Caught up as I am in the mad scramble that teachers and students face at the end of the school year, I have been unable to keep up with events unfolding in the study area. I am sorry about that. Of course……I am also not in the study area, so I have to rely upon accounts of loon activity from Linda and others who are able to see the birds!
The loons in northern Wisconsin seem oblivious to the pandemic that is plaguing humans at the moment. They have their own problems to worry about: other loons, eagles, and their early-season nemesis, Simulium annulus. During the past week or so, populations of this black fly have exploded, causing headaches for loons across the study area. (Thanks to Greg and Al for their reports of fly activity on their lakes.)
You might wonder why I use the scientific name of the species of fly that harasses loons. When humans are pestered by insects, we often think of the little varmints generically. That is, we place biting insects into classes that represent several or dozens of species — mosquitoes, black flies, horseflies, no-see-ums. Our crude classification scheme makes sense, because the behaviors of different species, the habitats where we find them, the timing of their attacks, and our strategies for eluding them are often similar across species. But loons face a laser-focused attack by females of one species of black fly whose sole purpose in life is to find a loon, extract a blood meal, and nourish their eggs with it. I loved this photo that Linda sent me
several days ago, because it illustrates two intriguing biological patterns. On the one hand, Simulium annulus makes life a living hell for loons for a few weeks every spring, as one can see from the cloud of flies on and around the head of the male loon in the water. (This bird is trying to work up the gumption to get back on the eggs.) On the other hand, S. annulus leaves all other birds alone, even those in plain view a few meters away (note the carefree Canada Goose standing on the island in the upper left corner).
It has been a rather cool spring in northern Wisconsin, and that is bad news for loons, as cool weather keeps female S. annulus alive longer than usual and prolongs the window during which they harass incubating loons. Reports so far suggest that there will be widespread abandonments of first nesting attempts, although some breeding pairs — like Linda’s intrepid duo, Clune and Honey — are so far enduring the welts and refusing to give up on their eggs. The coming weeks will tell us whether 2020 is a horrendous year for black flies, like 2014; a bad one, like last year; or an average one, like 2018. It pains me to say it, folks, but we are hoping to be average!
Let me end on an up note — well….kind of an up note. Our paper that reports reduced chick production, lower survival of young adult loons, and a decline in our study population has been well-received by a scientific journal. Thanks to everyone who helped with the decades of data collection that culminated in these findings and to our many supporters (including many who follow this blog) who made our work possible. During this year and the next few, we hope to learn what is causing these declines and to see if we can do something about them.
I just read a story about an Arctic research team that has been hamstrung by the pandemic. They are trapped in quarantine in northern Germany, awaiting the all-clear before they can conduct their crucial research on the melting patterns in polar ice. Their vigil is especially tense, because rising spring temperatures are likely to set in motion the very melting patterns they spend all year planning and waiting for before they can reach the Arctic to document them.
Although their situation is more dire and their mission more vital than my own, I know how these scientists feel. Recently, we too had to scale back our research efforts owing to the pandemic by abandoning plans for a thorough early-season census. Meanwhile, the virus-free loons have returned to their territories and are going about their nesting preparation, as they always do. They must be wondering where the inquisitive humans in their red canoes have gone.
Our field effort is not at a complete standstill. In fact, Linda has heroically visited dozens of lakes in the southern portion of our study area to ID returning pair members. She is perfecting the art of recording loon bands while keeping one eye on her grandkids! And Al and Nigel have patiently documented the male and female returnees on West Horsehead and Sherry, respectively.
