My nine week old hens will not roost. They go up and down the ladder no problem, but they choose to sleep in the run instead (it's a three sided coop and open run). They huddle together in a corner. I've been putting them in the roost area at night after dark, but they seem to be incapable of doing it on their own. Should I be concerned? It's a well protected coop, but it seems odd that they aren't roosting even after three weeks out there.