In Survival and Creative chickens glitch through a hoper to the block below. When they fall through they don't just glitch back but rather they actually fell through the hopper and started running around beneath in all of the redstone and such. I had to place a half slab on to of the hopper to stop this from happening. Weather there is a block below the hopper or not they still fall through it. When I had my chicken xp farm running for a while I was wondering why there weren't many chickens so I went into the guts of my farm and sure enough. I had 200 chickens running around in and around all of the redstone! I know this is a duplicate of another but the creator of the other is not updating the affected versions. That is why I am making another report.