What species is this bird?
It's a BLACK KITE (Milvus migrans). I bet you took the pics this summer because the great majority of the population is in Africa at the moment.

It is a black kite because:


rather uniform dark brown color
squared tail (it form a shallow v during gliding)
uniform underwing color and lighter head is a shared with marsh harrier but the absence of darker patch around the eye, the dark shoulder and 6 digitated primaries assure us is a black kite.


Here is a picture for reference: