population

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On the Loon Project, we are all out to band loons in Minnesota. This effort borders on obsession. Since adult loons must produce chicks to be easily catchable, our marking initiative depends upon finding pairs with chicks. “Have you seen any loon nests on your lake?” is a refrain Eric Andrews and I uttered to many residents of lakes in Crow Wing and Cass Counties back in May and June. “Have you seen any chicks?”, I have begun to ask in recent days, now that I am on my second tour through the Minnesota Study Area. This question is on my lips so often that I now smile inwardly each time I ask it. I hope that I do not sound desperate.

People have been happy to answer our loon-related questions. Driven by love of the state bird, scores of Minnesotans have shared their observations of loons, nests, and chicks, given us permission to launch canoes from their property, and even permitted us to post their photos of loons to spruce up our blog and Instagram posts. (Sheila Farrell Johnston’s cool photo, above, of a territorial battle on Upper Gull Lake this spring is a case in point.) Minnesotans, it seems, are as concerned about loons as we are and wish to help us enhance the current low-resolution picture of the state loon population with a robust, scientific analysis. The outpouring of support we have received this summer has ended any lingering uncertainty we had about continuing our research in the region. *

A growing demographic disparity lends urgency to our efforts in Minnesota. You see, accumulation of data from the Minnesota Study Population — and comparison with corresponding data from Wisconsin — has revealed that loons are returning to their territories at a lower rate in Minnesota than in Wisconsin. That’s right. In Wisconsin, where we already know the population is in some trouble, adult loons are returning to their territories at a higher rate than in Minnesota.

The numbers speak for themselves. In 2023, 63 of 74 Wisconsin territorial females (85%) returned to their 2022 territories, while 69 of 79 Wisconsin males came back (87%). Those numbers are typical for Wisconsin and for New England loon populations as well. In contrast, only 81% of Minnesota females (34 of 42) and 82% of Minnesota males (37 of 45) returned in May 2023 to the territories they owned in 2022. Now, these are not massive samples. So you might be excused for dismissing these numbers as sampling error from which no conclusion can be drawn. But this is the third independent analysis that has shown a higher rate of return in Wisconsin. We saw the same story in the data from last year and from Kevin Kenow’s marked adults from 2015-2017. So the time for hemming and hawing is over. We can no longer escape the fact that loons in Crow Wing County are returning to their territories less often than loons in Oneida County, Wisconsin.

Before you hurl yourself off of your dock, let me add some perspective. The lower return rate in Minnesota does not necessarily indicate lower survival there. Why not? Because a loon’s ability to return to its previous territory depends not only upon its being alive, but also upon its ability to defend its territory from challengers. Minnesota loons might be surviving just as well as — or even better than — Wisconsin loons. If so, however, they are being evicted from their territories at an astonishingly high rate.

Paradoxically, a high rate of eviction in Minnesota, if it is occurring, could be good news. A high eviction rate might indicate that Crow Wing County is overflowing with young 4-, 5-, and 6-year old adults looking to challenge owners for territories. If so, frequent eviction reflects high breeding success of loons in the County (4 to 6 years ago), because it is Crow Wing County loon pairs (for the most part) that have placed all of these young whippersnappers into circulation.

Ok, I admit it. I am putting lipstick on a pig. I do not truly believe that our Minnesota loons are kicking each other off of territories often enough to account for the low return rate we have found there. I do not know how to account for the pattern. But I am yet not unduly concerned about our Minnesota Study Population. Adult survival, even if lower in Minnesota, is only one piece of the puzzle. Still, the news is pushing me to be even more inquisitive of Minnesota lake residents. Someone listening closely late this afternoon might have heard my favorite question echo across the gently scalloped surface of Duck Lake: “Have you seen any loon chicks this year?”

*Mind you, we are still enthusiastically following our long-term study population in northern Wisconsin. Wisconsin loons continue to yield exciting insights about age-related behavior patterns and impacts of water clarity on the health and survival of loon chicks.

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It is easy to forget that research on the loons of Crow Wing County, Minnesota has been underway for over a decade. To be sure, this work has been spotty. From 2011 to 2014, Kevin Kenow and his USGS team placed geotags on a few dozen adults on four medium-sized lakes in the county. From 2015 through 2017, he shifted his efforts to the Whitefish Chain, where he captured 68 individuals, including 36 territorial adults.

