The Loon Project

The Study

The Loon Project is a scientific investigation of population dynamics, reproductive success, and territorial behavior of common loons (Gavia immer) in the Upper Midwest. We have two study populations: 1) 105-110 marked breeding pairs in Oneida, Lincoln, and Vilas counties of Wisconsin that have been under investigation since 1993, and 2) 105-110 marked breeding pairs in Crow Wing and Cass counties in Minnesota that we began to study in 2021. Historically, our work has focused on territorial and nesting behavior, but recent findings have turned our attention to conservation.

Why Our Work Matters

The loon population is declining in the Upper Midwest. Understanding the causes of the decline is essential if we wish to conserve loons in the region. Our findings from northern Wisconsin are clear; loons there are declining steadily in several respects. A parallel picture is gradually taking shape in Minnesota, where the body condition of adults has begun to decline as in Wisconsin and where the adult survival rate is lower than in Wisconsin.

The Common Loon: Beloved but Poorly Known

Few wild creatures are so well loved as the common loon. Considering their status as a symbol of the northern wilderness, one might expect that we would know a great deal about loons. But it is not so. Despite the abundance of loon-themed currency, mugs, sweatshirts, hats, jewelry, and mailboxes, we know rather little about many basic aspects of loon biology.

Our ignorance of loon populations and what sustains them is especially poor. We know that huge numbers of adult loons die each year in Wisconsin and Minnesota after ingesting lead sinkers. We know that eagles kill some adults and chicks. In recent years, we have detected two more worrisome population-level patterns. Black flies, whose populations have increased in recent years, are sharply reducing the number of offspring that breeding pairs of loons produce in the Upper Midwest. And just last year we found out that declining water clarity in Wisconsin lakes during the past decade has reduced the ability of loon parents to feed their young and raise them to fledging age. Still, we are not yet certain which of these causes — or what combination of them — can be linked to the population decline we have detected. Without knowing precisely what is causing the Upper Midwest loon population to fall, we cannot put together a plan to save it.

Could Loons Disappear from the Upper Midwest?

Our grandparents heard loons at night as they drifted off to sleep in their lakefront cabins. Our parents heard loons. Surely we too will always hear loons’ voices out on the lake at night. Yet a recent study projected that the breeding range of the common loon will shift hundreds of miles northwards in coming decades. Recent findings from our work in Wisconsin and Minnesota indicate that the withdrawal of the species from the Upper Midwest is underway. If these studies are accurate, then 30 to 50 years from now the unthinkable will occur — the plaintive cries of this northern icon will no longer echo across the lakes of Minnesota, Wisconsin, and Michigan. Instead, future generations will have to travel to Manitoba, Ontario, or Quebec to find loons. Surely we owe it to our children and their children to take what steps we can to learn the cause(s) of the current population decline and try to reverse it. If you share our commitment to keeping the loon populations of Wisconsin, Minnesota, and Michigan strong, please consider donating to our study so that we can continue our work.

The Wisconsin Loon Project

Since 1993, we have been investigating the breeding ecology of loons in the Wisconsin Study Area. Maintaining this traditional study area and ensuring that we collect high quality data there is essential. One of the most valuable aspects of the Wisconsin study population is that the loon pairs within it include over a hundred individuals that we banded as chicks, have followed throughout their lives, and have observed to settle on territories. Studying a known-age population has allowed us to learn how behavior, survival, and many ecological attributes change during a loon’s lifetime. From a conservation standpoint, the high resolution of our data has made it possible to produce a much clearer picture of population dynamics in northern Wisconsin than is possible in the rest of the loon’s breeding range. Michael Meyer, a loon conservationist in Wisconsin who studied loons for many years, calls our Wisconsin study population “the gold standard” for loon population research.

Loons Are in Trouble in Wisconsin!

In 2019, we noticed warning signs related to the survival and breeding success of loons in northern Wisconsin. So we turned our attention to investigating the health of the loon population there. Our analysis of loons in and around Oneida County, Wisconsin was quite shocking. The loon population in northern Wisconsin has declined overall by 22% during the past quarter century. Loons are producing fewer chicks; chicks are growing more slowly; and chicks are dying at much higher rates now than 30 years ago, when our work began. A population projection suggests, moreover, that the northern Wisconsin loon population is shrinking by as much as 6% each year. This is an alarming estimate. If it is accurate, we will see noticeably fewer loons on northern Wisconsin lakes within the next five to ten years.

A troubling dimension to the Wisconsin decline is that it is most pronounced among young adults that have returned to the breeding grounds to look for territories but have not yet settled. This means that much of the decline takes place not among the breeding pairs that we watch for many hours out on the lake but among the furtive, skulking individuals that wander widely in search of breeding vacancies. In other words, the Wisconsin population decline is largely hidden from view.

