I led a team on a work-study programme which involved building a prototype bird repeller using loud sounds in Singapore and then testing it out on a farm in Northeastern Thailand. We tested it there and found that it was not effective – the birds came back after a while, but this was a good learning experience nevertheless. We hacked a 15W megaphone and added an audio amplifier and MP3 player module to a microcontroller. A more detailed post on hackster.io can be found here.
Here’s a look at how we tested it:-
And here’s a video demo of how it works:-