I do not think of myself as a cheerful bearer of bad news. Yet I repeatedly bring it. Each time I meet a new lake resident and secure permission to cross their land and observe their loons, I brace myself for the inevitable question: “Is it true that loons mate for life?”. I gently share the truth with them. “No, they don’t; but they really have a strong allegiance to their territories!” The idea that loons love their homes, not their breeding partners, provides scant solace to most folks.
Having spent a quarter century disappointing loon lovers in Wisconsin and Minnesota, I have been searching for scientific news to share about breeding pairs that sheds a warm, wholesome light on loon mating behavior. My quest is not inspired by guilt alone. As a scientist, it makes sense to me that adults should become acquainted with their mates and benefit from doing so. How could complex, long-lived animals like loons jointly defend a territory, build a nest, divvy up incubation duties, and raise young together — as seen in Linda’s photo above — without benefitting in some way from their association?
At last, my current study of predictors of breeding success has revealed one way in which loon pairs do benefit from a long-term association. The graph below shows two patterns. First, there is a gradual improvement in hatching success over time as a pair remains together on a territory. These numbers jump around a lot owing to limited samples of pairs that have been together ten or more years.
Second and more clear cut is the improvement in hatching success between a pair’s first year together (Year 0) and their second (Year 1). As you can see, loon pairs improve their chances of hatching eggs by almost 10% between these first two years.
Now we can only speculate about the cause of this dramatic improvement in breeding ability among young pairs. Perhaps pair members synchronize their breeding behavior better in their second year together than in their first. Maybe pair members rotate incubation duties more crisply in year two, thus seldom leaving the eggs uncovered and unguarded.
Of course, the challenge that romantic couples face of living and working harmoniously, following an awkward adjustment period, has a familiar ring to it. That challenge is depicted in “Period of Adjustment“, a 1962 comedy-drama film based on a play by Tennessee Williams. It is heart-warming to see that loons — like actors Jane Fonda, Jim Hutton, Lois Nettleton, and Tony Franciosa — bounce back strongly after a rough first year.