The End of a Journey: Foothold Paper Accepted by Animal Behaviour


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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.

Loons Senesce!


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There are three main reasons why I do field research. First, I love the outdoors. While it is unpleasant and inconvenient to many, the field is my briar patch. Second, I love observing and being with animals and gain new insights by watching loons up close and not just looking at data in my office. And third — well, I enjoy looking at data in my office. Complex puzzles and contradictions concerning loon behavioral ecology often become comprehensible when I look hard the numbers and run statistical tests.

Yesterday I had one of those Eureka! moments during data analysis. For the past several months, I have been looking at factors that: cause loons to: 1) be evicted from their territories and 2) disappear from their territories (that is, die). Some months ago I shared with folks that having your mate get evicted puts you at risk for eviction yourself. That is an interesting pattern and one that I continue to explore. But yesterday, I conducted the most sensitive and powerful analysis to date on the potential impact of age on rate of eviction and death in territorial residents. The  results were clear: age has a substantial impact on both eviction and death rates. Specifically, old loons are at risk for being booted off of their territories and they are even more strongly at risk for dying. The pattern was a bit tricky to detect, because very young adults are also at risk for eviction and death. So loons — like humans — have a “prime of life”. Loons of 4 to 6 years of age are still developing and improving in condition; at this age, they have a rather high rate of eviction and death. They reach prime condition about age 7 or 8 and remain in good condition until about 20, then condition falls off again, exposing them anew to a high rate of eviction and death.

The figure above shows the shape of the pattern with respect to age and death rate, when other factors are controlled. Sorry for the arcane title of the Y axis, but here is how to interpret the pattern. The curve shows how often territorial loons die, higher values indicating a higher death rate. The values are higher for young ages and old ages. Thus, the “U” shape shows that young and old loons die at a higher rate than do loons of moderate age. If you look closely, you can see that old age has a much stronger, more consistent impact on mortality than does young age. So senescence is very clear from the graph.

If you are a loon aficionado, you know that male loons often die in the course of defending their territories, while females rarely do so. How does the new finding of senescence fit in with lethal contests among males? On the one hand, it fits, because senescence might make male loons “desperadoes”, who fight hard for their territories because they have no future to lose. On the other hand, the pattern of senescence cannot by itself explain male-only fatal battles, because females and males both senesce. Oh well….I am always looking for another excuse to look at data in my office.

A Last Rendezvous Before Winter


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LMG_3139 Clune n Honey Return


As this beautiful photo by Linda Grenzer makes clear, time is passing. Chicks have matured and left their natal lakes, territorial pairs have scattered. Juveniles and adults alike are preparing to head south. Most obvious to loon watchers, adults have shed their striking breeding plumage and donned dowdy winter garb.

Although we might mourn the significant loss of beauty that occurs among loons in the fall, molting is a pragmatic biological pattern. Feathers wear out with time and use, requiring replacement, so seasonal molting of some kind is essential to survival. But why do loons lose the white wing spots, the necklace and chinstrap, and the elegant black head? As usual, the answer is that we cannot be certain without experimental investigation. However, these prominent features of the plumage signal readiness to defend a territory and to breed. Hence, they are inappropriate and possibly costly signals to send during the autumn. An adult that maintained breeding plumage during the fall might attract the attention of others and trigger territorial interactions at a time when it should be feeding vigorously in preparation for migration. Moreover, the contrasting breeding plumage would probably make a loon more conspicuous to predators such as sharks, which could be costly during a long winter on the ocean.

The two loons in Linda’s photo are her breeding male and female — and two of our best-known individuals. They appear often in her photos, such as when 5 intruders came to call and when they refused to abandon their nest, despite merciless black flies. After all they had been through this year, it was a surprise to see the male (Linda calls him “Clune”) and the female (“Honey”) spend a short time together on the brink of fall migration, long after most pairs had dispersed. I find this photo poignant somehow. I suppose it symbolizes to me this pair’s unwavering unified front in the face of all challenges and changes that confront them.

