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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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.

Beating the Odds: Ancient Male at Townline Keeps Cranking Out Chicks


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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.

Home Alone on O’Day


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Why would a breeding pair of loons — which has made an enormous investment in defending a territory, finding a nest site, incubating their eggs for almost a month, and then rearing their chicks — leave them alone? Such behavior seems reckless, almost dysfunctional. Yet loon pairs commonly “desert” their offspring for periods of hours, while they themselves visit neighboring lakes. During such times, of course, chicks are left to cope with all manner of predators and other dangers without parental assistance.

The leaving of chicks behind by parents does not occur willy-nilly. That is, not ALL chicks are deserted, only those that have reached at least four weeks of age. Some chicks, like those I watched on O’Day Lake this morning, are highly alert to their surroundings, like adults, and capable enough hunters that they are already providing over half of their own food. (Note the expert-looking dive by the chick in the video.) One can imagine that temporarily leaving behind chicks of this age does not carry huge risks. At six weeks of age, chicks can detect and flee from eagles, when necessary. So perhaps the risk of leaving your chicks to fraternize with neighboring adults is not great.

Still, temporary chick-desertion surely carries some risk. If the choices are remaining on your territory with your chicks versus departing to a nearby lake to visit with other adults, the first option is clearly the safer one. The only conclusion to draw from what appears to be rather reckless socializing by pairs with chicks is that they must gain something nontrivial from doing so to compensate for the small risk that their chicks will be lost during their absence.

Their are several possible explanations for parents’ trips to neighboring lakes. One hypothesis maintains that parents encounter and become familiar with neighbors whom they might have to battle later for a territory or with whom they might pair in the future. If so, recognizing and learning about other adults might provide for more effective fighting or breeding. A second idea is that parents leave their chicks in order to forage on lakes other than their own so as to maintain robust food levels for the chicks. Thirdly, temporary desertion of the chicks might constitute part of the weaning process; chicks often beg incessantly when with their parents, and perhaps chicks must be without parents to begin foraging effectively on their own in preparation for adulthood. A fourth explanation is that parents, which are conspicuous to other adults owing to their bright plumage, desert their breeding lakes in order to avoid giving away the fact that they have chicks. (Behaving this way might reduce the likelihood that a young nonbreeder could target the territory for eviction, since we know that intruders use chicks as an indication of a good territory.  ) If this explanation is correct, then parents are essentially trying to “decoy” intruders away from their own lake by visiting a neighboring territory nearby. The hypothesis is plausible, because: 1) intruders are strongly drawn to other adults in the water, and 2) intruders appear to find chicks only after seeing and approaching the chicks’ parents.

One final curious behavior seen in loons and chicks provides partial corroboration for the “decoy hypothesis”. When faced with an intruding loon flying over their lake, adults and their chicks dive and scatter. That is to say, adults and their chicks make every effort to hide from intruders by diving and spreading out in the lake, which complicates discovery. If loon parents are desperate to hide their chicks from intruders, what better way to do so than by flying off to other lakes near their own — and thus using their conspicuousness to draw intruders to those lakes — and leaving their cryptic chicks at home, where they will most likely escape notice from the air.

The decoy hypothesis is complex. Its crux is that loon parents are protecting their own future breeding prospects by taking a slight risk with their current chicks. In time, we will be able to determine if parents that practice short-term chick desertion enjoy longer territorial tenure. If so, this will be a stunning example of effective long-term planning in the animal kingdom!


Misdirected Parental Care: Loons Rear a Goldeneye Duckling


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With Mother’s and Father’s days still fresh in mind, maybe this is an apt occasion to relate a quirky instance of parenting in loons. The topic came up abruptly last week, when Doug Giles, a lake resident in British Columbia, sent these photos. At first, I could not even

_IMG0771 fathom what species of duckling was receiving this unanticipated caregiving. A frantic web search of ducks breeding in the vicinity revealed that this is a young Common Goldeneye. But how could such a duckling escape the watchful eye of its own mother and blunder into the path of a pair of loons?

The curious breeding behavior of goldeneye ducks provides a clue. Goldeneyes lay 7 to 10 eggs in tree cavities, and the female is the sole incubator. (Male goldeneyes leave the picture shortly after incubation begins and play no role in rearing offspring.) Goldeneye ducklings follow their mother away from the nest a few days after hatching. Unlike loons, goldeneye young feed themselves; their mother merely protects them and guides them to feeding areas where they are relatively safe from predators. The task of herding ten or so ducklings about creates logistic hurdles; ducklings commonly fall behind or lose track of their mother and siblings. When goldeneye hens converge in the process of guiding their respective broods, young intermingle, creating creches of dozens of ducklings of varying parentage. Finally, female goldeneyes, especially those with small broods, often abandon them — leaving the ducklings to fend for themselves or coalesce with broods where the female is still present.



