A few years ago, a non-scientist collaborator of mine suggested that I place transmitters on loons. This was a cool idea in many respects. Transmitters would permit us to monitor loons’ locations in real time and share those data with the public on a splashy website. I agreed that the technique would be thrilling and draw lots of public interest. But when the surge of adrenaline subsided, I was left with two troubling questions. First, what scientific hypothesis could we test with transmitters? Second, how would attaching transmitters to loons help us conserve loon populations in the Upper Midwest?
I am not knocking the technique. Transmitters are a potent tool used by animal ecologists to learn about patterns of migration, dispersal, and nomadism. Kevin Kenow and his collaborators employed satellite transmitters to show that typical adult loons breeding in Wisconsin and Minnesota spend the fall on Lake Michigan before heading south for winter. Kevin’s team also learned that juveniles remain on or near their natal lakes until late November, at which time they make a beeline for their winter quarters. So transmitters have helped us pinpoint times and places that are crucial to the annual survival of Upper Midwest loons. At present, though, there is no burning question concerning loons that transmitters might address.
What questions are most pressing with respect to Upper Midwest loons? With another year behind us and the 2024 field season looming, let’s take stock. How healthy is the population of loons in the Upper Midwest? And how can we best use our resources to protect them?**
Population Surveys
Two broad censuses carried out by armies of volunteers look at loon populations across large swaths of Minnesota and Wisconsin during late July. These counts are prone to fluctuations caused by changes in personnel and weather conditions during a narrow window of data collection. Still, they provide valuable large-scale “snapshots” that, in the long run, tell us how each population is faring. Furthermore, by comparing Minnesota and Wisconsin snapshots side by side, we might discern a broader regional trend.
Wisconsin’s LoonWatch survey has been carried out every five years since 1976. The survey showed robust statewide gains in loon numbers during the 1980s, 1990s, and 2000s. The most recent survey, however, revealed a decline in the Wisconsin loon population between 2015 and 2020. (The next survey will occur in July 2025.)
The Minnesota Loon Monitoring Program generates data annually and is based on six “index” areas. The enhanced geographic dimension to the MLMP survey suits Minnesota’s loon population, which is three times the size of Wisconsin’s. From 1994 to 2010, populations in two of six areas increased, two declined, and two were stable. But trends have shifted downwards in recent years. Since 2010, two areas have been stable, two have declined slightly, and two have fallen sharply. Surprisingly, the strongest, most consistent declines have occurred in the two most northerly areas (Cook/Lake and Itaska).
If we stitch Minnesota and Wisconsin surveys together, we can see that the Upper Midwest loon population as a whole increased (Wisconsin) or remained stable (Minnesota) during the 1990s and 2000s. We can also detect an apparent decline across the region that began in about 2010 in Minnesota and five years later in Wisconsin.
Poor Breeding Appears to Explain the Wisconsin Decline
Our breeding data from Wisconsin shed light on the recent population decline there. During the 1990s and 2000s, Wisconsin breeders raised healthy chicks with high survival. Brood size was split 50/50 between one- and two-chick broods. Beginning in 2010, however, chick survival and mass fell, and only 20 to 30% of broods contained two chicks. Furthermore, young adult survival plunged by 60% in Wisconsin from 2000 to 2015. Thus, poor breeding success and loss of young adults seem to be driving the population decline. There are simply not enough young loons being produced to replace adults that die.
Wait a minute. The breeding decline began around 2010, whereas the population did not begin to fall until after 2015. Are these results consistent? Indeed they are. Most loons do not settle on territories until they are five to ten years old. Therefore, several years must pass before poor breeding success is “felt” in the adult population. Hence, a statewide population decline beginning in about 2015 is what we would expect from a reproductive downturn 5-10 years earlier.
Hints of a Similar Pattern in Minnesota
We have only three years of detailed breeding data from the Minnesota Study Area. These data are too few to make robust comparisons with population trends from the MLMP. Still, we can report two preliminary patterns from the state. First, the adult return rate in Minnesota (80 to 83%) has consistently run 5% below that in Wisconsin.* Second, 31% of all fledged broods in our Minnesota Study Area from 2021 to 2023 contained two chicks. This number puts Minnesota in line with Wisconsin, where the paucity of two-chick broods reflects challenges faced by breeders since 2010. The 2022 MLMP report too cites reduced chick production in recent years as a potential cause for concern. At first glance, then, the loon population in Minnesota seems to be facing the same difficulty as its neighbor to the east.
Environmental Causes of the Decline
Thus, the loon population across the entire Upper Midwest seems to be in decline owing to reduced breeding success. This is vital information. But if our knowledge ended there, we would stand no chance of fixing the problem. To do so, we must identify the precise environmental factor or factors that impair loons’ ability to breed. In the past few years, of course, we have learned that decreased water clarity and increased black flies are two such factors in Wisconsin. That is a good start. However, it will improve our understanding — and strengthen any case we might wish to make for using local, state, and/or federal resources to mitigate the problems — if we can extend these findings from Wisconsin to Minnesota.
