How do I get the chick's to want to go up at night so I can shut them in? Sometimes they go easily but it's not something all four seem into. Right now I usually can get two to go up on their own by moving in their food and water.... But two will always remain below and I'll have to wait and pick them up and put them in through the side door. I'd love to "train" them to know how to go up at night but am not sure how to get started with it.