Naturally, the discovery of a declining Wisconsin loon population served as a wake-up call. We can no longer presume that loons are a permanent, inviolable segment of the northern ecosystem. We no longer hope that giving loons a wide berth while boating will be enough to preserve them.

After discovering the Wisconsin decline, our first question was: Is the decline confined to northern Wisconsin or might it be part of a broader pattern in the Upper Midwest? This question caused us to broaden the scope of our research.

The Minnesota Loon Project

In 2021 we expanded the Loon Project to establish a second loon study population in north-central Minnesota. In 2021, 2022 and 2023, we captured and marked 245 Minnesota adults and chicks. We now have 67 of 105 focal pairs marked that will constitute our Minnesota study population. The Minnesota research team has begun to collect data on annual survival rate, nesting success, and causes of nesting failure in Crow Wing County. If funding permits, we will have a fully marked Minnesota Study Population by 2025. We will then be able to measure demographic parameters on Minnesota loons with the same resolution that we now measure them in loons of northern Wisconsin.

There are a number of advantages to having two widely separated study areas in the Upper Midwest. The first has to do with Minnesota itself. The data we collect on survival and breeding success in our Minnesota Study Area will permit us to generate a population model for Minnesota, just as we did in Wisconsin. Current efforts to collect data on Minnesota loons rely upon estimates of loon numbers from unmarked birds. These data are very useful, particularly because they come from six diverse regions within the state and thus provide a broad view of the state population, but they yield a somewhat puzzling and contradictory picture. For example, populations in some parts of the state seem to be increasing, while populations in other regions are decreasing. We will use our marked Minnesota study population to produce a quantitative population model based on rigorous estimates of annual reproductive success, adult survival, and fledging success of chicks. We hope that our model will complement the much broader but much less detailed work with unmarked populations to yield a reliable picture of the Minnesota loon population overall.

A second advantage of our new Minnesota Study Area has to do with comparison. By comparing the Wisconsin loon population to another that resembles it in some ways and differs in others, we can increase our understanding of threats to loons across the region. For example, if we find that our Minnesota loon population is stable (unlike Wisconsin) and that hatching success, chick survival, or annual mortality rate of adults differs between the states, we can infer that one or more of those differences might explain the Wisconsin decline. After 3-5 more years of data collection in Minnesota, we will learn whether there is one over-arching factor negatively affecting loon survival and breeding success across the Upper Midwest or a constellation of factors that affect loons differently in each state. These findings will inform efforts to support loon populations through specific, targeted actions.

Third, as I hinted above, we have become worried about loon populations across the Upper Midwest. If Wisconsin loons are in trouble, it seems likely that the nearby loon populations in Michigan and Minnesota are suffering similarly. A finding of population decline in Minnesota would suggest that the Wisconsin decline is not a quirk or a fluke but part of a broader pattern that is worthy of our immediate attention. Published scientific research documenting population decline in two study areas 200 miles apart (if Minnesota loons are, in fact, declining) would help us draw attention to the plight of loons in the Upper Midwest and mobilize local, state, and federal dollars to reverse the decline.

What We Have Learned So Far about the Decline

Since learning of the Wisconsin decline in 2019, we have turned our attention to potential threats to loons there. Through a collaboration with researchers who use satellite data to estimate water clarity, we have learned that: 1) water clarity has decreased in lakes across northern Wisconsin in the past 20 years or so, and 2) short-term declines in water clarity are linked to decreases in masses of loons chicks. In short, recent decreases in lake clarity seem to be making it difficult for adult loons to find food for their chicks and are likely to blame for the higher chick mortality that we have observed. Our statistical analyses indicate, moreover, that warmer temperatures and heavy rainfall lead to lower water clarity. So, as we had feared, climate change seems to be having negative impacts on loons. While it will take decades to reduce the impacts of climate change, people living on lakes containing loons can help improve lake clarity by reducing the amount of organic and inorganic matter — especially fertilizers and human and pet waste — flowing into lakes from lakefront properties.

A second line of research related to loon conservation has focused on black flies, which harass nesting loons and sometimes force them to abandon nests. Black fly populations have increased in the past few decades in Wisconsin, just as water clarity has declined. So black flies appear to be a second threat to Wisconsin loons. Again, heavier annual rainfall produces more running water, which boosts black fly populations. Thus, we can see a negative impact of climate change is at work here as well.

Timeline for Research

We are hard at work studying water clarity and black flies as potential threats to loon populations in the Upper Midwest. That research will continue. 2023 and 2024 are especially critical years for our new Minnesota study population. If we can field a complete field team (4 field interns, including one veteran researcher) in Minnesota, then we will be collecting high-quality data on breeding success and survival there, just as we do in Wisconsin. This effort will allow us to produce a preliminary population model (using demographic data on marked loons) by 2024 or 2025. Further data collection in Minnesota from 2025 to 2030 will allow us to refine that model and pinpoint specific ecological causes of any population decline we detect.

