phase, youngsters should keep their heads down during territorial intrusions, signal to territory holders that they pose no threat, and hope to escape attacks from the pair that way.

What about pair members? A territorial male in the process of a breeding attempt with his mate should virtually ignore the intrusions of nonbreeding females and also young male nonbreeders, because neither threatens his ownership of the territory. (It is important to note that pair members fight and defend their breeding positions alone; males never help females stave off eviction, nor do females participate in male battles.) Likewise a territorial female should let her mate worry about nonbreeding males that visit her territory and instead focus her attention on 5- through 8-year-old females, which are strong enough to evict her. The picture becomes more complicated when a pair hatches chicks. In the presence of chicks, which are helpless and easily killed by any intruder, both male and female pair members should quickly confront and drive off intruders of any stripe.

Finally, both pair members and nonbreeders should calibrate their territorial behavior to the quality of the territory. To be specific, both groups should exhibit more intense behavioral interactions and more aggression on territories with a record of producing chicks, because those territories are worth a lot to both groups.

Thus, we have a set of predictions about how nonbreeders and breeders should behave with respect to sex and age of intruders, presence of chicks, and territory quality. I am in the midst of testing these predictions using two decades’ worth of field observations. At this stage, I have analyzed only nonbreeder behaviors. Below is the crude table I just produced that summarizes my findings to date.

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I will spare you the challenge of deciphering my shorthand and tell you what I have found so far. First, we predicted that young nonbreeders would show little aggression towards territorial pair members. That is borne out by the data. The second column and second and third rows in the table show that age is positively correlated with aggressive behavior of intruders and aggressive vocalizations by male intruders (i.e. the territorial yodel). In short, young nonbreeders — 2, 3, and 4-year olds — show less aggression (lunges, chases, and other attacks) than older nonbreeders. Furthermore, the strong tendency for young nonbreeders to initiate short dives (IDs) and join dives (JDs) when circling with territorial pair members (2nd column; 7th row) suggests that these diving behaviors signal youth and lack of threat to pair members, which probably protects youngsters from being attacked by the resident pair.

We can already say a bit about my prediction that the presence of chicks should crank up the heat on territorial aggression. Intruders that visit pairs with either nests or chicks (4th column) show consistently more aggressive behavior and tense social interactions with pair members than do intruders to a territory without nest or chicks. We presume this pattern results from the heightened aggressiveness of pairs themselves, which bleeds over into their interactions with nonbreeders. I expect my ongoing analysis of pair members’ responses to intruders to reveal a similar pattern.

Finally, look at the third column, which shows very consistent results in territories that produced chicks the previous year. The “Strong positive”s here show that nonbreeders exhibit more splash dives, bill dips, circle dances, initiates dives, and joins dives when interacting with territorial pairs that reared chicks the previous year. I am still puzzling over these results (and the lack of an increase in aggression). At present, this pattern suggests that: 1) nonbreeders confront territorial pairs more often when the territory has been shown to be a chick-producing territory, and/or 2) pair members approach and interact with intruders more often when they are on a high-quality territory. In any event, the quality of a territory where pair members and intruders interact strongly affects the nature of their interactions.

We have far more data on pair members themselves than on nonbreeding intruders, so the results of that ongoing analysis are likely to be even more robust than those shown in the table. Needless to say, these findings are a vital salve for my current frustrations with the lockdown. If it extends through May, I will require quite scintillating discoveries indeed!

We all focus most of our attention on breeding pairs and their chicks. Why not? Breeders are the loons we get to know — day after day, year after year — as they struggle to hold their territories, choose nest sites safe from raccoons, incubate their eggs for 4 long weeks, and then protect helpless offspring from all manner of environmental threats. We admire the toil and turmoil they face each year and are downcast when they lose their breeding position, nest, or chick. And we grieve when they die. I am probably unusual in this regard, but I am also inspired by observing the challenges that breeding pairs routinely confront and overcome.

In our obsession with breeding individuals, though, we forget about the many loons living on the margins. These are “floaters” — mostly 2 to 7-year olds who spend the entire summer without a fixed home. Floaters are the individuals that forage alone on small lakes or skulk along the outskirts of defended territories, occasionally socializing with or accosting territory holders. Unlike territorial loons, they drift about.

