The Loon Project

Research on Territoriality and Population Dynamics

The Loon Project is an ongoing scientific investigation of territoriality, reproduction, habitat selection, and population dynamics of common loons (Gavia immer) in the Upper Midwest region of the U.S. We have two study populations: 1) 120 marked breeding pairs in Oneida, Lincoln, and Vilas counties of Wisconsin that have been under investigation since 1993 and 2) 120 loon pairs in and around Crosslake, Minnesota that we began to mark and study in 2021. We have now accumulated a large sample of longitudinal data that permits robust statistical analysis and provides a rare, life-history perspective on Upper Midwest loons. To date, we have followed the entire breeding lives of 65 individuals. We have also banded 357 loons as chicks that we later observed as adults nearby. This large sample of known-age individuals allows us to investigate the behavior of young birds — especially how young birds learn about and settle on breeding territories. The project has a number of research goals that we are now striving to achieve.

On the Loon Project, we reach conclusions scientifically. That is, we do not deal in anecdotes and gut feelings, but instead rely upon robust statistical analyses that are peer-reviewed by other scientists and published in scientific journals. To be sure, we sometimes speculate about why loons behave as they do; that is how science moves forward. But when we do, we make it clear that such statements represent hypotheses only. As scientists, we commonly use the very powerful words: “we do not know”.

Despite our cautious approach, the Loon Project has produced a wealth of findings. We learned over a decade ago, for example, 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!”. (In other cases, they are at least half right!)

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.

In fact, one of our most recent findings, which we are writing up for a journal article, 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.

The Loon Population in Northern Wisconsin is in Decline….What about Minnesota?

In the fall of 2019, we learned through rigorous analysis of our long-term data that our population is suffering a long-term decline in breeding success. Specifically, breeding pairs are raising fewer and smaller chicks than they did 25 years ago for reasons that we do not yet understand. In addition, the population of adult loons in northern Wisconsin has declined significantly, chiefly because of lower survival during the first five years of life. Naturally, we are suddenly very worried about our population, which we had thought was stable. Now much of our field effort is aimed at determining the cause(s) of these declines, in hopes that we might be able to reverse them. If you are as concerned as we are about preserving the Wisconsin population of loons, please consider donating to our work. Much of the effort we are putting forth in our new Minnesota study area will be aimed at learning if the Minnesota loon population too is in trouble. As in Wisconsin, we will assess the loon population in Minnesota by intensive efforts to capture, individually mark, and study breeding success of a large sample of adult loons. Only by this means will it be possible to estimate survival and annual return rates, estimate chick production, and feed this information into a robust statistical model that can inform us whether the Minnesota population is increasing, declining, or remaining stable. An ongoing study of the Minnesota loon population that relies upon data from citizen scientists has shown reason for concern, as two of six monitored regions in the state are showing downward trends.

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. I have recently accepted a position of Scientist at the National Loon Center in Crosslake, which will allow me to share my findings on the behavior and ecology of Minnesota and Wisconsin loons with the visitors to the Center. (This facility opens in 2024.)

The Loon Project is not the work of one person. I have had academic and field assistance from many collaborators over the years and support from many lake residents, who let us view loons on their lakes. The unsung heroes of the project are student research assistants, who work countless 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.  Many 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. In the crucial early years of the study, we received funding from the National Geographic Society, the Disney Conservation Fund, and Chapman and Cornell Universities. Beginning in 2021, the National Loon Center has provided substantial funds to support our work. Thanks to all of these funders. With scientific funding shrinking in the United States, we are finding it harder and harder to keep the project afloat. Private donations are welcomed.