Reports of loon activity of any kind are invaluable to us. Please send notes, photos, and any other records you might have of loons on our study lakes. These reports might be very basic, like: “I saw no loons on my lake until May 6th, and now there is only a loner.” or “There is a breeding pair on my lake, and I have seen them multiple times since ice-out”. A report might include a smidge of info on identity like “There is a regular pair on my lake; our neighbor spotted a red band on the left leg of one of them, when it preened”. And a few over-achievers might get very detailed information, like: “A loon pair was first spotted on April 26th. The male’s bands are copper over green on right and red over silver on left; the female is silver over blue on right, green over mint burgundy on left. They have a nest that we first noticed on May 8th on the south side of the island off the boat landing; GPS coordinates are N45.70063, W089.62474. The male engaged in a lengthy battle with an unbanded intruder on April 26th, during which he lost some feathers just behind his right eye.” Anyway….any loon-related info that you send us from our study lakes is greatly appreciated, because we have no data at all from 80% of them. Photos are tremendously valuable too, especially if they show a colored leg band or two that we can use to ID an individual. The earliest most of the team can possibly arrive in Wisconsin is May 27th. Thanks for any info and photos you can send to me at email@example.com to help us fill in the gap in our records.
Stuck in southern California as I am, I have become fixated on the changing seasons in Wisconsin. Although recent days have been wintry in Oneida County, typical May conditions are a few scant days away. Nesting has already begun; Linda’s breeding pair shrugged off some early territorial excitement and are now sitting on eggs — while all of our team members except Linda are sitting in lockdown.
Yet there is great hope for the research team this year, once the virus releases us from its clutches. Following decisions yesterday by my daughter and a friend of hers from college to devote their summers to helping with our research, we now have four new recruits to the project, two postdoctoral fellows from Chapman, and yours truly — seven researchers in all. This is an embarrassment of riches, because we now face the dilemma of how to equip and house all of these folks.
This brings me to the burning reason for my post. Please let me know if you might have space where some of the team can stay. While we have comfortable housing for a team of 3 or 4, thanks to the continuing generosity of friends of the Project, we have now outgrown it, and need to add additional housing (near Rhinelander, if possible). Secondly — in keeping with our lean research model, which maximizes lake coverage — we need 2 to 3 more vehicles so that each team member can visit lakes on their own. (I have recently learned the good news and bad news about renting cars for 21 to 24 year-olds: the good news is that it can be done; the bad is that it costs twice the normal rate, so that no one in their right mind would do it!) I would happily commit to: 1) paying a fee for the use of a vehicle from about 7 June to 31 July, 2) maintaining any loaner that folks might provide in good condition throughout the summer, and 3) repairing any damage to such a vehicle that might occur during our research effort. Please contact me at firstname.lastname@example.org, if you can help with housing, vehicles, or both.
Meanwhile, we continue our social distancing. Each passing sunset reminds me that time is marching on and that the loons are going on with their lives, despite our absence. Like the international crew in Germany, I wonder when on Earth I will be able to get back to my life’s work.
Identifying a loon from its colored leg bands is an incremental process. Once you spot a loon on a lake and approach the bird, you must develop a seat-of-the-pants strategy for recording its bands. The ideal situation is when you observe a preening loon, paddle slowly over to it, and simply wait for the bird to swing its legs up out of the water while distributing preen oil all over its feathers. One generally has at least five minutes to piece together the complete combination of four leg bands of preening birds from a quick view here or there. I talk to myself while getting bands, in hopes that I will remember what I have seen. “Yellow on top, right leg…wait….yellow over mint on right!” If the loon is not preening but foraging, identifications can take hours, and you must hope that, as you remain as close to the forager as possible, it happens to surface right next to your canoe and in good light when you happen to be looking its direction. In such cases, piecing together the bird’s band combination can be an arduous process, because one gets very quick views of bands underwater or for an instant just as the bird plunges beneath the water.
Despite diligent efforts, we often end up with only “partials” on loons’ bands during our hourlong visits to study lakes. However, since most of the loons we see are territorial birds on the lakes where we color-banded them, partials are often good enough to tell us the identity of the bird. Then again, sometimes — especially early in the year — we get surprised by a loon that was not banded on the lake where it is spotted.
Imagine what Linda must have experienced on Halfmoon Lake yesterday. After spotting a lone bird, Linda was expecting that it would be one of the two banded pair members from Halfmoon. She was no doubt pleased to see that the loner was preening, which gave her hope that she could nail its bands before it resumed foraging. Was this bird going to turn out to be “Grandma”, the female originally banded fourteen years ago on Muskellunge Lake, who had earned her name when she intruded onto Crystal Lake in 2015 at the time her son was rearing her grandchild? Or would the preener prove to be the rather skittish male from Halfmoon, which we had finally caught and placed bands on last July? As Linda’s crisp photo shows, the preener was “Yellow over Mint, Silver over Red-stripe” — neither Grandma nor her evasive mate.
