My chickens have stopped going in the hen house

[madtim]

I have a chicken tractor with a hen house attached. Recently i have noticed that 3 of 4 of my chickens have stopped going into the hen house at night. They all still lay eggs in the hen house but they stay in the run area on a perch all night. 1 chicken still goes in every night. I thought it might be due to the nice weather but right now it is pouring rain and the 3 of them are sitting out in it. They also stayed outside during some really cold nights towards the end of winter. Any suggestions would be greatly appreciated.

 

[faykokoWV]

any chance that the one that is still going in won't let the others in? Have they grown in size and its too crowded in there now?