OMG, it seems like all they do at night is poop! I get some serious piles under the roost in just a couple days. If the roosts are closer that ~8 inches, the birds on the top roosts will poo on those on the bottom, but as long as that is not occuring you are good. All my hens crowd up on the top roost anyway, but occasionally someone will be pushed out and have to go on the lower roost (there are a lot of social issues in a flock of hens!).