When do chicks start to roost?

[3chickadees]

My chicks are 11 weeks old, and have been living in their coop since they were 6 weeks. I had a small perch for them in the brooder box, and the would occasionally roost on that, but now they have no interest in roosting at night. Instead they all clamor to be in one corner of the coop; pushing and shoving and working to get as far into that corner as possible. Is there any way I can encourage them to start using the roosts, and stop being a writhing ball of chicken at night? Is there an age when they suddenly decide that sleeping up high is best?

 

[troy4]

Can I see pics at this age chickens have no interest in roosts unless its in front of their faces.