Patterns in General and A Puzzling One in Loons

It is my 60th birthday today. I ran 5.3 miles just to show that I still had it. Since I find running unpleasant, I listen to music in an effort to distract myself as I run. (This works poorly.) Amidst the classic hits on my playlist today (by Jim Croce, Don Henley, Talking Heads, David Bowie) was an outlier: “New Rules“, a 2017 hit by Dua Lipa. Wikipedia describes New Rules as a “tropical house, electronic dance music and electropop song with a drum and horn instrumentation”. While I do not understand most of that description, I understand enough to know that few men my age would find the song meaningful. When you consider that the song concerns a young woman’s efforts to break up with an unfortunate boyfriend, its profound significance to me becomes even more alarming.

I can explain. New Rules describes a very logical practice common to many of us: trying to interpret a vexing phenomenon and chart a course forward by looking, not at a single event, but a series of related events. The idea, of course, is that an isolated event might be misleading, whereas many events, studied together, offer a better picture of the world. And this is what scientists like me do. We resist the temptation to generalize to the world from a single event and instead study sets of related events and use statistical tests to discern patterns that may or may not align with our hypotheses. When I heard New Rules for the first time, I laughed out loud, because Dua Lipa sings “Now I’m standin’ back from it, I finally see the pattern” — referring to her boyfriend’s persistent misbehavior. This is just exactly what I have devoted my life to doing… a very different context.

Here is the latest puzzle in which I am trying to see the pattern: old female loons are reluctant incubators. That is, when sitting out in the open on a nest becomes unpleasant, old females are less likely to put up with the unpleasantness and continue sitting on the eggs. Instead, they tend to bail on the breeding attempt, to their great cost and that of their mate. In loons, of course, the unpleasantness derives from black flies that specialize on sucking loon blood, Simulium annulus, which are in profusion at the moment in the study area. (The photo below is from Clara Lake, where the pair is beseiged.)

2019-05-17 09.45.12

I observed the reluctance of an old female to sit on eggs on Oneida-West four days ago. The very tame male that just took over the territory this year  — a 9 year-old hatched on McCormick who settled first on Oneida-East, and then shifted to the territory on the opposite end of the lake — had a nape that was seriously chewed up. The feathers on his nape were misaligned, showing that the skin beneath them was swollen from countless bites of black flies. Disrupted nape feathers are a telltale sign that the loon has been incubating for a long period in the presence of many black flies. But the female of the pair, a veteran of 23 years breeding on Oneida Lake and mother of at least 18 fledged chicks, had a pristine nape. While her appearance was more pleasing to the eye than the male’s, it revealed her dark secret: she had been neglecting her incubation duties after laying an egg in the nest a few days before.

One pattern is clear here. Statistical analysis of known-age breeding pairs has shown a very strong tendency for pairs containing old females to abandon their eggs when black flies are severe. In contrast, old males, young males, and young females incubate clutches enthusiastically when black flies abound. Why on earth would old females have evolved to drop the ball on incubation as they do?

As a biologist, I have learned that most behavior is adaptive — it tends to increase the breeding output of the individual displaying the behavior — so I am inclined to interpret what might be called irresponsibility on the part of old females as calculated to help them in the long run. Perhaps old females have somewhat weaker immune systems than young females, so that exposing themselves to countless bites and the harmful protozoans that flies transmit might weaken them, making them vulnerable to territory eviction by a healthier female competitor. By refusing to incubate and weaken themselves, old females are costing themselves a single chance to rear young but might be protecting their ownership of the territory, which increases the young they raise down the road.

My explanation for old females’ behavior is just one possibility. It is quite likely to be incorrect. Like Dua Lipa, I will have to stand back a bit more — and collect more data on old females — to see the true pattern.