3 of my 4 chickens go into the hen house at dusk. One lonely hen (?) stays out and roosts on my grapevine trellis. She is also the only Hen that hasn't started laying. They are all almost 6 months. Occasionally the other Easter egger will also stay out of the coop and roost even higher up on the trellis. The two hens that routinely tuck themselves to bed are the Plymouth Rock and Rhode Island Red. What do you think is going on?