Many scientific journals are trying to add some color. That is, amidst the dry, highly-condensed scientific analysis and interpretation that is their standard fare, they are sprinkling lively photos and vignettes. These science tidbits vary from one journal to another in form and length. But all are much easier — and more fun — to look at than run-of-the-mill scientific articles.
In the past decade, I had observed the increasing frequency of short, splashy stories from a safe distance. Now that I have got scientific writing figured out, why should I diverge from it? (Okay….this blog is a dramatic departure from scientific writing, but I have settled into a good groove, so I do not count it!) In mulling over the possibility of a little splashy piece, I was not sure: 1) what I might write up as a colorful little story, 2) whether such vignettes are likely to be read widely, and 3) how hard it would be to get one published. So for many years I made no effort to report a loon finding in this new format.
The hypothesis of “spotlighting” by loon parents with chicks changed my mind. Having stumbled upon Frontiers in Ecologyand the Environment and read a few of their delightful little photos and attached stories, I thought: “Well, I could do one of those!” I was encouraged by the fact that my current “hot” idea, the spotlighting hypothesis, is perhaps the most exciting one I have ever had. When I made statistical findings that provided strong support for the hypothesis, I was just bursting to share them with other scientists.
Sad to say, sharing of a finding or hypothesis in the form of an “Ecopic”, as Frontiers calls their little photos/stories, is not a thorough and rigorous means of sharing. 250 words is simply too few to provide evidence in support of any idea. If you are a cynic, you might even claim that Ecopics and their ilk allow scientists to get their half-baked ideas out there without thorough scrutiny by their peers. Please take my word for it when I say that rigorous testing of the spotlighting hypothesis is very much on my mind!
I often thank my lucky stars that I am a field biologist. Being outdoors, especially in Wisconsin, is a huge perk of my profession. There is something thrilling about being in a situation where nothing is planned and anything can happen. Yet as glorious as it is to be outdoors, field work is perilous. Although I might tell the National Science Foundation, or Chapman, or the U. S. Geological Survey (who provide leg bands) that I have much of loon behavior figured out — that I have systematically tested all hypotheses and eliminated all plausible alternatives — I never feel confident when I am watching loons. They invariably surprise you by doing something that defies explanation. “What does that adult have to gain from wailing so often and so loudly when there is no other loon nearby to hear it?” or “Why is that loon wasting time alarm calling at the harmless muskrat?”. Rarely does a day in the field go by when I do not scratch my head at least once at inexplicable loon behavior.
Paradoxically, the best place to be when you are trying to figure out why animals behave as they do might be in your office, crunching the numbers, without any animals in sight. Free of distractions and laser-focused on the data, sometimes you discover a pattern that gives you a clear answer to a central question.
That happened to me yesterday. I was puzzling over a weird finding. In the midst of analyzing patterns in territorial intrusion, I was surprised to learn that territorial loons intrude more often into neighboring territories with chicks than do young, non-territorial floaters that are looking to settle on a territory. How on Earth could this be so? Floaters are young adults that are on the prowl. They search widely for territories with chicks, use those chicks as a badge indicating a good territory, and then return to try and evict a pair member in order to seize the territory for themselves. So it is floaters, not territory holders, that should be obsessed with finding, visiting, and competing for territories with chicks. Territory holders should have as their priority simply holding onto the territory they already own.
I must point out here that intrusions into territories with chicks, regardless of which loons make them, are generally a bad idea. As many of you have seen, territorial loons do not appreciate landings or close approach by intruders when they have chicks to protect and are much more apt to attack intruders at such times. This fact only thickens the plot. Now we must try to understand why a territory owner — a loon with something valuable to lose — would take a chance at being injured by visiting a nearby territory with a super-aggressive owner!
Lacking any other obvious path forward, I dove even more deeply into the curious tendency of territorial loons to seek out neighbors with chicks. Late in the breeding season, territory owners can be partitioned into two groups: those with chicks and those without. So I could look to see if, as one might predict, territory owners that had failed to raise chicks — and who therefore might be looking to trade up to a better territory — were those most likely to intrude. But quite the opposite was true. Territory owners rearing chicks of their own were much more likely to intrude at neighboring lakes with chicks than were territory owners that had no chicks.
As it happened, I discovered this last vexing pattern late in the day and could not dwell upon it. At 2:32 a.m. — during that inevitable hourlong period of sleeplessness that comes each night — I figured it out. While successful rearing of chicks is the ultimate goal of an adult loon’s life, chicks pose a great hazard too. To a floater, a territory owner’s chicks signify a high-quality territory, and so chicks raised in one year guarantee the owner will spend the next year fending off eviction attempts from floaters. It follows that owners should take any and all steps they can to keep floaters from learning about their chicks. Simply decamping and leaving your chicks alone during early morning is a good strategy, because floaters learn about chicks chiefly after spotting their conspicuous parents on the water and landing near them. If you are not on your territory, then no floater is likely to find your hidden chicks. But being away from your own territory and also intruding into your neighbor’s territory is doubly beneficial for a loon with chicks, because your presence will draw other adults to the neighbor’s territory (and away from your own territory nearby) and increase the likelihood that your neighbor’s chicks will be the ones that are spotted. That is to say, neighboring pairs with chicks seem to be locked in a desperate, reciprocal effort to expose each other’s chicks to floaters in order to protect their own territory ownership.