Linda knows this surprise visitor to Halfmoon better than anyone. You see, Yellow over Mint is “Mabel”, the female that has been a regular intruder into Linda’s lake since 2011. Years after Linda and our team had begun reporting Mabel as an intruder on our lakes, we expanded the study area to include Mable Lake and learned that Mabel was not a roving nonbreeder but the breeding female there. Mable is a tiny 25 acre lake near Tomahawk. With food so limited by the size of the lake, Mabel and her unbanded mate have struggled reproductively. Twice in the past three years the pair has hatched a chick but lost it at six to seven weeks of age — just on the brink of fledging.
Mabel’s breeding woes pale in comparison to the nightmare that befell her in 2019. As I described in a post last summer, Mabel swallowed someone’s fishing line on about June 20th of last year, was incapacitated by lead toxicosis, and only survived owing to Raptor Education Group’s heroic emergency surgery and extensive efforts at treatment and rehabilitation. Rescuing Mabel from lead sinkers was only half the battle. Although the REGI team had done what they could to feed her and get her fit for release, it was far from certain that she would be able to recover sufficiently to survive in the wild. In fact, we lost track of her after she was let go last July on Lake Alice. We simply hoped for the best, knowing full well that few loons survive a severe bout of lead poisoning.
Yet there Mabel was yesterday, looking (according to Linda) none the worse for wear. Indeed, having survived two migrations since her debacle, she has clearly returned to form. Mabel is still not back to her former status; she has lost her territory and joined the ranks of the many displaced female breeders who wait — often for years — for breeding vacancies to occur. But just surviving long enough to join that queue is a huge victory for Mabel — and for those of us who dared to hope that she could come back.
When you live on a lake with loons, you grow attached to them. You feel a sense of ownership and responsibility. You share in their failures and successes. If you are a real loon aficionado, your view of the entire summer can depend upon how your loons fare. When they are sitting on eggs, you are nervous and protective. When they hatch a chick or two, you are excited and hopeful. When the chicks mature and begin to fly, you look back at a job well done. And, of course, if they should lose a nest or — worse still — a chick, you are bitterly disappointed.
Those of us who visit 100+ study lakes live in a different world. Like lake-dwellers, we mourn lost nests and chicks — and we too are devastated by adult loons that are injured or killed during the summer, especially those we have come to know well over a decade or more. But we do not have all of our hopes riding on a single lake.Our disappointment at the failure or loss of loons on one lake is tempered by the success of a different breeding pair on the next lake we visit. Even during a truly dreadful year for breeding — like 2019 or 2011 — there are always a few breeding pairs that beat the odds to produce young on lakes where we thought they never would.
Despite being buffered somewhat from mood swings by our tendency to flit about from lake to lake, those of us who cover the study area do form attachments to certain loons. In fact, I was almost as alarmed as Linda when she told me last week that the first loon to return to her still mostly iced-up lake was not “Clune” — her beloved, 22-year-old banded male — but instead the banded male from neighboring Deer Lake. Things went from bad to worse the following day when “Honey”, the resident female, returned and quickly paired up with the interloper (as seen in Linda’s photo).
I have known Clune since he was a chick. He and his sibling and parents were almost comically tame back on July 22, 1998, when I visited them on Manson Lake. As always, I tried to keep my distance from the family on that day, while collecting behavioral data. Once, though, the foraging parents happened to surface on one side of my canoe, while the chicks surfaced on the other and only a few meters away. While I paddled as quickly as I could to escape that unfortunate situation, neither parents nor chicks called out nor showed the slightest degree of alarm. As an adult, Clune has been every bit as tolerant of humans as he was when young. So it is easy to understand how he has long been the favorite loon of the Loon Project team.
Clune made us sweat for two more days before returning, on April 10th, to reclaim his territory and drive off the male from Deer Lake. Now, it seems, things have returned to normal.
