It's not necessary to cover your cockatiel's cage with a heavy cloth at night. If you're concerned about his warmth and thinking a cover will increase his warmth, think again -- and just move his cage to a warmer spot. Many cockatiel owners do nightly cover or partially cover their birds' cages with light cloths, for a variety of reasons.
Cockatiels tend to have night frights, scary both to them and their owners. When something unexpected happens -- as simple as another pet's movement, sounds outside or headlights beaming through a window -- their natural response is to fly. Shaken from sleep, such a bird flies up and hits the top of the cage or a perch and falls to the bottom of the cage. Placing a light cover over the cage, but leaving an opening for natural light to filter in and let them know where they are, helps to eliminate or at least cut down on night frights. Some owners also add a night light and leave one side of the cage uncovered so he can see at night.
A cockatiel needs 10 to 12 hours of sleep at night. It can be difficult for him to settle down at night, though, particularly if you tuck him in before the rest of the household has gone to sleep. Covering the cage is a signal to your cockatiel that's it's bedtime. He'll become conditioned to equate the cover with sleep -- ultimately the conditioning will be useful if you want to put him to bed early or leave him at rest a little later some mornings.
Keeps a Routine
Routines are comforting. Your cockatiel will quickly become accustomed to being covered at night. Some new birds are already cover-trained. If you obtained your cockatiel from a breeder, store or another owner, ask if he was covered at night. If he was covered, you'll want to stick to that routine. This will be helpful in reassuring him in situations that break his routine, such as when you have house guests or have someone else care for him while you're away. His familiar cover will help him know all is well and he can settle into slumber regardless of what's going on in the space outside his cage.
Introducing a Cover
If your cockatiel isn't accustomed to being covered, he may not need it to sleep -- but it's worth considering, particularly if it will help your routine or if he has night frights. He'll quickly become accustomed to it and probably find it comforting. Start by only covering half of his cage for a few days. If he becomes agitated when he sees the cover, speak to him reassuringly until he's calm, and then gently place the cover over half the cage. Walk away and give him a few minutes to settle down. After he's accepted the cover, start inching it over a bit each night to cover a bit more of the cage until the top is covered. If he screams when the cover is on and never settles down, he may be that rare bird who can't accept a cover. Don't force it on him.