AHHHH you can't beat the old jokes can you.
Try Elephant repelent Boss I hear it works very well, after all you've never seen an Elephant round here have you.
Or try the updated DTC website and you might find out how they did it ( or didn't ).
On a serious note though Paul Google in bird scarers and you will find out all sorts of wierd and wonderful things just made for the job.
You could even download the sound of a bird of prey onto your mobile phone and try that, you may be surprised.
Good luck.
Ian...