If you watch birds for a bit - well, actually, I mean if you sit in a hide and observe them, probably with binoculars, for an hour or two - you realise that many of them are social and like to be in flocks together. You also realise that they can be cussed bad tempered things, just picking on other birds and seeing them off, often of their own species, even as there is plenty of room and food for all.
So here in this sequence of photos below we have a plover, minding his/her own business, when suddenly another turns up nearby....and then having pushed it under the water, it then a)dives on it
b) lands on it, beak out, pushing it completely underwater again, you can only see the attacking birds wings here
c)as the other bird tries to catch its breath, it still stands on its head, trying to push it down. next minute they are feeding next to each other again. So explain that to me? I did ask some real birders, but no-one had a perfect explanation. Ideas??