Historically, our work has focused on the territorial behavior of loons. We have documented both the methods that breeders use to defend their territories and the techniques that young nonbreeders employ to learn about territories and take them over after evicting breeders. However, our discovery in 2020 that the Wisconsin loon population is declining has shifted our focus towards conservation.

Suspecting that the downturn in the Wisconsin loon population might extend across the entire Upper Midwest, we began to establish a Minnesota study population in 2021 at a site 200 miles west-northwest of our Wisconsin Study Area. (Both study populations comprise 110 to 120 breeding pairs.) It has been a struggle to build the new Minnesota Study Area while keeping our research afloat in Wisconsin. But private donations have helped immensely. Thank you to everyone who has contributed funds, labor, or lodging to support our field work in one or both states. We hope that our attempts to secure state and federal funds to support our research in the two states will be rewarded soon.

Meanwhile, the work goes on. Two years ago we collaborated with researchers at Rensselaer Polytechnic Institute and made a critical finding. A drop in water clarity in northern Wisconsin is reducing survival of loon chicks. Specifically, loss of water clarity in summer caused by heavier rainfall is strongly associated with loss of weight and lower survival among loon chicks. The only plausible explanation for this pattern is that loon parents, which hunt fish visually underwater, cannot catch enough fish to sustain their young when water clarity falls.

While we are glad to have found a major cause of the breeding decline in the Upper Midwest, the long-term drop in water clarity we found is alarming. Loss of clarity is likely to have dire consequences for loons, if it continues. The northern Wisconsin loon population is already producing far fewer young adults than necessary to replace breeders that do not return from the wintering grounds. In the next decade or sooner, we expect to see breeding pairs disappear from one and then another breeding lake in the state, owing to this dwindling of young replacements.

In 2025 a new line of research exposed two new patterns related to the Upper Midwest population decline.

First, the Silver Spoon Effect is strong in the species. That is, loons that struggle to obtain sufficient food during the first few weeks of life develop into adults of inferior quality. Most of these underfed individuals do not survive long enough to return to the breeding grounds. Those that do return seldom settle and almost never reproduce. Limited food during the chick phase is thus a double whammy: it threatens a chick’s survival to fledging, and it greatly reduces the chance that a chick that happens to reach adulthood will ever produce offspring.

A second important discovery from this past year was a carry-over effect of ocean conditions on the loons’ wintering grounds. To put it briefly, loons that suffer from poor conditions from December to March (unclear water, high concentrations of harmful algae) along Florida’s Gulf Coast (where most loons from the Upper Midwest winter) are less likely to return to the breeding grounds in the following year. Moreover, adult loons that own breeding territories in Minnesota or Wisconsin but winter in poor ocean conditions are more likely to be evicted from their territories the following summer. In other words, difficult wintering conditions that a loon experiences in the winter season “carry over” into the breeding season and reduce the effectiveness with which a loon defends its territory from competitors.

While we are excited by the host of new findings we have made related to the loon population, we do not wish to simply observe and document the decline and eventual disappearance of loons from the Upper Midwest. In fact, our next goal is to probe the loss of water clarity and learn precisely what is making lakes less clear and hurting loons. We will be working with our collaborators to test three main hypotheses. First, water clarity might fall during times of heavy rainfall because of dissolved organic matter that washes into lakes. Second, loss of clarity might result from suspended sediments carried into lakes by rainfall. Third, a decline in clarity might come about if populations of aquatic algae explode after rainfall events that wash fertilizer from lakeside lawns into lakes. If we can determine precisely what is causing the loss of water clarity, we might urge state and local agencies to take action to curb the decline. That step might boost loon breeding success to levels we have seen in decades past.

We will also continue to investigate negative impacts of Florida ocean conditions on Upper Midwest loons. If deteriorating ocean conditions during winter are driving our loon population downwards, we would like to learn that now, leaving ourselves time to identify the problem precisely and — we hope — turn things around.   

Minnesota is crucial to our effort to learn about causes of breeding decline in loons. By the fall of 2025 we should have sufficient data from our loon work in Minnesota to determine if, as we fear, Minnesota loons are showing sustained low breeding success and are struggling to feed their chicks owing to declining water clarity. If so, we will have documented a long-term threat that is regional in nature and warrants a regional response. That will make an even stronger case for action to improve water clarity and help loon populations in both states.

Thanks for any support you can give us as we work to protect Upper Midwest loons.