It should also be mentioned that the cover/towel at night allows them a bit of extra warmth when the temperature goes down either due to lowering the A/C or just the general outside atmosphere.
In the summer,I've got the ceiling fan on full blast in the bedroom and the A/C is at a lower temperature than during the day so it really is necessary to cover the birds so they don't get a cooler draft....and, of course, in the winter, the temperature is also colder so a blanket/towel over their cage makes them cozier and warmer....once again, especially at night, when we lower the temperature to make it easier to sleep comfortably ourselves.
(just an extra thought besides the light/chirping issue.....)
