WOW! That's good stuff! The owl is a hit or miss thing, maybe moving it around is the trick. As has been mentioned , I've seen poop covered owls and I've seen thirty or forty pigeons on a rooftop with the owl right in the middle.
Shooting is a great solution if you have the time and space. I have a cemetery behind my house so not too many complaints from THOSE neighbors, but at a previous abode the police were called by a bird loving lady several times (pigeons shouldn't even be considered birds!). Just be sure of whats down range before launching a barrage of lead overhead, the pellets that miss may find windshields or children.
Set an oscillating fan on the balcony for a few days with tinsel or streamers in the front grate. Keep a light on at dusk (it will improve your aim).
Bird detrerent spikes can be purchased at
Bird Control From Nixalite, The Bird Control Professionals since 1950 or just do a google search for other retailers. you shouldn't have to leave them in place forever, just long enough to change their habits. They work for keeping kids from jumping your fences too!
Good luck!