A lack of oxygen and passing out from Carbon Dioxide rich air is so different, your not taking their oxygen from them, you are making the air richer in CO2, you can still breathe, you are only losing consciousness. If more CO2 exists in the air, you will simply "fall asleep" and not even know. Kind of like Carbon Monoxide, poeple who live didn't even know what happened, they just pass out like falling alseep. It is a painless way to kill your feeders.