As I write this, I am listening to the hideous whine of a circular saw next door. Our own neighbors have contracted with the loudest and most inefficient construction crew west of the Mississippi to renovate their home. I find the noise, the clutter, the truck traffic, and the ceaseless cursing and shouting tiresome, to say the least. But I am fairly confident that our neighbors are not conspiring with outside forces to get us evicted. So I guess we have it pretty good.
Sometimes, as a scientist, I get tunnel vision. I get so locked-in while running statistical tests to verify simple behavioral patterns that I cannot see beyond those patterns.
This past week, I got another illustration of the problem. I was asking a basic question: “Do territorial loons show stronger territory defense when they have chicks than at other times?”. We might expect such a pattern for two reasons: 1) young chicks are sometimes killed by “rogue” intruders, and 2) intruders learn that a territory is of high quality — and possibly worth fighting for later — from seeing a chick or chicks in it; so territorial pairs should hide their chicks from intruders. As stated, this question is binary; I am just asking if the chick-rearing phase is characterized by more intense territorial behavior than other phases of the breeding cycle (like the pre-nesting and and incubation periods). And there is nothing unsound about asking that question. It is just a bit narrow.
I didn’t see the limitations of the question until I plotted the data on territorial defense against stage of the breeding cycle. Here are those data.
At first glance, I suppose, the graph looks a little busy. “Why did he have to plot TWO lines on a single graph?”, you might ask. My goal was to allow the viewer to compare two kinds of territorial behavior towards intruders at once: 1) territorial yodels by males and 2) outright attacks of intruders and other forms of physical aggression — and to look at how those behaviors vary throughout the breeding cycle. The graph allows us to see not merely how territory defense varies when territory owners have chicks or do not have them, but how territory defense changes throughout the breeding season — from 20 days before the eggs hatch to 50 days after.
What do we see? Whereas the statistical analysis I did simply told me that both yodels and aggression are more likely during chick-rearing than at other times, the graph paints a more nuanced picture. First, we see that yodels spike sharply at hatching and are rather infrequent at other times (red line). That is, males yodel with surgical precision during the period when their chicks are less than two weeks old and seldom at any other time. In contrast, aggression (blue line) by male and female parents peaks much later — when chicks are three to six weeks old. In short, territorial pairs seem to employ yodels and aggression for different purposes.
Here is my interpretation. As a grad student of mine showed experimentally, yodels are effective tools for discouraging landing by intruders that have entered the airspace above a territory. By yodelling, a male can cause an intruder bent on making a territorial visit to change its mind and visit elsewhere. Frequent yodels by males with tiny chicks, then, keep intruders away from chicks when they are small and most vulnerable to being killed by territorial intruders. But if intruders are so dangerous to young chicks, shouldn’t territorial aggression also be very frequent at this time? No, it should not. Yodels are so effective at driving intruders away at this time that few intruders approach pairs with young chicks closely enough for aggression to be necessary! Instead, it seems, parents only need to defend their chicks with physical aggression when this critical stage has passed, fathers have stopped yodeling their heads off, and intruders are comfortable enough to land in a defended territory and engage in social behavior with territorial pairs.
As I was strutting about the house and congratulating myself for solving this small puzzle, I presented the idea to my wife. She inspected the graph and asked a very reasonable question: “Why do males stop yodelling?”. After making a mental note never to share my ideas in the future, I puzzled over my wife’s vexing but insightful observation.
Here is my tentative response. We know from Jay Mager’s work that yodels are costly. Why? Because, by yodeling, a male is telling young nonbreeders about its identity, size, and body condition. Such information might allow those young adults to decide whether or not to try to evict the male from his territory immediately, to do so at some point in the future, or never to try. So yodels betray valuable information about the yodeller that might best be hidden. In particular, a small old male that has fallen into poor condition is placing a great big target on its back by yodeling to protect his chicks. Since yodeling males keep intruders at bay — a short-term benefit — but are also giving away valuable information — a long-term cost — males should use this potent vocal weapon only in time of greatest need.
Now……that is just so much arm-waving. I have conveniently tailored my hypothesis about the laser-targeting of yodels to the observations we have made. But at least, by developing a testable hypothesis, I have laid the groundwork for future progress. One day experimental playbacks of yodels at different stages of the breeding phase — not just at the young chick stage, where they normally occur — will determine whether the hypothesis has merit. So it goes with science.
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.
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
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.
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.
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.
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.