What of the Deer Lake male, you ask? His effort to “trade up” by seizing Clune’s highly productive territory has been thwarted. After five consecutive years of breeding frustration on Deer — and at least nine consecutive nesting failures — he is in an unenviable position. Will he be desperate enough in late 2020, if his luck on Deer has not turned by then, to have another go at Clune’s territory?
As I gaze vacantly out my back window, I wonder, as all of you must, when life will return to normal.
Linda Grenzer reports that our southern study lakes are on the brink of opening. Eager to occupy their territories as soon as possible, fight off pretenders seeking to supplant them, and set about the business of nesting, our breeding birds are bottlenecking on the Wisconsin River and various dammed flowages along the river’s tortuous path, she says. Their vigil will end in the next week or so. Offered even a sliver of open water in their territory, breeding pairs — sometimes the male alone, for a few days — will take possession.
We, on the other hand, are trapped at home. Three of us, Brian, Annie, and myself, are in southern California, which has never seemed so far from Wisconsin. Lyn, another new team member (along with Annie) is homebound in Ontario, Canada. As each day of lockdown passes, and as forecasters assure us the worst is still weeks away, we wait, our uneasiness mounting. Will we be allowed to travel to the study area come May? June?
It seems logical that loons should take some time to develop physically and behaviorally; after all, similar maturation occurs in humans. But what is the larger importance of loon maturation to territorial behavior? That is, how should the fact that young loons are not initially a threat to the ownership of territorial pair members affect behavioral interactions between young loons and pair members?
Maturation should shape nonbreeder behavior strongly. Not being competitive for territories, 2-, 3-, and 4-year old nonbreeders must feed themselves well, learn about the lakes in the small region where they live, and get to know the local territorial loons of their sex — which they must ultimately defeat in battle in order to claim a territory. Since they are in an information-gathering phase, youngsters should keep their heads down during territorial intrusions, signal to territory holders that they pose no threat, and hope to escape attacks from the pair that way.
What about pair members? A territorial male in the process of a breeding attempt with his mate should virtually ignore the intrusions of nonbreeding females and also young male nonbreeders, because neither threatens his ownership of the territory. (It is important to note that pair members fight and defend their breeding positions alone; males never help females stave off eviction, nor do females participate in male battles.) Likewise a territorial female should let her mate worry about nonbreeding males that visit her territory and instead focus her attention on 5- through 8-year-old females, which are strong enough to evict her. The picture becomes more complicated when a pair hatches chicks. In the presence of chicks, which are helpless and easily killed by any intruder, both male and female pair members should quickly confront and drive off intruders of any stripe.
Finally, both pair members and nonbreeders should calibrate their territorial behavior to the quality of the territory. To be specific, both groups should exhibit more intense behavioral interactions and more aggression on territories with a record of producing chicks, because those territories are worth a lot to both groups.
Thus, we have a set of predictions about how nonbreeders and breeders should behave with respect to sex and age of intruders, presence of chicks, and territory quality. I am in the midst of testing these predictions using two decades’ worth of field observations. At this stage, I have analyzed only nonbreeder behaviors. Below is the crude table I just produced that summarizes my findings to date.
I will spare you the challenge of deciphering my shorthand and tell you what I have found so far. First, we predicted that young nonbreeders would show little aggression towards territorial pair members. That is borne out by the data. The second column and second and third rows in the table show that age is positively correlated with aggressive behavior of intruders and aggressive vocalizations by male intruders (i.e. the territorial yodel). In short, young nonbreeders — 2, 3, and 4-year olds — show less aggression (lunges, chases, and other attacks) than older nonbreeders. Furthermore, the strong tendency for young nonbreeders to initiate short dives (IDs) and join dives (JDs) when circling with territorial pair members (2nd column; 7th row) suggests that these diving behaviors signal youth and lack of threat to pair members, which probably protects youngsters from being attacked by the resident pair.