An Inseparable Pair


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With the first snowfall in the offing and adults and chicks feeding voraciously to steel themselves for migration, an odd and touching event has occurred. We have been able to track the local movements of a pair from their breeding lake to other lakes in the study area. This is not a traditional pair of male and female, but a father and his son who have remained together for an unusual stretch. Hatched on July 1st, the Fawn chick was attended closely by his father from the start. When his mother swallowed a fishing lure and anglers cut the line, leaving her trailing yards of monofilament, she abandoned her mate and offspring for several days to recover. Still his dad remained with the chick and increased his feedings to make up for the absence. (The female survived the ordeal and returned to Fawn Lake afterwards to resume parenting.) Dad continued to feed his son assiduously as he grew, matured and began to take flight. Two weeks ago, however, Fawn Lake was empty of loons. The sharp-eyed residents of Lumen Lake, right next door and almost touching Fawn, reported the sudden appearance of an adult loon and chick that turned out to be the missing father and son from Fawn. The two remained on Lumen for a week or so but then disappeared again. Judith Bloom, who for years has monitored several breeding pairs on huge Lake Tomahawk, e-mailed on Thursday to report that she had found (and ID’d!) an adult and chick feeding in a bay near her home that were not from any territory on Tomahawk (see Judith’s photos). Sure enough, the Fawn father and son had made another appearance in foreign waters. BloomTomahawkFawnMandck4 BloomTomahawkFawnMandck6

Now, it does happen that parents continue to feed their chicks at 13+ weeks of age.  What is unusual is that a parent-offspring pair has remained together on not just one shift to a foreign lake, but two shifts. Moreover, the second shift was a whopper, as the duo flew about 6 miles together to land on Lake Tomahawk. While it is tempting to view this event as a reflection of the trend that is becoming routine in human society — offspring remaining with their parents well beyond the normal age of independence — it might warrant scientific scrutiny. In fact, such “fawning” behavior by a father towards his son makes sense evolutionarily, providing Dad has improved his son’s chances of surviving migration and its first winter while still maintaining his own health. In three to five years, when this chick stands to reach adulthood, we will see if the father’s tireless investment paid off.

Chicks Take Wing


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LMG_2826 Three Month Old Chick Wing Span

I just got a report from Kristin, who is still in the study area. The chick hatched and reared on little Buck Lake popped over to Crescent Lake for a visit. Kristin was excited, because she had seen many cases of juveniles flapping their wings and practicing takeoffs, but this was the first flight of a juvenile she had recorded to a nearby lake. Thus begins the phase of juvenile wandering that characterizes the fall months. If this year proves typical, trips of maturing juveniles to neighboring lakes — sometimes up to 10-15 miles from their natal lake — will abound in the next 9 to 10 weeks.

But why do juveniles abandon the comforts and familiarity of their home lake to venture to lakes unknown? This is a difficult question with many possible answers. First, let’s think about the downside of such movements. In deserting its natal lake, a juvenile will be faced with new food sources to which it will have to adjust. Since it must feed itself and mature rapidly to put on weight for fall migration, leaving home seems a gamble. A new lake will also contain new risks in the form of predators or aggressive territory holders (although aggression is generally low in the fall, to be sure).

In order for wandering to new lakes to be a sound behavioral strategy, we would expect there to be advantages that more than offset these risks. One can imagine a number of potential benefits to shifting to a new lake. In the case of the Buck juvenile observed by Kristin, the bird was moving from a small lake with limited food resources to a much larger lake with a more abundant prey base. So the short-term benefit of being able to capture more food and put on weight for migration might be a large part of the explanation. Catching and consuming new food items might pay benefits down the road for young loons, as well, as this forces them to practice new modes of foraging that might be useful during migration and winter, when they will be faced with vastly different prey.

LMG_2823 Three Month Old Chick

There is a third and more nebulous hypothesis that might explain wandering by juveniles in fall. Three to four month-old individuals might be laying the groundwork for their lives as adults by exposing themselves to many different lakes and learning which are most suitable for them. That is, juveniles might try out lakes of different sizes and shapes containing different fish and invertebrates as a means of finding out what sort of lake allows them to feed most efficiently. If so, this period of exploration might allow them to target lakes more effectively when they return to northern Wisconsin (as they do) to look for a breeding territory in 2 to 5 years. It is even possible that young loons — especially males, which often settle to breed within a few short miles of their natal lake — move from lake to lake in order to create an internal map of the local area, which they will use in a few years when they return in adult plumage and seek a breeding territory.