Kevin’s goal was to determine migration and wintering routes of Minnesota loons, which he did after recovering many of the geotags placed on loons’ legs. Although his study was short-term, Kevin’s loons lived on. Each summer and fall they nested and reared young, foraged to build up their reserves for migration, staged on the Great Lakes, and made long overland flights to the Gulf of Mexico. Each spring they molted their feathers and made return trips back to the Whitefish Chain to restart the cycle.

When our Minnesota Loon Project began in 2021, we relocated many of the loons Kevin had banded 4 to 6 years before. We were quite thorough — obsessive, even — in our efforts to do so. At the time I regarded the USGS banding effort as fortunate for us, since it gave us a head start in our efforts to mark all territorial pairs on the Chain.

But Kevin’s marked loons have not merely reduced our loon marking workload. Kevin’s birds are charter members of the Minnesota Loon Project. The survival of these inaugural adults since the years Kevin’s team marked them provides our first multi-year snapshot of adult loon survival in Crow Wing County.

The data provide an unconventional snapshot. When one conducts a mark-recapture study, one normally searches diligently for all marked individuals during the years immediately after marking. This strategy produces data on annual return rate, which provides an estimate of annual survival. But we lack data on return rates from 2018, 2019, and 2020. So we must do the best we can to extract information from Kevin’s birds despite multiple years with missing data.

Fortunately, this is not rocket science. If “r” is the annual rate of return, then r2 is the probability of being on territory two years after banding, r3 is the probability of still being present three years later, and so on. Recognizing this, we can easily project how many of the 36 territorial adults that Kevin banded in 2015, 2016, and 2017 should have still been on territory in 2021. If annual rate of return were 90%, we would have expected to see 20.5 of Kevin’s loons in 2021. At 85%, the expectation is 15.1. If the annual rate of return were 80%, then we should have seen 11.0 loons. In fact, our exhaustive search turned up 13 of Kevin’s loons. So this places our rough estimate of annual loon survival for the Whitefish Chain at 82.5%.

To my knowledge, ours is is the first long-term estimate of adult loon survival from Minnesota based on a marked population. This is rather shocking; loons are well studied in the U.S., have been marked in at least ten states….and are the state bird, for goodness sake! In any event, this preliminary estimate gives us a ballpark figure for adult survival that we can compare with more robust estimates from other states.

A figure of 82.5% for Minnesota survival is lower than we would like. This long-term number based on Kevin’s birds, though, is slightly higher than the separate return rate of 51 Crow Wing County adults we banded in 2021 and looked hard for in 2022: 80%. For comparison, we have robust estimates of survival from a study done 15 years ago that included data from New England (88%; data from 1994-2001) and Wisconsin (87%; data from 1991-2001). We can also compare with longer-term survival rates from our well-known Wisconsin Study Area, which, again, were 86 to 87% for both males and females. In short, early data from the Minnesota Study Area indicate a percentage of adult survival in the low 80s, which is below the rates in the upper 80s we have grown accustomed to seeing in Wisconsin and New England.

The data from Minnesota so far only provide a glimmer about the loon population in Crow Wing County. However, these low survival estimates do bring to mind a worrisome downward trend in loon numbers for the region that can be seen in the 2021 Minnesota Loon Monitoring Report. But, really, it is early days. We need more data. Furthermore, the status of a loon population is not dependent upon adult survival alone. Low adult survival can be offset by a high reproductive rate. So we will have to spend at least two more years tracking return rates of marked loons and measuring breeding success before we can pull them together into a model that will tell us (preliminarily) how Crow Wing loons are doing. Still, if I am being honest, I wish the survival numbers were a bit higher.

Thanks to Katy Dahl, who photographed the Cross Lake-Arrowhead Point loon pair after we banded them in 2021. The male in the foreground with his bands out of water was spotted a few days ago just north of Minneapolis.

If, like us, you are concerned about the persistence of loons in Minnesota, consider a donation to support our field efforts. We run a lean program. Funds donated to the Loon Project do not pay overhead, administrative costs, or salaries for staff or senior personnel. They pay only field costs like: 1) stipends to keep student field workers alive, 2) travel costs to, from, and within our study areas, and 3) supply costs such as for colored leg bands and canoe paddles. Thanks!

