Black Guillemot - Courtship and Display (more below)
I could watch these guys for hours - and often do. At this time of year countship displays are well underway. On the water pair swim in tight circles around each other constantly calling. Wing flapping a presume by the male seems to play an important part showing off the strong flight muscles.
When a third party gets too close all hell can break loose with battles on, under and above the water. Having watched them for a while it appears that young unattached males try to improve their standing in the colony by approaching unattended females, sometimes at the nest hole. When her mate sees this then there is normally trouble!
Finally mating will take place and hopefully if there is enough food a new generation of Black Guillemots are added to colony - or hopefully new colonies will develop.