Like many behavioral hypotheses concerning free-living animals, these 4 hypotheses for fall wandering are vexing to test. But they are not wholly untestable. For example, if juveniles simply move for better foraging, those that move should have higher masses in the fall than those that remain on their natal lakes. And if shifting between lakes prepares juveniles for foraging during migration and winter, frequent-shifting juveniles should enjoy higher survival than infrequent shifters. Even the hypothesis that juveniles begin to map out the local area for their later use can be tested to a degree, as it predicts more rapid settlement by frequent lake-shifters than infrequent ones. So we may, in time, begin to understand juvenile shifting. (This will come as a great relief to Kristin, no doubt, as she is braving the cool, rainy weather to document lake shifts by juveniles that we banded in July and early August.)

As I have noted before, the more immediate reason for tracking local movements of young juveniles has to do with learning about the development of natal-site matching behavior that we found recently. (Natal-site matching refers to the striking tendency of young loons to settle as adults on lakes that are similar in size and water chemistry to their natal lake.) We are curious to see whether loons show preferences for natal-like lakes even in their juvenile movements. If so, short trips during the fall to natal-like lakes will, of course, reinforce natal-site matching and yield young adults that have very strong natal preferences indeed!

Thanks, as so many times before, to Linda Grenzer, who provided these nice shots of the 2014 chicks on her lake. Although it is bittersweet for her, Linda hopes that these two juvies will soon themselves fly off to nearby lakes to gain valuable experience — or maybe just weight — that will prepare them for migration and beyond.


Pondering Tameness


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Since the inception of the study, we have known that some adult loons permit a canoeist to approach to within 5 meters without alarm, while others become uneasy and dive at a distance of 30 meters or more. Over the past several years, we have worked hard to quantify such variability in “tameness”. Our efforts are motivated by the belief that — in a region well-known for human recreation — tameness must matter. That is, it seems inconceivable that loons’ survival rate and reproductive success are not impacted by the way they respond to humans.

At first blush, I would expect loons to have higher fitness (i.e. be able to survive and breed more successfully) if their tameness reflects the lake they inhabit. That is, loons that are very tame should fare well on lakes where humans are numerous and often approach loons closely. A skittish loon on a lake with abundant human traffic would spend a great deal of time and energy avoiding humans and might have to spend more time foraging to compensate for the extra energy expenditure. A skittish individual on a busy lake might even become distracted by humans and pay too little attention to eagles, which occasionally attack adult loons and often attack chicks. On the other hand, shyness towards humans should have no impact on fitness if it occurs in a loon that occupies a remote lake.

Tameness is surprisingly vexing to measure. While it is easy to see that loons vary in approachability by canoe, it is another matter to assign a number to the degree of approachability they show. One obstacle to measurement is simply that of measuring distances accurately across water. Another is the problem that we seek to know exactly at what approach distance a loon dives to avoid a canoe; once this critical distance has been reached, the loon has left only its wake on the lake’s surface for us to measure! After numerous trials, however, Seth Yund, a Chapman student, and I have found a technique that seems to work that requires use of a highly accurate laser rangefinder — and a lot of patience. In July we began to collect measurements on each banded loon in our study population, and this work will continue into the fall and in future years. (By the way, the technique requires paddling slowly in a canoe towards a resting loon until it dives, while taking constant measurements. Since the process must only be carried out once or twice per loon, it involves very mild disturbance. We have found that loons quickly resume normal behavior after we take a tameness measurement.)

It will be some months before we begin to see if our quantification of tameness is stable and consistent enough to constitute a useful behavioral measure. At that point, we can begin to test our preliminary hypothesis that a loon’s tameness should be correlated with amount of human usage on its lake. Since we have many parent-offspring pairs in the population and follow individuals throughout their lives, we can envision asking questions about the heritability of tameness and its constancy over time. We hope that tameness will become a rewarding topic of research for us. Perhaps our ability to quantify this behavioral characteristic will permit us to foresee negative impacts that increasing human-loon contact will have on our population and help recommend ways to minimize such impacts.

What We Know, and Don’t Know, about Territorial Intrusions


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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.


