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To most people, Memorial Day weekend is both a sacred and joyous occasion. It is a time to remember those who have given their lives for our country. And it is a holiday that lets us gather around the barbecue with friends or enjoy an extra day of rest followed by a short work week. In the northwoods of Wisconsin, Memorial Day often brings a hint of summer’s warmth at a time when we are not quite free of the clutches of winter. Memorial Day convinces us that summer will return to the north.

Since 1993, when I first starting studying loons in northern Wisconsin, I have dreaded Memorial Day. On this holiday weekend, throngs of anglers bolt from their southerly homes for the northwoods to throw a hook in the water. Meanwhile, loon pairs that have managed to fight off black flies, eagles, and raccoons are well into the four-week incubation period. Memorial Day is the time when hopeful loon parents and hopeful human anglers collide.

I used to gird myself for the disturbance to nesting loons that humans caused each Memorial Day weekend. Fishermen and boaters commonly disregard or do not see loon nests and venture close to them, driving loons off of nests for a time. But such incursions now seem innocuous. They seldom cause great problems for loons, who sometimes complain but dutifully jump back on their nests after boats have moved off.

Now that we have better connections to the local community, I see that the substantial danger posed by humans to loons on big fishing weekends is not from flushing off of nests but from fishhooks and monofilament line. On Memorial Day weekend, the loon pictured in Linda’s photo, a female that reared a chick on Nokomis Lake in 2010, was hooked in or near its throat while it foraged on Nokomis. As ugly as it is to look at the silver hook buried in its throat and the local swelling that resulted, the Nokomis female might recover. She appears to be hooked externally, and Linda reports that she dives strongly.

A second female fell prey to an angler’s lure this Memorial Day. This bird, the mother of many recent chicks on East Horsehead Lake, apparently swallowed a lure or bait used by a fisherman. Initially Linda found that this female was severely impacted, often trying to jump onto the shoreline, as loons do when seriously injured. Nelson and I raced up to East Horsehead to help Linda and her husband, Kevin, try and capture this bird and transport her to a wildlife rehabber for treatment. But our efforts were in vain. The bird had bounced back and begun to dive normally, despite the fishing line protruding from its bill. Having ingested a lure, this bird’s long-term prospects are rather dim. She will certainly die if she swallowed a lead sinker.

These two cases illustrate a vexing paradox often faced by those of us trying to protect wildlife: animals commonly become injured in a way likely to kill them eventually but not so catastrophically that immediate capture is possible. So we must wait and monitor them until creeping hunger or infection reduces their mobility sufficiently for us to grab them and see to their injuries. These are most unpleasant and heart-wrenching vigils. Moreover, these occasions often end badly, if the animal becomes compromised beyond the point of recovery before it can be captured and treated. Still, knowing that a grave injury of this kind has occurred gives us a chance.

An encounter with fishing tackle ended quite badly for the East Horsehead male last year. Although it was not reported to us until a few days ago, last year’s East Horsehead male — the long-time mate of the female who swallowed a lure a week ago — became hopelessly ensnarled in monofilament line last August. Based on our records, we surmise that he succumbed to this entanglement sometime after August 10th, as we observed the female alone caring for the chicks on our two visits after that date. (Since the chicks were 11 weeks old by late August, they likely survived to migrate south. That, at least, is a relief!)

We were disappointed to hear only now about the unpleasant entanglement and death of the East Horsehead male. Unlike the two females, this male was probably immediately compromised enough by the fishing line that we could have captured him and cut him loose in good condition and with no harm to his survival prospects. Indeed, we were able to save a female on Perch Lake from a similar predicament in 2010. Since the East Horsehead male’s plight was never communicated to us, he had no chance.

So, now, a plea. Please let folks know that angling casualties happen. We are anglers ourselves and understand this. But anglers who cut the line and flee the scene after accidentally hooking a loon — or observe a loon in distress and fail to report it — are turning a dangerous situation into a catastrophic one. As so often occurs, it is the cover-up, not the crime, that causes real damage. (I am happy to take reports of loons in distress at wpiper@chapman.edu.) Let’s try and have summer holidays in the northwoods bring to mind the events they were meant to commemorate, not the toll they exact on loons.

 

 

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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.)

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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.

 

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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.

 

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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.

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He doesn’t look it, but this male from Townline Lake, just outside of Rhinelander, is at least twenty-seven years old. He is among a dwindling few males from among those we banded in the mid 90s. This bird was banded in 1994, at which point he was certainly at least five years old, which means that he was hatched in 1989 or before. Thus, twenty-seven is a minimum estimate for his age.