We can already say a bit about my prediction that the presence of chicks should crank up the heat on territorial aggression. Intruders that visit pairs with either nests or chicks (4th column) show consistently more aggressive behavior and tense social interactions with pair members than do intruders to a territory without nest or chicks. We presume this pattern results from the heightened aggressiveness of pairs themselves, which bleeds over into their interactions with nonbreeders. I expect my ongoing analysis of pair members’ responses to intruders to reveal a similar pattern.
Finally, look at the third column, which shows very consistent results in territories that produced chicks the previous year. The “Strong positive”s here show that nonbreeders exhibit more splash dives, bill dips, circle dances, initiates dives, and joins dives when interacting with territorial pairs that reared chicks the previous year. I am still puzzling over these results (and the lack of an increase in aggression). At present, this pattern suggests that: 1) nonbreeders confront territorial pairs more often when the territory has been shown to be a chick-producing territory, and/or 2) pair members approach and interact with intruders more often when they are on a high-quality territory. In any event, the quality of a territory where pair members and intruders interact strongly affects the nature of their interactions.
We have far more data on pair members themselves than on nonbreeding intruders, so the results of that ongoing analysis are likely to be even more robust than those shown in the table. Needless to say, these findings are a vital salve for my current frustrations with the lockdown. If it extends through May, I will require quite scintillating discoveries indeed!
I sometimes dwell on the negative. In fact, those who know me well no doubt would regard that as an understatement. Strangely, I myself forget that I possess this trait. As a result, I often careen downwards over periods of days or weeks, seeing one after another of the unpleasant aspects of a certain committee I sit on, a basketball team I watch, or a politician whom I hear speak. Eventually though, my negative jag launches me into something unambiguously positive that contradicts all earlier evidence and forces me to pause and reconsider.
As Dave pointed out to me, the picture of loon breeding in other parts of the U.S. is quite a bit rosier than in northern Wisconsin. While not all of the data are reliable, there seems no question that loons are thriving in Maine, New Hampshire, Vermont, and Massachusetts, having experienced double-digit increases in adult populations in the past decade. These findings contrast sharply with Upper Midwest loon populations, which have shown little or no change. In Minnesota and Michigan, according to our latest measures, populations are merely stable. Wisconsin loon populations, while they increased greatly during the 1980s, 1990s, and even early 2000s, have been measured as stable or declining in recent years.
So the overall picture of loon populations along the southern edge of the breeding range is mixed. But things look so good for the species in New England that, even after considering the slightly negative recent trend from the Upper Midwest, we must conclude that overall the U.S. loon population is doing fairly well.
The uneven geography of loon population patterns raises an important issue. Could the burgeoning New England loon population supply young adults that settle in the Upper Midwest, breed there, and thus rescue our struggling population? No, this cannot happen, because young loons do not disperse far from their natal lakes to breed. A few of the chicks that we have marked in Wisconsin have made it to Michigan, and one or two of these thousands probably has settled in Minnesota (though we have no reports to date), but none has gone farther afield than that. The stability of the Upper Midwest loon population relies solely upon the successful reproduction of Upper Midwest adults. In other words, we are on our own.
Still, the mere fact that loons are reproducing well and expanding their population somewhere is heartening. It suggests that factors causing the decline in the loon population in Wisconsin might be local ones, not sweeping ones, like climate change. Or it might mean that factors that could lead to loon population declines — whatever those factors are — can be reversed by intense local conservation efforts, such as occur in New England states.
At any rate, I am looking at the world a bit more cheerily now, after learning about thriving loon populations in New England. With my tunnel vision always focused more on things loon than things human, there is reason for hope.
I have just finished a rough draft of a manuscript describing the population decline of loons in my study area. That effort forced me to count and calculate, estimate and project. I like math, so the work was not unpleasant. I thought that I would pause and share some of the numbers I produced. First, let me share a complex graph!
This graph shows two sets of values over an 18-year period. The blue line shows the proportion of all adults in the population that are floaters — that is, adults that lack a territory. This group includes both adults too young to have settled and old adults that have been evicted from a territory. The grey bars show the number of chicks banded in the study area three to four years before, adjusted for the number of territories covered those years. In short, the bars show how good the breeding years were in the study area three to four years before. I plotted things this way because three- and four-year-old loons make up the bulk of the new floaters each year, so by comparing the grey bar to the blue line, you can see what impact the breeding success three to four years ago had on the floating population. We expect that lots of chicks produced three to four years before will produce a surge in floater numbers. So the blue line should track the grey bars.
