For many decades, loon biologists have puzzled over aggregations of adults that occur on breeding territories in July and August. Thanks to our relentless efforts to band loons of all ages and follow those birds throughout their lives, we now have a pretty good understanding of such “social gatherings”. The key to understanding these distinctive aggregations, it turns out, is not to accept them at face value, as loon biologists often do. In other words, these “flotillas” — consisting of a territorial pair and from one to a dozen intruders — might appear to be friendly get-togethers. They are not! In fact, in order to understand social gatherings, we must first recognize that the loons attending them comprise three distinct sets of stakeholders with mostly opposing interests. These stakeholders are:

the territorial pair that owns the lake — this male and female want nothing more than to be rid of their visitors. Why? Because young adults without territories (termed “floaters”) spy on breeding pairs, find their chicks (as a measure of territory quality), and then return the next year to evict the pair member of their sex.

floaters seeking a territory — these youngsters spend their second, third and fourth years learning about breeding territories. They then seek to settle on a territory that: 1) resembles their natal lake in size and pH and 2) produced chicks in the previous year. If they locate chicks in a territory, they try to boot a pair member off of the lake and take its place, forming a breeding pair with the mate of the bird they evict.

neighbors visiting from a nearby territory — this is the strangest cohort of adults that attend social gatherings. What benefit could a breeding pair possibly derive from visiting their own neighbors breeding nearby? There are two possible benefits, in fact. Neighbors without chicks show a strong tendency to visit neighbors that had chicks the previous year, probably because they hope to “trade up” from their failed territory nearby to one with a good track record. On the other hand, neighbors with chicks themselves apparently leave those chicks hiding at home and go visiting for a very devious purpose. By temporarily abandoning their own chicks in Territory A, the breeders of Territory A hope to lure floaters in the area to join them in a social gathering at Territory B, induce the floaters to spot the Territory B chicks, and thus set the stage for floaters to evict the Territory B pair members, not themselves! This last surprising conclusion is not written in stone. Rather, it is a hypothesis based upon the strong statistical tendency for loon pairs raising chicks to target their intrusions mostly into other territories with chicks. We call this idea the Spotlighting Hypothesis.

Obviously, the three sets of adults that attend social gatherings differ enormously in their reasons for doing so. We are currently in the process of testing the Spotlighting Hypothesis, which predicts, among other things, that intruding neighbors with chicks should actually behave so as to help floaters discover the chicks of the home pair!