There was a Rook on the ground today, most obliging for a photo too. This doesn't happen often.
They're usually seen flying over fields, feeding in farm fields and sitting in the trees.
An area with Rooks nesting in trees is called a Rookery. Rooks are often heard 'crowing' from their Rookeries. http://www.british-birdsongs.uk/rook/
We have seen many Rookeries on our travels in recent weeks - even in trees in the middle of a small roundabout !
Easily distinguished from Jackdaw and Carrion Crow by their thick grey-ish bill.