Becky, I'm with you on not wanting to kill the snakes. Although they do get some baby birds, they also keep the mice and rats away from my house and bird feeders now that my old cat is too dignified to hunt them. So don't kill off your snakes if you want to keep the rodents under control!! Nature is a delicate balance.
Try greasing the pole that the purple marten nest boxes are on, so the snakes can't climb up? I use an old toothbrush and SuperLube on my feeder poles.
I stopped using the bird netting altogether, once I discovered that the black snakes got entangled in it. My neighbor's daughter used to come over and help me free the snakes if they were still alive when I found them - just put a thick sock on your hand and grab the snake then have somebody else make the hole in the bird netting bigger so the snake can pass through forwards. A pair of scissors is all the tool needed, and I happened to have an old pair of bandage scissors (blunted on the lower blade) that were perfect.
