Resilient Females

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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.

So….it begins!

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LMG2693 Loon Between the Ice

I always dread ice-out. While I am excited to know that I am scant weeks away from seeing the loons, ice-out now tends to occur during the high-stress period of the Chapman spring semester — and I am seldom ready for the event. As Linda’s photo from the Wisconsin River shows, loons are coming back, accumulating on the river, waiting for their breeding lake to open up enough to permit landing there. Meanwhile, my Animal Behavior students are sweating their behavioral experiments and write-ups.

Let’s focus on the positive of early ice-out for data collection. Rain and warming temperatures mean that ice-out is only days away. Soon we will begin to log the identities of returning veterans anxious to attempt another year of breeding. Since the lakes will be habitable two or more weeks before the historic mean date of ice-out, while many returning birds are still en route from the wintering grounds, we have an opportunity. In theory, adult loons that are in good physical condition generally should be those that can complete the breeding molt early and also migrate early. So the loons that show up first on breeding lakes should be those in good condition. Recent findings have shown us that this group comprises males and females about 8 to 15 years old — the prime of life for a loon. Thus, we predict that the early arrivals are in this age-class. The laggards should be breeders that are either very young — 5 to 7 years old — or very old — 20 years and older. We might expect the territories of such individuals to remain vacant for a week or more after the ice has come off of them.

If age does turnout to be a good predictor of date of territory occupation, then late return from migration could be another source of trouble for an old established breeder. That is, an old territorial bird whose body condition has begun to decline might not only need to worry about being evicted by a young, fit nonbreeder in the midst of breeding; danger might also come from the tardy return of the old bird to its territory in the spring, which could open the door for a youngster to seize the territory, pair with the old bird’s mate, and hold off the former owner when it returns.

I have painted a dire picture. We will have to use the increasingly early ice-outs like this year’s to measure date of return accurately and see if early ice-outs truly destabilize territory ownership. At the moment, I will tantalize you by reporting that breeding success across the population is higher when ice-out comes late. It is speculative at this point, but this pattern might indicate that early ice-outs lead to ousting of old, experienced breeders from their territories, which in turn suppresses chick production of the entire population. If so, I have one more reason to rue early ice-outs!

 

Senescence Paper Accepted!

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Our paper that describes basic features of senescence has been accepted for publication Journal of Avian Biology. With the lightning-fast turnarounds and early views that the public is now granted to scientific articles, you can search for the paper and read an advance copy…months before copy-editing and proofing of the final version is done. Let me know if you find any typos!Screen Shot 2017-03-10 at 12.47.06 PM

The paper describes findings that I have been blogging about for some months now. First, both sexes of loons senesce (begin to die at a high rate) once they reach their mid-20s. Second, at first blush it seems that the sexes do not differ substantially in the senescence pattern. Third, this paper looks only at territory holders, which are the creme de la creme of adult loons, because they have not only survived to adulthood, but also claimed a territory and produced chicks there. Thus, this group of birds analyzed does not include the many adults who tried but failed to settle on a territory or settled briefly but did not reproduce. Fourth, old males (but not females) suffer a decline in territory resettlement after being evicted from a territory. Finally, we present in the paper preliminary evidence that suggests male might increase or at least maintain high breeding success at advanced age, while it seems that females fall into reproductive decline. So there is a glimmer of possible terminal investment by males (increased investment by animals near death) at which this paper hints. If you have followed my blog, you know that we have data from a separate analysis that deals more directly with the possibility of terminal investment by males.

That is all I have for now. I have just finished hiring the four field staff members for this year. They are a strong bunch and include one of our seasoned hands from 2016. Since we are on the verge of ice-out already, I have gotten the crew hired none too soon. By the time most of us arrive in May, nesting will be well underway. No matter. We are accustomed to scrambling to keep up with the loons.

See you out on the lakes!

 

A Clearer Picture of Terminal Investment by Males

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Science is a cumulative pursuit. That is, the thirst for knowledge is never fully quenched. Rather, we answer one question, only to reveal another puzzle or two more. And thus begins another search for answers. That is certainly how my 24-year-old loon project has gone. But sometimes we reach a point where a vexing question is finally laid to rest, and it feels as though we have made real progress. I am at such a point now.