What We Have Learned about Loon Behavior

At present, we are laser-focused on loon conservation, because of the alarming decline we have recently discovered in northern Wisconsin. However, before we discovered that decline, we spent most of our time and energy learning about loon behavior and breeding ecology. The Loon Project has produced a wealth of findings.

We learned over a decade ago that loons breed in socially and genetically monogamous pairs and that, contrary to popular opinion, loons do not mate for life. Yet both members of a breeding pair do tend to return year after year to the same small lake or portion of a large lake and are likely to enjoy long lives. So lake residents are often correct when they hear a loon call in early May and remark, “The loons are back!”

Some of our results have been perplexing, such as the finding that male loons select the nest site. Other findings have been shocking, such as lethal battles for territory ownership, which occur chiefly among males. Certain patterns we have seen in loons, like senescence, are reminiscent of the human condition.

A good deal of our time and energy has focused on learning about the reasons for territorial intrusion. We have learned that intruders seek information about breeding success. Recently, we have come to find out that intruding adults also try to learn about territorial residents, perhaps so that they can plan eviction attempts in the future. One odd fact about territorial intrusions, however, is that a large percentage of them are by neighboring territory owners, rather than adults that lack a territory and are looking for one. We think that most of these neighbors intrude outside of their own territory in order to “decoy” young birds that are searching for territories away from their own lakes. A recent finding — that territory holders target only those territorial intruders that most threaten their ownership — shows that loons with territories behave quite pragmatically towards intruders.

In fact, one of our most recent findings is that pairs with chicks themselves are among the most frequent intruders into territories of other pairs with chicks. Why? We hypothesize that pairs with chicks attempt to “spotlight” the chicks of other nearby pairs in order to increase the likelihood that young adults looking for territories will try to evict those nearby pairs, not themselves. This finding, if correct, means that we have come to a fairly complete understanding of late-summer “social gatherings” of loons. Social gatherings consist of members of a home territorial pair, young nonterritorial adults looking for chicks so that they can use them as a cue for later eviction attempts, and neighbors, which are spotlighting the chicks on someone else’s territory in order to safeguard their own territory ownership.

In the past several years, breeding habitat selection by loons has come to be an important topic of investigation for us. We have learned that loons seek to settle to breed on lakes of certain size and pH based on their experience on natal territories, even though preferences for natal-like lakes sometimes leads them to settle on poor territories. The tendency for individual loons to form specific habitat preferences also has important implications for efforts to reestablish extirpated populations in regions south of the current breeding range.

We invite you to examine our findings and many others related to loon territorial behavior, habitat selection, breeding, and population decline. We have provided links to scientific papers there, but you can also look at our popular articles, which, while a bit easier to comprehend, still employ scientific rigor.

Updates from the Loon Project: The LP Blog

The Loon Project is ongoing. This site enables us to describe recent findings, activities and accomplishments for folks who are interested. Check out “LP Blog” for the most up-to-date information. If you are really gung ho, sign up to “follow” the blog and receive an e-mail each time I add a new post. During the breeding season (May to August), I provide frequent updates of what we are seeing in the field — nests, chicks, territorial battles, research activities, and so forth. At all times of year, I will let you know about published papers and presentations by the Loon Project.

Loon Video!

We make available here video that shows what our leg-banded loons look like (under “Why Band Loons?”). In addition, if you look under “Findings” > “How does a loon acquire a territory?”, you can watch a couple of vicious battles between loons for ownership of a territory.

Who We Are

The project is directed by Walter Piper of Chapman University in Orange, California. But the project has grown out of the work of over 100 individuals. I have had academic and field assistance from many collaborators over the years and support from countless lake residents, who let us view loons on their lakes. The unsung heroes of the project are student research assistants, who work many lonely hours collecting data on loons, usually as a means to get field experience in preparation for a career in animal behavior, ecology, or wildlife biology.  Some assistants take on side projects that allow them to devise a new means of data collection or an experiment, which can be written up for presentation or even publication after the season. In recent years, Linda Grenzer (whose photo appears above) has become an invaluable contributor by taking great photos, monitoring the breeding pairs in the southwestern section of the study area, and staying on the lookout for loons that are in danger and can be rescued. To find out more about the people on the study, look under People.


The National Science Foundation provided funding for our work from 2003 through 2018. Between 2021 and 2022, the National Loon Center provided substantial funds to support our work. However, we have no major source of funding for Minnesota or Wisconsin for 2024 and afterwards. With sources of scientific funding shrinking in the United States, we are finding it harder and harder to keep the project afloat. Consequently, private donations are welcomed. Indeed, they are keeping us afloat.