Of Wrens and Loons

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in “stepmother groups” — those in which a past dominant female that was the mother of all the male helpers had died and been replaced by a “stepmother” from an unrelated outside group.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.