They are rodents. First step is realising that. Plastic ravens? Peppermint? If you had rats, you'd put down traps and poison. Same should apply to these flying rats, unless of course you intend to eat them afterwards - but even I would not eat street pidgeons.
My mother-in-law-to-be lives in Schwabing
, and for the last few years, all the balconies are covered in netting to stop the things nesting. Its nuts. If there was too many rats, they'd get retcatchers to sort it. In London, you can actually see litter bins with a plastic base that's full of rat pellets. Like a dispenser so that rat-man does not have to go back so often. So when there is a pidgeon problem, why not a mass pidgeon cull. Instead of a yearly palava with netting, spikes, plastic novelty birds etc, they should just sort out a yearly cull. Lithe young children could hop around the rooftops (as they do anyway) collecting eggs. Prize for the winner and all that. Get a brass band, few food stalls, shitloads of beer. Great day out. Like whacking day in the Simpsons. Could even sell leather wrapped culling sticks. With a little hook to hang from lederhose. Let the Bavarians think up some silly name for it, and it might even catch on.