Okay, now let’s see what we can learn from the graph. Notice, first, that the blue line descends overall. This means that the proportion of the adult population made up of floaters declined during the past 18 years. Notice, next, that the grey bars are roughly the same height throughout the graph, which means that chick production was relatively stable over this interval. Already you should be thinking that something odd is going on. The blue line is NOT tracking the grey bars as closely as we expected. The bars and line DO track each other pretty closely at many points, however. For example, the stable chick production from 2002 to 2006 is paralleled by the stable floater population. 2008 went as we expected: good chick production 3-4 years before meant a positive bounce in the floater population. 2013 saw a loss of floaters, as we expected from low chick numbers 3-4 years before.
Now, focus on the last four years. Floater number had fallen to less than 40% of the adult population by 2015. Huge chick production from 2012 and 2013 should have “rescued” floater numbers in 2016 (caused them to spike upwards), but we only see a small bump up in floater numbers that year. And 2017 is worse as, despite big crops of 3- and 4-year-olds, there is a sharp downward turn in floater numbers! Likewise, 2019 should have seen an uptick, but floater numbers actually declined to an all-time low.
I know it is messy to look at this plot. If you find my fine-scaled analysis too picky, forget about the trees I have been discussing and look at the forest. Chick production during the past 18 years has been okay, yet consistently we see fewer floaters than we expect. This is the main puzzling finding of the paper I have written.
It is the mysterious loss of floaters, in fact, that seems to imperil the population of Oneida County loons. We estimate that there are about half as many floaters now as in the late 1990s and that the entire adult population has fallen by 22%. We do not know what is happening to the missing floaters — whether they are dying in their first fall, on migration, or perhaps during winter. But those floaters, which are future breeders, will have to stage a comeback to get the population back on track.
Having read that northern Wisconsin loons are reproducing poorly and returning to the breeding grounds in very low numbers, many of you are probably wondering, “How widespread is the problem?”. Alas, most efforts to mark and monitor loon populations in other parts of the Upper Midwest have been fragmentary, short-term, and limited in scope. Lacking longitudinal data from other studies of marked individuals — the only kind of data that will permit a reliable assessment — we cannot say whether other populations in the Upper Midwest have experienced the same downturn as our study population.
Two points are worth making here. First, the loons that we study in Oneida County do not exist in an isolated pocket. Rather, they are part of a continuous swath of loons that stretches from central Wisconsin to the Great Lakes, and northwards across most of Canada. Moreover, loons exhibit the sex-specific natal dispersal pattern characteristic of birds generally: males settle to breed close to where they were hatched and reared; females disperse much greater distances. So the female breeder on your lake is likely to be tens or even hundreds of miles from where she grew up, like the current female from Two Sisters Lake, who was reared on Crab Lake in Vilas County, or the female on Manson, who grew up on Rock Lake, also in Vilas County — or the female that dispersed over 200 miles east and wound up in Antrim County, Michigan. Hence, the loons in northern Wisconsin are part of a vast interdependent network that stretches to adjacent counties, states, and provinces. Females raised in Oneida County breed in Price County, Wisconsin, Michigan, and even Minnesota, while females from those distant places provide breeding females back to Oneida County. The whole system relies upon a dynamic exchange of females across great distances. In short, the downturn in chick production in northern Wisconsin does not spell trouble merely for local loons, it means fewer females are available to breed in outlying counties and adjacent states.
The second point to make is that the reproductive downturn we are seeing is not a short-term pattern that seems likely to reverse course. The inexorable nature of the decline — the fact that the numbers have been slipping downwards steadily for the past two decades — implies that some relentless, slowly-worsening environmental factor has been at work that reduces the abundance of small fishes in northern lakes and will continue to do so in the coming decades.
