Birds love fresh berries as much as we do and will often strip fruit plants before the crop has fully ripened.
There are lots of methods for scaring the birds, either visually or by making noises. Old CDs or strips of tin foil hung from strings attached to tree branches will catch the light and frighten the birds away. However, Magpies are attracted to shiny things so this may not be the best option for you. You can also buy tape that makes a humming noise when it is tied between two stakes, which can be quite useful for deterring birds from low growing fruit and vegetables. Take a look at the following link: Birdscare Humming Line. Of course, you could always try a traditional scarecrow!
However, if you dont want to scare the birds from your garden completely, then the only sure way of protecting your crop is to erect a fruit cage covered in flexible netting. This will physically stop the birds ever reaching the fruit so will be able to keep your entire crop without actually frightening the birds. You can easily create a temporary frame yourself but are lots of different fruit cages available on the market, and they are definitely worth the investment.