2016-08-01 02.16.10

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.

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.

 

 

 

 

 

 

 

 

LMG_9628 Manson Lake Male Yodeling

Loons do not settle on territories as we think they should. Traditional models in long-lived animals maintain that hopeful young individuals should be systematic in settling on territories. By current theory, a young loon should explore a certain region within proper habitat, find several territories that might be suitable for breeding, and then routinely monitor those potential breeding spots, waiting for a vacancy to occur. During this exploratory period, it is thought, the young loon gains familiarity with this small cohort of territories that will lead to a competitive advantage in territorial battles with other would-be settlers once a territorial slot opens up. The “foothold hypothesis”, as I call this model, is quite pleasing and logical. What’s more, there is evidence that many territorial animals gain territories in this manner. Loons do not.

We got another reminder of the quirky territorial settlement pattern of loons this past week, when Linda and Kristin scoured the study area and ID’d the pairs that had taken possession of the lakes we monitor. Among these settlers were many familiar faces — including a male on Townline Lake that has been in possession of the territory since 1994 and a female on West Horsehead who has bred there with a series of different males since 1995. One of the surprises was a 9 year-old female hatched on Rock Lake in Vilas County who settled on Manson, replacing a female that had bred on Manson for a dozen years. Owing to Linda’s careful observations, we know this Rock Lake female as a frequent intruder during 2014 and 2015. But she did not intrude into Manson Lake, where she eventually settled; instead she intruded repeated onto nearby Muskellunge Lake! Thus, our expectation that the Rock female was laying the groundwork for settlement on Muskellunge was not fulfilled.

There are several possible reasons why loons often do not settle on lakes that they seem to prefer. One of the most obvious is that settlement is not merely a matter of finding a desirable territory.  A loon bent on settling must also contend with the current resident on a territory where it hopes to settle. So a young nonbreeder that visits Territories A, B, and C might prefer Territory A but be prevented from settling there by a healthy and aggressive territorial resident of the same sex. In that case, the nonbreeder might end up settling on Territory B or Territory C. The Rock female is fortunate; Manson Lake, where she has settled, is one of the most productive territories in the study area. So even if she could not take possession of the territory she seemed to prefer, her future breeding prospects are bright.

You can read more about our testing of the “foothold model” for territory settlement in this blog post, which is based on a paper published in Animal Behavior. E-mail me if you would like a pdf of the paper.

The crisp photo above is by Linda Grenzer. It shows the Rock female performing a wing flap on Manson, her new breeding lake, while her mate, an 18 year-old male, yodels in the foreground.

This past winter was a mild and relatively short one in the upper Midwest. The ice never became as thick as in most years. So the warming temperatures during the past few weeks succeeded in melting that thin blanket of ice covering our study lakes. I have gotten reports in the past few days that many of our study lakes now are mostly or completely free of ice. And the avian summer residents of those lakes are beginning to return.

LMG_8789 Clune on Territory

The first male reported back was “Clune”, seen here in Linda Grenzer’s photo from Wednesday. Playfully named by Linda after the voice-to-text feature on my iPhone butchered the word “loon” during one of our exchanges, Clune is well known to us. We first observed him as a chick on Manson Lake in 1998, found him when he settled as an adult on Deer Lake in 2003, and tracked him when he shifted to his present territory on Muskellunge Lake five years later. He and his mate have produced a whopping seven chicks since 2011 on Muskellunge — eight if you include the rehabbed chick that we released on the lake in 2014 and that Clune and Honey readily accepted and reared as their own. (Yes…Linda has named the female too!)

I am a scientist. I try to stick to the data and not be influenced by emotions and superstition and unsubstantiated inklings. Nonetheless it cheered me when Linda reported that Clune had returned very early this year and already yodeled to defend his territory from a skittish intruder who dared to enter it. Despite my better judgment, I cannot help but think that this will be a productive year for loons in northern Wisconsin.

2015-01-31 11.10.42

Publishing papers in scientific journals is hard work. It requires patient and well-planned data collection, thoughtful statistical analysis, and painstaking writing and editing of a manuscript. And then the real work begins! Among the dozens of scientific journals that might publish the paper, one must select a journal that suits the topic of the paper, employs competent editors and reviewers, and makes its published papers available to a wide audience so that it will be read and cited by many colleagues in one’s field. Most crucial, one must convince the journal’s anonymous reviewers that the findings reported in the paper are robust and valuable. In short, publishing a paper is a journey.