Let me back up. If you have been following this blog, you know that senescence in old loons is a phenomenon we have recently discovered. Senescence, loss of body condition and decline in survival rate in aging individuals within a species, is all too familiar to me and other humans. During the past twenty years, many studies have reported senescence in birds, mammals, fish, and reptiles. So what? Well, we expect that animals that lose condition as they grow old will change their behavior in response. In other words, scientists have long predicted that senescing individuals should start to behave so as to leave more to their offspring and care less for themselves. To put it another way, old individuals should be willing to take a hit to their survival if it allows them to pour more resources into their young and help their young survive. This makes sense, of course, because old individuals reach a point where they stand little chance of surviving longer, so they would do well to give whatever they can to their offspring, which DO have a bright future. Animals that behave this way should leave more and healthier offspring, and thus this behavior should spread in populations. This very logical idea is termed “terminal investment”. Again we can all probably think of human parallels.

Terminal investment, which I have mentioned before, has become a central theme of the loon project, ever since we published a paper 9 years ago on fatal fighting of males. Terminal investment became interesting to us because it was the most plausible explanation for such lethal contests. Our reasoning was as follows. If males are willing to die to defend their territories, then they must reach an age at which they have little to lose. And if males have little to lose, this must mean that senescence hits males (but not females, which seldom battle to the death) very hard to the point where old males have little future to look forward to. In this case, it might make sense for them to fight like crazy to hold a territory for another year or two, rather than give it up easily and leave themselves nowhere to breed during their last year or two of life. So we have two clear predictions here: 1) males, but not females, must start to die off at a certain age, and 2) males beyond this age must still fight like hell for their territories. It is this clash of body condition and behavior among old males that might cause fatal fighting.

At the time we started to consider the terminal investment hypothesis as a means to explain reckless battling by males, we had almost no solid information on the ages of males in our population. With patience and tireless field work by dozens of us, we have now turned things around. Analysis of loons of varying age has shown us that many males hit the wall at age 15. First, and most important, they start to die at a high rate. You can see from the figure below that males (blue bars) are suffering higher mortality than females (red bars), whether they are on territory (Terr) or without one (floaters: “Float”).

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But males also lose mass at age 15, indicating loss in body condition, as shown here:

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Finally (and predictably), males get evicted from their territories at a high rate at age 15:

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Wow, males are really getting slammed after they pass the age of 15 years!

So all of these data tell us that the first prediction of the terminal investment hypothesis, abrupt senescence at a certain age in males but not females, is clearly met in loons. That age, surprisingly, is only fifteen. Females clearly remain strong, healthy, and vigorous well past age fifteen.

As hard as the first prediction of terminal investment was to test, the second prediction is even harder. You see, fights are common in loons if you take the perspective of a loon’s lifetime, but they are quite uncommon if viewed from the standpoint of human observers in canoes. In other words, most individual loons have engaged in several major battles during their long lives, but territorial battles are not common during day to day observations and often occur so quickly that we are not present to witness them.

Patience pays, however. Since we can draw upon 24 years’ worth of field observations, we now have a trove of observations that we can search for any evidence of aggression and territorial behavior. I made this search, looking for two kinds of evidence: 1) territorial yodels, which serve to communicate a male’s aggressive tendencies and willingness to battle, and 2) out and out aggression, in the form of battling, lunging, chasing and underwater attacks launched by territorial loons on intruders to their territories. I was simply asking “Do old male loons (above age 15) tend to maintain a high level of yodeling and aggressiveness towards intruders?”.  The answer is a resounding “Yes”:

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As you can see from the figure above, old males actually increase their tendency to yodel (yodels per intruder), compared to young males. Similarly, old males step up their aggression (see below) and contrast in this way with females, who show no increase:

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By the way, all of these patterns I have shown are “statistically significant” via tests that I have performed.

You cannot be as excited as I am about this set of results. No one is. But, as I mentioned, this is one of those rare cases where we have finally managed to answer a burning question to our satisfaction. Even better, the question is one that had been the foundation of my research funding from the National Science Foundation. So I can now report to them that I have found the holy grail! What makes this clear finding even more significant is that terminal investment is quite rare in vertebrates. Of the hundreds of species studied thus far, the only other one to show such a clear pattern of terminal investment is the California Gull. Appropriate, don’t you think?

(Photo by Woody Hagge.)

