A Mammal Weighs in on Avian Parental Care

I got a phone call last week from a lake resident in Wisconsin whom I had consulted the day before about the whereabouts of a territorial pair and their chick. “She was out there along the shore with the chick this morning”, he reported. I have grown accustomed to such reports. During the incubation period, I often hear: “She was on the nest all day yesterday.” In short, humans give female loons most of the credit for parental care.

It is, of course, reasonable that we should look at birds from a mammalian perspective. In mammals, females carry young internally throughout development. For this reason, male mammals are limited in the extent to which they can contribute to the development and rearing of young. As a consequence, male mammals instead spend their time competing vigorously for access to limited females (those that are not already pregnant). Dominant males in such breeding systems often succeed in pairing with and mating with many females. Thus, the result of mammalian females carrying and nourishing young within their bodies for an extended period is that about 95% of mammalian breeding systems are polygynous (one male mated to multiple females).

In birds, females lay eggs early in the embryo stage, so young grow outside the female’s body. Leaving their developing embryos in the nest “frees up” female birds and means that male birds can contribute to warming and protection of those embryos and young just as well as females can. And female birds are also available to mate almost as often as male birds. Since there is no reproductive asymmetry, monogamous pairings (one male mated to one female) typify birds. Indeed, roughly 90% of all bird species are monogamous. In many monogamous species the father’s parental efforts are equal to or even greater than the mother’s. (Loons are a good example, as Linda Grenzer’s photo of the male on her lake shows.)

Since mammalian mating systems differ so fundamentally from avian mating systems, it makes sense that humans often misinterpret avian patterns of breeding and parental care. In other words, humans are familiar with the concept of mothers providing most of the care for offspring, so they naturally presume that an adult loon that they see feeding and protecting the chick is a female. Of course, humans are also used to seeing female ducks on the water leading a great long string of ducklings behind them, so the superficial similarity between ducks and loons reinforces the concept that maternal care should occur in loons. But loons, along with thousands of other birds, defy mammalian expectation.

I wonder if, one day, greater understanding of loon biology will prevail. It will bring a tear to my eye — and a profound sense of accomplishment — to hear this simple, rather uninformative message in my voicemail: “The chick was out there with one of the parents.”