Training my girls to go in their coop

[jestes2252]

My 8 week old girls, I have eight, have been in their mobile tractor for two or three weeks now. Every night except for one I have had to go out and put them in their coop. I usually find them all balled up together in the front corner of the pen.
How do I get them to go in their coop at night without having to put them in there?

 

[nuthatched]

Any light or large ventilation in the coop?

 

[jestes2252]

Coop is well-ventilated, there is plenty of room, bed is a hay bed, and they go in and out of it all day, sometimes roosting in it during the day.