The age of “Silver over Red, Orange over Green” (as I call him affectionately) is not his only remarkable attribute. What sets this individual apart from most others is his ability to hold onto his territory year after year while fledging healthy chicks. (Below, he relaxes near his mate and two strapping chicks from 2016.) A successful common loon is not only good at locating safe nest sites and defending and feeding young. A breeder that wishes to

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reproduce successfully must confront intruders that land in the territory without warning throughout the breeding period.

Intrusions are especially frequent during the chick-rearing period. A common scenario plays out as follows. Early in the morning, a male is diving for food, while his two chicks track his progress from the surface. Each time he surfaces, the chicks rush over to him, snatch food from his grasp, and nibble relentlessly at his bill, neck and chest, signaling their unquenchable appetites. On one occasion, he surfaces holding a small yellow perch, only to find five adult loons in flight above his lake. He drops the fish, gives a short barking call, and the chicks dive and head to the nearest shore. The male too dives but surfaces near the middle of the lake, drawing the now-descending intruders to himself. Three quarters of an hour later he has driven off the intruders, thanks in part to a lunge and point yodel that caused his five visitors to scatter and tremolo. Shortly afterwards his mate returns, and both parents forage for the chicks. The family suffers no further disruptions until the evening, when another group of three nonbreeders circle and land, causing yet another brief skirmish.

Considering that a large pool of territorial intruders are constantly sizing up the resident male or female of any successful territory for an eviction attempt, it seems remarkable that residents are able to hold on to their territories for even a single year. Yet Silver over Red, Orange over Green has put together a string of 23 years of straight ownership, the only blemishes a half-year in 1996 and another in 2003, when he was briefly deposed. He has fledged 20 chicks during his breeding career with four different mates. This male is not the only resident with an impressive resume. A female on nearby Langley has fledged 17 chicks on that territory since 1995, while the O’Day female has been on territory since at least 1997 and has produced at least 16 full-grown chicks during her breeding career.

But female loons are survivors. Females enjoy a high rate of survival and no detectable senescence well into their twenties. Males, on the other hand, hit the wall abruptly at age 20; almost half of all territorial males of age 20 will perish before the subsequent year. So when we see a male who defies the odds, like this one, it is worth looking closely to see if he possesses an attribute that sets him apart. As a scientist, I am loathe to draw conclusions based on a sample of one. Colleagues in my field would dismiss any such conclusions out of hand. But today Nelson, one of my Chapman research students this year, reported that Silver over Red, Orange over Green is the tamest bird we have ever measured in the study area. So let me invite ridicule by advancing a very preliminary hypothesis. Perhaps the key to lifetime productivity in a habitat rife with human recreation is picking one’s battles carefully. Maybe by ignoring the inquisitive, well-meaning primates in their watercraft, this male has been able to conserve his metabolic resources for provisioning young and driving off pesky intruders.

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The first round of censuses in the study area each year is always bittersweet. On the one hand, it is exciting to see the crop of new young adults that have settled and to wonder how well they will defend their new territories. On the other hand, some old familiar loons are missing. This year is typical in that the disappeared veterans are mostly males. Three of 12 males of 20+ years have failed to reclaim their 2015 territory; only 1 of 12 20+ females have not resettled on their territory from the year before. Thus, male senescence lives!

Among the 2016 no-shows are the Jersey City Flowage male, who bounced back from a nasty fishing entanglement in 2014, regained his territory in 2015 and hatched a chick there. Another loss is the Soo Lake male, who was among the most aggressive in our study area. I still tremble when I recall his response when we played a few loon calls in his direction in 2000. He approached my canoe to within 2 feet, sat right next to me in the stern and glowered for the better part of two minutes. A spine-tingling experience for sure!

Yet the news is not all bad. Six young ABJs (“adults banded as juveniles”) have settled in the study area, providing us with valuable data on loons whose age is known precisely. New settlers include two females hatched in Vilas County — a 9 year-old that settled on Manson and a 6 year-old now paired with the male on Harrison Flowage. New male faces belong to an 8 year-old that took over Brandy Lake (near Woodruff) and a 7 year-old that battled and evicted the 22 year-old male from Oscar Jenny. (Thanks to Jeremy, who observed this eviction in progress.)

Perhaps the most intriguing findings from the first round of lake visits by Kristin and Linda are the serendipitous ones. Kristin relocated one of our oldest males — a bird known to be 27 years of age or older. Evicted two years ago from Muskellunge Lake, this loon licked his wounds and got himself back in the game by settling on nearby Swanson Lake, which had fallen into disuse in 2015. We had not seen this bird in two years and were almost ready to give up on him. Linda found a female with even greater resiliency. This old loon produced a dozen chicks over the years as the breeder on Buck Lake from 1998 to 2009. After her eviction from Buck in 2010, she floated, found a breeding position on Hildebrand in 2012 and produced a chick there in 2013. But she was driven off of Hildebrand last year. Her response to this second setback was typical of female loons — she bided her time and claimed that territory again when the opportunity presented itself. As I confront another season of hauling canoes from lake to lake, my back begins to ache in anticipation. I hope the examples of these two dogged old codgers gives me the strength to persevere!