In short, rearing of massive goldeneye broods seems haphazard and impersonal when compared with the parental behavior of common loons. If common loons are modern-day human parents in the era of small families, abundant participation awards, and kindergarten SAT prep; goldeneyes are the all-out reproducers of the pioneer days, never quite certain of how many young they have and where they all are! So we should not be surprised to encounter a misplaced or forgotten goldeneye duckling.

But why would loons adopt a young animal that differs markedly from a loon chick? First, it is important to understand that loons — like many animals — are hormonally primed to care for young. That is, young production is the crucial measure of evolutionary fitness, so we should expect all species to be committed to the rearing of young, if parental care is obligatory for survival in that species. Apparently, the drive to provide parental care is sufficiently strong that it can get misdirected at times. Among all ducks that loons might adopt, goldeneye are a good match, as they are diving ducks (not dabblers, like mallards) and subsist mainly on aquatic invertebrates and occasional small fish. Clearly this duckling is developing more of a taste for fish than is usual for its species, as Doug Giles’ first photo shows. The duckling’s willingness to accept food from another individual, moreover, shows impressive flexibility in behavior that we might not have expected.

While we can understand how the adoption of a goldeneye by loons is plausible, it is still a remarkable event. The likeliest outcome of a close brush between a small duckling and a loon pair is an attack; many ducklings are killed by loons each year. Perhaps this loon pair was primed for adoption by having lost their second chick shortly before they encountered the stray duckling.

One factor to which we definitely cannot attribute the successful adoption is relatedness between ducks and loons. Ornithologists have long known that ducks and geese are not closely related to loons. In fact, goldeneyes are cousins of turkeys and chickens, while loons are in the evolutionary lineage that includes herons, cormorants and penguins. The superficial similarity in appearance between loons and ducks results from evolutionary convergence, not common ancestry. In my view, the distant relationship between loons and goldeneyes is yet one more reason to marvel at the odd parent-offspring bond that has formed here — and hope that it leads to a good outcome.


More Carnage at Blue-Southeast


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Mina caught the tail end of the battle. By the time he arrived for his observations, the territorial male on Blue-Southeast was on his heels. No doubt shell-shocked from a beating he had received from an aggressive four-year-old male that had lurked in the neighborhood for two years and was making a play for territory ownership, the territorial male beat a hasty retreat, actually flying off of the lake with another intruder.

The strategic retreat of the territorial male left his mate in dire straits. Without another parent to engage intruders, the female alone had to defend the week-old chick from the aggressive onslaught of the four-year-old male. The situation was hopeless, the suspense only fleeting. The young male quickly discovered the chick and — in the grisliest moment we have observed while studying loons — snatched the chick out of the water and carried it for a time while pursuing the retreating female. When he dropped the lifeless youngster, it was over.

When the shock wears off, we will one burning question about this episode: “Why is Blue-Southeast the site of such frequent territorial controversy?” Can it be coincidence? One must never be hasty to rule out chance, but I think that is not the explanation here. Rather, evictions of the territorial male in 2015 and the same individual again this year resulted from his relatively poor fighting ability. Intruding loons are adept at sniffing out weakness in territorial residents. When a breeding male or female is unable to drive competitors forcefully off of the lake, intruders congregate, leading to further confusion and attempted evictions, in a disheartening positive feedback cycle. The Blue-Southeast male, while a capable parent, has often encountered intruding males that he could not drive off of the territory in years past. It is quite possible that his troubles in 2015 occasioned more territorial challenges in 2016 by the same set of challengers.

I am by nature a rather negative person, always quick to point out the downside of every cheery situation. But I see one bright spot here. If the usurper of the territory and killer of the chick becomes the territorial male, he would appear to be a strong and aggressive individual and one likely to defend the territory with greater success than his predecessor. This 2012-hatched product of nearby Bolger Lake would be a record-setter too, since he would be the youngest male ever documented to seize a territory by force. (Most young males, like very old males, settle on vacant territories rather than fighting their way onto occupied ones.) I wish I could offer more meaningful solace to Blue Lake residents, who will be dismayed at today’s turn of events. The best I can do is to suggest that the future for the Blue-Southeast pair is likely to be brighter than the recent past.









A Challenge with a Possible Upside


Our field work is fundamentally challenging. We observe a large aquatic bird that spends much of its time underwater and surfaces unpredictably. With rare exceptions, individual loons are impossible to distinguish, so we must observe their colored leg bands to tell who is who. Thus, we can only conduct our research by obsessively monitoring leg bands when we can and matching what we see of leg bands with behaviors that the birds carry out. A typical field observation is: “Blue on right leg two-note wailed at 0643 while an eagle flew overhead more than 50 meters away — while the caller’s mate and chick were more than 20m away”, which would elicit a datasheet entry of “643twmc/EF” in the slot on the datasheet reserved for that loon. But sometimes important behaviors occur that we cannot assign to an individual loon. If we are only just approaching a pair when a behavior occurs, or have lost them between dives, we might have to make such an entry into a section of the datasheet entitled “Unknown Pair Member”. Such an entry would indicate that we knew that the caller was one breeder or the other, but could not be certain of identity. Naturally we try to minimize entries into the Unknown Pair Member field, as they reduce our capacity to quantify commitment to parental care and territory defense by the male and female.

