Harriers Fighting

This photo was taken yesterday morning through light fog and after a heavy frost. This looks as if it's a serious fight but I'm not completely convinced of that - they just seem to have too much fun doing it. It's not unusual for two or more of these birds to be hunting together (they often hunt singly of course) and then they will rush each other and have a short confrontation in the air and then resume hunting together as if nothing had happened.

The same thing often occurs when one harrier is perched on the ground and another happens by (as in this case). A furtive confrontation, then normalcy. I know it's anthropomorphic of me to think they might be doing it for fun but I can't help myself... I've seen it so very often and it's so different from when they are actually fighting directly over food. That I have also seen and believe me it's very different from this and very serious.

This is the first time I've seen this blue in the primaries (top bird). Perhaps a prismatic effect from the angle of the light and feathers?

7D, 1/3200, f/7.1, ISO 800, 500 f/4, 1.4 tc, shot from pickup window, cropped to 49% of original image but then added a narrow strip of canvas at top for composition, not baited

Comments/critique appreciated