When we got our first 3 hens and there chicken tractor from our friends, the girls had slept in the nesting boxes for there entire year's lifetime. The chicken tractor had no room for a roost. When we built our new coop (in my signature below), the three 1 year olds were the first ones up to the top roosting bar. It seemed instictual like others have said. Now our 5 pullets, they originally liked to sleep on the floor like the original posters chickens. They have gradually began moving higher and higher.
Be patient, it will happen. We have had to put at least 2 of our pullets on the bottom roosting bar for the past 2 weeks. We find them resting on the poop board in the evening when we put them to bed. Part of me believes they are on the poop board, because of the pecking order. I have also witnessed three times now, the adults from the top bar trying to peck the younger pullets sitting on the bottom bar. I think they might be to close together. Time will tell, as the pullets only get older and bigger.
We have a ramp in our coop for future silkie's in our flock too...
