Just Good Friends?

Struggled to get a pic to post as it has rained all day. I came across Snowy and the mallard pair on the bank of the lake. They were quite a way away but I like how they're lined up. Snowy is a crossbreed with mallard in his make-up, he's got that mallard curl of feathers on the top of his tail. These three have been inseparable for a while, I've got lots of images of them together on land and in the air over the past weeks. I've seen Snowy trying unsuccessfully to chase the mallard drake away. It must be in the nature of mallards to fly around in threes otherwise the plaster ducks like the ones Hilda Ogden had on her wall in Coronation Street wouldn't have come about. 

I've found a scientific paper on the subject by John Hori. "Three bird flights coincide with maximum activity in the gonad cycle. .... It is suggested that the flights are primarily sexual in origin, but that latent gregariousness is also a causal factor."