Eighteen pigeons ascending

I know there were eighteen because I counted them when they alighted on the roof. The pigeon army has grown in recent weeks. They forage for spilt birdseed on the ground below my mid-floor flat. When I open the window with a squeak, they all take off as if armageddon has been announced. Then they sit in a row on the edge of the roof wondering when it might be safe to return. (They always do.)