A Bit of Cheer amidst the Gloom


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By any reasonable measure, 2014 has been a dreadful year for loon reproduction. Even if we capture every remaining loon chick that we know of, our total number banded will be almost exactly half of last year’s total. Clearly, the black flies hit the loons’ breeding efforts in the mouth, and they could not recover. Still, it is only one year. As my work has shown me over the past two decades, breeding success is a roller-coaster. In fact, if you combine last year’s bumper crop of chicks with the withered output of this year, the message is that loons are producing enough chicks to sustain the population. So all is not lost.

There have been a few bright spots this year. Though we were alarmed in early June when the Jersey City Flowage male ingested a fishing lure and became hopelessly entangled, the folks at REGI were able to save the bird, he was released near his old territory and recovered — except for possession of his territory! The REGI folks were brought an emaciated chick found by a roadside that they fed back to reasonable health and that we were able to foster successfully to a loon family that has raised it as their own. We recently banded both this fostered chick and its sibling, a true biological chick of the pair. Both chicks have become big healthy, strapping young birds, thanks to their parents’ tireless efforts.

In short, life goes on. I am confident that we will long remember 2014 and not wish to repeat the experience. But perhaps we should best remember 2014 as a year that, while dismal for chick production, was balanced out by strong reproductive years surrounding it and did not pass by without a few cheerful tidings.

Former Male Breeder on Jersey City Flowage is Back in the Game!


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Good news has been scarce this year. Black flies snuffed out first nesting attempts by virtually all breeding pairs and will reduce chick production by about 40%, compared to last year. One of the few pairs to continue incubating in defiance of the flies hatched chicks, only to lose them to infanticide when a new young male evicted the male breeder. And one of our most consistent chick producers and well-loved birds, the 19 year-old male on Jersey City Flowage, barely survived severe entanglement in fishing line that caused him to lose 20% of his body weight.

A few days ago, we received a bit of good news. The Jersey City Flowage male, after surgery and rehab work done by the folks at REGI and release near his original territory, has not only shown the capacity to feed himself normally, but has re-paired with a female hatched on Fisher Lake in Vilas County in 2010. This May-December pair seems settled at the north end of Jersey City Flowage, according to Linda Grenzer. Now, whatever judgements we are tempted to make about the age disparity in this relationship, it is nice to see the old male get himself back in shape and ready to give life another try.

The Lasting Impact of Black Flies


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black fly impact


Since 2014 marked by far the most intense explosion of black flies in recent memory, I wanted to look at how loons are faring reproductively this year compared to last. It has now been over a month since the peak of “black fly season”, which was miserable for loons but lasted only about a week. Yet the flies were thick enough and their outbreak coincided so closely with the start of incubation for most pairs that about 70% of all loon pairs in our population abandoned their nests.

It seemed certain that the epic abandonment of early nests in 2014 would negatively impact the number of chicks produced by our population. And it has. Based on my analysis of 96 territories covered in 2013 and 2014, I have the following results. Last year, 41 pairs  had hatched chicks by 30 June, while 14 had nests close to hatching, 10 had early nests whose outcome was uncertain, 21 pairs had failed for the year, and 10 pairs had never nested (to our knowledge). In 2014, the numbers were 6 chicks, 30 promising nests, 15 early nests, 21 failed pairs, and 14 pairs without no nest during the season.

The disparity in chicks produced is alarming, of course. This is the most important number. The picture gets a bit rosier when you crunch the numbers and recognize that many pairs currently on nests will eventually hatch chicks. Based on an assumption of 70% hatch rate among pairs in the “likely hatch” group and 40% in the early nest stage — perhaps slightly optimistic — the total estimated chicks produced in 2013 and 2014 are 54.8 and 33.0, respectively. To put it another way, about 57% of all pairs reared chicks in 2013; 34% will in 2014. This is a decline of 40% in the number of territorial pairs producing chicks.

Now, we need to step back here. Loons are long-lived animals, and most pairs that failed to raise chicks, owing in large part to black flies, will try again next year. So, in the big picture, the decrease in rate of chick production is not so awful. In a few more years, we will look back on 2014 as just a worse-than-average year for loon chicks, not a year that threatened to end loon life as we know it. But it is hard to be very upbeat at the moment.


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