Among the most curious and talked-about aspects of common loon behavior are “social gatherings” — groupings of three to twelve adults that occur in July and August, which feature loons swimming together and interacting socially for an hour or more. During social gatherings, adults exhibit stereotyped social behavior, such as circle-dancing, bill-dipping, excited peering, and splash-diving. Occasionally one loon lunges at a second, which touches off a point-yodel by a male or two and fleeing across the water by a few panicked participants. If the gathering is on a territory with chicks, those chicks hide near shore, while their parents swim with their adult visitors. However, as shown in Linda’s photo (above; the observer is Nelson Gould, who spent two years helping run the Project) and my video (below), the most frequent and obvious behavior seen in social gatherings is what appears to be relaxed, slow, joint swimming by a large raft of adults. Peaceful swimming of this kind could be described as the hallmark of social gatherings.

Of course, it is tempting to offer a simple, unitary explanation for social gatherings. I have been asked a number of times whether the visitors at social gatherings might not be chicks that were hatched on reared on a lake and have returned as adults to re-connect with their parents. Setting aside the fact that young adults looking for a territory would seem to have little to gain from visiting their parents — and might even harm their parents by drawing more attention to the territory (see below) — we have many marked loons of all ages in our study area and can look at the number of times that young adults have revisited their natal lakes. Of 1743 visits to lakes by adults that we marked as chicks that we have recorded so far, only 13 have been visits to the natal lake. We have not yet run statistics on this pattern, but it seems clear already that young loons actually tend to avoid their natal lakes — intruding at many lakes in the neighborhood but seldom visiting their natal one.

A second common speculation is that social gatherings are mere aggregations of birds for foraging purposes. But, as Jim Paruk has noted, foraging rarely occurs at social gatherings. Finally, social gatherings are sometimes described as being groups that form in anticipation of migration; but gatherings occur in late summer, not fall, so they happen far too early to be a prelude to migration.

In fact, a crucial first point to grasp as we seek to understand social gatherings is that participants in these events comprise a hodge-podge of adults with competing interests. In other words, the key to understanding social gatherings will lie in understanding their makeup. Therefore, we will be powerless to solve the riddle of social gatherings without a large population of marked birds, including both territorial adults and young intruders.

The first set of participants in social gatherings are simply territorial pair members defending the lake where the gathering occurs. If this “home pair” has chicks, the intruders within the gathering are unwelcome guests, and the home pair’s chief goal is to steer the intruders away from their chicks and make sure they do not stay too long. Why? Because nonbreeding loons that are part of the gathering try to find chicks, use the presence of chicks as a badge indicating the quality of the territory, and often return to evict owners on lakes that produced chicks the previous year. Home pairs that have failed to produce chicks probably also benefit from limiting the duration of gatherings, so as to protect their territorial position. (However, we have not verified this last hypothesis statistically.)

A second set of participants in social gatherings — the largest segment — are nonbreeders who seek information for future territory settlement. Unlike others who have tried to explain social gatherings, we on the Loon Project are in a unique position to describe this important segment, because we have been marking chicks in our study area for over twenty years and these marked chicks have returned as adult nonbreeders in many cases. Thus, we know that nonbreeders are: 1) adults two to four years old that are too young to settle on a territory, or 2) individuals five to ten years old that are in prime condition and on the brink of territory settlement, or 3) adults of various ages that have been evicted from a previous territory and are looking to resettle on a new one. Again, all nonbreeders have in common that they are learning about a variety of territories in a certain region — chiefly which have chicks; which do not — in order to settle on one of them, usually by evicting a territorial owner. So nonbreeders are a particularly dangerous segment of the loon population, from the standpoint of home pairs.

The third cohort of attendees, and perhaps the most interesting, consists of neighboring territory holders. These adults, which may or may not have chicks on their own territory, at least have a territory and therefore obviously have reasons very different from nonbreeders for joining the gathering. Since they have left their own territory undefended to make the flight to this neighboring lake — and often their chicks, as well — it seems clear that neighbors must gain something from the visit. The most plausible explanation for participation by neighboring pair members is that they are trying to draw nonbreeders in the neighborhood to someone else’s lake instead of their own. Neighbors seem to be exploiting the fact that adult loons of all stripes are strongly attracted to other adults that they see on lakes. In decoying nonbreeders to another lake near their own, neighbors are decreasing the odds that their own chicks hiding back on their lake will be discovered, while increasing the chance that the home pair’s chicks will be seen by nonbreeders. From the home pair’s standpoint, then, neighbors are competitors whose visit is potentially harmful in the long run, but at least they pose no threat to territory ownership.

I will have more to say about social gatherings. Indeed, I am currently analyzing and comparing the behavior of territorial pairs and intruders at social gatherings. So I will have further findings to share in the coming weeks. For now, try to keep in mind the key point of this post: loons in social gatherings constitute a broad swath of individuals that differ in age, territorial status, and current reproductive stage. Although the behavior of all participants might look similar during the gathering, each loon has its own goals in attending the event and its own hopes for the outcome.