Most damaging to loon legend, however, is the indifference with which each loon seems to view the territorial battles of its mate. Moreover, when a loon is driven off its territory, it departs alone, leaving his or her conqueror and erstwhile mate as the new breeding pair in possession of the territory. Any eggs or chicks produced by the original two birds are lost, although the remaining member of the original pair often attempts to renest with its new mate. Thus, the much-vaunted pair bond of loons does not outlast each pair member's ability to defend its breeding position from intruders of its own sex. I don't mean to suggest that all breeding loons must fight constantly to maintain their breeding status.
Violent fights are, in fact, quite rare.
In most cases, an intruder spends five to 15 minutes engaging in a series of stereotyped interactions with the pair that includes approaching, circling, and head bowing and then it flies away, perhaps to intrude elsewhere. Eventually an intruder will arrive that does not leave quickly, and this leads to an escalated battle that might cost the embattled resident its territory and its mate. We are currently trying to understand the factors that lead to such escalated contests. One female attempted unsuccessfully to breed in the new lake in the year after losing her territory. A second female became a nonbreeder but made frequent visits back to her original territory and once fought unsuccessfully with the resident female in an attempt to regain her old territory.