Oh I should have mentioned that as long as I am recommending rigidity, hardware cloth would be another good option. It is like giant screen, with square holes of 1/4 inch or 1/2 inch. It is easily bendable and holds its shape well. You wouldn't need a frame. (But you'll need gloves and small pair of tin snips.) Poultry wire holes are too big and certainly would allow chipmunks in, Although it would likely keep most birds out, they would still be able to put their heads through and peck.
N.B. If that''s a picture of a snake entangled in netting, it wouldn't happen if the netting was taught. A scary thought, though ....