I have some month-old chicks in a fenced ranging area using a small tractor for shelter. I want to switch them to a larger shelter in the same fenced area. Is it necessary to close the chickens into the new shelter to get used to it, or if I put the new shelter in there next to the old one and leave the door open and food/water in it, will they migrate in there? Should I remove the small tractor? I need the small one for other chickens so I can't leave it in there for too long. Thanks.