I am sorry for all of my gloomy forecasts of late. I know: I have only made it worse here by stating that I think loons might be in trouble throughout the entire Upper Midwest. In truth, I am deeply worried. But I am also thinking of strategies that we might use to learn what is hurting the loons and even possibly turn things around. First, of course, we must understand the problem. If it is food, that is not entirely bad news, because humans have been altering fish populations in myriad ways for hundreds of years. By targeted manipulations of small fish populations in certain lakes that we observe closely, we might be able to pinpoint the cause of loons’ reproductive decline, design a strategy for reversing it, and put loons on the comeback trail.
In the wake of my litany of negative findings related to loon breeding success, one burning question presents itself. What is the cause? I am sure that this obvious question occurred to readers of my blog more than once. I feel now as if I have been dodging it. Although we are still gathering information, I will tell you what we currently know. I think I owe you that.
First of all, we must remember that this is a longitudinal decline. By this I mean that the declines are not based data from one, two, or even five years. Rather, these declines have been occurring since the beginning of my study in 1993. Look, for example at the increase in the number of singleton (1-chick) broods over the course of the study.
It is a noisy pattern, but the pattern marches steadily upwards. There have been good years and bad years for 2-chick broods, but the overall pattern is clear. Progressively fewer pairs have been able to rear 2-chick broods as the years have passed. In the mid-1990s, about half of all pairs had 1- and 2-chick. Now almost all broods are singletons. Even more striking is the decline in returning chicks (below). In the mid-90s, we could expect about half of all chicks that we banded to come back to the study area as adults a few years later. Now, only about 1/6 of all banded chicks are ever seen again as adults.
The longitudinal nature of the decline makes it difficult to dismiss the results as a blip resulting from a bad winter here or a severe outbreak of black flies there.
Secondly, the patterns connect logically in a worrisome way. There are not only fewer chicks these days but lighter chicks, leading to the obvious conclusion that low chick mass is a reflection of harder conditions for chicks that leads to lower survival. Furthermore, fewer chicks surviving to fledge should result in fewer young returning as adults, and indeed there are now far fewer young adults in the population than was the case two decades ago. Finally, the smaller young adult population should mean less pressure on territorial breeders to defend their territories. Consistent with this expectation, we now see significantly fewer intruders into territories than we did years ago, and, as I pointed out recently, territorial breeders are evicted much less frequently than they used to be. In short, the entire set of measurements paint a stark and coherent picture.
Third, the lower fledging rate of chicks together with their decreased mass over time points rather strongly to food as the likely cause. Starvation of chicks, if it is occurring, would by itself explain all of the “downstream” patterns (i.e. fewer returning adults, lower intrusion and eviction rates in territories) we have detected.
Pulling threads together, we have a consistent picture of long-term decline in loon breeding success across a broad swath of lakes, probably owing to a fall in food levels. This summary leads to the most vexing question: Why should food levels fall? To be more specific, what factor or factors might result in populations of small fishes falling gradually over the course of a 27-year study? The answer, it is clear, has to be some environmental factor that acts like a slow, incessant march, not a lightning strike.
What environmental factor influences fish communities broadly but gradually? Could a recent increase in recreational fishing be the cause, which has led to fewer large fish capable of producing the small ones on which loons depend? Possibly. If overfishing is to blame, it must be true that the problem has gotten especially severe in the last few decades and was not a great problem in the 1980s and 1990s. Yet small fish (“panfish”) populations apparently declined most during the 1960s through 1990s and have somewhat rebounded during the past 20 years. Could the problem be instead that anglers are now more apt to practice “catch and release” of large fishes, whereas they caught and kept their fish in the old days? If so, these released large predatory fishes might be competing with loons for small fishes and driving small fish populations down so much that loon chicks suffer. Again, the “catch and release” explanation would only work if this practice has intensified across all kinds of lakes in Oneida County over the past quarter century. Yet catch and release increased most sharply in the 1980s and had hit a plateau by the time I began my loon study in 1993. So, upon quick inspection, neither obvious explanation for a reduced small fish population over the past quarter century passes muster.
Our search will continue until we learn what factor — probably related to a decrease in small fish populations — explains loons’ recent reproductive slide. I feel confident that we will ultimately learn what is causing our loons to struggle. We must all hope that the cause is reversible.