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We all love loons. So naturally we should take any step we can to help them. Right? In that light, artificial nesting platforms (ANPs), or loon rafts, would seem to be a no-brainer. Platforms make it easier for loon pairs to produce chicks.

ANPs fit neatly within the framework of loon conservation. Accepted enthusiastically by most loon pairs, they would seem to provide a perfect, low-cost solution to increase loon populations. They are easy to construct; a person with a modicum of carpentry experience can find plans online and build a platform in a day or less. So platforms provide a simple method by which a single loon enthusiast can improve the breeding success of a pair of loons for many years. Across the loon breeding range, platforms have become a panacea for bolstering reproductive success.

But are nesting platforms all that we need them to be? Now that loon populations appear to be in trouble in Wisconsin and perhaps even in Ontario — and now that some of the causes of declines are beginning to come into focus — maybe it is time for us to step back for a moment. Maybe we should ask whether platforms address the actual problems that loon populations face. To state it technically, can platforms mitigate the specific negative factors hurting loon populations and make populations viable in the long term?

We first need to recognize that platforms address a single, very narrow problem faced by loons. Loon pairs must sit on their eggs — in an exposed location — for 28 days. If a mammalian predator wanders by during that month, the nest is lost. Platforms solve this problem beautifully. They increase the rate of hatching by about 70%. But increasing of hatching success is all platforms do. Platforms put more small chicks in the water — a pleasing outcome for folks that deploy them — but they do nothing to help those chicks reach fledging age. They do not feed chicks; they do not protect chicks from predators. They do not boost adult loon survival. They have no effect on the rate of boat strikes or angling casualties or lead poisonings of adults and chicks. In short, if loon populations suffer declines owing to reduced hatching success, then nesting platforms are just what the doctor ordered. If declines are caused by anything else, then platforms would appear ill-suited to the task.

What do we know at this point about the status of loon breeding populations and factors that might threaten them? Precious little, I am afraid, especially if we are speaking of the entire species range. But we have begun to identify specific threats to loon populations in the Upper Midwest.

At present, the four most significant hazards to loons in northern Wisconsin appear to be: 1) larger populations of Simulium annulus, a black fly that targets incubating loons and causes massive abandonments of loon nests in May and early June, 2) decreased water clarity during the chick-rearing period, which increases chick mortality, 3) increased deaths of adult loons and chicks from ingestion of lead sinkers and jigs, and 4) a mysterious die-off of young adults in recent years that has caused the population of future breeders to plummet. Black fly numbers are highly dependent upon rainfall during the previous year, we have recently learned. More rain means more flies. Increased June and July rainfall also reduces water clarity during the month of July. Both increased black flies and decreased water clarity have become much more severe in the past few decades, probably as a consequence of increased rainfall from climate change. Lead poisoning is known to be a big problem for loons in New England; animal rehabbers in the Upper Midwest feel that lead poisoning has increased in frequency there in recent years. The severity of lead poisoning, of course, should depend upon how much angling occurs and the extent to which anglers switch out their lead tackle for alternatives that are not deadly to wildlife. Finally, we have measured a clear and sharp increase in young adult mortality in our study population in northern Wisconsin. We have no idea, at present, what its cause might be.

How well does the use of nesting platforms to boost hatching success of loons map onto the quadruple threat of increased black flies, decreased water clarity, lead poisoning, and spiking mortality of young adults? With respect to black flies, platforms might mitigate the problem somewhat. Platform-nesting loons suffer abandonments just as severely as do loons nesting at natural sites, but the increased hatching success of second nests on platforms offsets the hit to hatching success caused by black fly-induced abandonments of first nests. Platforms, of course, have no impact on the decreased growth rate and increased mortality of loon chicks owing to declining water clarity and the resultant difficulty of feeding chicks. Likewise, platforms cannot affect the incidence of lead poisoning in an area. And platforms cannot possibly save young adult loons from whatever has caused them to die at such an alarming rate in recent years.

On the whole, then, floating nest platforms do not appear to address effectively the threats faced by loon breeding populations (to the extent that Wisconsin represents loon populations generally).