Recently, we completed a successful journey, as our paper describing the process of territory settlement in young loons was accepted by Animal Behaviour. Although we would like to celebrate this event, we are more relieved than joyous; relieved because the paper represents a vast amount of field work, number-crunching and writing and became long and unwieldy enough that it earned harsh criticisms from some reviewers. So its publication became, as some journeys do, a story of survival in the face of adversity.

The paper will make available a trove of valuable findings. We report in the paper that young loons do not adhere to the most prominent model for territory settlement. This idea, termed the “foothold model”, maintains that young animals in search of breeding territories target a small set of established territories for intrusions, gradually gain confidence through increased familiarity with that limited set of territories, and then evict the owner of one of those territories (or outcompete another young loon for the vacancy, in the event of the owner’s death) in order to claim the territory as their own.  We show in our paper that, instead of using a foothold of this kind to gain a territory, young loons merely settle on a territory that is similar to their natal one. In some cases, they are able to occupy a vacant territory and breed there. In other cases, they wait to mature and improve in body condition and then evict an owner. But the repeated intrusions that young loons make to specific lakes are not attempts to build upon their familiarity with the lake and thereby increase their competitive ability there.  Rather, they are efforts to assess the fighting ability and perhaps the motivation of the current owner to defend its territory so that the young loon can judge when an attempted eviction is likely to be successful.  Reviewers described our findings as “provocative” within our field, and we hope they are right!

Thanks to all our supporters, especially landowners and friends, who allowed us to study their loons year after year. Publication of this meaty paper is evidence that our mutual investment in loon research is paying off.

 

LMG_2087

A few days ago, I was conducting observations on the lake where Linda Grenzer lives when she snapped this photo of me, the two pair members on the lake (the two loons closest to my canoe), and five territorial intruders. Linda’s picture captures beautifully what transpired during my visit of an hour and a half. Better yet, the photo shines a spotlight on an enduring question that drives much of my research on loon territoriality: what is the purpose of territorial intrusion. This is a question that we have only half-answered.

We do know that many intruders visit in order to learn whether or not a territory has chicks; if they detect chicks, they are more likely to intrude in the following year and attempt to evict the breeding pair member of their sex. (This makes some sense, as the presence of chicks is an indication of good nesting sites and plentiful food for young.) We also know, from a recent analysis, that loons practice natal-site matching; that is, they attempt to settle as a breeder on a lake that is similar in physical size and in pH to the lake they were reared on. So undoubtedly some intruders must be learning about lakes where they intrude so that they can settle on one similar to their natal lake.

But there must be more motivation for intruders to visit lakes defended by breeding pairs. Among the 5 intruders pictured in the photo, for example, were: a banded 9 year-old loon not known to be settled on a territory yet (i.e. a probable “floater”), an unbanded loon whose status is wholly unknown, and three banded loons known to be members of breeding pairs from neighboring territories. While the first two birds could plausibly be shopping for territories through chick detection or natal-site matching, the neighbors are unlikely to be doing so.

What, in fact, could neighbors stand to gain from intruding next door? Several hypotheses are possible here. Neighbors might gain by becoming familiar with other loons with which they might become mated in the future, if they both lose their current breeding positions and must settle elsewhere in the general area. Neighbors might also be trying to learn about the territory, which they might occupy in later years, providing one of the current pair members dies. Another possibility is that neighbors have no particular interest in the territory where they intrude but, rather, are intruding in order to draw attention away from their own territory (since loons on the water tend to attract flying loons to land and investigate). That is, intruders might be attempting to “decoy” loons away from their own territory so that others do not learn about it and attempt to settle there. Finally, neighbors might simply visit to forage in someone else’s territory, depleting the food supply there instead of at home.

An additional question raised by the photo is: what is the breeding pair’s response to intruders? One might expect that the breeders would react aggressively towards intruders, driving them out immediately so that they cannot learn about their chicks (of which there were two in this case, hiding our near shore and far from the intruders) or harm them. Yet this pair — typical of breeders — was tolerant of the intruders and allowed them to roam freely throughout the territory for over an hour. Are the breeders feigning nonchalance to reduce the likelihood that intruders will look closely for and detect the chicks? Or do large numbers of intruders pose a severe threat to territory ownership such that territory owners must tolerate them or risk losing their positions?

