I have two beautiful little cockatiels, ages 2 and 1. I have always covered their cages at night to let them know that it's lights out and bedtime. They respond well to this, and whereas initially when I cover them, they protest, after a few moments, they pipe down and become quiet. They signal to me each morning, by chirping loudly and persistently that they're up, and that I should be too, that's it's time to uncover them, and to let them out of their cages! They're both fully-flighted, very active, and spend most of their time out of their cages flying around when I'm at home.