One of my neighbors has a big issue with birds, they have this device that squawks and blinks lights when the birds fly near it or if people walk up to their door. Maybe if you were to make the owl make some squawking sounds, it would help as well.
The stronger twin I just built has a stronger motor to spin the impeller faster. And so I can let something slap the frame it will sit on. When I first put the first one up the foil tape just touched the solar panel behind it and the slapping sound made the pigeons fly off. At least a while. So the next one will be louder. And I am thinking of making two motorized vibration balls to lay near each of those panel arrays with a single motion sensor. Make this ball JUMP around each time they walk in front of the sensor.