The Reproductive Persistence of Males

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Most of us think of adult females as the main care-givers and protectors of the offspring. I am reminded of this constantly during my work. Several times a year, when I chat with a lake resident about their loons, I hear them say “She was on the nest today” or “The mom was feeding them down at the south end” or “She hollered like crazy when the eagle flew near the chicks”. It is natural for humans to infer that the female takes the lead in breeding activities; after all, we are mammals. In almost all mammals, females protect the young within their bodies for many weeks or months before they are born and continue to care for the young by themselves after they are born. Lengthy gestation makes male parental assistance superfluous, so mating systems have evolved in which males occupy themselves in other ways. Most mammals are either polygynous (one male mated with multiple females) or promiscuous (rapid mating and the lack of a pair bond). Females, in such cases, are left to provide most or all of the parental care, because males are either engaged in seeking out new mates or are not around at all.

Birds are different. Laying of eggs “frees” females, in the sense that they are not physically connected to the eggs and are no better equipped to care for eggs or young than are males. In birds, therefore, monogamy and biparental care are the rule. Most male birds  mate with a single female and provide substantial assistance to her in rearing the young. Male loons, as I have noted in the past, incubate the eggs equally with females and actually provide somewhat more parental care for chicks. Thus, more often than not, when folks tell me that the female hollered at a menacing eagle, or the female was feeding the chick lots of minnows this morning, they have mistaken the male for the female. (This puts me in the awkward position of either correcting the mistake, at the risk of embarrassing my friend, or grinning good-naturedly and leaving the error unchallenged.)

I got one more reminder of male loons’ central role in reproduction during a statistical analysis this past week. I asked whether males or females show age-related changes in fledgling production as they mature from young territory holders to middle-aged to senescent adults. (Note that one bar is missing for each sex in the figure below: too few females settle by age 5 and too few males survive to age 24 to produce reliable estimates of reproduction for those age-classes.) Both sexes show an increase in fledgling production after their first few years on territory, a pattern seen in many animals. Females showsenescence-paper-figure-3

“reproductive senescence”, another widespread pattern, in that fledgling production declines near the end of life. What is surprising here is that males do not show a decline in fledgling production as they reach old age.

What is odd about the male pattern? We have growing evidence that male loons decline at a younger age and more severely than females do. Recent analyses have shown that males lose body weight as they age, and that males suffer a high rate of mortality, especially as they reach their late teens. And, of course, males engage in dangerous battles. So the capacity of old males to produce lots of chicks into their 20s runs counter to what we would expect based on male survival and body condition. How do they do it? We are still puzzling over the pattern, but the most likely explanation is that old males invest heavily in chick production — perhaps through extra feedings of chicks or an extended period of care — to crank out a few more chicks before the wheels come off completely. Hence, old male loons appear to make a “terminal investment” in breeding success. Of course, nothing is free. Terminal investment is a deal with the devil; high chick-rearing success comes at the cost of earlier death.

 

An Annual Tradition? …and Complex Patterns of Senescence

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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

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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

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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.

Do Territories Get on a Roll?

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LMG_2782 Muskellunge Chicks Hide from Intruders

Linda Grenzer’s striking photo from two weeks ago got me thinking about loon breeding success. The picture is a sight that will please loon fanciers — two big healthy 9-week-olds resting side by side while their parents circle with intruders. (The chicks are holding their legs out of water, as resting loons commonly do.) Since territorial pairs almost never lay more than two eggs or hatch more than two young, the photo depicts a monster year for the breeders on Muskellunge Lake. Despite black flies and raccoons (which threaten nests), eagles, muskies and snapping turtles (which attack chicks), and constant intrusions by competing adults (which seek to drive adult breeders off of their lakes), the male and female on this lake reared two chicks to adulthood. Quite an achievement!

For Muskellunge, 2016 marks the sixth year in a row of chick production. Ten chicks in all have been raised by the pair during this stretch (including one rehabbed chick we added to their singleton brood in 2014). While I am thrilled to see such an abundance of chicks come from a single lake, it is not the norm. As residents on most lakes well know, loon breeding is a dicey proposition.

Consider, for example, South Two Lake, a normally productive breeding lake where the sudden disappearance of two successful breeders after 2015 left the lake wholly without a pair in May and June of this year, until it was finally resettled by a male and female in July — far too late for nesting. Or look at the Boom Lake-Hodag Park territory, where the pair had fledged five chicks across the past four seasons until the male became entangled in fishing line in the spring of 2016 near Panama City, Florida and never reached Wisconsin. Baker Lake was a consistent chick producer until 2013, when a five year-old male settled there with an unmarked female; they have lost nests to predators each year since then. Most spectacularly, the productive pair on Blue Lake-Southeast weathered the storm of parasites, egg robbers and chick predators only to see the male lose territorial ownership to a young usurper, which resulted in the chick’s death. Finally, pity the pair on tiny Liege Lake or Wind Pudding-West where, despite successful territory defense and incubation, the parents were unable to locate enough food to raise a single chick past six weeks of age.