The Plan for 2024
2024 is going to be a pivotal year for the Loon Project. Why “pivotal”? Because we have built a conceptual and logistical platform in Wisconsin for understanding the entire Upper Midwest loon population. And we have painted a clear picture of a declining Wisconsin population and its causes. In 2024 we must pivot towards Minnesota.
Thanks to the hard work of our field crews, seed money from the National Loon Center, and the growing ranks of folks in Minnesota, Wisconsin and elsewhere who support our work logistically and financially, we have spent three productive years in Minnesota. We have identified 115 territories in Crow Wing and Cass counties that constitute our Minnesota Study Area and marked adults in about 3/4 of these territories. Our task now is to place a large enough team in the field to collect high-quality breeding data from our new Minnesota study lakes.
We will use methods in Minnesota that have proved successful in Wisconsin since 1993. In the spring we will clear cobwebs from our canoes, head to our 115 study lakes, and confirm the return or non-return of each pair member. On subsequent weekly visits single team members will locate and identify each pair member and document their nesting status or number of chicks. Most critical to our effort will be recording causes of nest failure and chick loss, because, of course, poor breeding success is the root cause of the Upper Midwest population decline.
Our growing sample of survival data from adult return rates will allow us to build a population model for the Minnesota Study Area. In addition, accumulating return records will allow us to determine whether the curiously high annual mortality of Minnesota adults that we have measured by three separate means holds up over time. If so, we will try hard to identify the source of the mortality, which would be very costly to the population.
Following the field season, we will determine whether the low breeding success in our Minnesota Study Area persisted in 2024. Then we will turn our attention to environmental factors that are causing nest failure and/or loss of chicks in Minnesota. That is, we will follow up our increased field effort with a statistical search for likely causes — especially water clarity, black fly populations, and weather patterns — that might be driving a breeding decline. It will likely take several years of intense field work to get a clear picture of such causes.
Support for Our Low Tech Approach
As you have surmised, our future promises to be unglamorous and low tech. We will not use drones, satellite transmitters, amphibious vehicles, or hovercraft to collect data. Instead, trained observers will employ the field techniques that have gotten us where we are today. We will carry our canoes to boat landings, put paddles in the water, find loons, and collect as much data as grit and elbow grease allow.
Now I am asking for your help as we do this important work to save loons in the Upper Midwest. If you believe in our work and wish for it to continue, please consider a tax-deductible donation to support us. In keeping with our theme of simplicity, we run a lean operation. None of our funding goes into the pockets of senior researchers. This year we will use our funds to support: 1) field interns who visit study lakes by canoe and collect data (about $6,000 for each of four interns covers a monthly stipend and reimbursement for gas); 2) lodging for the interns and myself (about $10,000, if recent experience is a useful guide); 3) economy airfare for me to make two trips to and from the Upper Midwest and gasoline for the motorboat we use to cover breeding pairs on the Whitefish Chain ($1800); and 4) color bands for marking loons and costs to replace broken equipment and needed supplies ($4,000). So I estimate our need to be about $40,000 for the expanded 2024 field effort in Minnesota.
By the way, we currently have enough funding in place to support a modest field effort in Wisconsin. However, increased funds directed to Wisconsin would also strengthen our effort in this most valuable long-term study population. You may earmark your donation to go towards our Wisconsin work, if you so choose.
You may use this link to go to our “Donate” page. Thanks for any support you can give us. We promise to make every penny count!
The Future
Our future prospects seem bright. In addition to cultivating a large number of supporters across the Upper Midwest, we are forming an Upper Midwest research team. Obtaining funding is always uncertain, but our new collaborators have a good track record of acquiring major regional funding. We will apply for such funding this year and, if we are fortunate, might receive it by late 2025.
If all goes well, lake dwellers in Crow Wing and Cass counties will soon get used to the same peculiar sight to which lake residents in Oneida and Lincoln counties have become accustomed: paddlers in solo canoes, wearing bleached PFDs and binoculars, scanning the lake’s surface ceaselessly for loons.
FOOTNOTES
* This pattern is enigmatic. I can think of no reason why Minnesota loons should die at a higher rate than Wisconsin loons. One hypothesis is that the pattern is the higher density of loons in the Minnesota Study Area than the Wisconsin Study Area results in greater competition for territories in Minnesota. If so, what appears to be a low adult survival rate might instead be a higher rate of eviction. From a conservation standpoint, we must hope that eviction explains the apparent difference. If Minnesota loons truly die at a substantially higher rate than Wisconsin loons, Minnesota birds would have to offset that mortality rate with considerably higher breeding success.
** The beautiful featured photo, as usual, is by Linda Grenzer. It shows a foot waggle by two-year-old male that tried to claim her lake as its territory this past summer. We are slightly worried that this youngest-ever settler is a sign of population decline in Wisconsin, because four-, five-, and six-year-old nonbreeders would normally outcompete it for this territorial opening.