Although their lives might seem simpler and less stressful than those of territorial loons, floaters — even young ones — face challenges of their own. Our work has shown that 2- to 4-year olds are much lighter than 5- to 7-year olds, are more submissive to territory holders during territorial intrusions, and almost never initiate battles for territorial ownership. Yet these youngsters do intrude into breeding territories. We presume, therefore, that even as they mature, young floaters collect information about owners. Our data show that young floaters intrude strategically into territories within a focused area (usually about 10km in diameter, see figure below from our recent paper) so as to meet and interact with owners of their own sex that they might

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evict down the road.

Having reached optimal adult condition, floaters of 5+ years of age begin to size up owners with greater urgency, choosing to battle those that appear weak or are noticeably weaker than they were on a previous visit. Male floaters probably also listen to the quality of a male owner’s yodel, because certain acoustic elements of the yodel convey information about the yodeller’s body size and condition. As we have seen repeatedly, intrusions by floaters of 5+ years of age are not welcomed by territory holders — and can be dangerous for both parties.

Considering that 2 to 4 year-olds are still reaching optimal body condition and 5 to 7 year olds are putting themselves at risk by actively seeking territories, it is surprising that floaters of both age groups survive at a rate just as high (about 90% annually) as established pair members (see figure below). Apparently the risks of probing and competing for a territory among young loons are roughly equivalent to those that come with


territory defense and chick-rearing among older individuals. (Note from the figure that only older age-classes, and only males, show lower survival.)

We are used to the invisibility of floaters. That is, we see and study them as intruders into defended territories, but we seldom consider where they come from or how they live. So I always get a jolt when a dead floater turns up, like the tame 5 year-old male in Linda’s photo from the Lake Nokomis area. These rare unpleasant finds are a good reminder that gaining a territory is a long and difficult slog.


As many of you know, I am a worry-wart. Normally I get so stressed-out about my kids, my teaching, my research, my health — and many other matters that are going well — that I hardly have time to obsess about loons in the study area. But Linda Grenzer’s bleak photo of conditions on her lake today gave me a jolt. Could the late ice-out that we are facing in 2018 delay the season so much that it damages the breeding prospects of our loon population?

One might think that the later the ice comes off of the lakes, the later the loons nest, and the less time parents have to fatten up their chicks and prepare them for their first southward migration. Thus, a late ice-out might well lead to reduced breeding success for the population. Although there are many “if”s in this string of logic (and a preliminary analysis did not bear out the pattern), I felt concern  gnaw at me.

So I did what scientists often do to stave off despair: I looked at the data. First, I looked to see if loons nest later when the ice goes out later, which almost has to

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be true. It is true, but there is a lot of noise in the data. That is, loons are constrained to nest somewhat later in years when the ice goes out later, but the picture is not simple. The reason for the noise becomes clear when you look at the lag time between when loons settle on their territories and when they hatch their

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young. There is a very strong pattern here. When the ice goes out early (left side of graph), loons dawdle and wait weeks before nesting. But when the ice goes out late, as it will this year, pairs get down to business quickly, nesting within a week or so of territory return. So loon pairs are somehow able to catch up in years of late ice-out so that their breeding schedule does not differ greatly from other years. (Notice also that the orange line in the top graph is flatter than the blue line.)

What accounts for this pleasing pattern? We can make a pretty good guess based on findings in other migrant birds. Spring migration is an energetically costly process. In an early year, the ice is gone so quickly that loons settle on their lakes as soon as they return from the wintering grounds. In such cases, their fat levels are very low from migration when they first occupy their territories, and it takes a good deal of foraging before they return to good condition. In a late year, loons cannot settle on their territories right away but must wait on nearby rivers that have open water. There, they are able to forage and restore their bodies to good condition. As a result, loons hit their territories in prime body condition and fully recovered from the migratory flight in years of late ice-out. Thus, they can get down to breeding quickly.

Although I was heartened by the data I saw above, I had a look at the numbers that most directly addressed my concern about late ice-out and population breeding success. There is a no statistical tendency for the population to produce more loon chicks in years of early ice-out, despite the many years of data we have to look for such a pattern. Indeed, some of our best years for loon breeding (2013, for example) have occurred when the ice goes out late. So those many of you shivering in northern Wisconsin and other frigid regions can relax about one thing; the loons are no worse off in years when spring comes late than when it arrives early.