In light of the many hazards facing loon pairs, it seems remarkable that we ever see a photo such as the one above. As one might surmise from the preceding paragraphs, there are several requirements for successful breeding. Abundant food is essential, of course. Each year, many pairs attempt to breed on tiny lakes where food limitation prevents them from rearing even a single chick, let alone two. Nesting habitat is vital; lack of boggy or marshy shoreline or an island prevents many pairs from even attempting to breed. Two less obvious factors can make or break a breeding effort: 1) the ability of both pair members to maintain their breeding positions throughout the season despite an onslaught of young adults looking to evict them, and 2) the male’s familiarity with proven successful nest sites, which dictates whether the nest is positioned in a location likely to survive four weeks of incubation.

Some breeding pairs have everything going for them, so that they surmount all obstacles and raise chicks to fledging year after year. Muskellunge (see photo) is large enough — at 160 acres — that food abounds, and the lake features several shoreline zones that support nesting. The resident female is much larger than average and aggressively repels intruders that challenge her. She is paired with a tough 18 year-old male — a bird experienced enough to know the locations of multiple nest sites on the lake but young enough to be in good physical condition and not vulnerable to eviction. In short, Muskellunge Lake is currently in a “sweet spot” for raising chicks, like Townline, Manson, Little Bearskin, East Horsehead, and Buck Lake. Lakes that get on a roll like these produce a disproportionate number of chicks, which will mature, return, and sustain the population. In time, these productive territories will falter, owing chiefly to the loss of one or both members of the vigorous, experienced breeding pair. For now, though, let’s enjoy the bounty of offspring that these lakes produce and look forward to the emergence of new productive territories that will succeed them.

 

No Silver Lining

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

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

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

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

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

 

Why Do Old Females Often Pair with Young Males?

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In many recent posts, I have emphasized a certain theme: male loons begin to die off at a rapid rate after age twenty, while females linger on. Part of the reason for this contrast is the nature of territorial contests in each sex. Territorial males fight hard in attempting to hold their breeding position on a lake and commonly die in territorial battles. With rare exceptions, territorial females survive eviction from a territory, move to an unoccupied lake nearby, and resettle on a new territory when opportunity permits.

While the escalation of male territorial battles is interesting in itself, it also impacts the composition of the breeding population. Specifically, adult male loons’ propensity to die frequently in battle skews the sex ratio towards females in the breeding population.

These excess females are “floaters” — adults capable of breeding but prevented from so doing by the lack of a mate and/or a territory. Floaters are the loons that one sees living alone on small lakes, drifting about aimlessly on large lakes, and intruding into territories from time to time to confront breeders. A large proportion of the loons that gather in flotillas of five adults or more during July and August are floaters. Floaters can be thought of as “hopeful breeders”; that is, they are always ready to settle and breed with a mate and territory, if they can find one. The excess of female floaters means that there are always far more of them looking to settle and breed than there are male floaters able to pair with them. In effect, males are snapped up by females as soon as they become available for breeding.

In May of this year, we re-encountered one of our veteran breeders, “Silver over Blue, Green over Orange” (or “S/B,G/O”), whose breeding history illustrates the striking contrast between males and females brought about by male-biased mortality. S/B,G/O was first captured and marked as an adult in 1997 on Dorothy Lake, where she raised two chicks with her mate. Her mate was evicted in 2001 and died either during eviction or shortly afterwards. But she lingered on. When an opening became available in 2002, she settled and nested with a different male on Hasbrook Lake, just a few miles to the northwest. Having failed to raise chicks on Hasbrook, S/B,G/O (now at least 14 years old) evicted the female breeder on Hodstradt in 2004, paired with a third male, a six year-old, and reared four chicks there during the next three years. She followed this young male to Horsehead Lake in 2008, when he was driven off of Hodstradt, and the pair fledged 3 more chicks over the next four years on their new lake. When the male was evicted yet again in 2013, S/B,G/O traded experience for youth and found a new six year-old male as a breeding partner. We breathed a sigh of relief when she broke up with this youngster after a year together, as he was unfortunately her son from Hodstradt! Then 23+ years old, S/B,G/O again became a floater, forced to return to the breeding grounds in 2014 and 2015 with no clear prospects for breeding.

