I have spent my entire academic career making logical deductions about animal behavior. In the early 1990s, I was part of a team of ecologists at Purdue University studying the peculiar cooperative breeding behavior of stripe-backed wrens in central Venezuela. This species could hardly be more different from the common loon. Stripe-backed wrens live in social groups of up to 10 adults, headed by a dominant male and a dominant female, which, we thought, were the only group members to breed. The other group members comprised adult offspring of the dominant male and female that had remained at home as breeding helpers instead of dispersing to breed on their own. When DNA fingerprinting revealed that subordinate males in some groups sired young through matings with dominant females, it surprised us. Seeking to follow up on the striking genetic pattern, I reasoned that the behavior of the wrens should reflect the mixed paternity of the offspring. Specifically, I predicted that: 1) subordinate males were probably actively pursuing matings with dominant females, 2) dominant females were likely seeking out matings with subordinate males, and 3) dominant males were probably not happy about these liaisons and might be expected to attack subordinate males in an effort to deter their amorous proclivities.

My predictions were not rocket science, of course. Though we had no inkling from past behavioral observations that anything but strict monogamy was occurring in wren groups, it stood to reason that we had missed some social behavior that might have clued us in to the mixed parentage pattern we discovered in the lab. Indeed, my behavioral study of the wrens during April and May of 1990 and 1991 revealed all three predicted behavior patterns. During the “fertile period” of the dominant female, the dominant male and various male helpers vied to remain in close proximity and copulate with her when she was receptive. Aggression among competing males was fierce. Dominant females, it seemed, encouraged competition among males wishing to mate by openly advertising their readiness to mate. However, this suite of aggressive and mating behaviors only occurred in “stepmother groups” — those in which a past dominant female that was the mother of all the male helpers had died and been replaced by a “stepmother” from an unrelated outside group. In fact, the death of a dominant female was a crucial event in a wren group, because it turned a staid, monogamous breeding system into all-out warfare between her husband and sons to mate with her successor. Sorry…….I had not meant to go on about my old wren work, but those interested can check out this paper.

Here is my point. As I said, one could hardly hope to find two species more different than common loons and stripe-backed wrens. From the standpoint of a behavioral ecologist, the wrens would seem to offer a cornucopia of research opportunities: helping behavior, living in social groups, deferred breeding by helpers, mating competition. Many questions about the complex wren breeding system remain unanswered. (It does not help that one must travel to an unstable country that generally dislikes Americans and tolerate dreadful living conditions on a ranch overrun by aggressive feral pigs.) But one lesson I have learned is that close scrutiny of any animal’s behavior reveals unsuspected richness and complexity.

The monogamous mating system of loons would seem to offer little to the behavioral ecologist. But the peculiar — possibly unique — system by which young adults seek to learn about breeding territories and established breeders seek to deter their efforts is a gold mine. Consider late-summer social gatherings. The three sets of attendees at these gatherings have recently come into sharp focus, as I describe in a new page I have added to the website. Now that we understand which loons are attending social gatherings and why, we can generate specific predictions about how different attendees should behave that provides a framework for future research.

If members of a territorial pair are trying to safeguard their territorial tenure from floaters, which try to find chicks and use chicks as a badge of quality to target pair members for eviction, pair members should take pains to hide their chicks from floaters during social gatherings like the one shown below.

Thus, we can predict that parents of chicks should lead floaters and other intruders at social gatherings away from the part of the lake where their chicks are hiding and generally discourage exploration of their breeding lake. Furthermore, parents with chicks should behave aggressively towards intruders in cases where a “flotilla” of adult loons approaches the place where the chicks are stowed. How should breeding pairs behave that have failed to produce chicks? They should encourage intruders to explore all parts of their territory, because they want floaters to conclude that there are no chicks present and that the territory is not worth fighting for. For their part, floaters should always try to move about the territory as widely as possible in an effort to spot any chicks present. Finally, how should intruding neighbors behave? Like floaters, intruding neighbors should wander widely in another pair’s territory and induce other intruders to do likewise, in order to maximize the likelihood that floaters spot the chicks of the home pair and return the next year to evict them. In cases where one or two loons appear to “lead” the flotilla about the territory, such as the two left-hand adults in the video, the leaders should tend be floaters or intruding neighbors, not members of the home pair (unless the home pair is without chicks).

Naturally, it will take a lot of work by observers skilled at identifying loons from color bands to test these fine-grained, specific predictions about loon behavior during social gatherings. But now that our long-term probing of loon social behavior has exposed a richly textured system of social information and deception, I relish the challenge.

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.