It is a common misconception that, within the bird community, females do all the nest sitting. Although that may be the case for the majority of bird species, it is heavily influenced by the large number of Passerines (songbirds). In other bird orders (and some Passerines), nest duties are shared by the mated pair. And in a few species, such as some penguins, the male does all the incubating.
Common Loons share the nest duties. Each pair seems to work out its own schedule for who is on the nest at any time. Shifts can last from an hour or two to twelve hours or more. Earlier studies, mainly in the 1970s and 80s, concluded that females did most of the nighttime incubating and males would relieve them at dawn. But our observations show that it varies between pairs.
The loons on this territory fly in the face of conventional wisdom and demonstrate that the more we learn, the less we know. At this time, the male is doing most of the nest sitting and virtually all of the night shifts. But don’t be surprised if you tune in tomorrow night and the female is on the nest.
We honestly don’t know what drives the variations in nest sitting behaviors but it’s fun to speculate. This female is well into her twenties, at minimum. By loon standards, she’s an old lady. Nest sitting actually can have higher energy requirements and stress levels than other normal daily loon activities. Contributors to this are temperature, insects (black flies in particular), and being out of its natural element. Loons are essentially aquatic animals. As the temperature warms up, we might see the female take on more of the nighttime sitting, when it will be cooler and less stressful. But I’m not putting money on that.