Nominal power output on one of the radars on A320 is 125 Watts... over a 30" antenna flat plate, that is about 239 cm2. That is 8 times less powerfull than a home microwave, and 16 times less powerfull than a vaccum cleaner.
I bet I can scare the birds off with the vacuum cleaner on full power with better efficiency than the radar!
Now, if we strech the theory reaaaaaally good: many migrating birds have magnetite crystals in parts of their beak or brain, which supposedly helps them navigate. Having an electromagnetic wave pointed directly at them could have a disturbing effect, maybe? But even if that ws the case, would it really make the birds fly away? And in which direction? Maybe they'd come flying straigh towards the source!
