Loon territory acquisition occurs by one of three means: 1) takeover, in which an intruder defeats a resident breeder in battle and claims its territory; 2) passive occupation, wherein a loon simply replaces a breeder that has died; and 3) founding, which entails establishment of a new territory, where none existed previously. All three modes of acquisition occur in both sexes, and all three are common, as I describe here.
The video below provides a sense of the violent nature of territorial contests. In this case, one loon eventually dove to avoid the other.
As the video suggests, a battle for a loon territory can be quite dangerous, sometimes leaving one combatant severely injured and unable to defend itself from further attacks by its opponent. Indeed, male fights for territories are commonly fatal. In most cases, the male that perishes is the previous owner of the territory, as described here.
We have another, lengthier video of a loon fight, this one on Currie Lake from 2008.