I had a similar problem. The problem solved itself as the mulberry trees grew larger. There were too many berries for the birds to eat so I was finally able to harvest big bowls full.
Earlier, I hung bright CDs on a couple of the trees, similar to Christmas ornaments. It worked well for a few days, but the birds (mynahs) became accustomed to them. They work for me if I leave them on for 3 days, then off for 3 days.
John