While the dog is feeding, make sudden noise (banging a pan lif if you are in the house, buy a toy cap gun (or starter pistol) and pop a cap).
Get them on the birds first!, alot of dogs become gun shy because of the stuff mentioned above. You let the dogs build up the excitement and then introduce the noise. Just going around banging pans and things can confuse a dog very quickly and the next thing you know you have a gun shy dog. So becarefull on breaking in the noise.