While that quick analysis might seem reasonable, I have ignored one crucial fact about loon nesting habitat and platforms. Platforms often provide loons with an opportunity to breed in lakes or parts of lakes where they otherwise could not because of the absence or poor quality of nesting habitat. In other words, platforms actually create new nesting habitat. If the new nesting habitat that platforms make available contains enough food that parents can fledge the chicks they hatch there, platforms might provide “bonus chicks” that give the loon population a boost. *

Of course, platforms are so enticing to loons that they must be deployed thoughtfully. A platform placed on a very small lake might lure a pair of loons to use it but result in starvation of the chick(s) because of food limitation. Since a pair lured into such a tragic situation might otherwise have nested and reared chicks successfully elsewhere, such misuse of nesting platforms exacts a cost on the breeding success of the population. (Loon conservationists recognize the pitfalls of using nesting platforms thoughtlessly and only deploy them where they are likely to do more harm than good.)

While loon platforms seem effective at boosting loon populations in some respects but appear ineffective or even harmful in other respects, what conclusion can we reach? Lacking hard data, we can only speculate. However, it is probably safe to conclude that judicious use of nesting platforms in lakes or parts of lakes that lack good nesting habitat adds enough “bonus fledglings” to the population to make platforms an effective conservation tool. Indeed, with the list of threats to loon populations growing, we might soon face a situation where we are casting about for new loon habitats with plenty of food but nowhere to nest — so that we can rely upon platforms to place a good many more chicks in the water.

* Population ecologists will recognize a potential flaw in my reasoning. Even if platforms result in a huge increase in fledged chicks in a population, density-dependent mortality during winter or migration (e.g. owing to food shortage) might wipe out all of these extra individuals. In that case, platforms would not be an effective conservation tool. In fact, increased adult mortality from a variety of causes could produce population decline even in the event of huge “bonus” chick production via platforms.

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Yesterday, I heard the cheerful, buzzy calls of Japanese White-eyes* flitting about in the trees in my backyard. They are handsome and engaging little birds, but they don’t belong in southern California. They never lived here before humans did. As recently as ten years ago, white-eyes were quite difficult to find in the area.

A few weeks ago my wife, son, daughter, and I visited my ailing mother in Houston. On our first morning there, we were awakened by the incessant cooing of White-winged Doves*. They too are a striking species. The flashy white stripes on their wings and tails set them apart from the more familiar and homely Mourning Doves. Even the ceaseless calling of White-wings is rather pleasant. Don’t trust me on this; the abundant murmurings of this species inspired Stevie Nicks to write an entire song about them. But White-winged Doves have not always lived in the Houston area. I remember scouring trees around the Galveston County Courthouse in vain for this species with my mentor, Fred Collins, on a Christmas bird count a half century ago.**

Of course, while new species colonize new regions; well-established residents also vanish. In the Upper Midwest, the Piping Plover, a cute little shorebird, has recently become severely threatened. Though I have never seen a Piping Plover in all my years in Wisconsin and Minnesota, I do have experience with a second threatened species, the Black Tern. These agile fliers flit about marshy areas, plucking insect larvae and small vertebrates from the water and vegetation. They are appealing birds — with jet-black bodies that contrast tastefully with greyish wings and tail. But it is a longshot to find them in the Upper Midwest nowadays. What seemed a healthy breeding colony fifteen years ago on Wind Pudding Lake in northern Wisconsin — where we have always had a breeding loon pair — has disappeared altogether. It has been so many years since I last saw Black Terns on Wind Pudding that I have stopped looking for them there.

In short, my years as a bird-watcher have taught me that populations of birds change dramatically over time. Some species magically appear in new places, and other species disappear. I suppose it is my first-hand experience with the dynamics of avian populations that infuses my current research on loon populations in Wisconsin and Minnesota with such urgency. This is why I sweat the black fly season in May and June, worry about boat strikes and lead poisoning, and am in a bit of a panic over the recent loss of water clarity in the region. I have now seen — as I had not in 1993 when my loon work began — that birds can disappear.

* Photos by Natthaphat Chotjuckdikul and Ted Bradford from eBird.

** In fact, the picture is a bit complicated in the case of this species. White-winged doves occurred commonly in the southwestern U.S. 100 years ago, but the population was devastated by the expansion of the citrus industry. However, in the past three decades, the species has begun to nest in citrus trees and has come roaring back.