I lived for a few months in Berlin and it's amazing the massive amounts of sparrows Berlin has compared with other cities in Europe I lived in, including in warmer places were I expected sparrows would survive better (since unlike Berlin those places pretty much never have below zero temperatures) but which still had nowhere the number of sparrows as Berlin.

Apparently people over there are much more likely to have bird feeders out on their balconies, even though Berlin is pretty urban.

It was actually quite a pleasure to watch the antics of the flock of sparrows that lived in the ivy on the walls of the appartment building I was living in when I was there.

Are they making a nest inside a stone??