Common loons are large, fish-eating birds that winter on the ocean but breed on freshwater lakes. Loons have been studied for years, but it is only in the last fifteen years that we have a large enough population of banded individuals to begin to understand the details of their behavior. Breeding territories can be founded on vacant lakes by replacing a missing pair member or by actively evicting a member of the pair. When an intruding female takes over a territory, the displaced female moves to an adjacent lake. In contrast, when the intruder is male, about 30 percent of the territorial battles are fatal. If a loon is killed, it is always the resident male, never the intruder. We don't know why there is this asymmetry in the behavior of the two sexes. But since it is the male loon that seems to select the nest site with improving reproductive success every year, this may be the reason.

Many of us know loons by their haunting vocalizations. There are three long distance calls: the wail, the tremolo, and the yodel. Each plays a role in the establishment and maintenance of the breeding territory.

Loons are at the top of the food chain and tend to accumulate toxins, like methyl mercury, in their tissues. One reason for studying loons is to see whether an increase in mercury has any effect on their reproduction or behavior. These CyberTower videos describe how this research is conducted.

This video is part 5 of 6 in the Understanding Loons series.