Buzzard behaviour

Since the fields around my local patch have been harvested lots of Buzzards have appeared from nowhere all rising on the heat thermals on a sunny day.
These Buzzards are not my local ones but they may have come from a different area.
I could see between six to ten Buzzards flying higher and higher, smaller and and smaller in circles above the fields starting in the West and heading South Eastwards.
They could be a group of juveniles who do sometimes gather together in groups, chasing, diving and playing. This behaviour will continue until the group strays into a territory that is already taken, where the male from the territory will scare them off, or after 30 minutes the group will break up anyway, which seems to happen over my house because our local Buzzards seem completely unaffected by the Buzzards passing over as H3 and her mate stay low over the woods and don't bother to chasing the passing ones away.
On this occassion two of the Buzzards, one male and one female (the females are bigger than the males) were doing acrobatices, twisting and turning, sometimes flying upside down with their talons out stretched, this is called dive on- turn over.

In this photo both buzzards are flying upside down with talons out stretched

Information taken from a really good article called
The Social behaviour of the Common Buzzard by Robin J. Prytherch which I need to spend a lot more time reading!