I live in a South London leafy Borough in a road lined with huge trees but it is also very developed with many blocks of flats. The last few weeks I have noticed a large flock of Greenfinches turn up, there is approximately 50 birds, I've attached a photo of some of them in one of our huge trees. I've lived here for 10 years and never seen a Greenfinch here before (we are lucky to have so many different birds but never Greenfinches). I've noticed they have decided to nest in a tree in our courtyard for the first time, at 5pm the tree is alive with fluttering of so many birds settling down for the night, it's amazing. My question is: is it usual for such a large flock of Greenfinches to change nesting sites?