I have just seen a flock of approx 20 Red Kites circling above some houses and a small copse of wood in the middle of Corby, Northamptonshire.
I've never seen so many together. Is this a normal behaviour for so many of them?
Yes. Where they are at high density large flocks can be common, especially where they are being fed, or where there is a communal roost. With the warmth and sunshine today the kites are very active around my house.