I have become attached to the birds in the study area, so I was delighted to find S/B,G/O back at Hodstradt in May of this year with her fifth recorded mate. At 26+ years of age, she is perhaps fortunate to be paired again. Her mate this time: a four year-old hatched on Clear Lake. We observed no breeding attempt by this new pair – only a small percentage of four- year-old males that settle on territories actually nest – but it is likely they will nest in 2017.

As a human, I like to think of S/B,G/O’s life as a lesson in resilience – the dogged refusal of an animal to forsake breeding despite repeated setbacks and advancing age. But, as a behavioral ecologist, I think of this female more as a striking example of how animals adapt to maximize their breeding capacity regardless of the breeding environment they face. By the way, S/B,G/O is not the only female in our study area who has continued to breed despite frequent changes of partner. S/R,O/O, another 26+ year-old from Swamp Lake that we recaptured a few nights ago (see photo with Eric), has gone through at least 5 younger mates during her 20 years of breeding there. Clearly the pairing of tough, old females with much younger males is – as my daughter says – a thing.

A Revelation from Loon Capture: Small Lakes Are Ecological Traps

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2016-07-31 01.32.29

Loon capture is a blur. We set out from our house at 8:45 pm, launch our small motorboat on the first lake, wait for nearly complete darkness, and catch any loon chicks and parents that we can net easily. By the time we have repeated the process four more times, we are rubbing our eyes, our weariness justified somehow by the presence of the sun lurking just below the horizon.

As an essentially negative person, what I often recall after a night of capture and banding are the physical demands of the process and my complete exhaustion. But there are dimensions of the work that are exciting and rewarding. Each loon is unique, and one never knows whether an individual will permit itself to be approached closely and netted or will be wary and elude us. So we experience many disappointments, but they are tempered by the occasional thrill of capturing an individual that, at first glance, appeared too skittish to catch.

The fruits of loon capture are obvious. By marking individuals and resighting them year after year, we learn about survival rates of adults and juveniles, territory fidelity, natal dispersal, and habitat preference. We glean a good deal of important information from these data. For example, survival rates of young and adults allow us to learn whether the  local population is increasing, decreasing, or remaining stable. And tracking of young loons from egg to first territory has revealed that loons develop strong preferences for breeding lakes that closely resemble their natal lake. Finally, capture is essential as a means to disentangle loons that have been run afoul of angler’s lines or lures.

This year’s capture exposed another distinctive pattern in loon ecology: the presence of ecological traps. An ecological trap is a breeding habitat that appears at first glance to be a good one but ends up being poor for reproduction. For example, a field might experience a burst of insect activity during early spring, enticing songbirds to settle there for breeding, but a crash in insect levels after eggs hatch might occur that suppresses the number of young birds produced. Two nights ago, we captured two chicks from two different lakes back to back. The first territory was a shallow 11-hectare portion of Wind Pudding Lake (my favorite lake name). The chick captured there was a five-week-old that weighed a scant 0.92 kg — less than half what we would expect from a chick of that age. Our daytime observations show that the chick’s parents are no slouches; they respond to its constant begging by making frequent dives and retrieving what food they can to feed it. Moreover, the chick itself dives often to forage. But this shallow lake, covered almost entirely by lily pads (which impair loon foraging), offers scant sustenance. I am afraid that the emaciated Wind Pudding chick will ultimately starve to death, as did the chick on nearby Liege Lake, another shallow lake choked by vegetation. Loon parents on small, acidic lakes struggle to rear even a single chick, whereas those on large lakes of neutral pH often raise two. This stark contrast was highlighted for us, as the lake we visited following Wind Pudding was 1373-hectare Lake Tomahawk. To be sure, loon parents on Tomahawk must steer their chicks through countless jet skis, water-skiers, anglers, and speed boats at all times of day. But vigilant parents are rewarded with abundant food for themselves and their chicks. The Tomahawk-Sunflower Bay chick held by Mina in the photo weighed 3.02 kg, yet it was only a few days older than the chick on Wind Pudding. Clearly the strapping youngster in the photo is heading for a healthy future and likely fledging.

Why on Earth would loons settle to breed on lakes that often provide too little food for their chicks? The answer might relate to the disconnect between nesting and foraging requirements. Alas, large lakes that contain many fish for loons often lack the islands, emergent marshy bays, and bogs that allow loons to avoid egg predators like raccoons. So loons looking to breed seem to be lured onto small, marshy lakes that yield successful hatches but doom their offspring to starvation.