Damn Will... you beat me to it!
Sorry Cath - I don't have any suggestions for whilst you're not there. Mike at Estupendo has been asking the same thing about the pigeons that have developed a liking for his place.
We suggested a water pistol... but it's a bit hard to fire that if you're not about. tell you what. pay me - and I'll sit on your balcony sipping cool drinks, and sunning myself... whilst squirting anything that comes near!