Every year there manage to be two Loons out in front of the cabin, up in Minnesota’s lake country. They nest on the same, ever-expanding semi-floating but occasionally shrinking nest over behind the point, so we can’t see the nest without going across the marsh in a canoe. It is a great place to nest, but for one small detail. Behind the embayment formed by the point is a tall bluff, the edge of an ancient river valley that passed through the area during one or more (probably a few) prior interglacials. Maybe it was a version of the Mississippi River, maybe it was a version of the Warren River, likely both. Atop the ridge, where no one will ever build cabins because it is too high up, is a grove of white pines. A good way up one of the tallest pines is an Eagle’s nest.
Every year there manage to be two eagles up there in that nest. Plus hungry offspring.
So the Loons produce, probably, two chicks. Often there is only one after a few weeks. Sometimes that one reaches adulthood, but just as often it disappears. And, every now and then one of the Loons disappears too. I strongly suspect that the rate of attrition on this Loon family is inversely proportionate to the abundance of ducklings in the bay. Ducks are easier prey for the Eagle.
You can tell when the Eagle is aloft because the Loons alarm call. Every now and then you see an Eagle and a Loon interact a bit. More alarm calling. Earlier this year a neighbor saw an Eagle take a Loon. I’m not sure what really happened. Non-bird watchers without binoculars and experience are notoriously bad sources of information. But, indeed, two Loons went to one. A few years back I watched, over a few weeks, when a third Loon showed up and did battle with one (or more … you really can’t tell the Loons apart or even guess at sex) of the Loons, frequently. Every now and the the loosing Loon would disappear like it had been killed and sunk. Then it would reappear way far away and they’d stay apart for a while. Eventually an epic battle ensued that went on for hours, and when that was over the second of the two embattled Loons failed to reappear.
I assume that the two Loons that nest at this spot sometimes includes the same two Loons from the pervious year, sometimes not, with a replacement mate showing up and taking over that role. The year there were three Loons, including the interloper, we saw what must have been a takeover. I’d love to know if it was one of the offspring from a previous year, or a Loon from a different home nest elsewhere on the large lake, or even from a different lake.
In any event, by mid summer or so, the babies are not so small and more or less do OK on their own and hang around the nest. The adults move to flocks, there may be two or three of them, that hang out mostly far off shore in the larger part of the lake, abandoning their embayments or otherwise protected areas. Then one day they are gone. The new offspring of that year hang back and leave later, finding their way to their wintering grounds using something other than experience, and something other than being taught by their parents. Apparently. (Maybe they meet up later, I’m not sure.)
When I lived out east, and often visited the rocky coast of Maine, there would be a lot of Loons there in the winter. (Yes, Maine is a great place to visit in the winter; no tourists.) The tend to stay asea, bobbing and rolling in the surf, staying away form shore and presumably eating small fish.
Prior research has shown that the Loons that return in a given year to a given nest on a lake somewhere in Canada or the norther tier of US states are often the same ones that were there the previous year, though with some never returning because they did not survive the trials of migration. The relatively heavy turnover of our Loons, the ones that nest back behind the point, is probably on the extreme end of the range of variation, caused by the Eagles. But until recently it has not been known for sure if loons returning to their wintering sites are faithful to that geography.
But now there is some research on that.
From a press release about that research:
Common Loons (Gavia immer) nest on lakes across Canada and the northern U.S., but every winter they disperse, many to the open ocean where they’re difficult to track. It’s been well established that many Loons return to the same nesting sites every spring, but new research in The Condor: Ornithological Applications shows for the first time that they are similarly faithful to their wintering sites. Over the course of nearly 15 years, James Paruk of the Biodiversity Research Institute and his colleagues used a combination of methods to investigate winter site fidelity at four locations across North America and found that birds had an 85% chance of returning to a site in subsequent years. Because Loons’ coastal wintering habitats can be severely impacted by oil spills and other human activities, this information has important implications for wildlife managers.
Here’s one of the maps from that paper:
FIGURE 1. Breeding and wintering locations of Common Loons in western Maine (Rangeley and Moosehead Lakes region), USA, that received PTTs in 2011 and 2012.
The research used banding and racking technology to characterize winter time home ranges. Since you are reading this blog you are probably a bird expert, so you can read the original OpenAccess paper yourself for all the details. The implications of this research, from the original paper, are:
Our finding that Common Loons exhibit winter site fidelity has important implications for assessing damages that occur after a marine oil spill (Natural Resource Damage Assessment [NRDA], administered by the USFWS). Two fairly recent NRDA studies investigating the impacts of marine oil spills on Common Loons in New England (North Cape in 1996, Buzzards Bay in 2002) would have benefited from knowing whether Common Loons exhibited winter site fidelity. Models based on the population dynamics of color-marked individuals indicate that ~3,900 Common Loon–years were lost in the North Cape event, but the numbers might have been higher if winter site fidelity were known (Sperduto et al. 2003). Thus, in light of recent marine oil spills (e.g., Deepwater Horizon, 2010; Paruk et al. 2014b), and given the high probability of another oiling event, our data on wintering site fidelity in Common Loons will increase the accuracy of predictive models during NRDA investigations.
All this exploitation of fossil fuels is lunacy.
Anyway, I would like to know more about the history, the deep time history, of this system. It might be true that every single Loon occupied lake is in a glaciated area, though perhaps there are driftless lakes in the western part of the genus’s territory. But most Loons live on lakes that did not exist 20,000 years ago. The history of a pattern of geographical fidelity under dramatic landscape change has to be interesting. Was there a time when Pleistocene Loons occupied periglacial lakes, sitting atop melting continental glaciers? (That would of course require that fish lived in those lakes.) If so, note that while vegetation could grow on dirt field atop shrinking glaciers, it would be unlike for there to be tall pines persisting there. So, no Eagles maybe. Anyway, over time, those lakes would disappear and move around considerably, and glacial lakes would become more common and the Loons would live there, changing their geography a bit, and those lakes eventually drain and regular lakes replace them, again requiring a change in geography. As these changes occur, Loon communities might have combined or split, and along with that, the winter range communities may change composition. Like when a mother and father Loon from different winter ranges end up on the same newly formed glacial lake. Where do the offspring go?
We need a time machine.
James D. Paruk, Michael D. Chickering, Darwin Long, Hannah Uher-Koch, Andrew East, Daniel Poleschook, Virginia Gumm, William Hanson, Evan M. Adams, Kristin A. Kovach, David C. Evers. Winter site fidelity and winter movements in Common Loons (Gavia immer) across North America. The Condor, 2015; 117 (4): 485 DOI: 10.1650/CONDOR–15–6.1