In Linda‘s last round of photos from Bear Lake, you can see the numbers clearly. At the narrow end of the metal band, a fuzzy, curling “6” followed by a clear, swooping “2”. Those two digits — either one of them, actually — identify the Mystery Female of Bear Lake as the chick we banded on July 18, 2005 on North Nokomis Lake. This photo culminates several days during which Linda patiently stalked the female with her camera lens until the bird finally pulled her metal band out of water in an orientation that permitted Linda to photograph the two digits we needed to see from the nine-digit number code.

The story of the Mystery Female concerns more than just solid detective work and crisp photography; it relates to the crucial decisions that a loon must make while attempting to settle on the best possible breeding lake and rear as many offspring as possible. The Mystery Female, Orange over Mint-burgundy — OMb for short — faced such a decision. OMb returned to the study area as a 4-year-old in 2009 and began hunting for a place to breed. She settled on Upper Kaubashine (at the end of the long arrow below) in 2012 and lost clutches of eggs to predators there in both 2012 and 2013. OMb then

N Nokomis to Bear w UK also

faced a stark choice — remain on a poor territory attempting to breed or abandon Upper K and try to move to a more promising locale.

Shifting from a poor territory to a good one might seem like an easy call to make, but female loons must cope with a shortage of potential mates owing to early senescence and frequent fatal fighting in males. Every year we see many loner females, some of which live on good breeding lakes, waiting for a mate. So it is an open question whether a female should desert a mate and breeding territory — even a poor one — to try and move to a better location. You see, in trying to secure a new territory, a female must temporarily leave her current one, risking its loss to another female on the prowl.

OMb decided to abandon Upper Kaubashine in 2013, establishing herself as the new breeding female on Bear Lake (shorter red arrow), whose female had died. This appeared to be a wise move; Bear had yielded chicks in 9 of the previous 13 seasons, while Upper K had not fledged a chick in 35 years.

Chance plays a big role breeding success of loons, as in all animals. In a curious twist of fortune, Upper Kaubashine stunned lake residents by hatching two chicks from a terribly exposed nest site. Since Bear Lake only produced a single chick this year, OMb’s choice of Bear over Upper K looks like a poor one, as of now. But chick production in these two lakes will probably return to form. If so, and if OMb can hold onto her new territory, her decision to leave a perennial failure for a proven chick-producer will have been a good one.

I am still shaken by the recent spate of fishing entanglements. Perhaps my sadness and vexation over these troubling events prevented me from looking clearly ahead. I thought: “Well, the hooked female at East Horsehead will die slowly from the ingested lure, and that will be miserable, but another female will settle on the lake and replace her.” I gained some measure of relief from anticipating the orderly progression of events that would unfold on the lake. As expected, the afflicted female, “Iceberg”, has declined, although she is still not yet weak enough to catch. Her mate, “YellowBlue”, has not stuck to the script, however. Far from waiting passively for another female to settle with him, YellowBlue is proactively seeking a new territory. And that is the problem.

It should have been obvious to me when Nelson reported, last Wednesday, that he saw YellowBlue intrude onto nearby Alva Lake. Females leave their breeding lakes occasionally to intrude onto the neighboring territory; males do so rarely in the height of the breeding season. So YellowBlue’s intrusion was a sign that something was afoot. But I dismissed his visit as an anomaly — the distracted antics of a male whose mate was unwilling to initiate a nest. As it turned out, YellowBlue was probing neighboring lakes for a weak spot, a territory whose owner he could defeat in battle and whose territory he could seize. Based on the aggression and chasing that occurred when YellowBlue visited Alva, the Alva male was not on board with this plan.

