For the health of my subjects, I pump in a small amount of oxygen into the baffles you see in the images. This allows the squirrel to perform at peek performance. In the wild, there is not such thing as a polycarbonate baffle. Some test subjects would stay in the baffle for hours thus depriving themselves of air. I have also placed thin radio antennas/sensors in common clothes line to inform me of any CO2 build up. I have not lost another squirrel to suffocation for 322 days now.