I hate to raise so many questions that we cannot answer immediately. Testing of most of these hypotheses for intrusion and defense towards intrusion is feasible in our population. For example, we can look statistically at the “decoy” hypothesis by seeing whether pairs that vacate their territories and intrude next door experience a lower rate of territorial eviction than pairs that remain on their territories faithfully throughout the season. And we can test whether pairs that attack and stalk intruders, rather than tolerating their intrusions peacefully, suffer a higher rate of territorial eviction, because they betray the presence of their chicks and place a target on their own backs.

Such statistical analysis requires large samples of lakes and intrusions, so it will take time. Meanwhile, we will have to enjoy the experience of tracking intruders and breeders around territories by canoe and wondering what peculiar combination of evolutionary interests of breeders and intruders could produce such flotillas.

 

After the black fly debacle in recent weeks, we were all ready for some good news. Indeed, most territorial pairs had shaken off the flies and gotten back to the business of reproduction. Good tidings seemed the order of the day. Yesterday, Al Schwoegler of West Horsehead Lake called with a thrilling and unexpected report: the eggs laid by the pair, which they had left unattended for many long hours on several days because of the torment of black flies, had begun to hatch! At first neither Al nor I could believe that the eggs were viable. As Al described the behavior of the female on the nest — who has reared a whopping 19 chicks to fledging since 1996, when she was first banded — we gradually let ourselves believe that the impossible had occurred.

But our positive feelings were dashed suddenly by the cruel realities of loon territorial behavior. You see, the last few weeks at West Horsehead have been marked by frequent territorial intrusion. At the very time that the pair was trying to recover from the onslaught of biting insects, the male owner was facing repeated challenges for his position. Finally, by yesterday, both Al and Sally Yannuzzi of my team confirmed that male ownership had passed from the 14 year-old male hatched on Alva Lake who had resided on the lake for most of the past decade to a 9 year-old upstart from Harrison Lake in Lincoln County. The new male, confident in his new position, spent much of the morning resting and foraging near the nest, while the female patiently sat on the eggs. Finally, the female slid off of the nest into the water, revealing a newly hatched chick and second egg, which was on the brink of hatching. Alas, the new male behaved as animals typically do when confronted with helpless young that are not their genetic offspring: he quickly pecked the chick to death as its mother looked on helplessly. The celebration of an unexpected hatch gave way to a wake for a young loon doomed by territorial usurpation. Al took this photo of the female, still mildly protective of her nest containing the dead and unhatched chicks. (Shortly after the photo was taken, the female left the nest to forage with her new mate, with whom she might still renest.) IMG_20140616_134217_724Sorry for the unpleasant photo and description. But there is a valuable lesson here. Loons, like lions and langurs and mice and water bugs, behave so as to promote their own reproduction. Despite the ugliness of this episode, we can hardly hold it against the 9 year-old that he is looking to produce his own biological offspring — before a new usurper comes along and shows him the exit.

Dozens of territorial pairs in our study area are now on nests. Several pairs have failed. Early indications are that failures this year will be caused mainly by predation. Raccoons are the most frequent culprit, according to work done by the DNR in our region using nest cameras. In spite of the havoc wreaked by raccoons, we still hope for a high rate of hatch.

Territorial visitors are a common sight on breeding territories these days. They will become increasingly common as the season wears on. Many lake residents wonder who these territorial intruders are and what they are doing. These loons are not, as many folks surmise, chicks that have matured and are returning to visit their parents. They are true territorial intruders — individuals that are young and have never possessed a territory or are older and had one but were booted off of it by another loon. Intruders intrude to learn about the territory and its defenders, primarily because they hope to usurp the territory by force on this or a subsequent visit.

One interesting pattern that we have seen in the last few years among intruders is a higher rate of long-distance intruders. For example, On Big Carr Lake a few days ago, we saw a female from Moon Lake in Vilas County. This is a bird banded by my collaborator, Mike Meyer of the DNR. More recently I identified a 5 year-old intruder from Powell Marsh: again, this was a DNR-banded bird from up in Vilas County. Of course, we value every banded intruder, as each gives us an opportunity to track a loon’s movements and the strategy it uses to gain a breeding slot. But the long-distance intruders are especially valuable, because they are chiefly females, which disperse much longer distances than males, on average, and which, therefore, we have learned less about.