But YellowBlue’s search continued. In the next few days, he found a vulnerable male on a different neighboring territory: West Horsehead. We were not present to observe the entire sequence of events, but Al Schwoegler reported yesterday that CopperGreen, the West Horsehead male, was skulking about and hunkering down at the northern end of the lake, far from the nest that he had built with his mate (a 28+ year-old female, “WhiteYellow”, who is among our oldest birds). A quick look at the middle of the lake explained CopperGreen’s diffidence. YellowBlue was foraging and resting there, acting like he owned the place. (Melanie confirmed that this state of affairs continued today.) Now loon behavior in many ways is unsubtle, and territorial behavior is a good example. When a loon is in the middle of a lake, acting like he owns it, he owns it! So YellowBlue had clearly battled CopperGreen, defeated him, and forced him to lay low along the lake’s periphery to escape further attacks. We have seen this sequence of events scores of times. If events proceed normally, WhiteYellow will ultimately cease her efforts to incubate the eggs alone, and the nest will be abandoned. Perhaps WhiteYellow and YellowBlue will renest again this year, but that is doubtful. (CopperGreen, if he is healthy enough, will fly to a nearby undefended lake, like Bearskin, where he can lick his wounds.)

What is troubling about this latest turn of events is the central role played by humans. That is, an angler — a careless or perhaps just an unlucky one — hooked Iceberg on East Horsehead and fled the scene. Iceberg immediately ceased breeding behavior and began a struggle to survive. This turnabout forced her mate, YellowBlue, to go with Plan B, leaving his lake to find another nearby with a healthy female on it. In leaving his own territory and evicting a male on West Horsehead that was sitting on eggs, YellowBlue likely doomed both East and West Horsehead to breeding failure in 2017. So a single fishing casualty affecting a single adult loon has precipitated the loss of breeding opportunities on two of our most productive lakes.

While we are concerned for the impacted loons, this latest eviction has some scientific value. YellowBlue is quite a phenomenon — the youngest male ever observed to evict an established male from his territory. Hatched on Little Bearskin Lake, YellowBlue is only four years old. Perhaps it was his good fortune that CopperGreen was himself only six years old (a product of Oneida Lake). So the YellowBlue-CopperGreen contest featured the youngest combatants ever. I hope that the novelty of this latest encounter takes away a bit of the sting from the event that set it in motion.

All is not lost among loons this year. In fact, one advantage I have, as someone who tracks breeding behavior on 120 lakes, is the capacity to shift my attention away from those where things have gone south to lakes that where all loons are healthy and productive. So let me end with a beautiful photo of Linda’s from Muskellunge Lake that will remind us that there are lakes where loons are free of hooks, where they defend their territories successfully, and where the next generation thrives.

LMG5508 Clune Yodeling Tight with Family2-2


I do not know why I am still surprised by it. Again and again we see territorial females vanish, only to reappear as intruders in their former territory or another in the same neighborhood. The theme has been consistent throughout my quarter-century-long research project on loons. In fact, it is about a 50-50 proposition that a female who disappears from her territory will be resighted nearby in the next year or two.

I suppose the reason why I am always wrong-footed by female reappearances is that I am calibrated to human social conditions. Unlike loons, humans are highly social and benefit from a vast network of family ties and friendships. Humans have evolved to cultivate those bonds — leaning upon family and friends when necessary; providing support, in turn, when called upon to do so. Humans, therefore, rarely vanish without a trace from an area where they have lived for many years. We typically maintain most or all of our social connections even when we shift from one location to another.

Loons, in contrast, are quite alone. To be sure, an adult male or female has the companionship of its mate for several months each year. But this companionship is ephemeral and conditional. When a loon’s mate is evicted by an intruder, the loon faces a stark choice: remain with its mate of many years but move to a new territory, or stay on its territory and accept the evicting intruder as its new mate. Adult loons always spurn their long-term partner and make the coolly pragmatic choice.

Knowing loons as I now do, I should not have been surprised when Linda sent me this crisp photo of an intruder departing from Muskellunge Lake. Although the bird is missing a colored leg band from its right leg, it was not difficult to determine that this intruder is the former female from Manson Lake, who has not been seen since fall 2015. Since loons almost never desert a territory, we can surmise that “Silver over Red, Mint Burgundy over White” (as we affectionately call her) was evicted by the 9-year-old female from Rock Lake in Vilas County who was first seen on Manson in April 2016 and still owns that territory. The eviction forced “Silver over Red” into an itinerant existence. Though you might think that a veteran of 12 years of breeding and mother of 11 fledged chicks had earned better treatment, this 20+ year old now spends her time drifting from one inhabited lake to another as an intruder, searching for a new mate and territory so that she can resume breeding.