To maximize the quality of our recorded observations, we carefully select contrasting color bands for pairs that we capture and mark. The breeders on Swamp Lake, for instance, are: FEMALE -> silver over red – right leg, orange over orange – left leg; MALE -> silver over yellow, mint over white. On Swamp, a quick glimpse of either leg of either pair member suffices to identify it, so we do well at assigning behaviors to the correct pair member.

Territorial evictions mess up our plan of having each breeder banded in a way that differs strikingly from its mate. When a new banded bird usurps a territory, its bands might happen to be quite different from those of its new mate or might not. Back in 2006, when a young male that we had banded as a chick (we term such loons “ABJs” for “adult banded as juvenile”) kicked the resident male off of the Oneida-East territory, the new pair had bands: FEMALE -> Silver over blue, orange over orange; MALE -> orange over orange, green over silver. It instantly became rather difficult to obtain good data on this pair, because they were skittish and because the occasional flash of orange color that we could see on a loon did not allow us to I.D. it unless we were certain of which leg we had seen.

Yesterday, Julia (pictured in her selfie above) reported our worst yet case of eviction leading to headaches in identification. Julia’s observations showed that “white with blue stripe over silver, green over green” had just evicted the resident male on Hilts Lake and paired quickly with the resident female, who is “silver over white with blue stripe, green over green”. Hence, the Hilts pair now consists of a male and female that are identical in the four bands on their legs and differ only in the transposition of the two bands on the right leg. Naturally, behavioral observations of this pair will be taxing for the observer — a real test of our ability to spot subtle differences in band combinations under field conditions. A great many observations of this pair will have to be dumped into the “Unknown Pair Member” box.

Often it is the unwelcome challenges in scientific research that can lead to advances in understanding. Loons do exhibit slight differences in details of the white stippled chin strap and the triangular patches of fine white stripes on the collar. Maybe photos we take of the Hilts male and female will reveal consistent differences in these markings that permit us to distinguish pair members there. I have long mused about the ability of the loons themselves to tell each other apart from a quick glance and without vocal cues. Perhaps the inconvenient turn of events on Hilts will spawn a new, more detailed look at how loons solve that essential but most vexing task — rapid visual discrimination between mates and territorial opponents.

Are Canada Geese Pushing Loons off of Prime Nest Sites?


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The goose population has been increasing in northern Wisconsin. Ten years ago, a Canada Goose was an infrequent sight on one of our study lakes. Geese were confined chiefly to a few large lakes and seen overhead only as they migrated northwards. But no more. Now we encounter adult geese and often pairs with goslings on about half of our study lakes.

Apparently the increased availability of waste grain from agriculture, the proliferation of lawns, and increased temperatures have fueled the explosion in goose numbers, which has the potential to impact loon reproductive success. You see, geese and loons both prefer nesting sites safe from mammalian egg predators like raccoons and foxes. Such sites are often on islands and are limited in number. If a small island offers the only available safe nesting on a lake, goose and loon pairs are both likely gravitate to it.

The problem is not merely that loons must now compete with geese for nesting sites; geese actually get “first dibs”. While both loons and geese incubate their clutches for about four weeks, geese initiate their clutches two weeks or so in advance of loons. (The earlier onset of goose nesting is evident right now in our study area, as many goose pairs are rearing their broods of two to six goslings, while the earliest loon nests will not hatch for another week or ten days.) On occasion geese and loons nest within a few meters of each other on islands — as we observed on Oneida Lake a few years ago. Coexistence between the species is possible. But the presence of a sitting goose appears to discourage loons from nesting nearby, which often forces loon pairs to select sub-optimal sites for incubation.

Consider the plight of the Clear Lake loon pair. The safest, most desirable nest location on Clear Lake is a small shrubby island off of the public boat landing. Loons have shown a strong preference to nest on this island during most years. This year, the geese got their first, and the loons had to settle for a new nesting location on a long peninsula about two kilometers south. They may hatch chicks off of this peninsula, but the site is not offshore, like the shrubby island, so it is clearly vulnerable to mammalian egg predators.

I am optimistic that this spunky loon pair will be able to pull off a hatch. As can be seen from our shaky video, the male (on the right in the video) is still working on improving the surrounding nesting area, and the pair has a well-constructed nest with two eggs (visible to the left of the female, after the camera pans left). Still, this well-constructed nest will not protect them from a scavenging raccoon that ambles by.