 

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My mother-in-law came to visit us in California last week. She is an avid follower of my blog (!), so I was excited to learn what she thought of my most recent post. She hated it. That is, she said of my report that loons get old:”I could have told you that!”. Naturally, I was deflated. To think that 23 years in the field had produced a result deemed pedestrian by my mother-in-law!

While one might argue that she is family and should have been blindly supportive of my work, Joanne is right, in a sense. As humans, we are accustomed to old age and deterioration of the elderly. But, as I tried to explain, senescence is not the rule in all animals. Birds are unusual, in fact, as they exhibit relatively late and gradual senescence compared to mammals of similar body size. So the striking and rather sudden senescence that I reported recently is mildly surprising for the taxonomic Class Aves. Still, I think I agree with Joanne that it is not terribly shocking!

But there is more. The blog where I reported senescence in adult loons was based on an analysis that pooled male and female individuals. Since then, I have analyzed the sexes separately. The results are striking. As the figures below show, the senescence that I reported for the species as a whole (measured by decreased survival) is driven purely by males. While males and females that have been on territory from 1 to 14 years survive at a rate of 95% annually, males with 15 or more years on territory only survive at a rate of 58%. (Old females show a very modest decline in survival to about 91%.) Since males and females that settle on territories are almost always 5 years old or older, we can say with confidence that territorial males in their twenties drop like flies; females, in contrast, are survivors.

young males and females do not differ in survival rate

old males die at a much higher rate then females

I don’t know if my mother-in-law will be impressed by these data. For the moment, I must be content in the knowledge that I have found a strong and highly unusual survival pattern. As a behavioral ecologist, this stunning disparity leads to several other questions. Among them are: 1) Do older males exhibit any other evidence of deterioration such as in territory defense, chick production or body condition? and 2) Does the high mortality of older males cause the adult sex ratio to swing towards females such that females are forced to wait years before finding a mate? Rest assured that I am exploring these possibilities with great enthusiasm.

 

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When loon biologists measure reproduction, they often count chicks older than five or six weeks of age as having fledged. This is reasonable. Even though loon chicks remain dependent upon their parents for 11 weeks or more, almost all chick mortality occurs in the first few weeks of life. If a chick makes it to five weeks, it is almost certain to make it to adulthood.

Not so during this past week. As the unpleasant photo by Dan Pagel shows, one of the the Blue-Southeast chicks died quite violently several days ago after a sudden attack by an adult. Based on the photo and the swiftness of the death, we suspect that severe heart or liver damage caused the death. Since Dan was a few hundred meters away when the murdered Blue-SE chick IMG_3960vicious attack occurred, he was unable to identify the perpetrator. Regardless of what loon committed this act, it comes as a shock. The departed chick was over twelve weeks of age, healthy, and off by itself feeding when it fell victim to the brutal assault. Twelve weeks is much older — I believe as much as eight weeks older — than we had ever observed a chick to be killed by a foreign adult. In light of the tempestuous territorial scene at Blue-Southeast recently, it is tempting to view this chick as a casualty of the conflict that caused its father to lose his territory. Certainly, the new, unmarked male that had taken over on Blue-Southeast and had already been observed to peck the chicks in his first weeks of ownership is a suspect. A second possibility is that the chick carelessly strayed into the west territory on Blue Lake and was attacked by a member of the West pair for territorial reasons. But territory defense is scant and subdued at this time of year, so that explanation is problematic.

I was still coming to grips with the events at Blue Lake a few days ago when I received a second piece of news, equally discouraging. One of the chicks at Buck Lake, near Rhinelander, had died. The cause of death in this case is less clear; the chick’s leg became injured a few weeks ago — a lake resident reported that a snapping turtle latched onto it! — and the chick was not able to move about effectively afterwards. Like the Blue chick, the Buck chick was far past fledging age, having reached 11 weeks.

What can we conclude from the co-occurrence of two deaths in very large and healthy chicks? I think these two unfortunate events simply remind us that, while chicks that have reached near-adult size are far more likely than 2-3 week old chicks to survive to adulthood, they are still young animals. As we have reported in a scientific paper, loons suffer a higher rate of mortality during their early years. Adult loons have had years to hone their ability to feed themselves and cope with environmental hazards, including conspecific attacks; youngsters are still getting it down.