It is tempting to pity Silver over Red. These past two years have been difficult and dangerous for her, no doubt. But rather than viewing her and others like her as individuals whose best years are behind them, I always feel an intense admiration for displaced female loons. While many of us humans respond to setbacks with a shrug of acceptance, female loons never stop hunting for a new opportunity.


It’s like deja vu all over again at Muskellunge Lake this week. Thanks to Linda Grenzer’s vigilance, we have learned that the productive and photogenic pair on Muskellunge came back together this week — just as they did about this time in 2014! As Linda’s photo shows, “Clune” and “Honey” (Linda’s names for the banded pair) were a bit wary of each other at first. This shyness should not be surprising, as they have both lost their breeding plumage and donned winter attire. According to Linda, though, they rather quickly recognized each other and paddled off contentedly together. Apparently after 6 years of being together, and rearing of 10 chicks to fledging, familiarity with your partner involves more than just feathers!

We have very poor information on the behavior of territorial loons in the fall, so we can only speculate about what it means that an established pair seems to come together routinely just before fall migration. As a behavioral ecologist, I am inclined to interpret such meetings as more calculating than romantic. I cannot resist the temptation to view such a meeting as a final patrol of this precious breeding lake by its owners to ensure that no intruders have tried to put down roots in hopes of claiming Muskellunge in 2017. To any such pretenders, the presence of a tight pair late in the fall would signal that the territory was not available without a costly battle. But that is just speculation.

I must apologize for taking so long for this post; I have been busy exploring loon survival patterns. Indeed, I have been able to sharpen our view of senescence considerably. Some of you will remember that I announced several months ago that males senesce, while females do not. While I was excited about the apparent finding, it seemed to defy logic and begged for elaboration. With the return rate data from 2016 in hand, I was able to reanalyze survival patterns of both males and females banded as adults on territory. As is becoming all too common, I must eat crow. It is still clear that males senesce — those between 5


and 19 years of age survive at a rate of 94% annually, while those 20 years and older survive at an estimated rate of only 71% (see graph, above). That is a steep drop-off in survival rate, indicating clear senescence. But the newer, more robust dataset has shown that females are not immune to the march of time. Indeed, 5 to 19 year old females survive at about 94%, like males; 20+ year old females fall off to 79% survival (see above graph). It is a tad deflating to realize that the world was more complicated than I had reported before, but also a relief to know that — and don’t take this wrong — females are not immortal!

One more tidbit relating to senescence. I have been able recently to complete a survival analysis of loons that were banded as chicks in the study area or nearby. (We call these birds “ABJs”, or “adults banded as juveniles”.) The most striking outcome of the ABJ survival analysis is, again, a difference between females and males. In this case, male survival plummets from 94% at ages 4 to 14 to 78% at ages 15 to 18 among both territory holders and floaters (adults without a


territory; see graph above). In contrast, females show steady survival of about 92%, regardless of age or territorial status (see above graph). Males, in addition, suddenly begin to lose their territories to eviction at the rate of 38% when they turn 15 years old, while females only suffer eviction at a rate of 12% from 4 to 18 years of age. So here we have evidence that males not only die at a higher rate once they turn 15, but that they also become vulnerable to being booted off of their territory.

If you have paid attention closely through the litany of data I have dumped on you, you have probably noticed one final pattern: the ABJ analysis showed senescence occurring in a younger age class than did the analysis of territory holders! That is, male ABJs senesce at age 15, while male and female territory holders show no senescence until age 20. This is a brand new finding that I am still puzzling over, but there is an obvious explanation. Territory holders are likely to comprise a fitter class of adult loons that have shown their ability to fight for and defend territories and also rear chicks. In contrast, ABJs are only chicks that have survived to adulthood and returned to the study area. They are not “battle-tested” by having claimed a territory and bred there. Much later senescence among the evolutionarily fittest set of loons in the study area should not surprise us.

I am not ready to stake my reputation on this latest finding, but if it holds up, it dovetails nicely with one of the long-standing debates among ecologists concerning territorial breeders and floaters. We have long wondered whether territory holders should be regarded as floaters who got lucky and found a territory, or whether the two groups are, in fact, distinct classes in terms of fitness. The steep drop off in survival of male floaters in loons, compared to male territory holders, would strongly support the latter interpretation.