You can save yourself some aggro and simply eat the delicious, wild blackberries. Or else, built a mesh cage w. mesh roof and a gate....a huge pain. Only mechanical deterrents will keep the birds away. If you built it big enough, perhaps you can use it also as a gazebo.

aside from getting there first and hungrier or gail's gazebo, only a shotgun will help. and then it will only be a matter of time until the birds are packing heat too.