Shake your tail-feather

I don’t know if anyone else has noticed this but in the winters in Canberra I observe a behaviour amongst Crimson Rosellas I don’t see at other times of year.

At this time the rosellas seem to go around in larger groups, and some of the birds (maybe the males) give a cackling call from time to time while they are interacting and shake their tails from side to side simultaneously with the calls. I haven’t seen them do this at other times of the year. Eastern Rosellas do the cackling but not the tail shaking.

I haven’t noticed that this behaviour coincides with obviously aggressive behaviour, but I suppose it has to do with social dominance &c

John Leonard