Before eating its prey, the bird holds it by its tail and whack it to death against the perch, as the live fish may extend its fins in the bird's throat, choking it, sometimes to death.
Common Kingfishers are highly territorial because they are to eat about 60% of their body weight a day. They fiercely defend their territories, even from their mates and offspring. As a part of it, they perform a ritual display perched some distance from each other. This involves displaying feathers and beaks, accompanied by whistling. Usually the dispute is resolved without actual combat. But in rare instances, combatants will lock beaks and attempt to drown each other.
Info Source: http://www.naturia.per.sg/