The bottom green portion of this birdfeeder is what is known as a Can Baffler. Its main purpose is to deter squirrels and other wildlife from stealing the birdseed from your birdfeeder. It is hollow with a dead end to prevent the squirrels from getting in from below the birdfeeder. It is also about 6" in diameter, which makes the Baffler too wide for the squirrels to wrap their arms around it to climb upwards. So, squirrels can't enter the birdfeeder from above either.