Bird scarer - with noise
I'm looking for any ways of building a repurposed material bird scarer. Not a visual scare (scarecrow, CDs/foil, silhouette) but something that makes a bit of noise.
I know a keen allotment owner who has purchased an air gun to shot into the air and scare parakeets ! He would hate to actually hurt a bird - and I feel there has to be a better way.
Rattles - tape recorders that can be set outside, wind powered stuff ?
Anything that might stop my friend eventually hurting himself (I'm also concerned about the effect air gun pellets could have on the soil).
Thanks for any suggestions.